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The present study reports the hot deformation behavior, microstructural evolution, and the alloying effects of refractory elements (Ta, Mo, W) in Ni 48.6 Al 10.3 Co 17 Cr 7.5 Fe 9 Ti 5.8 Ta 0.6 Mo 0.8 W 0.4 (at. %) high entropy alloy (HEA). The vacuum arc melted specimens were characterized using a scanning electron microscope, X-ray diffractometer, and Differential scanning calorimetry, which revealed the two-phase structure consisting of γ′ precipitates embedded in the γ matrix. The Energy Dispersive Spectroscopy analysis in a scanning electron microscope revealed that Mo and W partitioned into the dendritic region (K Mo = 1.23 and K W = 1.28) while Ta is found to be partitioned in the interdendritic region composed of mostly γ′ precipitates (K Ta = 0.67). Further, the specimens were subjected to hot deformation in the 800 °C - 1100 °C temperature range at the strain rate of 0.01s−1. The maximum flow strength was around 278 MPa and 183 MPa at 1050 °C and 1100 °C, respectively. The flow behavior is correlated with the microstructure evolution, which is characterized using electron backscattered diffraction (EBSD). In the cases of hot deformation below 1000 °C, localized plastic flow in the form of shear bands developed in coarse grain microstructure, whereas fine grains evolved due to dynamic recrystallization (DRX) in the sample deformed above 1000 °C. Further, the role of refractory elements in retaining high-temperature flow strength has been discussed. [ABSTRACT FROM AUTHOR]

The effects of Cr and Ni content on the low-temperature toughness and supercritical CO 2 corrosion resistance of high-strength low-alloy steel (HSLAs) were investigated by optical microscopy, scanning electron microscope, electron backscattered diffraction, transmission electron microscope, X-ray Photoelectron Spectroscopy, electron probe X-ray micro-analyzer, critical crack tip opening displacement, and supercritical CO 2 corrosion experiments. In this study, the complex structure of high-strength low-alloy steel is identified and quantified, and related to the critical crack tip opening displacement (CTOD). The further addition of Ni and Cr promotes the formation of granular bainite (GB) and martensite-austenite (MA). The proportion of high-angle grain boundaries in the GB structure is small and does not significantly hinder crack expansion, while MA frequently leads to the initiation and expansion of cracks, deteriorating the low-temperature toughness of the material. Supercritical CO 2 corrosion experiments displayed that further addition of Cr and Ni will improve the density and protection of corrosion products. But high-density dislocations will destroy the integrity of the lattice structure of the material and may serve as diffusion channels to affect the formation of the passivation layer and repair. Moreover, dislocation-dense areas are more likely to capture impurity elements, forming a micro-battery effect and accelerating local corrosion. This reduces the extent to which Cr and Ni alloy elements improve the corrosion resistance of HSLA steel. [ABSTRACT FROM AUTHOR]

Nickel-based single crystal (SX) turbine blades typically experience varying load conditions during operation. It is essential to consider the effects of changing stress and temperature when evaluating creep damage. The commonly used time-fraction method, based on the linear damage rule (LDR), has been demonstrated to be inconsistent with experimental results under certain loading conditions. There is a lack of research on damage accumulation under variable loading conditions specifically for SX superalloy. This paper conducted two-stage creep experiments for SX superalloy DD6 at 980 °C with stress levels of 230 MPa and 320 MPa, and at 1050 °C with stress levels of 135 MPa and 230 MPa. The load for the experiment was set based on the typical operating conditions of the SX turbine blades. The evolution of the microstructure under variable loading was observed using scanning electron microscope (SEM) and transmission electron microscope (TEM). The result of creep experiments revealed that the damage accumulation behavior of the SX superalloy does not conform to the LDR. Furthermore, in two-stage loading tests, the creep damage accumulation behavior differs from the classical sequence effect of fatigue loading. SEM and TEM analyses suggested that this phenomenon might be associated with the varying degradation rates of microstructures in SX superalloy. • Investigated damage accumulation in SX superalloy under variable loading. • The evolution of microstructure under variable loading was observed. • A novel creep damage model was proposed and validated for SX superalloy. [ABSTRACT FROM AUTHOR]

