Search

Sawing is a commonly utilized undercutting process for machining in the steel and forging industries. With the continuous improvement of modern processing requirements and increasing demands for higher sawing efficiency, accuracy, and surface quality of workpieces, bi-metal band saw blades are facing greater challenges. In addition, the development of new and difficult-to-cut materials such as nickel-based alloys, titanium alloys, and other heterogeneous alloys has presented novel challenges to band sawing technology. However, the wear of the band saw blade has become a major hindrance to the application and development of sawing processing technology for new materials, high efficiency, high precision, etc. Based on the principle of metal cutting using a band saw blade and considering the wear process of teeth, this paper provides a comprehensive analysis of the impact of cutting parameters, cutting fluid, heat treatment, and surface treatment technology on tooth wear. Additionally, measures to enhance wear resistance are summarized. Furthermore, an overview is presented regarding the latest advancements in monitoring wear for bi-metal band saw blades. Finally, the future direction of research on wear in bi-metal band saw blades is anticipated. [ABSTRACT FROM AUTHOR]

In this paper, a disk laser welding was developed to join 3-mm thin-Sect. 30Cr3 ultra-high-strength steel which was widely used in aerospace. The microstructure and mechanical properties of welded joint were investigated in detail. The results indicated that the recommended laser linear energy range were between 150 and 165 J/mm to guarantee that the melting width was up to 1 mm as well as less oxidation, spatter, and depression on the weld. Meanwhile, for the as-welded (AW) condition, the base metal (BM) consisted of ferrite matrix with distributing small spherical carbides, also known as spherical pearlite. While, the fine grained region, coarse grained region, and weld metal were all composed of martensite. However, the partially transformed region mainly consisted martensite with a little of spherical pearlite. Meanwhile, the average grain sizes of weld metal, HAZ, and base metal were 1.3 μm, 1.5 μm, and 1.8 μm, respectively. However, for the post-weld heat treatment (PWHT) condition, the whole welded joint was all composed of tempered martensite, and the average grain size of welded joint was about 1.7 μm. The tensile strength of the welded joint was higher than that of the base metal both in the AW and PWHT condition as all the fracture with shrinkage occurred in the BM of the specimens. Additionally, the average yield strength of the AW and PWHT are about 600 MPa and 1700 MPa, respectively. [ABSTRACT FROM AUTHOR]

The thermal cycles necessary to produce galvanized transformation-induced plasticity (TRIP) steels on a continuous hot-dip galvanizing line involve several processing parameters that must be chosen and strictly controlled to achieve the required mechanical properties. The resulting mechanical properties strongly depend on the optimal determination of each heat treatment variable. In this paper, a novel memetic algorithm named kernel-based gradient evolution (KGE) is implemented and coupled with a support vector regression (SVR) model to efficiently optimize the production of a cold rolled hot-dip galvanized TRIP steel. For this purpose, the most significant processing parameters (cooling rate after intercritical austenitizing, isothermal holding time at the galvanizing temperature in the bainitic region, and last cooling rate to room temperature) were thus optimized to achieve the required hardness values. In general, SVR fits in a satisfactory manner the relation between experimental parameters and resulting hardness which is highly non-linear in nature, and hence, it is used as objective function. Besides, KGE algorithm reveals an impressive performance since it solved the problem in less than 10 iterations. As a result, optimal solution is successfully achieved by the proposed SVR-KGE model. [ABSTRACT FROM AUTHOR]

This paper presents constitutive equations that describe the hot flow behaviour of Virgin (VG) X20 and rejuvenated heat-treated creep exhaust (CE) X20 steels. The study provides a foundation for determining the effect of rejuvenation heat treatment on CE steels by making comparisons to the VG steel. Hot compression tests were conducted in the temperature range of 900 °C to 1050 °C, at strain rates of 0.1–10 s−1 to a total strain of 0.6, and stress–strain curves were obtained. The flow stress curves of both steels exhibited dynamic recovery (DRV) characteristics as the main softening mechanism. Constitutive constants of steady-state stresses were determined. The stress exponents, n, were 6.62 (VG) and 5.58 (CE), and the apparent activation energy values were 380.36 kJmol−1(VG) and 435.70 kJmol−1 (CE). Analysis of the activation energies showed that VG steel had better workability properties than CE steel and was easier to deform at high temperatures. Constitutive equations for predicting the flow stress in the two steels were established. This were verified by statistical tools: Pearson's correlation coefficient (R) and Absolute Average Relative Error (AARE). The results showed R-values were, 0.98 (VG) and 0.99 (CE), and the AARE values for VG were 4.17% and 9.01% for CE. The statistical parameters indicated a good correlation between the experimental and predicted values. The constitutive equations therefore adequately described the flow stress behaviour of both steels and can therefore efficiently analyse industrial metal forming schedules. [ABSTRACT FROM AUTHOR]

Additive manufacturing of composite materials is a promising technology. It could solve one of the most critical drawbacks of 3D-printed fiber-reinforced thermoplastics: their low out-of-plane mechanical properties. Due to this factor, it is still unknown how most design and manufacturing parameters affect the out-of-plane properties of composite materials. As a solution, this paper proposes an experimental methodology to characterize out-of-plane printed composite materials. For this purpose, existing standards for traditionally fabricated composites are adapted, investigated, and validated for 3D-printed laminates reinforced with long fibers using the fused filament fabrication technique. Consequently, the methodology is employed to study the impact of stacking sequence and heat treatment conditions on the composites' out-of-plane mechanical properties. The main results showed that increasing the thickness between stacking layers increases the mechanical response due to reducing the number of fiber/matrix interfaces and, consequently, the reduction of porosity. Compared to the initial sample, a heat treatment at 175 °C for 6 h increased the interfacial strength by 101.09% and reduced the porosity in the fiber produced by the additive manufacturing process by 72%. [ABSTRACT FROM AUTHOR]

Stainless steel (SS) alloys produced by laser-based powder bed fusion (LPBF) offers comparable and sometime superior mechanical properties compared to conventionally processed materials. Some of these steels have been extensively studied over the last decade; however additively manufactured martensitic SS, such as AISI 420, need further research in characterizing their post-built quality and mechanical behaviour. This lack of information on martensitic SS is not consistent with their growing demand in the automotive, medical and aerospace industries due to their good corrosion resistance, high hardness and good tensile properties. Selection of the appropriate process parameters and post treatments plays a fundamental role in determining final properties. For this reason, the effect of LPBF process parameters and different heat treatments on density, defect characteristics and locations, roughness and mechanical properties of AISI 420 were investigated in this paper. A first experimental campaign was carried out to establish a set of suitable process parameters for industrial applications. Starting from this result, detected defect properties were investigated by computed tomography (CT) scans. Dimensions, sphericity and distributions of defects inside the volume were analysed and compared between samples manufactured with different parameters. In the second part of the paper, the influence of process and post-process conditions on mechanical properties was investigated. The final presented results establish a correlation between the employed production cycle and the resulting properties of LPBF AISI 420 specimens. [ABSTRACT FROM AUTHOR]

