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Environmentally assisted cracking can significantly affect the performance of high strength alloys and limit material selection to minimize the risk of subcritical crack growth in service. UNS N07718 is widely used in marine service applications and under a variety of conditions, such as: alternate immersion, different levels of cathodic protection, and freely corroding galvanic couples, because of its demonstrated corrosion and fracture resistance in these environments. In this work we developed a representative model of the material microstructure including the metal grains, the material texture, and the precipitates along the grain boundaries and within the grains. The microstructural model was subjected to the boundary conditions identified at the notch root of a fracture mechanics sample and the results are used as input for a simulation of hydrogen diffusion from the surface of the notch, assuming the material has been introduced to a hydrogen producing environment. The diffusion of hydrogen was modeled by Fick's law and included both hydrostatic stress and mobile dislocation velocity as driving forces. The influence of immobile dislocations was also modeled to account for the irreversible trapping. The results show that hydrostatic stress and immobile dislocation trapping can significantly alter the highest concentration of hydrogen and its location within the microstructure towards the fracture process zone. Mobile dislocation velocity has a small influence in determining the hydrogen distribution near the fracture process zone. [ABSTRACT FROM AUTHOR]

The performance of modern dual hardening steels strongly relies on a well-controlled precipitation processes during manufacturing and heat treatment. Here, the precipitation of intermetallic β-NiAl in recently developed dual hardening steels has been investigated during aging using combined high-energy synchrotron X-ray diffraction and small-angle scattering. The effects of heating rate and aging temperature on the precipitation kinetics and lattice mismatch in two alloys (Hybrid 55 and Hybrid 60) were studied. Precipitation starts already during heating, typically in the temperature range 450 °C to 500 °C. The precipitation process is significantly faster at 570 °C compared to 545 °C for both steel grades, and the number density reaches its maximum already within 1 hours during aging at 545 °C and within 15 minutes during aging at 570 °C. The effect of heating rate is limited, but the precipitation during heating increases in Hybrid 60 when slower heating rate is used. This led to slightly higher volume fractions during subsequent aging, but did not affect the particle size. The lattice mismatch between β-NiAl and the matrix initially develops rapidly with time during aging, presumably due to a developing chemistry of the β phase, until a particle size of around 1.5 nm is reached, whereafter it saturates. After saturation, the lattice mismatch is small, but positive, and independent of temperature during cooling. [ABSTRACT FROM AUTHOR]

The study investigated the effect of retrogression and re-aging (RRA) on the structure and properties of the new Al–3.5Zn–3.5Mg–3.5Cu–1.6Er–0.2Zr–0.2Cr alloy through the use of scanning electron microscopy, thermodynamic calculations, hardness tests, current density, and corrosion potential. During the crystallization process, chromium is distributed between primary intermetallic compounds with an approximate composition of (Al,Zn)79.8Mg4.7Cu3Cr5.5(Er,Ti)7, with a size of approximately 10 μm and an aluminum solid solution. Following two-stage homogenization heat treatment, the Al8Cu4Er and Mg2Si phases exhibit minimal morphological changes, with the θ‑phase (Al2Cu) being completely dissolved and the T‑phase (Al,Zn,Mg,Cu) transformed into the S‑phase (Al2CuMg). Thermodynamic calculations indicate that the alloy should also contain the Al3Zr and Al45Cr7 phases, which precipitate from the supersaturated solid solution during homogenization. Age hardening in the temperature range of 150–210 °C occurs due to the release of metastable modifications of the T‑phase. The combination of hardness (140 HV) and corrosion resistance (minimum corrosion current density 1 μA/cm2) is optimized by retrogression and re-aging. [ABSTRACT FROM AUTHOR]

Additive manufacturing is gaining wide acceptance in the manufacturing industries, but the joining of additively manufactured components is a rarely researched area. In this study, diffusion bonding of directed energy-deposited (DED) Mg alloy (AZ31), using an electric arc as an energy source was analyzed. Diffusion bonding (DB) was performed in a non-vacuum condition with gallium treatment at the faying surfaces to eliminate the oxide formation and promote metallurgical contact. Microstructural and elemental distribution analyses of additively manufactured AZ31 alloy and diffusion-bonded joints were carried out using FESEM and EPMA. EBSD analysis indicated that the bonding interface is characterized by discontinuous dynamic recrystallized grains featured by grain boundary bulging and grain boundary migration. The 90° triple junction observed at the interface migrates to reduce the grain boundary energy. The fine precipitates of β-Mg17Al12 were distributed uniformly throughout the material, which enhanced precipitation hardening. High integrity joints without any voids could be obtained by diffusion bonding and the joint line was not discernible. The high-intensity elemental content at the joint interface highlights the enhanced interdiffusion of constituent atoms across the faying surfaces. [ABSTRACT FROM AUTHOR]