This article concerns the effect of strain accumulation during low-cycle fatigue on the post-fatigue tensile behavior of metal matrix composites (MMCs) with identical layers of aluminum reinforced by Fe 3 O 4 nanoparticles produced via the accumulative roll bonding (ARB) technique. Work-hardening behavior, deduced from ratcheting curves, was evaluated by the post-fatigue tensile test. The key finding in the mechanical properties of homogeneous nanocomposite in terms of reinforcement distribution, evolving due to microstructural evolution during the ARB process, is that accumulation of ratcheting strain decreases, and fatigue and post-fatigue tensile behavior significantly increases. The rupture mechanism, analyzed by scanning electron microscope, revealed that deep hemispherical-shaped dimples, a well-known feature of ductile rupture, were changed to elongated shallow shear dimples by the impact of microstructural evolution due to imposed 1000 cycles of ratcheting test. [ABSTRACT FROM AUTHOR]

Propagating Lüders bands with pronounced strain localization are often observed in medium-Mn transformation-induced plasticity (TRIP) steels, which adversely limits the application of such alloys in engineering structures. The present work aims to understand this phenomenon from a dislocation-based perspective, with a focus on the specific role of dislocation multiplication. The material studied is a typical dual-phase medium-Mn steel with a ferrite matrix and a second phase of retained austenite. A warm-rolling process was used as a pre-straining approach to adjust the microstructure of the material, such that materials with two different microstructural states can be obtained: as-received material and pre-strained material. They show distinct differences in initial dislocation density. Stress-controlled rather than conventional strain-controlled tensile testing was adopted, which allowed the Lüders band to develop in an unconstrained manner. In this way, the intrinsic Lüders-strain-rate can be obtained. The results show that the Lüders band-related mechanical parameters, including Lüders strain, Lüders-strain-rate and yield stress drop, all depend on the initial microstructure state and the dislocation evolution process during Lüders band formation. In particular, Lüders-strain-rate is a critical microstructure-sensitive factor. It is closely related to the dislocation multiplication in the formation of Lüders band, which can be characterized and quantified using scanning transmission electron microscope and synchrotron X-ray diffraction. Finally, a quantitative relationship between Lüders-strain-rate and dislocation multiplication rate is established, which allows providing a better understanding of the exceptional Lüders band phenomenon in medium-Mn steels. [ABSTRACT FROM AUTHOR]

The microstructural evolution of Cu–3Ti–2Ni alloy under primary and secondary cold rolling combined aging was investigated through various characterization techniques including transmission electron microscopy (TEM), scanning electron microscope (SEM), and X-ray diffraction (XRD). Additionally, the electrical and mechanical properties during different stages of aging were examined to reveal the organizational changes and performance variations of Cu–3Ti–2Ni alloy under primary and secondary aging. This study revealed that the alloy exhibited optimal primary aging performance at 450 °C for 4 h, with a strength of 954 MPa and an electrical conductivity of 21.5 %IACS (International Annealed Copper Standard for Conductivity). In comparison to primary aging, both strength and electrical conductivity were effectively improved under secondary aging conditions. The optimum secondary aging process was determined to be aging at 400 °C for 3 h, resulting in a strength of 1133 MPa and an electrical conductivity of 24.2 %IACS. During the aging process, the matrix witnessed the formation of numerous elliptical disc-shaped NiTi and Ni 3 Ti phases. Notably, the interface of NiTi phases exhibited a stronger coherency effect compared to Ni 3 Ti. β′-Cu 4 Ti precipitated uniformly within the matrix during aging, enhancing the alloy's strength. A recovery and recrystallization process occurred during aging, leading to the formation of sub-grains within the matrix. [ABSTRACT FROM AUTHOR]