This paper studies printing parameters and post-printing heat treatment for laser powder bed fused Inconel 718. The printing scanning speeds and energy densities per unit volume were varied, and each print group was subjected to combinations of three different types of heat treatment: homogenization, hot isostatic pressing, and solution heat treating following with aging. The quality of the samples was measured by the porosity present in the samples, hardness, size/quantity of defects, and identification of phases and defects in the microstructure. Both optical and scanning electron microscopy observations showed that a scanning speed of 1250 mm/s and energy density of 54.5 J/mm3 result in the lowest porosity. Reduction of porosity and precipitation hardening increased material hardness to 470 HV. The Laves phases, normally seen in the as-printed samples, were effectively minimized after these thermal heat treatments. An increment of 550% of fatigue life was seen in axial fatigue testing at 525 MPa on samples after hot isostatic and aging treatment. [ABSTRACT FROM AUTHOR]

The ultraprecision machining of the mold surface is important because the performance of optical components produced using optical injection is related to the surface roughness and shape precision of the mold core. To process hard-to-cut mold core materials such as stainless steel, electroless nickel-phosphorus (NiP) plating is applied to the surface of the substrate, and ultraprecision processing is performed on the plating surface using diamond turning (DT) and magnetorheological finishing (MRF). Although MRF processing can remove tool marks caused by diamond turning and improve shape accuracy, it suffers from poor processability for NiP. In this paper, an ultraprecision processing method with a heat treatment process was presented to improve the MRF processability of electroless NiP. The plating was heat-treated under each condition and subjected to DT processing followed by MRF. The surface roughness and reflectance were measured and evaluated after processing. As a result, the surface roughness of NiP subjected to a 1-h heat treatment at 450 °C significantly decreased from Ra 7.0 nm to Ra 1.5 nm when compared to the specimen that did not undergo any heat treatment. An improvement in surface roughness confirmed that reflectance improved by more than 9% and 18%, respectively, compared to that for the diamond-turned and non-heat-treated specimen. These results confirmed that the MRF performance was improved through the NiP heat treatment process and contributed to quality improvements in ultraprecision injection optical parts. Furthermore, this technology can be applicable to various fields that used NiP plating, including the manufacturing of metal reflectors in the visible and ultraviolet regions. [ABSTRACT FROM AUTHOR]

Collapse mechanism dictates plateau behavior for a lattice. Sharp large drops in this region are due to formation of diagonal shear bands. They may ruin energy absorption capacity of lattice. This paper is an attempt to evaluate the possibility of improving collapse mechanism in favor of energy absorption. A significant number of tests were conducted to investigate the influence and effectiveness of changes in cell topology, solid material properties, and relative density. It was demonstrated that alteration of solid material properties (through heat treatment) as well as relative density can affect fluctuations in the plateau region significantly. This has been possible through replacing shear bands with normal layer failure, or through thickening the shear band and smoothening the transitions. One of the practical achievements for this study is that the best energy absorption performance was obtained at relative density ranging from 20 to 30%. At this range, the specific absorbed energy (energy per unit weight) reaches its maximum peak for all examined lattices. However, magnitude of the peak is highly dependent on the lattice topology. This highlights the superiority of lattices as engineered structures over conventional metallic foams. Among the wide range of examined strut- and surface-based lattices, face-centered cubic (FCC) and Schwarz D lattices performed the best for weight-sensitive energy absorption applications. [ABSTRACT FROM AUTHOR]

Internal gear is an important transmission component. However, it is restricted by its ring−shaped structure, which hinders the finishing process of the tooth surfaces after the heat treatment. Honing is the most commonly used finishing technique for external gear, but it is inconvenient for internal gear. In this paper, a new type of cone−shape honing wheel is proposed and the honing mechanism for improving the honing performance of the internal gear is studied. First, the mathematical model of the honing technology that employs a cone−shape honing wheel is built, and the merits of the new honing method are discussed. Then, the contact conditions between the honing wheel and the internal gear are analyzed. It is established that the tool tilt angle of the honing wheel has a good effect on the honing velocity distributions. Finally, the simulations of honing and profile measuring of the internal gear by employing the cone−shape honing wheel are carried out, by which the feasibility of the new honing technique is verified. [ABSTRACT FROM AUTHOR]

Current paper is devoted to the study of formation process of a nanoporous structure in porous ammonium nitrate granules during their humidification and heat treatment in vortex devices. We briefly present the main methods for porous ammonium nitrate granules formation. We demonstrate that it is necessary to control the process of nanoporous structure formation by varying different technological parameters. We present a brief description of a method for producing porous ammonium nitrate granules with nanoporous structure in vortex granulators based on ordinary ammonium nitrate granules. The nanoporous structure of porous ammonium nitrate granules is investigated under various technological parameters of the modification process. We provide porous ammonium nitrate quality indicators and propose optimal parameters for its production. [ABSTRACT FROM AUTHOR]

The known studies of heat treatment of copper slag are mainly directed to the recovery of metals from copper slag at the melting temperature. The conditions of increasing the strength of copper slag grains as a result of transition from amorphous to crystalline state during heating have not been studied. That is why the paper presents studies of microhardness and cutting properties of copper slag particles after heat treatment. Treatment regimens were assigned after calorimetric measurements of phase transition from amorphous to crystalline state of copper slag grains under isothermal conditions. It was found that for copper slag grains, crystallization proceeds in two stages. The first crystallization stage started at 762.6 °C (1035.75 K) and the second one at 795.1 °C (1068.25 K). Metallographic examination of microslides of copper slag grains after heat treatment at 800 °C showed that the HV microhardness value increased 1.5 times. It was found that the use of heat-treated copper slag grains for water jet cutting resulted in an accurate cut and smooth surface compared to the original abrasive. It has been revealed that heat treatment of amorphous copper slag contributed to the appearance of crystallites of sillimanite, pyrope, hematite, and zinc ferrite. [ABSTRACT FROM AUTHOR]

High-performance heat treatable aluminum alloy sheet is widely used in aircraft and automobile industries because of its excellent mechanical properties, including low density, good corrosion resistance, and high specific strength. Many heat treatment and forming methods have been developed for aluminum alloys, such as warm stamping, hot stamping in die quenching, in order to maximize the formability, and the formed strengths. Among which, electrically assisted process (EAP) becomes attractive due to its improvement of convenience, energy saving, and efficiency. Many investigations have been published in recent decades to show that the heat treatment can be accelerated and the formability can be improved due to the thermal and non-thermal effects of electric current and tried to characterize the possible mechanisms. Hence, this paper gives a comprehensive review of the effects of electric current on the heat treatment and forming of aluminum alloy from macro- and micro-aspects. Based on this, some perspectives in developing trends of EAPs are proposed, including the mechanisms of EAP, the mechanical properties under complex stress states, and the industrial applications of EAP. [ABSTRACT FROM AUTHOR]