The PH 13-8 Mo family of steels belong to the martensitic precipitation hardening stainless steels (MPHSSs) category, which exhibits a good combination of mechanical properties and corrosion resistance. Additive manufacturing (AM) offers advantages, including reduced material waste and the capability to produce complex, near-net-shape parts. Consequently, the application of AM techniques to the PH 13-8 Mo family is being increasingly explored across various industries. This review paper presents the existing literature on the topic and provides an overview. The review starts by presenting information about the PH 13-8 Mo family, including microstructure, chemical compositions, heat treatments, and mechanical properties. Afterwards, the work focuses on presenting the microstructure and resulting properties of PH 13-8 Mo family processed by three different additive manufacturing processes: Powder Bed Fusion using a Laser Beam (PBF-LB), Directed Energy Deposition using an Electric Arc (DED-Arc), and Directed Energy Deposition using a Laser Beam (DED-LB), both in their as-built condition and following post-processing heat treatments. The review concludes with a summary and outlook that highlights existing knowledge gaps and underscores the need for further research to tailor the microstructural evolution and enhance the properties. The findings indicate that AM of the PH 13-8 Mo family has the potential for industrial applications, yet further studies are necessary to optimize its performance. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The influence of ageing and ageing time on the mechanical properties, such as tensile strength and wear behaviour, of Al18Si3.6Cu0.34Ce alloy have been discussed. The As-cast alloy was subjected to T6 heat treatment (solutionization at 510° for 1 hr and ageing at-210°C) for different ageing durations like 1 hr, 3 hr, 5 hr and 7 hr, the morphology of as-cast and age hardened samples is examined by SEM and optical images, the sharp edges of primary-silicon and α-Al matrix with a columnar grain structure of untreated alloy changed after ageing, they are rounded off, spheroidisation with uniform redistribution of Al2Cu blocks, Al2CeSi intermetallic precipitates are formed with improved grain boundaries, and it develops obstacles in larger scale to the flow of dislocation mechanism, so it strengthens the metal matrix. Compared to as-cast alloy, the mechanical properties are improved after ageing. For 5-hr aged samples, the yield strength (YS) elevated to 127.44 MPa (improved by 83%) with an elongation rate of 1.64% (41.4%) as compared to as-cast alloy, and the ultimate tensile strength of as-cast alloy (158.2 MPa) enhanced to 193.835 MPa and 168.7 MPa after 1 hr and 3 hr ageing, respectively. Ageing improves the flow stress, which is predominantly the effect of homogenisation. Considerable improvements in the wear resistance after age hardening were noticed; both VWR and COF both a linear relation, with applied load at constant speed. As-cast and 7-hr aged samples show poor wear resistance due to co-existence of incoherent phases (Al2Cu and Si) in the metal matrix, and alloy ageing for 1 hr, 3 hr and 5 hr improves the load bearing and shear strength. [ABSTRACT FROM AUTHOR]

Precipitation hardening has been demonstrated as a good practice to suppress domain wall mobility and reduce losses in piezoceramics, especially when subjected to high-power drive. The hardening effect is generally determined by the morphology of precipitates introduced during the high-temperature aging treatment. In the present work, impedance spectroscopy is performed on the as-quenched and aged (Li, Na)NbO3 (LNN) solid solution to clarify the influence of aging treatment on the conductivity and electrical heterogeneity of LNN samples. The as-quenched LNN sample shows a lower resistivity due to higher oxygen vacancy concentration, which can be largely eliminated by reoxidation during the aging process. Moreover, the LiNbO3 (LN) precipitate-caused electrical heterogeneity is clarified by analyses of the impedance spectra fitted by an equivalent circuit and the activation energy calculated from relaxation peaks. The revealed impedance changes provide a foundation for future optimization strategies of precipitation-hardened piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

This paper investigates the metallurgical factors contributing to the non-conformance in mechanical properties observed in Maraging 250 steel (M250) holding pins after the aging process. Results revealed a significant difference in the mechanical properties between the aged as-received pins and the aged as-annealed rods. Microstructural analysis highlighted the influence of processing conditions, including straightening and centerless grinding, on the material's behavior during aging. Moreover, the presence of retained austenite was found to exceed specified limits in the as-received rods that exhibited mechanical property non-conformance. In this study, a comprehensive metallurgical analysis was conducted to understand the factors contributing to the non-conformance in mechanical properties of aged M250 holding pins and essential steps required for improving the reliability and performance of these components. By gaining insights into the microstructural changes and associated material behavior, appropriate process optimizations and quality control measures can be implemented to ensure the attainment of desired mechanical properties. [ABSTRACT FROM AUTHOR]

A novel accelerator, cerium cysteine (Ce-Cys) was synthesised by double replacement reaction. The complex was characterised by FT-IR analysis, thermal analysis, EDTA titration and elemental analysis, respectively, to determine that the molecular formula of the complex was Ce (Cys)3Cl3·3H2O. Cure characteristics, crosslink density, mechanical properties and thermo-oxidative ageing of NR compounds were investigated. The research revealed that the vulcanisates containing Ce-Cys manifested high scorch time, outstanding mechanical properties, and better thermo-oxidative ageing properties. Furthermore, based on kinetic calculations, it was concluded that as the amount of Ce-Cys increased, the reactivity of the crosslink precursor increased while the activation energy decreased. [ABSTRACT FROM AUTHOR]

The Guinier–Preston (GP) zones have an important influence on the improvement of the age-hardening level of alloy. We here prepare six kinds of Mg-6Zn-5Al (ZA65) magnesium alloy samples to investigate the microstructural evolution, precipitation behavior, and strengthening mechanism using an optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), and micro-hardness tests. The finding reveals that the GP zones are observed in non-dendritic alloys experiencing pre-aging at 80°C for 24 h, whose formation creates more nucleation sites and accelerate kinetics for precipitated phases. Consequently, the introduced pre-aging has been successful in promoting the increase of the age-hardening level of non-dendritic alloys. The double-aged non-dendritic alloys show a significantly changed microstructure with a high density of long rod-shaped β1′ precipitations, making the age-hardening level of double-aging much better than that of single-aging, and the peak value 90 HV was obtained 4 h in advance, which is an increase of 4 HV compared with that of the direct aged non-dendritic alloy. The strengthening mechanism of non-dendritic alloys is mainly summarized as grain boundary strengthening, GP zone strengthening, and the shearing strengthening of β1′ and β2′ precipitations. Among these, the GP zone strengthening is a fundamental contributor to improving the age-hardening level. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Our study investigates the interaction of dislocations with hexagonal close-packed (hcp) and chi-phase (χ) particles in body-centred cubic (bcc) tungsten (W) using molecular dynamics simulations. The research aims to understand how these interactions influence the mechanical properties of W, particularly in the context of neutron irradiation environments. The simulations were conducted with spherical and cylindrical particles at various temperatures and cell sizes to observe the effects on critical shear stress. Results indicate that the shape and size of the particles significantly affect the critical shear stress required for dislocation movement, with cylindrical particles requiring higher stresses than spherical ones. Additionally, the study found that temperature variations have a more pronounced effect on χ-phase particles compared to hcp-phase particles. Our findings provide insights into the strengthening mechanisms in W-Re alloys and suggest potential pathways for enhancing the material's performance under extreme conditions. [ABSTRACT FROM AUTHOR]