Zn alloy has attracted much attention as a biodegradable material for biomedical applications. However, due to the significant strain softening of Zn alloys, how to break the bottleneck of synergistic yield strength and uniform elongation is an urgent problem to be solved. In this work, a Zn-2.3Cu-0.8Mn (wt.%) alloy was fabricated via low-temperature extrusion and annealing at 330 °C for 1 h to attain dual heterostructures with bimodal grains and multi-scale second phases, focusing on the effect of heterostructure on the mechanical properties. Uniaxial tensile test and loading-unloading-reloading test were applied to reveal the mechanical properties of the Zn-2.3Cu-0.8Mn alloy, while scanning electron microscope, electron backscatter diffraction, and transmission electron microscope were used to characterize its microstructure. Compared with the as-extruded alloy with uniform and fine grains, 330–1 alloy achieves a better combination of strength and uniform elongation (yield strength: 287.8 ± 8.5 MPa, ultimate tensile strength: 321.4 ± 6.8 MPa, and uniform elongation: 14.2 ± 1.8%). The high strength was primarily attributed to the coordination of grain boundary strengthening, hetero-deformation induced strengthening, Orowan strengthening, and dislocation strengthening. Besides, the coarse grains, twinning, as well as the suppression of grain boundary sliding and phase boundary sliding promoted dislocation proliferation and storage capacity, thereby improving work hardening capacity. The large strain hardening capacity was responsible for excellent plasticity. This study provides a feasible strategy for the design of Zn-based alloys with an excellent combination of high strength and strain hardening capacity. [ABSTRACT FROM AUTHOR]

A notable discrepancy in tensile ductility was observed between two 2205 duplex stainless steels (DSS) containing layered and island-like austenite microstructures. The deformation behavior of both DSS 2205 was compared through in-situ Electron Backscatter Diffraction (EBSD) and Scanning Electron Microscope (SEM) techniques. The results indicated that the microscopic deformation mechanism for both DSS 2205 was governed by dislocation slip. The observed tensile ductility disparity was attributed to differences in dislocation slip behavior. In DSS 2205 with island austenite, slip transfer and blocking across grain boundaries occurred simultaneously, which was determined by the geometrical compatibility factor (m') calculations of adjacent ferrite and austenite grains. This intensified plastic inhomogeneities and promoted non-Schmid dislocation slip behavior. While in layered austenite of DSS 2205, the activation of slip system strictly adhered to the principle of maximizing the Schmid factor. Multiple slip systems in the ferrite on {110} and {112} planes were activated, inducing cross-slip, which enhanced ductility. The better ductility of DSS 2205 featuring layered austenite compared to the counterpart was further explained by quantitative analysis of geometrically necessary dislocations (GND) distribution in both phases and kernel average misorientation (KAM) values during deformation. [ABSTRACT FROM AUTHOR]

The phenomenon that the ultrasonic vibration (UV) can reduce the flow stress in the metal plastic deformation has been shown in many studies, however, the mechanism of the flow stress decline when the copper-nickel alloy sheet undergoes the UV is unclear yet. In this study, a series of tensile tests are conducted on the copper-nickel alloy sheet. The results indicate that the UV induces softening effect, i.e., the significant decline of the flow stress and the tensile strength. Nevertheless, the elongation of specimens decreases obviously in the tensile tests. To investigate the mechanisms, the microstructure evolution of the copper-nickel alloy sheet in the UV assisted tensile tests are explored by the scanning electron microscope (SEM), the electron backscattering diffraction (EBSD) and the transmission electron microscope (TEM). It is found that after the UV superimposition the high-angle grain boundaries (HAGB) retain more and the reduction of the twinning decreases in the copper-nickel alloy sheet, which impairs the plasticity and the elongation. The results also show that the average grain size under the UV conditions is bigger, which leads to the decrease of the flow stress and weaken the plasticity of the metal. [ABSTRACT FROM AUTHOR]