There has been limited studies on corrosion behaviour of post-processed electron beam melted (EBM) Ti6Al4V, given that the factors affecting corrosion resistance of AM Ti6Al4V remain unclear. This paper proposes using heat treatment method to improve the pitting corrosion resistance of EBM Ti6Al4V. Different treatment profiles alter the microstructure of EBM Ti6Al4V. A clear trend is observed between microhardness and α lath width. As-printed EBM Ti6Al4V exhibits an inferior pitting potential, while heat treatment provided a significant improvement in the corrosion resistance. This study finds that the β phase fraction is a better indicator than the α lath width for pitting corrosion resistance. Solution air-cooled and ageing heat-treated EBM Ti6Al4V exhibits good mechanical and corrosion properties, and even performs better than commercial cast Ti6Al4V. [ABSTRACT FROM AUTHOR]

The residual stress of large aluminum alloy ring after heat treatment will cause serious deformation in subsequent processing. The conventional methods for reduction of residual stress (such as stepwise cold pressing and bulging) have little effect in the residual stress reduction for large-scale ring component and will induce inhomogeneous stress distribution. In this paper, roll bending process is adopted to reduce the quenched residual stress of 2219 aluminum alloy super-large ring. The numerical model of roll bending process was established, and the evolution and distribution of stress and strain after roll bending were studied. The influence of roll winding number on the uniformity of stress and strain was analyzed. The results show that the arch-shaped quenched residual stress of the ring changes to N-shaped distribution from inside to outside after roll bending process. The value of the residual stress reduces from ± 180 MPa in quenched state to the value within ± 50 MPa in roll bended state. With the increase of roll winding number, the stress uniformity is improved, but the stress reduction amplitude is basically the same. By analyzing the elastic–plastic strain distribution characteristics and strain springback law of the ring after roll bending, the formation mechanism of N-shaped residual stress distribution after roll bending is revealed. [ABSTRACT FROM AUTHOR]

In the present paper, authors have demonstrated how a localized induction heat treatment can be advantageously applied, controlled, and mechanically characterized on a specific part—i.e., on steel hose fittings for hydraulic applications. More specifically, the study shows how this specific type of heat treatment facilitates significant localization effects on mechanical properties, and how such a treatment could act as a powerful tool for material optimization in diverse applications. The instrumented micro-indentation test was adopted as the investigation method for mechanical characterization and, due to the reduced amount of material required for the test, has the double advantage of retrieving potential spatial gradients of the mechanical properties without causing permanent damage to the analyzed parts. A measurement of both Vickers hardness and plastic work are required in order to make the indentation necessary to quantify the strength and ductility capability of the parts' materials. In addition, a customized tensile test, based on a strains measurement obtained through an optical full-field method—i.e., digital image correlation (DIC)—was developed with the aim of identifying and quantifying the correlation between the material properties attainable through a conventional tensile test and those measured by the instrumented micro-indentation test. Finally, it was demonstrated that the proposed customized tensile test, due to the localized heat treatment, is capable of retrieving potential spatial gradients of the material properties. [ABSTRACT FROM AUTHOR]

This paper aims at analyzing the effect of heat treatment using Concentrated Solar Energy (CSE) on the martensitic microstructure evolution of Ti-6Al-4V alloy manufactured by Selective Laser Melting (SLM) technology. The application of CSE, a renewable energy sources, in post-processing of SLMed Ti-6Al-4V alloy is discussed based on heat treatments performed at Plataforma Solar de Almeria, Spain, using solar furnace SF40. In SLM process of Ti-6Al-4V powder because of local high heating followed by a rapid cooling the microstructure consists of an acicular martensite (α′ phase). Decomposition of α′ martensite of SLMed Ti-6Al-4V after heat treatment in solar furnace, using CSE, by SEM, EDX, TEM, SAED, and XRD analyses, was investigated. It has been found that for treatment below β-transus at 705 °C, because of low temperature, the α′ martensite was not fully converted into α + β and the β phase was not identified by XRD analysis. Heat treatments below (940 °C followed by 650 °C) and above (1050 °C) β-transus have revealed that α′ martensite was converted into a lamellar α + β mixture and also β phase was identified by XRD and TEM analysis. In the analyzed areas, middle areas of the samples contain an area fraction of β phase greater than the top areas. Area fraction of β phase, after heat treatment above β-transus, at 1050 °C, is greater than that obtained after treatment below β-transus. [ABSTRACT FROM AUTHOR]

In this paper, a novel gradient-based algorithm named Kernel-based hybrid multi-objective optimization (KHMO) is implemented and coupled with a support vector regression (SVR) model to efficiently optimize the production of a cold rolled hot-dip galvanized TRIP steel. For this purpose, several heat treatments using an isothermal bainitic transformation (IBT) temperature compatible with continuous hot-dip galvanizing were performed. The most significant processing parameters (cooling rate after intercritical austenitizing ( C R 1 ), isothermal holding time at the galvanizing temperature in the bainitic region t 2 , and last cooling rate to room temperature ( C R 2 )) were thus optimized to achieve the required mechanical properties values. In general, SVR model fits in a satisfactory manner the highly non-linear relationship between experimental parameters and resulting mechanical properties; hence, it is used as objective function. Besides, KHMO algorithm reveals an outstanding performance since it found a dense and spread Pareto front. Moreover, the processing window to manufacture TRIP-aided martensitic steels is suggested in a range of 57–63 ∘ C/s, 33–37 s, and 1–2 ∘ C/s for C R 1 , t 2 , and C R 2 , respectively. The developed computational methodology for modeling and optimization of operating parameters is successfully applied for the first time in the experimental processing of advanced TRIP steels. [ABSTRACT FROM AUTHOR]

Ultrasonic additive manufacturing (UAM) is a solid-state metal additive manufacturing process, with the combination of layer by layer ultrasonic seam welding and CNC machining. Due to the friction and deformation at the bonding interface, the ultrasonic softening effect and temperature generated, the microstructure of the substrate materials is evolving constantly. In this paper, in order to better understand the bonding mechanisms, the good practice and the capability of UAM, and the influence of different key process parameters on bonding quality, the microstructure evolution during UAM is reviewed in detail. Defects can be generated at the UAM bonding interface, but by choosing the right material combination and the right process parameters, defects can be reduced to minimum. Plastic deformation is very important for the bonding between layers during UAM, and plastic flow is important for redistribution of oxide layer, forming of mechanical interlocks, filling micro-valleys on the mating surface, and filling the gaps when embedding elements. UAM process can cause recrystallization and grain refinement at the welding interface and the intimate bulk materials around, and it will also gradually change the texture from rolling texture to shear texture. In the meantime, when further layers of materials are deposited on the top of the existing part, the microstructure will have some accumulative change. In order to reduce the defects number and increase the strength, sometimes, heat treatment needs to be carried out to the as-deposited parts, which will change the microstructure as well. Finally, the relevant research is summarised and the perspectives of further research are recommended. [ABSTRACT FROM AUTHOR]