Heterogeneous grain structures with coherent L12 nanoprecipitates were constructed in a medium entropy alloy with chemical composition of Co34.5Cr32Ni27.5Al3Ti3 (at. %). The volume fraction and size of L12 nanoprecipitates are observed to become higher and larger, and the interspacing is found to become smaller with increasing aging time, resulting in a severer heterogeneity. The domain of tensile properties was expanded by varying the size and volume fraction of coherent L12 nanoprecipitates after aging treatment. The samples after longer-time aging treatment show stronger strain hardening as compared to those after shorter-time aging treatment. The hetero-deformation-induced (HDI) hardening plays a more vital role in the longer-time aged samples than the shorter-time aged samples, especially at the elasto-plastic transition stage. The dominant precipitation hardening mechanism is observed to transit from dislocation-cutting to Orowan dislocation-looping with increasing precipitation size, as predicted by a theoretical model and validated by experimental results. Multiple deformation defects, such as deformation twins, stacking faults and Lomer-Cottrell locks, are the dominant deformation mechanisms for all samples, while interactions between these defects and L12 nanoprecipitates were observed to be more intensive in the longer-time aged samples than in the shorter-time aged samples, resulting in stronger precipitation and HDI hardening.

The effects of Nb and Ni contents on the precipitation of the Ni16Nb6Si7-G phase and the resulting hardening behavior in Fe–20Cr ferritic alloys were systematically investigated using micro-hardness, electron microscopy, and atom probe techniques. The results demonstrate that an optimal Nb content of ∼0.75 wt. % promotes the precipitation of the Ni16Nb6Si7-G phase, leading to a maximum micro-hardness of approximately 430 H V when aged at 560 °C for 24 h. Excess Nb content (>0.75 wt. %) introduces the Fe2Nb-Laves phase at grain boundaries and within the grains, which competes with the G-phase for precipitation. Conversely, an increase in Ni content effectively raises the dissolution temperature of the Ni16Nb6Si7-G phase to approximately 850 °C. The austenite phase begins to form when the Ni content exceeds 4 wt. %. Finally, the strengthening effect of the Ni16Nb6Si7-G phase and its underlying competition precipitation with the Fe2Nb-Laves phase as well as the possible benefit of inducing austenite phase was discussed in the context of developing 20Cr ferritic alloys with high strength and good ductility. These findings provide valuable insights into the influence of Nb and Ni contents on the microstructural evolution and mechanical properties of the newly developed 20Cr alloy, which may be helpful in guiding the design of high performance ferritic alloys by optimizing composition and heat treatment processes.

The aim of the present study is to investigate the effect of accumulative roll bonding (ARB) and precipitation hardening on the microstructure development and there of mechanical properties of ultrafine grained Al–Ag-Sc alloy. For this purpose, the samples were heated to a temperature of 600 °C for 24 h, and then they were quenched in water. In order to carry out the two-stage precipitation hardening process, the samples were placed in the furnace at a temperature of 350 °C for 5000 s in the first stage, which was followed by quenching in water. In the second stage, they were heated to 250 °C for 5000 s following by water quenching too. Following, the samples were subjected to the ARB for up to 8 cycles. Scanning Electron Microscope (SEM) equipped with Electron Backscatter Diffraction (EBSD) and energy dispersive spectroscopy (EDS) techniques, and X-Ray Diffraction (XRD) was used to verify the microstructure and phase analysis of the prepared samples. Also, tensile and microhardness tests were conducted to confirm the mechanical properties, and pin-on-disk tests were done to check wear behavior. Microstructural parameters such as crystallite size, microstrain, and density of dislocations in rolled sheets were estimated using the Rietveld method. The Results have shown that applying various cycles of the ARB process leads to the development of ultra/nano grain structure. In that sense, performing 8-cycle of the ARB transformed the low angle grain boundaries (LAGBs) of the 4-cycle ARB condition to high angle grain boundaries (HAGBs). Results showed that there is proper welding between different layers, except for the layers created in the last cycle. Similarly, the obtained size of the crystallites demonstrates that the samples become finer when ARB cycles are increased. The results of the mechanical tests indicated that after 8 cycles, there is approximately 3.5-fold and 2.5-fold increase in the tensile strength and hardness compared to the original (annealed) sample, respectively. While the elongation decreased slowly and reached 1.5% in the 8th cycle. A fractography of the fracture surface of the original sample included deep and coaxial dimples, indicating a ductile fracture. Analysis of wear surface degradation showed that scratch wear occurred for all samples.

In this study, we investigate the age-hardening behavior and mechanical properties of direct chill (DC)-cast Al–10Si-0.35 Mg alloys subjected to melt thermal rate treatment (TRT). Our findings reveal that TRT refines the microstructure and precipitation morphology. Grain analysis indicates the prevalence of twin dendritic grains in both TRT and non-TRT (NTRT) alloys during casting, with the TRT billet exhibiting smaller grains. The microstructural analysis demonstrates that TRT reduces the size of secondary dendrite arm spacing and eutectic phases while ensuring a uniform distribution of intermetallic particles. The precipitation mechanism in both alloys remains consistent, with the TRT alloy exhibiting a higher density of fine precipitates. Additionally, we observe a novel coprecipitation mechanism of Si and β″ phase, attributed to a lower misfit between (003)β″ and (011)Si compared to that between (003)β″ and (0 2‾ 0)Al. Furthermore, the TRT alloy displays slower precipitation kinetics due to homogeneous solute distribution, resulting in higher activation energy for precipitation nucleation. Consequently, a single age-hardening peak is observed in TRT alloys during aging. TRT alloys exhibit higher hardness and tensile strength after artificial aging at 190 and 210 °C, while maintaining comparable elongation to NTRT alloys. Theoretical calculations of precipitation strengthening also show higher values for TRT alloys, consistent with experimental results. Thus, our findings comprehend the underlying mechanisms of melt treatments crucial for improving precipitation hardening behavior and mechanical properties of Al–Si–Mg alloys.