In recent years, much attention has been directed towards multi-material systems produced using additive manufacturing technologies. Especially directed energy deposition-based systems provide a powerful tool for relatively simple production of components with controlled chemical composition in certain directions and locations. In this contribution, the potential of bimetallic material manufacturing based on the combination of nickel alloy Inconel 625 and 42C steel using direct laser deposition process was investigated. The monolithic single material blocks as well as graded blocks with alternate material deposition order were produced and investigated via light and scanning electron microscope. In addition, the miniaturized tensile tests at ambient and high temperatures were performed. It was observed that the character of two-material joint changed with the order of deposited materials. Based on the maps of chemical composition, it was shown that joint Inconel 625 to 42C was rather gradual, while 42C to Inconel 625 had sharp distribution of the main elements around the fusion line. The tensile test results demonstrated that the location of preferential failure was the joint itself in the case of gradual interface regardless of the test temperature. On the other hand, the sharp joint failed within Inconel 625 material at room temperature, while at elevated temperature the failure was observed in 42C steel region. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) allows for manufacturing intricate and accurate component designs that are challenging, expensive, or impossible to achieve using traditional methods. To achieve a high-quality final product with SLM, it is necessary to optimize the process parameters carefully. This optimization helps to minimize internal structural defects and control the microstructure. In this study, the optimum production parameters of Ti6Al4V alloy were determined using the Response Surface Method (RSM). The micro-CT analysis was utilized to calculate the relative densities of the samples fabricated using different production parameters. Furthermore, the influence of heat treatment, conducted below and above the β transformation temperature, on the mechanical properties was examined. The results were analyzed by considering the microstructure images obtained from Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) analysis. The optimum production parameters for the SLM method were found to be 80W laser power, 1125 mm/s scanning speed, 25 μm layer thickness, and 45 μm hatch distance. Samples created with these optimized parameters achieved 99.919% relative density, 1050 MPa ultimate tensile stress, and 13.8% elongation, surpassing the minimum standards outlined in ASTM F3001-14. Additionally, the systematic parameter reduction approach used in the study led to savings in both powder consumption and time in SLM, a method that could be applied to various metallic materials. • Ti6Al4V-ELI alloy was manufactured with selective laser melting method. • The response surface method was used to determine the optimum production parameters. • Micro-CT analysis was performed and density ratios were calculated. • Mechanical properties were improved with post processing operation. [ABSTRACT FROM AUTHOR]

Solute clustering and precipitation in an Al–Cu–Mg–Ag–Si model alloy has been investigated by atom probe tomography (APT) as well as high-angle annular dark-field (HAADF) imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM). Nine types of solute clusters (Cu, Ag, Mg–Cu, Mg–Ag, Mg–Cu–Si, Mg–Ag–Si, Mg–Ag–Cu, Cu–Ag–Si and MgAgCuSi) were observed by APT in both the as-quenched alloy and after ageing the alloy at 180 °C for 1 h. Three types of precipitates (Ω (AlCuMgAg), θ (Al 2 Cu) and Mg 2 Si) were observed by APT and HAADF-STEM after further ageing at 180 °C for 24 h and 100 h. We propose that MgAgCu and MgAgCuSi clusters are likely to be responsible for the formation of the Ω (AlCuMgAg) phase. Furthermore, we also suggest that the θ (Al 2 Cu) phase forms from Cu clusters and the Mg 2 Si phase forms from the decomposition of MgAgSi and MgAgCuSi clusters by losing Ag to Ω phase growth. Many early binary clusters (Mg–Cu, Mg–Ag) do not seem to undergo a significant further growth during ageing; these are more likely to be transformed into complex ternary and quaternary clusters and be subsequently consumed during the growth of large clusters/precipitates. Furthermore, it is proposed that the plate-like Ω (AlCuMgAg) precipitates evolve continuously from the MgAgCu and MgAgCuSi clusters, rather than via heterogeneous nucleation on their precursors (i.e. MgAgCu and MgAgCuSi clusters). More interestingly, even after ageing at 180 °C for 100 h, the Ω (AlCuMgAg) precipitates remain coherent with the α-Al matrix, indicating that these precipitates have a high thermal stability. This can mainly be attributed to the presence of a single Mg–Ag-rich monolayer observed at the interface between the Ω precipitate and the α-Al matrix, significantly improving the coarsening resistance of the Ω (AlCuMgAg) precipitates. Our results thus reveal links between a variety of solute clusters and the different types of precipitates in the Al–Cu–Mg–Ag–Si model alloy. Such information can in the future be used to control the precipitation by tailoring solute clustering. [ABSTRACT FROM AUTHOR]