When reporting surface quality, the roughest surface is a reference for the measurements. In LPBF due to recoil pressure and scan movement, asymmetric surface is shaped, and surface roughness has different values in different measurement orientations. In this research, the influence of the laser powder bed fusion (LPBF) process parameters on surface tension and roughness of Ti-6AI-4 V parts in three orientations are investigated. To improve the mechanical properties, heat treatment was carried out and added to the designed matrix to generate a comprehensive data set. Taguchi design of experiment was employed to print 25 samples with five process parameters and post-processing. The effect and interaction of the parameters on the formation of surface profile comprising tension, morphology and roughness in various directions have been analysed. The main contribution of this paper is developing a model to approximate the melting pool temperature and surface tension based on the process parameters. Other contributions are an analysis of process parameters to determine the formation and variation of surface tension and roughness and explain the governing mechanisms through rheological phenomena. Results showed that the main driving factors in the variation of surface tension and formation of the surface profile are thermophysical properties of the feedstock, rheology and the temperature of the melting pool. Also, the results showed that while the value of surface tension is the same for each test case, morphology and the value of roughness are different when analysing the surface in perpendicular, parallel and angled directions to laser movement. [ABSTRACT FROM AUTHOR]

Recently, there has been a significant amount of interest in additive manufacturing of aerospace parts from heat-resistant alloys due to the ability of producing more complex shapes parts in comparison with conventional technologies. This paper describes the research results of selective laser melting (SLM) of nickel-based IN-738 superalloy powder. The main research results of studies are microstructure investigation after SLM, hot isostatic pressing (HIP), and heat treatment on the cylindrical samples. The article presents results of short-term strength tests of cylindrical specimens at room temperature and 900 °C, and long-term strength. The research studies the influence of HIP on stress-strain behavior of specimens, which are built at different angles: 0, 45, 90°. The tensile strength of vertical samples is increasing by 60 MPa, at 45° is decreasing by 75 MPa, and at 0° is increasing by 139 MPa compared with the initial state. The developing IN-738 selective laser melting technology is approving by fabrication of GTE nozzle guide vane. [ABSTRACT FROM AUTHOR]

15-5PH parts that are fabricated using direct metal laser sintering (DMLS) has shown mechanical properties comparable to conventionally manufactured parts. However, DMLS-fabricated 15-5PH parts have shown high anisotropy in their mechanical properties due to the layering nature of additive manufacturing process. In addition, the fatigue life and strength of DMLS 15-5PH varies significantly between horizontally and vertically fabricated parts and both orientations are inferior to conventionally manufactured parts. Reliability and large variations in performance remain as a barrier from employing 15-5PH parts fabricated using DMLS. Standard heat treatment of 15-5PH is insufficient to eliminate the anisotropy and homogenize the DMLS parts. Modified precipitation hardening heat treatments did not show further improvement in published literature. Therefore, in this paper, we investigate the influence of different solution annealing heat treatments on the microstructure and mechanical properties of 15-5PH steel produced using DMLS. Three different solution annealing heat treatments were investigated: the standard solution heat treatment, the second heat treatment extended the time from 1 to 3 h, the third heat treatment increased the temperature from 1038 to 1200 °C. For each heat treatment, three patches of specimens were fabricated each in one of the three principal orientations X, Y, and Z. In addition, three patches, one of each orientation, were tested in as-built condition. The specimens were tensile tested and their microstructure and fractured surfaces were imaged. It was found that extending the time of the heat treatment improved the homogenization while increasing the temperature of the heat treatment to 1200 °C had detrimental effects, especially on vertically fabricated specimens. [ABSTRACT FROM AUTHOR]

This paper explores the structure and phase composition of laser welded joints of Al-Cu-Li alloy without and after post heat treatment (annealing, quenching, and artificial aging). Changes in the structure and phase composition of welds and the base alloy before and after heat treatment are studied using scanning electron microscopy, X-ray diffractometry, and synchrotron radiation diffraction. The investigation results have shown that the formed agglomerates of intermetallic particles are mainly represented by the Т1(Al2CuLi) phase. The change in the strength of the Al-Cu-Li alloy samples after laser welding and heat treatment is not due to the absence or presence of the strengthening Т1(Al2CuLi) intermetallic phase but rather due to the different localization of particles of this phase in the weld joint. The segregation of the phase at dendritic grain boundaries leads to a significant strength decrease, and, vice versa, its homogeneous distribution in the solid solution achieved by post heat treatment (annealing, quenching, and artificial aging) increases the strength of the laser welded samples. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study of the tensile performance, heat treatment, fracture, decrease of residual stress, second-phase particle and microstructures of a 316L stainless steel fabricated by directed laser deposition (DLD) and thermal milling (starting milling temperature at 250 ± 50 °C), a typical hybrid additive and subtractive manufacturing process. Experiments of different post-heat treatment temperatures and tensile tests at room temperature were performed. The residual stress was eliminated with heat treatment at 400 °C for 2 h, and the average residual stress decreased 53.7% while the yield strength and ultimate strength decreased slightly. The fracture surfaces of different heat treatment temperatures were observed. The typical ductile fracture microstructures of dimples were seen in almost all specimens whenever the heat treatment temperature was low or high. The evolution of dimples from formation to destruction by heat treatment was analyzed. The different morphology and composition of the second-phase particles of different heat treatment temperatures were compared. The yield strength of 427.5 MPa, the ultimate strength of 599.27 MPa, and the elongation of 36.48% showed the new hybrid manufacturing technology could be used for further fabrication of components. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) has various independent parameters that affect the mechanical properties and quality of the produced parts that are not linearly the function of each other. Process parameters in metal AM are very hard to control, analyse and optimise because they affect each other even though they can be independently changed. Changing process parameters in a wide range is not possible due to the formation of problems such as cracks, balling, unmelted powders, porosity and distortion. In this paper, a numerical model to predict the value of tensile strength of selective laser melting (SLM) Ti-6Al-4V parts and analyse the effect of process parameters on the results has been proposed. Taguchi L25 Design of Experiment (DOE) across 125 samples to create a comprehensive and general overview of influential parameters on the build process was investigated. Specifically, parameters included laser power, scan speed, hatch spacing, laser pattern angle and heat treatment (HT). To evaluate and analyse the build process according to established statistical variances, a minimum of five samples based on ASTM standard (for tensile test) were prepared. Heat treatment was added to the DOE to analyse the combined process and post-process effects. Results were compared (cross-validated) against existing values found in the literature and were found to effectively predict and explain the behaviour of tensile strength when changing process parameters. [ABSTRACT FROM AUTHOR]