Lattice structures are widely used in load-bearing and energy-absorption applications for their lightweight, high specific stiffness, high specific strength and excellent energy-absorption. A novel hybrid lattice cell that combining octet cell and body-centered cube cell was proposed, and quasi-static compression experiments and finite element simulations were performed to investigate their energy-absorption characteristic and deformation mechanisms. The effects of the relative density, configuration of cell and component ratio sub-cell on the compression responses were also explored. The results showed that hybrid lattice improves compression modulus and yield strength by 10% and 16% maximally, respectively, and the energy-absorption of enhancement is 20% higher than the conventional lattices. In addition, the hybrid lattice can significantly alleviate the stress softening. By increasing the volume ratio of body centered cubic in the hybrid lattice structures, the energy-absorption can be improved. Under dynamic loading, the proposed hybrid lattice structures displayed outstanding normalized yield strength, which is superior to majority of porous structures. Inspired by the precipitation hardening mechanisms used in metallurgy to design high-performance alloys, two dual-phase lattices are developed. The quasi-static compression of dual-phase lattices shows three stages plateau stress and has a higher third stage than that of traditional dual-phase lattices. These findings provided design strategy for lightweight structure. [ABSTRACT FROM AUTHOR]

Al–Ni-Sc alloys exhibit superior mechanical properties at both room and elevated temperatures, owing to the high thermal and chemical stability of Al3Ni microfibers, and Al3Sc nanoprecipitates. This study explores the impact of scandium additions (0.2 and 0.4 wt%) in eutectic Al–6Ni casting alloys and the influence of aging treatment on electrochemical corrosion behavior in a 0.05 M NaCl solution. Scandium addition did not alter the polarization curve direction but reduced the anodic current density, slowing corrosion. Scandium strengthened the passive film, evident in Electrochemical Impedance Spectroscopy (EIS) with higher Rp values. Sc addition influences the susceptibility to localized corrosion in Al–Ni alloys by promoting the coherence of passive films through the formation of Al3Sc nanoprecipitates and affecting the distribution of Al3Ni. XPS results show that as-aged Sc-containing increases the density of coherent Al3Sc nanoprecipitates, which could result in the formation of Sc2O3 film along with films like Ni2O3 and Al2O3. These synergistic effects contribute to improving the overall corrosion resistance with Sc additions subjected to aging treatment. The microgalvanic effects between the matrix and reinforcement phases, as a result of the formation of nobler Al3Ni and Al3Sc that serve as cathodes within anode Al matrix, cause severe pitting. Nevertheless, after aged treatment, the corrosion resistance dramatically drops for alloys with 0.2 wt% Sc and remains unchanged for 0.4 wt% Sc, due to higher density of nobler Al3Sc nanoprecipitates phase that can counteract the microgalvanic effects and lead to less extensive pitting than as-aged Al–6Ni-0.2Sc.

Precipitation hardening, a cornerstone of alloy strengthening, finds widespread application in engineering materials. Comprehending the underlying mechanisms and formulating models bear crucial significance for engineering applications. While classical macroscopic theoretical models based on the line tension model have historically guided research efforts, their reliance on simplifications, assumptions, and parameter adjustments limits their predictability and expansibility. Moreover, the challenge of understanding the intricate coupling effects among various hardening mechanisms persists. One fundamental question to achieve the transition of material design paradigms from empirical trial-and-error methods to predictive-and-design approaches is to develop more physics-based multiscale modelling methods. This review aims to elucidate the physical mechanisms governing precipitation hardening and establish a tailored bottom-up multiscale modelling framework to steer the design of new alloys. The physical scenarios of precipitation hardening are firstly summarized, including particle shearing, Orowan bypass, and dislocation cross-slip and climb. Afterwards, an in-depth discussion is given regarding the application of macroscopic models and their correlation with the mechanisms and precipitation characteristics. As for the multiscale modelling methods, we categorize them into three main types: slip resistance based approaches, misfit stress field based approaches, and energy based approaches. By integrating multiscale modelling with the physical scenarios, we systematically addressed the key idea of the multiscale coupling framework, and their scale transfer procedure, applicability, advantages, and limitations. Some examples of coupling different types of multiscale methods and considering precipitates with complicated shapes are also presented. This study not only furnishes insightful comprehension of precipitation hardening, but also guides the development of multiscale modelling methodologies for other types of hardening effects in alloys. [ABSTRACT FROM AUTHOR]

In this work, a novel body-centered tetragonal boron nitride (bct-BN)-reinforced 6351Al-based cast metal matrix composite of various reinforcement contents is synthesized for the first time adopting a low-cost hybrid route of liquid metal infiltration-cum-stir casting followed by subsequent treatments of forging and age hardening. Not only a new low-density ultra-hard reinforcement (bct-BN) is incorporated but also a new hybrid casting route pertinent to the low-density reinforcement incorporation is attempted for the first time in order to achieve high specific ultimate tensile strength (SUTS) value. As a noteworthy outcome, a significant value of SUTS (113 MPa/g cm−3) and modest ductility (%Elongation = 10) are achieved in 6351Al-12.3 vol.% BN composite on casting followed by forging and age hardening treatments that is quite comparable or superior to many common aluminum-based metal matrix composites and steels for structural application. In view of structure-property correlation, such an enhanced property (YS = 196 MPa, UTS = 291 MPa, % Elongation = 10, SUTS = 113 MPa/g cm−3) as compared to the initial property of cast 6351Al alloy (YS = 131 MPa, UTS = 144 MPa, % Elongation = 2, SUTS = 56 MPa/gcm−3) is attributed to reinforcement effect of coherent bct-BN particles, matrix grain refinement effect on bct-BN particle incorporation, evolution of nano-twinned region within BN particle on forging and the age hardening effect of coherent Mg5Si6 (β″) precipitates. This asserts an emergence of a new cost-effective structural material in the form of 6351Al/bct-BN composite. [ABSTRACT FROM AUTHOR]

In this work, mechanical vibration was applied to the weldment during welding. This technique is called simultaneous mechanical aging and combined with post-weld thermal aging to form a mechanical-thermal hybrid aging process that was used to strengthen the HAZ of the MIG welded joint of 6082-T6 aluminum alloy. The HAZ softening was significantly reduced through the mechanical-thermal hybrid aging treatment, thereby substantially enhancing the joint strength. The β″ precipitated by post-weld thermal aging and the α precipitated by simultaneous mechanical aging give rise to precipitation hardening in the HAZ and therefore strengthen the HAZ. Degassing of the weld pool and grain refinement in the weld can be achieved by means of mechanical vibration to stir the weld pool. The fracture of welded joints is ductile fracture. [ABSTRACT FROM AUTHOR]