The paper presents the first experimental verification of dislocation repulsion during springback of Dual Phase (DP) steel, a mechanism which is suggested to cause non-linear unloading due to micro-plastic strain generation. In-situ loading-unloading tests are conducted within a Scanning Electron Microscope (SEM). It is shown that strain partitioning between ferrite grains as well as within a single ferrite grain occurs. It was observed that dislocations pile up during loading and repel or bow out during unloading. Only dislocations that were mobile during the initial deformation were able to move during unloading. [ABSTRACT FROM AUTHOR]

The variation of the tensile ductility of a directionally solidified nickel-based superalloy M4706 with temperature is investigated in the temperature range from room temperature to 980 °C. It is found that intermediate temperature brittleness occurs in M4706 at temperatures between 400 and 650 °C. Tensile tests on single crystal M4706 and in-situ nano-compression tests on the freestanding γ′ particles show that the intermediate temperature brittleness of the experimental alloy is not associated with the grain boundary and the deformation capacity of γ′ precipitates in the temperature range. Scanning electron microscope and transmission electron microscope observations disclose that the phenomenon is associated with the glide plane decohesion, which in turn corresponds to the frequent stacking fault shearing during tensile deformation. [ABSTRACT FROM AUTHOR]

In this article, we probe the strain partitioning between the microstructural features present in a continuously cooled carbide-free bainitic steel together with damage nucleation and propagation. These features mainly comprise of phases (bainitic ferrite, martensite, and blocky/thin film austenite), interfaces between them, grain size and grain morphology. A micro Digital Image Correlation (μ-DIC) technique in scanning electron microscope is used to quantify the strain distribution between these microstructural features. The results show a strong strain partitioning between martensite, bainitic ferrite and retained austenite that provides weak links in the microstructure and creates conditions for the crack initiation and propagation during deformation. Blocky austenite islands accommodate maximum local strains in the global strain range of 0–2.3% and undergo strain-induced austenite to martensite transformation governing the local strain evolution in the microstructure. However, the local strains are minimum in martensite regions during entire in-situ deformation stage. Narrow bainitic ferrite channels in between martensitic islands and martensite-bainitic ferrite interfaces are recognised as primary damage sites with high strain accumulation of 30 ± 2% and 20 ± 3% respectively, at a global strain of 9%. The inclination of these interfaces with the tensile direction also affects the strain accumulation and damage. [ABSTRACT FROM AUTHOR]

During hydroforming of Al alloys, cracking often limits the production of specific frames for next-generation transportation vehicles. In this study, microstructural evolution and cracking behavior of an extrusion welded aluminum alloy blank tube were characterized to uncover the failure mechanisms during hydroforming process. Electron back-scattered diffraction, transmission electron microscope, and scanning electron microscope were employed to characterize the grains, textures, and local micro-crack sites. Experimental results demonstrated that grains in the welds region were significantly larger than those in the neighboring regions. Along the weld region, large grains typically with high-misorientation with respect to neighboring grains were identified as the preferred crack nucleation sites. Plastic incompatibility due to preferential yielding in the larger (softer) grains as compared to the surrounding finer (harder) grains is postulated as the origin for local strain localization that leads to cracking in the weld regions during hydroforming. [ABSTRACT FROM AUTHOR]