The paper presents a study concerning the characterisation of EN 1.4136 stainless steel heat-treated by means of concentrated solar energy in orde to improve some mechanical properties. In addition to the standard chemical composition, this steel was alloyed with nickel (Ni 1.5%wt) and copper (Cu 0.30%wt). Nickel was added to increase corrosion strength in acids, oxidising or non-oxidising environments, also facilitating an improved tenacity of the material. The addition of copper allows an increasing atmospheric corrosion strength (for copper content over 0.20%), at the same time intensifying the austenitising effect of nickel. The obtained steel was subjected to a solution heat treatment (hyper-hardening) with a heating time up to a austenitisation temperature (TA = 1050 °C) for 20 (lot A) and for 33 min (lot B), respectively. The maintaining duration for austenitisation was 7 (lot A) and 21 min (lot B), respectively, followed by cooling in water. After the heat treatment in the solar furnace, the specimens were analysed from the structural point of view as well as to their behaviour when subjected to tribological stress, in accordance with the operational requirements for these types of steels. The analysed characteristics were the dynamic friction coefficient (CoF), the wear rates and the hardness (HRC) tests. Based on the collected data, a specific characterisation was made for EN 1.4136 stainless steel heat-treated in a solar furnace. By applying the thermal treatments in the solar furnace, the hardness values have been increased (of about 55%) and the average wear rates have decreased compared to the base material. [ABSTRACT FROM AUTHOR]

As a high efficiency and high precision machining process, internal gearing power honing is often used in gear finishing after heat treatment. In order to improve the machining accuracy of internal gearing power honing, this paper analyzes the influence law of motion control error and machine setting error on tooth surface contour error. First, the tooth surface of the honing wheel and the workpiece gear is established by using homogeneous coordinate transformation and meshing principle. Second, the tooth surface of the workpiece with the control error and the setting error is constructed. The contour error and the sensitivity matrix of the tooth surface are also put forward. Finally, two numerical examples and an experiment are used to study the influences of control error and setting error on the machining accuracy of workpiece gear tooth surface. The research results can provide reference and precondition for the error compensation and improvement of machining precision of internal gearing power honing. [ABSTRACT FROM AUTHOR]

There are many drawbacks of traditional mold manufacturing technology, especially for dies used on large-scale hydraulic press, such as poor forging penetration, high difficulty of open die-forging process of modules, inferior hardness after heat treatment, high cost, massive waste of invalid forging dies, and so on. Therefore, a new method of mold making is put forward in this paper, which is to do surface welding on casting-steel. The FEM simulation experiments were done to establish a simplified finite element model of the surface welding mold based on JXZG casting-steel. Then, the thermal cycle curve method was used to simulate the surface welding and tempering process. Meanwhile, the temperature field and residual stress field under different welding thickness were analyzed. The finite element modal of landing gear used in a large civil aircraft was established, and then elastic-plastic finite element method was utilized to simulate the forming process of billet and to analyze the temperature field and residual stress distribution of different time. The results demonstrated that FEM could simulate the actual process of surface welding on casting-steel effectively. The equivalent stress close to welding line decreased when the welding thickness inclined, and then it leveled out when the welding thickness was 15 mm; on contrary, the equivalent stress far from welding line increased when the welding thickness declined and the impact of weld pass on casting-steel matrix enlarged which increased the possibility of defects when the casting-steel was used. In sum, when the impact of welding thickness and the cost of mold making are taken into consideration, 16 mm was chosen as the optimal surface welding thickness under given working conditions of landing gear. [ABSTRACT FROM AUTHOR]

The paper shows the possibilities of using ultrasonic vibrations in the processes of laser welding and cladding. Optical and electron microscopy, local elemental analysis, X-ray tomography, and series of tensile tests were used to investigate the effect of vibrations on the respective processes. It is shown that ultrasonic vibrations can be used in two different ways: ultrasonic online processing during welding and surfacing and post processing of the finished weld seam and cladded metal. In the first case, ultrasonic effect leads to reduction of the weld seam thickness and an increase of the depth of weld penetration. In the second case, ultrasonic post-treatment of the samples produced by layer-by-layer direct laser wire deposition results in an increase of tensile strength of the cladded material up to 1.3 times. It is shown that the effect is caused by formation of an oriented thin-plate structures on the surface of the samples. [ABSTRACT FROM AUTHOR]

In the hydroforming of curved sheet parts with a small thickness-diameter ratio, qualified parts are difficult to be manufactured when using the traditional hydroforming process. To solve this problem, double-layer sheet hydroforming was proposed and the wrinkle-free sheet parts were obtained in the authors’ previous study, but the inhibition mechanism of forming defects is far from perfection. Therefore, in this paper, the inhibition mechanism of forming defects is investigated by the combination of FE simulations and technological experiments. Different from the previous research, 2198 Al-Li alloy sheet was selected as the lower sheet. Other conditions such as heat treatment status and thickness are the same as before. The principle of wrinkle elimination can be concluded into the following two aspects. On the one hand, the upper sheet cannot be wrinkled during hydroforming, On the other hand, the surface blank holder pressure is applied in the suspending area. In addition, the beneficial friction between this two sheets changes the radial stress state of the lower sheet and makes the radial strain at some specific area (punch contact area and die corner area) decreased. In conclusion, qualified sheet parts can be manufactured by double-layer sheet hydroforming. [ABSTRACT FROM AUTHOR]

In recent years, additive manufacturing (AM) has been developed for industrial applications due to its superior performance, such as in building complex parts, which are especially difficult to build when using traditional methods. However, the surface quality, and dimensional and geometric accuracies of AM parts do not exceed conventionally machined parts, which hinders the AM applications. To overcome these limitations, hybrid manufacturing (HM) technology, which combines AM and subtractive manufacturing (SM) technologies in a single workstation has received a great deal of attention in academic and industrial circles to enhance material utilization, part complexity and quality control when producing functional parts. In this paper, we present research achievements using ANSI 316L stainless steel parts via the HM process and analysis of its surface morphology and microstructural characteristics, densification behaviour and mechanical properties. Specimens before and after heat treatment were analysed and compared. The study also dealt with material characterization via the Archimedes method, scanning electron microscopy (SEM), X-ray polycrystalline diffractometer (XRD) and tensile measurements. This study provides a valuable guide to determining the effectiveness of the HM process and its use when producing engineering parts. [ABSTRACT FROM AUTHOR]

In this paper, Fe3Al-based alloy with a designed 30 at% Al content is fabricated using an innovative wire-arc additive manufacturing process. In order to investigate the influences of postproduction heat treatments on the additively manufactured alloy, three postproduction heat treatment methods were applied to the as-fabricated material. The morphologies, phase constituents, and mechanical properties of samples produced by the different heat treatments were characterized and analyzed in detail. According to the results, the applied heat treatments can considerably change the microstructure and mechanical properties of the as-fabricated Fe3Al-based alloy. Also, the hardness and tensile properties of Fe3Al-based alloy are found relevant to the Al-rich precipitates observed in the morphologies, which are generated by the additional thermal processes on the homogenized Fe3Al-based alloy. [ABSTRACT FROM AUTHOR]