For centrifugal casting 27Cr44Ni5W3Al+MA alloy used in ethylene pyrolysis furnace, its creep behaviours at 1050°C are investigated. The results show that the alloy undergoes three stages during the creep tests under different stress levels ranging from 18 MPa to 30 MPa. The apparent stress index n of the alloy is 6.11, and the creep deformation mechanism is mainly dislocation climbing. During the creep test, the fishbone-like M7C3 inside eutectic precipitates in casted alloy gradually transform to massive M23C6 at the edge of the precipitate. Creep induced voids germinate and connect at the interface of austenite/M23C6 and austenite/Ni3Al, the cavities expand along the M23C6 and Ni3Al, forming micro-cracks and the alloy eventually cracks. [ABSTRACT FROM AUTHOR]

The present study investigates the tensile properties, activation of slip, and grain boundary cracks in Al–Cu–Li ternary alloys with varying precipitations resulting from different aging treatments. The size and distribution of precipitations were ascertained using transmission electron microscopy. The slip activtiy with tensile strain was observed by the electron back-scatter diffraction and scanning electron microscopy. Furthermore, the influence of precipitated strengthening was quantitatively evaluated. The presence of precipitations hinders dislocation movement, increasing strength but reducing the appearance of deformation mechanisms like slip activity, slip transfer, intragranularly misoriented grain boundaries, and lattice rotation, ultimately resulting in reduced ductility. In the sample of T6 aging for 72 h, the coarsed θ′ phase promotes the formation of dislocation rings, resulting in a decrease in the percentage of grains activated with slip to 9.7%. The percentage of grain boundaries with crack initiation reaches 6.9%. On the contrary, in the sample dominated by the T1 phase, the percentage of grains that activate slip is 14.6%, and the percentage of grain boundaries that initiate cracks is only 1.4%. This is because the continuous shear of the T1 phases helps disperse coplanar slip, thereby avoiding cracking caused by excessive stress concentration. Hence, to enhance alloy strength while preserving a certain level of ductility, it is vital to promote the precipitation of the T1 phase and avoid the coarsening of the θ′ phase. This study provides a new insight into the influence of precipitations on the strength and plasticity of Al–Cu–Li alloys. [ABSTRACT FROM AUTHOR]

Periodic electric current pulses, i.e. electropulses, were applied on selective laser melting prepared 15-5 precipitation hardening stainless steel for direct aging. Traditional aging treatment typically takes hours to achieve peak hardening and could induce reverted austenite. Herein, electropulsing treatment on as-built sample can dramatically reduce the processing time to 6 min. Moreover, the nucleation of reverted austenite triggered by the segregation of Ni atoms on the interfaces between Cu-rich precipitates and martensite was not observed. These two unique phenomena were rationalized to the unsynchronized enhancement of diffusivity of Cu and Ni atoms under electropulses due to their different electron configurations. Electropulsing treatment selectively boosted the diffusivity of Cu atoms in additive manufactured maraging stainless steel and dramatically reduced the direct aging time from hours to minutes without inducing reverted austenite. [ABSTRACT FROM AUTHOR]

The phase transformations in an as-cast Fe-30Mn-8.8Al-0.3Si-0.15C steel were analyzed experimentally and numerically with a Calphad-based method during heat treatment. The nonequilibrium phases were determined using the Thermo-Calc Scheil module and the equilibrium phases with Themo-Calc based on the steel chemical composition. The precipitated phases were analyzed with TC-PRISMA using the chemical composition, nucleation site, and temperature among other factors. An ingot of this chemical composition was vacuum-melted using pure elements under an Ar gas atmosphere. As-cast steel specimens were annealed and solution-treated, quenched, and then aged at different temperatures. Heat-treated specimens were analyzed by different techniques. The results indicated that the microconstituents are the α and γ phases for the as-cast, homogenized, and quenched conditions. The main difference among these conditions is the distribution and size of the γ phase, which produced a change in hardness from 209 to 259 VHN. In contrast, the aging treatment at 750 °C caused a decrease in hardness from 492 to 306 VHN, which is attributable to the increase in volume fraction of the γ phase. On the other hand, the aging treatment at 550 °C promoted precipitation hardening from 259 to 649 VHN because of the κ precipitate formation. The calculated results for the different heat treatments with the Calphad-based method agreed well with the experimental ones. In addition, the intragranular precipitation of the κ phase could be simulated using the nucleation and growth and coarsening mechanisms based on a Calphad method. [ABSTRACT FROM AUTHOR]

Copper alloys used in connectors rely significantly on stress relaxation resistance as a key property. In this study, a heavily deformed Cu-Cr-Ag-Si alloy underwent aging at varying temperatures, with a subsequent analysis of its mechanical properties and microstructure, with a particular emphasis on understanding the mechanism of improving stress relaxation resistance. As the aging temperature rose, the Cr precipitated into a Cr-Si composite element precipitated phase. Both work hardening and precipitation strengthening played vital roles in enhancing the stress relaxation resistance of the Cu-Cr-Ag-Si alloy, with the latter exerting a more pronounced impact. The notable performance enhancement observed after aging at 450 °C can be attributed to the synergistic effects of work hardening and precipitation strengthening. Following aging at 450 °C, the alloy demonstrated optimal performance, boasting a tensile strength of 495.25 MPa, an electrical conductivity of 84.2% IACS, and a level of 91.12%. These exceptional properties position the alloy as a highly suitable material for connector contacts. [ABSTRACT FROM AUTHOR]