To evaluate the role of Fe-rich intermetallics on crack initiation, two fully modified Al-Si alloys, one containing plate-like β-Fe and the second containing primary α-Fe intermetallics, were investigated by in-situ tensile testing in the scanning electron microscope. In the first alloy, large plate-like β-Fe intermetallics oriented parallel to the test direction were the first to crack at an elongation of about 1.8%. More transversely oriented intermetallics caused crack initiation in the matrix which linked up with the final fracture. In the second alloy, the cracking of α-Fe intermetallics initiated at an elongation of about 0.9%. It is concluded that large α-Fe intermetallics crack first and that clusters of α-Fe are the most potent crack initiation sites. [ABSTRACT FROM AUTHOR]

The through-silicon via (TSV) approach is crucial for three-dimensional integrated circuit (3-D IC) packaging technology. However, there are still several challenges in the TSV fabrication process. One of the widely known challenges is via protrusion phenomenon. Annealing a TSV wafer makes the copper (Cu) TSVs under high stress and may form a protrusion where the Cu is extruded out of the TSV structure. The phenomenon occurs because of the large mismatch in the coefficient of thermal expansion between Cu via and silicon (Si) layer. Cu protrusion is able to cause crack, delamination of the back-end-of-line and short circuit of the chip, thus, it is a dangerous threat to the metal layer interconnect. Experiments are conducted to characterize the protrusion using several techniques. Scanning electron microscope is used to observe the protrusion topography and measure the height. Electron backscatter diffraction (EBSD) technique is implemented to study the grain size distribution, local texture and microstructure evolution inside Cu vias. For the experiment, arrays of 10 μm diameter TSVs are fabricated and annealed in argon gas environment in six different temperatures. In this paper, finite element analysis (FEA) is carried out to study the Cu protrusion under different annealing conditions. Correlation between numerical results and experimental data is then performed. Based on the verified FEA methodology, several parametric studies are then conducted, including the effects of annealing temperature on Cu protrusion, residual stress distributions of TSV structures. The simulation results are helpful to understand and solve the key problem in TSV fabrication process and reliability challenge. [ABSTRACT FROM AUTHOR]

Gradient nanograined Ti (GNG Ti) samples were produced by a surface rolling treatment. The mechanical properties were evaluated by microhardness and tensile tests. The results indicated that GNG Ti achieved an optimized combination of strength and ductility relative to the free-standing nano/ultrafine-grained Ti. The deformation and fracture mechanisms were studied using transmission electron microscope (TEM) and scanning electron microscope (SEM). As the grain size reduced from the coarse-grained (CG) matrix to the nano/ultrafine-grained (NG/UFG) layer, the transition from conventional plastic deformation mechanisms, such as dislocation activity and twinning deformation, to grain boundary-mediated deformation mechanisms, such as stress-inducing grain growth, was identified. At the early stage of tensile deformation, the microcracks were first initiated in the CG and deformed grain (DG) regions rather than in the NG/UFG region and the CG/DG interface had a deflection effect on crack propagation. After tensile failure, the fracture morphology showed a mixture of ductile dimples and shear band-like regions. [ABSTRACT FROM AUTHOR]

The effect of pre-deformation induced by the tensile fracture at room temperature on the microstructure evolution of Ni Al model single crystal superalloy during thermal exposure at 1000 °C, was investigated by scanning electron microscope and transmission electron microscopy. Recrystallization occurs near the fracture surface where the most severe plastic deformation was suffered. The average size of recrystallization grains in front of the recrystallization area is much larger than that of at the fracture surface. Far from the fracture surface, the average size of coarsened γ′ precipitates in the slip bands is larger than that of out of the slip bands. [ABSTRACT FROM AUTHOR]