Surface quality is a significant factor in machining that affects the accuracy of spherical components. In this research, Ti-6Al-4V prosthetic acetabular shells have been printed using selective laser melting (SLM). Two post-processes, heat treatment and machining, have been carried out on the printed samples to improve the mechanical properties, dimensional deviations, and surface quality. Samples were printed based on Taguchi L32 design of experiment (DOE), and in order to predict the surface roughness multilayer perceptron (MLP) artificial neural networks (ANNs), Poisson and Taguchi methods have been used. The novelty of this work is in explaining the mechanical properties of asbuilt SLM parts such as hardness, ductility, and strength and their effect on machinability of spherical components. Characterising the effect of cutting conditions and heat treatment on the surface quality based on mechanics of cutting process and tool geometry is another contribution of this paper. Results showed that MLP ANN has high potential in the modelling of surface roughness in 5-axis machining of spherical components. To improve the surface quality of SLM parts, it is recommended to design appropriate tool paths, and machining parameters with lower scallop height, finishing allowance and higher spindle speed than normal and a higher annealing temperature. [ABSTRACT FROM AUTHOR]

With weight reduction and component reliability being the top priority while designing automobile components, the selection and use of materials of a high strength-to-weight ratio is of vital importance. Less weight ensures low fuel consumption and hence low emissions thus having a great impact on the environment on a large scale. Brake rotors are one of the most important components in an automobile, which aid in stopping the vehicle by converting the kinetic energy of the moving vehicle into heat energy by means of friction. This study focuses on the use of abrasive particle (SiC)-reinforced aluminum metal matrix composite material for brake rotors which is expected to generate less heat during braking (due to friction) and also reduces the unsprung mass of the vehicle resulting in better handling. This paper discusses the design, structural, and thermal analysis; the manufacturing method; and the testing of silicon carbide-reinforced aluminum (Al 6061) matrix composite material for motorcycle brake rotor. [ABSTRACT FROM AUTHOR]

Additive manufacturing is a powerful process to build complex geometry. Besides the numerous process parameters influencing the mechanical part performances, other parameters related to the initial powder feedstock or component machining are of most importance. In this study, the combined effect of a wide particle size distribution, surface machining and stress-relief heat treatment on the microstructure and mechanical properties (tension and fatigue) of a stainless steel AISI 316L, produced by laser powder bed fusion, is investigated. In order to correctly investigate those parameters separately, the netshape/machined character of the sample, alongside with the heat treatment, is studied for two kinds of powder having different particle size distributions, i.e. narrow and widely spread. Results show that a large spread of particle size is only slightly detrimental to the fatigue life, in particular in high-cycle conditions due to a larger porosity related to a weakly more uneven particle spatial distribution in the bed. Nevertheless, this effect is of a second order compared to machining or heat treatments which greatly affect the mechanical behaviour. Surface machining and moderate heat treatment are then the best post-operational steps to increase the fatigue life in high-cycle fatigue conditions independently of the particle size distribution. Results are discussed in terms of defects, microstructural modifications, surface roughness, martensitic transformation and mechanical loading. [ABSTRACT FROM AUTHOR]

Performing high-quality repair on aging hydro power equipment is a challenging issue for utilities. Weld repair deteriorates the mechanical properties of the base metal in and around the heat-affected zone. For martensitic stainless steel runners, there is no way to perform post-weld heat treatment (PWHT) on site to restore those properties without dismantling, a very expensive job for such large components, typical of power utilities. To perform in situ high-quality repairs on such components, a new robotic heat treatment process is developed. Heat is generated and controlled using a flat spiral coil mounted on a compact, portable robot and moved over the area needing heat treatment. Unlike conventional induction heating, which requires a customized coil, this new approach combines a universal coil and a flexible robot to heat a broad range of complex shapes. One critical aspect is to set heating and path parameters in order to generate a target spatial and temporal temperature field. This paper proposes a numerical method combining thermal finite element analysis and a non-linear optimization algorithm to set these parameters. The temperature resulting from the electromagnetic field induced by the coil is modeled using an average heat input source to improve computation speed. Good agreement is obtained between numerical and experimental results for PWHT under laboratory conditions. [ABSTRACT FROM AUTHOR]

This paper investigated the grinding machinability and surface integrity of premium thread gauge material 9Mn2V in conventional surface grinding by using seeded gel (SG) abrasive (3SG80KV) under different heat treatment processes. Serious meshy segregation of carbide, excessive amounts of retained austenite, coarse and inhomogeneous distribution of material structure were significant causes of grinding burn and grinding crack. In order to improve the abrasion resistance and mechanical properties of workpiece material, cryogenic and tempering treatment was added. After adopting cryogenic and tempering treatment for two times, the disappearance of the meshy segregated carbide and network carbide was eliminated, the amount of the retained austenite content was within 4 %, and martensite became much more fine and homogeneous. The grinding experiment results indicated that workpiece material 9Mn2V could provide superior grinding integrity with the occurrence of grinding burn and grinding cracks reduced by using this process. [ABSTRACT FROM AUTHOR]

This study presents the development and experimental verification of a simulation model for estimating the local microstructure of a tool geometry after heat treatment. The experiment involved subjecting a metallic block of dimensions 40 × 50 × 50 mm, made of the ledeburitic cold work steel DIN EN 1.2379 (X153CrMoV12; AISI D2), to a heat treatment in a laboratory furnace at 1000 °C for 20 min. Thermocouples were strategically placed to record time-temperature profiles at different locations within the block. Following the heat treatment, the local microstructure was determined through quantitative image analysis, and the local hardness was measured as a function of the distance from the block's edge to its core. These measurements were then correlated with the corresponding time-temperature curves obtained from the thermocouples. To replicate the local time-temperature profiles, the thermophysical properties of the steel were experimentally determined and incorporated into a finite element analysis heat transfer simulation using Abaqus FEA® software. This simulation approach, combined with the MatCalc software, facilitated the calculation of various local microstructural characteristics such as carbide content, carbide type, carbide distribution, and chemical composition of the matrix. Furthermore, the content fractions of the microconstituents of the matrix, including martensite and retained austenite, were determined based on the simulated martensite start temperature, employing an optimized function fitted to experimental data. The developed simulation model offers potential applications in two important areas. Firstly, it can be used to adapt heat treatment processes for tools of different sizes in production, optimizing their mechanical properties. Secondly, it enables efficient optimization of heat treatment routes by considering changing initial states, leading to high process quality in terms of mechanical properties. Overall, this study provides valuable insights into the estimation and control of local microstructure in tool geometries through the use of a validated simulation model. [ABSTRACT FROM AUTHOR]