In the present work, a Ni–Fe–Co–Cr–Al-based medium entropy alloy (MEA) was developed by exploring the vast compositional space provided by the birth of high-entropy alloys (HEAs). The composition was designed via the CALPHAD approach and the designed alloy was melted through the vacuum induction melting (VIM) technique using commercial elements. Post-homogenization treatment, the material was cold deformed up to 73 pct reduction in thickness. This cold-rolled material was annealed with varying duration at a fixed temperature of 900 °C for a better understanding of the static recrystallization mechanism. The systematic static recrystallization study was performed to design a heterogeneous grain distribution within the matrix via partial recrystallization. Post-establishment of the annealing schedule, ageing treatment at 600 °C for 5 hours was carried out. The room temperature mechanical properties were evaluated for selected ageing conditions. An excellent strength of > 950 MPa accompanied by an appreciable ductility of 60 pct was obtained for the fully recrystallized and aged specimen. The obtained results surpassed the strength-ductility synergy exhibited by various solid solution-strengthened (SS) Ni-based superalloys and heterogeneous HEAs and hold the potential to be explored for elevated temperature applications. A systematic study has also been carried out to estimate the contribution of various strengthening factors in the designed alloy and the predicted results corroborate well with the experimental findings. [ABSTRACT FROM AUTHOR]

Precipitation hardening (PH) stainless steels, such as 15-5PH, have a high strength combined with excellent corrosion resistance. These properties make them valuable in critical industries such as defence, construction, aerospace, energy and maritime. Recent advancements in additive manufacturing (AM) technology enable the rapid and cost-effective production of components. In the case of 15-5PH components manufactured using wire arc additive manufacturing (WAAM), the as-deposited mechanical properties are not suitable at present for industrial applications. This paper explores the mechanical properties of this process and alloy combination without post weld heat treatment with the aim of eventual adoption in this condition by industry. The impact of weld heat input on the microstructure and mechanical properties of stainless steel 15-5PH produced using WAAM was investigated. The microstructure was examined using hardness testing in addition to optical and electron microscopy. Furthermore, mechanical properties were measured with tensile and impact testing. Investigations were conducted on material produced using weld heat inputs of 0.223 kJ/mm and 0.565 kJ/mm. These results indicate that reducing the weld heat input leads to a minor decrease in strength but an 80% increase in impact toughness. This reduction in weld heat input is correlated with a 50% reduction in volume fraction of δ-ferrite while also noting a 55% increase in carbide precipitates. In addition, the fracture surfaces were predominantly cleavage or quasi-cleavage in morphology. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive metallurgical analysis conducted on representative samples obtained from two batches of 17-4PH steel rods in order to investigate the underlying factors contributing to the observed differences in their mechanical properties. The samples underwent a solution annealing process followed by an aging treatment to achieve H1025 temper condition. Surprisingly, the mechanical properties of one batch namely 91/5 were found to be inferior compared to the other batch 91/7, with only the latter meeting the specified requirements. To gain a deeper understanding of these differences, a range of analytical techniques were employed. Local variation in austenite stabilizers and its corresponding effect on microstructure of batch 91/5 was found to be the root cause of lower mechanical property. [ABSTRACT FROM AUTHOR]

• The high rolling temperature would impede the DRX occurrence for these final-rolled sheets. • The reduction of the volume fraction of this β phases led to the highest peak-aging hardness in R-450 °C sheet. • The precipitate chains in R-385 °C + A sheets were beneficial for strength and elongation. • The traditional precipitation characteristic in R-450 °C + A sheet was bad for elongation but good for strength. • The peak-aging R-450 °C sheet showed the highest strength, i.e. UTS of 518±17 MPa and YS of 438±18 MPa. In this investigation, a high-strength Mg-12Gd-1.0Er-0.5Zr (wt.%) alloy sheet was produced by hot extrusion (HE) and subsequent hard-plate rolling (HPR) at different temperatures. The results indicate that the microstructures of these final-rolled sheets are inhomogeneous, mainly including coarse deformed grains and dynamic recrystallized (DRXed) grains, and the volume fraction of these coarse deformed grains increases as the rolling temperature increases. Thus, more DRXed grains can be found in R-385 °C sheet, resulting in a smaller average grain size and weaker basal texture, while the biggest grains and the highest strong basal texture are present in R-450 °C sheet. Amounts of dynamic precipitation of β phases which are mainly determined by the rolling temperature are present in these sheets, and its precipitation can consume the content of Gd solutes in the matrix. As a result, the lowest number density of β phase in R-450 °C sheet is beneficial to modify the age hardening response. Thus, the R-450 °C sheet displays the best age hardening response because of a severe traditional precipitation of β' (more) and β Η / β Μ (less) precipitates, resulting in a sharp improvement in strength, i.e. ultimate tensile strength (UTS) of ∼ 518 ± 17 MPa and yield strength (YS) of ∼ 438±18 MPa. However, the elongation (EL) of this sheet reduces greatly, and its value is ∼ 2.7 ± 0.3%. By contrasting, the EL of the peak-aging R-385 °C sheet keeps better, changing from ∼ 4.9 ± 1.2% to ∼ 4.8 ± 1.4% due to a novel dislocation-induced chain-like precipitate which is helpful to keep good balance between strength and ductility. [ABSTRACT FROM AUTHOR]

In the present investigation, an Al-18Si-3.6Cu alloy was modified by cerium (Ce), heat treated (T6), and aged for 1, 3, 5, and 7 h at 210°C. The resulting microstructures revealed that the addition of Ce as a modifier changed the morphology of the primary Si from coarse with a sharp edge to spherical, large-acicular/needle-like eutectic Si into a fibrous state, and dendrites of the Al phase into round branches with less interface separation. After thermal ageing, the microstructure of the modified alloy revealed no change in the morphology of the primary Si phase. However, a considerable change in the eutectic Si phase and the formation of fine precipitates of Al2Cu and Al2CeSi intermetallics in the matrix. Hardness was found to be significantly higher in the modified and age-hardened alloys. A Pin-on-disc wear tester was used to investigate the dry sliding wear behavior of alloys at different loads (10, 20, 30, and 40 N) and 1.0 m/s sliding velocity. The results indicated that the wear rate in the modified alloy was lower than the base alloy. Furthermore, the modified alloy after 5 h age hardening demonstrated high wear resistance and improved wear bearing capacity compared to the 1, 3, and 7 h age hardened alloys. [ABSTRACT FROM AUTHOR]