The friction deposition process is well known for surface repairs and depositing corrosion and wear resistant coatings. In this study, we explored friction deposition additive manufacturing (FDAM) for producing alloy 718 components. The microstructure evolution, temperature distribution during the process, and room temperature tensile properties of the FDAM processed alloy 718 were studied. Multi-layer deposits with sound metallurgical bonding at the layer interfaces were obtained. The deposits showed fine equiaxed grains with grain size varying from 4 to 7 μm across the deposit height, having finer grains (~4 μm) closer to the substrate and coarser grains (~7 μm) at the top of the deposit. Thermography analysis was employed to analyze the temperature distribution during friction deposition, revealing a maximum peak temperature of 1121°C on the deposited material. Subsequently, the material cooled rapidly at a rate of 30°C/s. The FDAM sample in the as-deposited condition exhibited higher tensile strength than the wrought alloy 718 in the solution-treated (ST) condition. The post-direct aging (DA) of the FDAM sample resulted in a 41% improvement in tensile strength than the as-deposited condition and met the tensile properties of wrought alloy 718 in aged condition as per aerospace material specifications (AMS). Furthermore, there were no significant variations observed in the tensile properties across different regions of the FDAM deposit height. [ABSTRACT FROM AUTHOR]

AA2024 was developed to investigate how heat treatment might affect its mechanical and corrosion characteristics. The samples underwent different heat treatment processes: three solution heat treatments at 495 °C for 2 h followed by natural aging for 5 days, and two artificial aging treatments, one at 190 °C for 2.5 h and the other at 130 °C for 6 h. After the heat treatments, all samples were immersed in a 3% Nacl salt solution for a total of 2880 h. The metallurgical characterization of the samples was performed using optical microscopy, and scanning electron microscopy. The observations revealed the formation of corrosion product nodules on some samples, while others showed pitting corrosion, and one sample (T6) experienced intergranular corrosion. Moreover, the microstructural analysis indicated an evolution of dimples in the AA2024 T4 alloy, along with the development of fine grains compared to the non-heat-treated samples. Mechanical characterization was carried out using a Vickers hardness tester and a tensile testing machine. The Vickers hardness test showed that the AA2024 T4 sample exhibited the highest hardness value (Hv = 145) compared to the other samples. However, the tensile strength of the AA2024 alloy decreased from 512.20 MPa to 411.02 MPa after the T4 heat treatment. The yield strength (YS) and elongation properties also experienced changes after the heat treatments. [ABSTRACT FROM AUTHOR]

In automotive industry, heat treatment of components is implicitly related to distortion. This phenomenon is particularly obvious in the case of gearbox parts because of their typical geometry and precise requirements. Even if distortion can be anticipated to an extent by experience, it remains complex to comprehend. Scientific literature and industrial experience show that the whole manufacturing process chain has an influence on final heat treatment distortions. This paper presents an approach to estimate the influence of some factors on the distortion, based on the idea of a distortion potential taking into account not only geometry but also the manufacturing process history. Then the idea is developed through experiments on an industrial manufacturing process to understand the impact of residual stress due to machining on shaft bending and teeth distortion during heat treatment. Instead of being measured, residual stress is being neutralized. By comparing lots between each other, connections between gear teeth geometry and manufacturing steps before heat treatment are obtained. As a consequence, geometrical nonconformities roots can be determined more easily thanks to this diagnosis tool, and corrective actions can be applied. Secondly, the influence of product geometry on bending is experimentally considered. Moreover, metallurgical observations enable to explain the influence of workpieces geometry on shaft bending. Thanks to the obtained results, process and product recommendations to decrease shafts bending are proposed. [ABSTRACT FROM AUTHOR]

Grind hardening process utilizes the heat generated in the grinding area for the surface heat treatment of the workpiece. The workpiece surface is heated above the austenitizing temperature by using large values of depth of cut and low workpiece feed speeds. However, such process parameter combinations result in high process forces that inhibit the broad application of grind hardening to smaller grinding machines. In the present paper, modelling and predicting of the process forces as a function of the process parameters are presented. The theoretical predictions present good agreement with experimental results. The results of the study can be used for the prediction of the grind hardening process forces and, therefore, optimize the process parameters so as to be used with every size grinding machine. [ABSTRACT FROM AUTHOR]

In this paper, the influence of tube material, microstructure, and heat treatment on process responses of tube hydroforming has been studied. One of the most important parameters in performing a successful tube hydroforming process is the selection of appropriate material for tubes. In the analysis section, effective parameters for the selection of an appropriate tube material for the hydroforming process have been investigated; it was concluded that higher strain hardening exponent ( n), elasticity modulus ( E), and anisotropy index ( R) can enhance formability in this process; and the effects of microstructure and heat treatment on the formability of ASTM C11000 copper and ASTM AA1050 aluminum have been investigated. Consequently, four different heat treatment processes, which had different heating temperatures and durations, were selected, in addition to different cooling methods for each of the materials. In the experimental tests, the effects of these heat treatment methods on maximum bulging height, thickness strains, and final forming pressures were scrutinized. The effects of heat treatment on copper microstructure were also studied through metallographic tests; on the other hand, the effects of microstructure on tube hydroforming process were justified. As a result of these analyses, two heat treatment methods, namely, heating to 450 and 350 °C for 15 min and cooling in water, were recommended for copper and aluminum, respectively. Using these methods and due to their consequent fine and homogenous microstructure, higher mechanical strength and increase in material formability was achieved by attaining higher thickness strain and bulging height values. Finally, after extracting the mechanical properties of the two materials and comparing them with each other, parameters of strength coefficient and strain hardening exponent were reported as two effective factors that would improve tube deformation by tube hydroforming process. [ABSTRACT FROM AUTHOR]

Aluminum alloy tailor-welded blank (TWB) forming can achieve both material lightweight and structural lightweight, especially that dissimilar aluminum alloy TWB forming can better adapt to the different performance requirements of different parts of aerospace and automotive lightweight components to further achieve weight reduction and has a wide range of engineering application prospects. In this work, 2024-O and 7075-O aluminum alloy are used as the object of study. By observing the microstructure and measuring mechanical properties, establish the multiple- materials strength-mismatched of dissimilar friction stir welding (FSW) AA2024-7075 joints, to research the formability and deformation behavior of dissimilar FSW AA2024-7075 joints under different strength-mismatched conditions. Results show that during the tensile deformation of the dissimilar FSW AA2024-7075 joint, the equivalent stresses and strains in the weld nucleus area (WNZ) experience several abrupt changes. In the mixed WNZ of microstructures of the 2024WNZ and 7075WNZ, the AA7075 with high yield strength will have a restraining and protective effect on the AA2024 with low yield strength, which suppresses the deformation of AA2024. The heterogeneous microstructure of the dissimilar FSW AA2024-7075 joint leads to severe inhomogeneous deformation, which reduces the elongation. The 350 ℃ annealing heat treatment effectively reduces the inhomogeneity of the microstructure of each zone, lowers the difference of mechanical properties between AA2024 and AA7075, improves the uniformity of deformation of the dissimilar FSW AA2024-7075 joint, and increases the elongation from 8.5% to 12.8%. [ABSTRACT FROM AUTHOR]