This study focused on investigating the wear properties of a T6 heat-treated A6082 composite reinforced with Yttria-stabilized zirconia (YSZ). The primary objective was to assess how the reinforcement and heat treatment affected the wear parameters of the composite material. The base material chosen for the composite was A6082 alloy, which possesses excellent mechanical and tribological qualities. YSZ, known for its high hardness and wear resistance, was selected as the reinforcing phase. The T6 thermal treatment was applied to the A6082 composite to enhance its mechanical properties and induce precipitation hardening. To evaluate the wear characteristics of the composite, a pin-on-disc tribometer was utilized. This test setup represents real-world sliding contact conditions that the composite material might encounter. Several parameters were measured during the wear testing, including wear loss, friction coefficient, and wear mechanism, to assess the composite's durability under abrasion. The results of the study demonstrated that increasing the YSZ concentration in the base alloy led to a reduction in material loss and friction coefficient. This improvement can be attributed to the hardness and wear-resistant properties of YSZ. The addition of YSZ reinforcement significantly enhanced the wear resistance of the T6 heat-treated A6082 composite. Furthermore, the T6 heat treatment process also improved the wear properties of the composite. Precipitation hardening occurred, resulting in improved mechanical qualities such as strength and hardness, ultimately leading to increased wear resistance. Microscopic analysis of the worn surfaces revealed that the wear mechanism of the composite shifted from severe abrasive wear to moderate adhesive wear after undergoing the T6 heat treatment. The transformation in wear mechanism is believed to be facilitated by the formation of strengthening precipitates during the heat treatment. These precipitates limited the amount of material lost during the wear test, thereby decreasing both material loss and friction coefficient. In summary, this study demonstrates that the addition of YSZ reinforcement and the T6 heat treatment process effectively enhance the wear properties of the A6082 composite. The presence of YSZ reduces material loss and friction coefficient, while the T6 heat treatment produces precipitation hardening, leading to improved wear resistance. [ABSTRACT FROM AUTHOR]

The heat treatment of aluminum alloys is very important in industries where low weight in combination with high wear resistance, good strength, and hardness are important. However, depending on their chemical composition, aluminum alloys are subjected to different mechanical and thermal treatments to achieve the most favorable properties. In this study, an Al-Zn-Mg alloy was heat-treated including solution annealing at 490 °C for 1 h with subsequent artificial aging at 130, 160, and 190 °C for 1, 5, and 9 h. The hardness (HV1) and abrasive wear resistance with three different abrasive grain sizes were measured for all samples. The highest hardness was measured for the samples artificially aged at 130 °C/5 h, 227 HV1, while the lowest hardness was measured for the samples aged at 190 °C/9 h. The highest and the lowest wear resistance was also observed for the same state, i.e., artificially aged at 130 °C/5 h and 190 °C/9 h, respectively. The critical abrasive grain size was detected for some samples, where a decrease in wear rate was observed with an increase in the abrasive grain size from the medium value to the largest. The Response Surface Methodology (RSM) was applied to demonstrate the influence of the input parameters on the material wear rate. [ABSTRACT FROM AUTHOR]

In this research, a phase-field model was developed to investigate the retrogression process in 7075 aluminum alloy sheets. The model predicts the kinetic of metastable η' phase dissolution during retrogression treatment at a prescribed temperature. The input parameters of the model are achieved from experimental and molecular dynamics investigations. To validate the model, the average diameter and size distribution of η' precipitates attained from the developed phase-field model were compared with those measured from transmission electron microscopy examinations. The experimental as well as the model results demonstrated that only a few percent of η' precipitates are dissolved completely after 100 s of retrogression at 200 °C. In this condition, the alloy hardness can be recovered by a re-aging process, but by increasing the retrogression time to 500 s the major part of the precipitates is completely dissolved and the hardness of the alloy cannot be recovered by a re-aging process. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation was applied to investigate the interaction between precipitate and 10 1 ¯ 2 twin in Mg-Al alloy in this work. Three sets of simulation including twin nucleation, propagation and growth affected by precipitate were performed. The results show the introduction of precipitate has little effect on neither the homogeneous twin nucleation at random site inside the grain nor the heterogeneous nucleation at grain boundary. During twin propagation, the blocking effect of precipitate to the twin tip depends on its size. The twin tip can bypass the precipitate when the precipitate is not long enough. When the length of precipitate is much larger than the thickness of twin, the twin tip will be completely blocked by the precipitate with elastic bending occurring at the junction. During the twin growth, it is found that the precipitate plays not only an obstacle but a source for the twinning dislocations gliding along the twin boundary. The blocking effect of precipitate on twin growth shows a size effect. The influences of width and thickness on precipitation hardening are significantly greater than that of length. [ABSTRACT FROM AUTHOR]

The microstructural evolution and room/elevated-temperature tensile properties of Al-Mg-Si 6082 alloys subjected to thermomechanical processing (homogenization, hot rolling, T6 heat treatment, and thermal exposure) were investigated. Four experimental 6082 alloys were studied, including a Mn-free base alloy and three alloys containing Mn individually and in combination with Cr + V or Mo, in which a number of α-Al(MnFe)Si, α-Al(MnFeCrV)Si and α-Al(MnFeMo)Si dispersoids were formed, respectively. The results showed that both α-Al(MnFeCrV)Si and α-Al(MnFeMo)Si dispersoids had a higher coarsening resistance compared to α-Al(MnFe)Si dispersoids. The presence of α-dispersoids hindered the formation of Mg-Si clusters, which decreased the precipitation of β″-MgSi precipitates, resulting in reductions in room-temperature strengths. During thermal exposure at 300 °C, the α-dispersoids remained thermally stable and became the predominant strengthening phase, resulting in increases of 71 to 126% in the yield strength at 300 °C relative to the base alloy without dispersoids. Among the three dispersoid-containing alloys studied, the alloy containing Mn and Mo exhibited the highest yield strength of 70 MPa at 300 °C, providing the best combination of room- and elevated-temperature tensile properties. [ABSTRACT FROM AUTHOR]

The increase in the yield stress due to the presence of obstacles to dislocation motion such as precipitates is a multiscale phenomenon. The details on the nanoscale when an individual dislocation runs into a precipitate play an important role in determining plasticity on a macroscopic scale. The classical analysis of this phenomenon is due to Bacon, Kocks and Scattergood (BKS) from early 1970's and has been followed by a large body of work both developing the theory and applying it to real experiments and their understanding. Beyond the microscopic details the next level of complexity is met in the micrometer scale when the physics of the yielding and the yield stress depend on two mechanisms: the dislocation-precipitate interaction, and the collective dynamics of the whole ensemble of dislocations in the volume. In this review we discuss the BKS relation and collective dislocation dynamics in precipitation-hardened crystals in the light of recent research, including large-scale discrete dislocation dynamics simulations, statistical physics ideas, and machine learning developments. [ABSTRACT FROM AUTHOR]

Strain-controlled low cycle fatigue (LCF) tests were conducted on conventionally grained (CG) and ultrafine-grained (UFG) Al-Mg-Si alloys treated under various aging conditions. In the cyclic stress response (CSR) curves, CG peak-aged (PA) alloys showed initial cyclic hardening and subsequent saturation, whereas CG over-aged (OA) alloys displayed cyclic softening behavior close to saturation. The UFG materials exhibited continuous cyclic softening except for UFG 3; it originates from the microstructural stability of the UFG materials processed by severe plastic deformation (SPD). Using a strain-based criterion, the LCF behavior and life of the CG and UFG materials were analyzed and evaluated; the results are discussed in terms of strengthening mechanisms and microstructural evolution. In the CG materials, the LCF life changed markedly owing to differences in deformation inhomogeneity depending on the precipitate state. However, the UFG materials displayed a decreasing LCF life as cyclic softening induced by dynamic recovery became more severe; additionally, a relationship between the microstructural stability of the UFG materials and the cyclic strain hardening exponent n′ was suggested. [ABSTRACT FROM AUTHOR]

In order to ascertain the mechanical properties and fracture performance of AA6016 aluminum sheets after cold forming and heat treatment processes, uniaxial tensile tests and fracture tests were conducted under various pre-strain conditions and heat treatment parameters. The experimental outcomes demonstrated that pre-strain and heat treatment had significant impacts on both stress–strain curves and fracture properties. Pre-strain plays a predominant role in influencing the mechanical and fracture properties. The behavior of precipitation hardening under different pre-strains was investigated using Differential Scanning Calorimetry (DSC). The results indicated that pre-strain accelerates the precipitation of the β″ strengthening phase, but excessive pre-strain can inhibit the heat treatment strengthening effect. To consider the influences of pre-strain and heat treatment, a constitutive model, as well as a predictive model for load–displacement curves, was established using a backpropagation (BP) neural network. An analysis of the number of hidden layers and neuron nodes in the network revealed that the accuracy of the model does not necessarily improve with an increase in the number of hidden layers and neuron nodes, and an excessive number might actually decrease the efficiency of the machine learning process. [ABSTRACT FROM AUTHOR]

This paper presents the results of tribological tests on WE43 and WE54 magnesium alloys with rare earth metals performed in linear reciprocating motion for four different material couples (AISI 316-L steel, silicon nitride—Si3N4, WC tungsten carbide, and zirconium dioxide—ZrO2). Additionally, magnesium alloys were subjected to a complex heat treatment consisting of precipitation hardening combined with a deep cryogenic treatment. The study presents the effect of deep cryogenic treatment combined with precipitation hardening on the tribological properties of WE43 and WE54 alloys. Tribological tests revealed the most advantageous results for the magnesium alloy—AISI 316-L steel friction node. For both alloys tested after heat treatment, a nearly 2-fold reduction in specific wear rate has been achieved. Furthermore, microscopic examinations of the wear track areas and wear products were performed, and the wear mechanisms and types of wear products occurring in linear reciprocating friction were determined. Wear measurements were taken using the 3D profilometric method and compared with the results obtained from calculations performed in accordance with ASTM G133 and ASTM D7755, which were modified to improve the accuracy of the calculation results (the number of measured profiles was increased from four to eight). Appropriately selected calculation methods allow for obtaining reliable tribological test results and enabling the verification of both the most advantageous heat treatment variant and material couple, which results in an increase in the durability of the tested alloys. [ABSTRACT FROM AUTHOR]

In-situ electron irradiation and aging are applied to introduce high-density precipitates in an Mg-10Gd-3Y-1Zn-0.5Zr (GWZ1031K, wt.%) alloy to improve the hardness. The results show that the hardness of the Mg alloy after irradiation for 10 h and aging for 9 h at 250 °C is 1.64 GPa, which is approximately 64% higher than that of the samples before being treated. It is mainly attributed to γ′ precipitates on the basal plane after irradiation and the high-density nanoscale β′ precipitates on the prismatic plane after aging, which should be closely related to the irradiation-induced homogenous clusters. The latter plays a key role in precipitation hardening. This result paves a way to improve the mechanical properties of metallic materials by tailoring the precipitation through irradiation and aging. [ABSTRACT FROM AUTHOR]

The influence of homogenization and quench-aging treatments on the dry sliding friction and wear behavior of Al-40Zn-3Cu bearing alloy was experimentally studied. These treatments removed dendritic structure of the alloy and caused the formation of zinc-rich precipitates distributed homogenously in the matrix of the alloy. It was observed that quench-aging treatment carried out at temperatures of 100 °C and 150 °C significantly improved both hardness and strength of the alloy as compared to homogenization treatment. However, aging at 200 °C lowered these values of the alloy but increased its elongation. Dry sliding wear test results displayed that homogenization and quench-aging treatments increased the wear performance of the alloy. However, it is found that the quench-aging treatment created more powerful effect for improving wear performance of the alloy than homogenization. Quench-aging treatment at 100 °C for 300 min resulted in a decrease in the lowest specific wear rate of the alloy by causing the highest increases in its hardness (from 119 HB to 178 HB), yield strength (from 288 MPa to 383 MPa) and tensile strength (from 319 MPa to 407 MPa) due to the age hardening mechanism. It was observed that the worn surfaces of the alloy samples were composed of adhered and smeared material and delaminated areas. This observation suggested that adhesion and delamination were the operative wear mechanisms of the alloy. The results were explained and discussed in terms of microstructural features, mechanical properties, and wear mechanisms of Al-40Zn-3Cu alloy. [ABSTRACT FROM AUTHOR]

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