Vacuum brazing is a black box process, so component distortion that occurs during the heat treatment is difficult to prove experimentally. Thus, a novel FE-model was developed in ANSYS Workbench to calculate the time and location resolved component deformation of AISI 316L/B-Ni2 brazing assemblies. In this regard, a new method of radiation and contact modeling was developed that enabled a significant reduction of the calculation times and solved the convergence issue for simulating the distortion of large-scale, thin components. The results showed that the component deformation during heating can be easily kept in the elastic range and can be almost completely eliminated by using a geometry-dependent soaking time. In contrast to this, high cooling rates were found to result in thermally induced stresses well above the elastic yield limit, causing significant component deformation. With further cooling, the deformation decreases significantly, but it depends on the initial stress state, the geometry, and the cooling rate whether the deformation can be completely leveled out during the shrinkage of the component. Thus, the initially high cooling rates were identified to be responsible for the final distortion. Furthermore, this was highly affected by the local position in the heating chamber. The simulation results were used to design a fixture for vertical positioning, which reduced the max. temperature difference in the brazing assembly from 141 to 79 °C, the max. interim distortion from 275 to 31 µm, and the final distortion from 14 to 8 µm. [ABSTRACT FROM AUTHOR]

This work investigates deposition strategies using arc oscillation to manufacture steel solids by wire arc additive manufacturing (WAAM) in order to avoid excessive grain growth, one of the main challenges in solid manufacturing by WAAM. The components were characterised morphologically, mechanically, metallurgically and in terms of material efficiency and geometric uniformity. The results show that the solids fabricated with arc oscillation resulted in an average grain size similar to the original base material or even smaller in completely continuous depositions, i.e. without idle time. The strategies can be used to produce solids without heat treatments or waiting time between layers, therefore increasing the deposition rate and reducing costs. Smaller oscillated beads generated solids with more uniform and accurate dimensions, showing better use of material and less material waste in the case of machining. [ABSTRACT FROM AUTHOR]

This study investigated the microstructures and tensile properties of as-build and heat-treated (including T6, T2, and T6-T2 treatments) AlSi10Mg samples fabricated by laser powder bed fusion (LPBF). The microstructure analysis revealed that the trend of eutectic Al-Si phase distribution along grain boundaries for heat-treated samples was significantly weakened, and the eutectic Al-Si phase was transformed into Si particles which were uniformly distributed in α-Al matrix. For the T6-T2-treated specimens, the Si content in particles was the highest. Meanwhile, the T6 treatment increased the proportion of equiaxed grains on vertical section most significantly. However, in the wake of heat treatments, the average grain size on horizontal section had little change while the average grain size on vertical section was increased. The properties analysis demonstrated that the T6-T2-treated specimens obtained the best elongation and worst strength. Besides, the T6 treatment eliminated the anisotropy of the LPBFed specimens basically and synergistically obtained the best combination of strength and plasticity. The T6 treatment weakened the direction difference to the greatest extent, whereas the T2 treatment minimized the stress concentration. According to the comparative finding, the Si content in particles played an important part in properties. Besides, the relationship among inverse pole figure (IPF) maps, pole figure (PF) maps, the mass fraction and distribution of Si in Al matrix and Si particle, the grain size, kernel average misorientation (KAM), and mechanical properties under different heat treatments was established, which provided a new idea for the selection of heat treatments on LPBFed parts. [ABSTRACT FROM AUTHOR]

The effect of T6I4 and T6I6 interrupted aging processes on the machinability of 7075 aluminum alloy is investigated. The cutting force, cutting temperature, surface roughness, and tool wear variations of the alloy in T6I4 and T6I6 states are identified at the macroscopic and microscopic scales with the help of a dynomometer, a roughness tester, an optical microscope, a scanning electron microscope, and ABAQUS 6.14 and through experiment and simulation. The results show that compared with T6 peak-aging, T6I4 and T6I6 greatly improve the machinability of 7075 aluminum alloy; under the same cutting parameters, 7075-T6I4 and 7075-T6I6 alloys have smaller cutting force, cutting temperature, and surface roughness, with 7075-T6I4 displaying the best performance. Increasing cutting speed and reducing feed rate, together, effectively improve the workpiece surface finish. The tool wear is also better and mainly comprises tool chipping and adhesive wear. XRD analysis indicates that during cutting, the precipitates of 7075 aluminum alloy are primarily η-phases; the Al peak of 7075-T6I4 alloy is significantly higher than that of the other two heat treatment states. Its grain size is smaller, too. [ABSTRACT FROM AUTHOR]

The objective of this work is to study the microstructure and the texture evolution in welded joint of X70 steel with duplex stainless steel joined by gas tungsten arc welding (GTAW) process and heat treated at 200 °C and 600 °C. Then, the microstructural evolutions are correlated to their hardness mechanical property. The characterization techniques used are optical microscopy, scanning electron microscopy, EDS, Vickers microhardness, tensile tests, X-ray diffraction, and electron backscatter diffraction (EBSD) technique. Two heat affected zones were observed in welded joint with different microstructures. Heat affected zone on the X70 steel side and another on the duplex stainless steel side. A solidification microstructure was observed in the fusion zone such elongated ferritic grains and a growth direction < 100 > was found. The most microstructural transformations were observed in the vicinity of the interface which connects the heat affected zone to the fusion zone either on the X70 steel side or on the duplex stainless steel side. The effect of heat treatment on the hardness of the welded joint was noticed in the side of the duplex stainless steel. The fusion zone is the hardest zone of the welded joint (309.4 Hv) and which is not affected by the applied heat. X-ray diffraction analysis did not reveal the formation of new phases after the heat treatments applied to the welded joint. The tensile tests have shown that the welded joint treated at 200 C presents the highest value of ultimate tensile strength (667 MPa). [ABSTRACT FROM AUTHOR]

Dissimilar joints are often used by the oil and gas industry to join components such as forged flanges and piping used in subsea operations. The technique consists of buttering the forged flange before the closure weld is made. After the buttering runs, the forged flange is subjected to a post-weld heat treatment. However, the true effectiveness of this procedure has been questioned after failures began to occur in the fusion zone of the forging piece and nickel alloy. The present work aims to investigate the influence of post-weld heat treatment on the mechanical and microstructural behavior of the buttered dissimilar interface of AISI 4130 steel with nickel alloys. Gas metal arc welding processes in continuous and pulsed current modes were employed. AWS ERNiCrMo-3 (Inconel 625) and AWS ERNiCrMo-15 (Inconel 725) solid wires were used as filler metals. Post-weld heat treatment was performed on the buttered plates. The microstructure at the interface of the buttered fusion line were characterized by optical microscopy and scanning electron microscopy. Microhardness analyses were performed at the interface of the buttered weld. The results showed that gas metal arc welding process with pulsed current mode and Inconel 625 as filler metal showed lower levels of dilution and greater control of the partially diluted zones, proving to be more suitable for this type of application. It was also found that regardless of the welding procedure, post-weld heat treatment made the interface more brittle. [ABSTRACT FROM AUTHOR]