Abstract Low-cycle fatigue (LCF) behavior of wrought superalloy GH4742 was studied at room-temperature (RT) and 700 °C. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) were used to study the development of cracks and deformation mechanism. An obvious decrease in fatigue life occurred as the temperature was increased from RT to 700 °C and as the total strain amplitude was raised from 0.5% to 1.0%. The Halford-Marrow relationship based on plastic strain energy density was used to predict the fatigue life, which is in good accordance with experimental data. At RT, for all investigated samples, initial cycle hardening is followed by gradual cycle softening especially at higher strain amplitude (∆ ε t ≥ 0.8 %). Detailed TEM observation revealed that γ′ phase was sheared by dislocations. The shearing mechanism, reducing the ordering degree and diameter of γ′ phase, should be responsible for fatigue softening. Differently, at 700 °C, the tested samples exhibited continuous cycle hardening. A sharp drop in the number of stacking faults occurred. Lots of dislocation loops existed around tertiary γ′ phase and paired dislocations moved in secondary γ′ phase, indicating that Orowan and shearing mechanism have occurred. Fatigue cracks usually initiated from the surface. SEM investigation showed that the failure mode changed from transgranular to mixed transgranular and intergranular modes with increasing temperature. [ABSTRACT FROM AUTHOR]

Abstract This study aim to determine the growth rates of crystallized layers and to evaluate the effects of the thickness of the crystallized layers and the intrinsic properties of formed phases, including residual stresses, on the bending strength of glass-ceramic compositions of the LZS and LZSA systems. For this purpose, commercial raw materials (Li 2 CO 3 , ZrSiO 4 , Al 2 O 3 , SiO 2) were dry mixed and melted at 1550 °C/2 h in a Pt crucible. The glasses obtained were then annealed. Subsequently, glass samples were submitted to chemical and crystallographic analysis. The thermal behavior of the obtained materials was evaluated through dilatometric analysis and differential scanning calorimetry. The growth rates of the crystallized layers in the glass-ceramic compositions were calculated from measurements of the thicknesses of the crystallized layers (with the aid of optical and/or scanning electron microscopes) at 775 and 700 °C, respectively for holding times in the 480–780 min range. In order to evaluate the mechanical strength of the thermally treated samples and with different thicknesses of crystallized layers, three-point bending strength tests were performed. Residual stresses in the thermally treated samples were also evaluated from X-ray diffraction analyzes. The results showed that it is possible to obtain LZS glass-ceramics with crystallized layers containing Li and Zr silicates with thicknesses between 70 and 200 µm, which grow at a rate of 0.54 µm min−1. In the LZSA glass-ceramic, the crystallized layers containing mainly β-spodumene and Li and Zr silicates exhibited thicknesses between 33 and 53 µm which grow at a rate of 0.08 µm min−1. The formed crystalline layers significantly increased the mechanical strength of the produced glass-ceramic materials from 71.97 to 118.69 MPa for the LZS glass-ceramics and from 59.26 to 134.15 MPa for the LZSA glass-ceramics. [ABSTRACT FROM AUTHOR]

Abstract As-cast and as-extruded Mg- x at% Co-6 at% Y (x = 0, 1, 2, 4) alloys were prepared. Their tensile strengths and microstructures were examined by using a WDW-200E material testing machine, X-ray diffractometer (XRD), optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The tensile strength of the as-cast Mg- x at% Co-6 at% Y (x = 0, 1, 2, 4) alloys reached the peak value of ~246 MPa with the addition of 1 at% Co. Additionally, the tensile strength of the as-extruded Mg- x at% Co-6 at% Y (x = 0, 1, 2, 4) alloys reached the peak value of ~369 MPa with the addition of 1 at% Co. The long-period stacking-ordered (LPSO) phase played a highly important role in the strengthening mechanism of the as-cast and as-extruded Mg- x at% Co-6 at% Y (x = 0, 1, 2, 4) alloys. [ABSTRACT FROM AUTHOR]

Abstract Microstructural evolution of modified 2.5Al alumina-forming austenitic steel after isothermal aging at 973 K was investigated by scanning electron microscope (SEM), and X-ray diffraction (XRD). Tensile and vicker's hardness tests were also carried out to study mechanical properties during isothermal aging. The average particle diameter of precipitates was statistically measured and the kinetic model was employed to describe the coarsening of precipitates. The results show that the precipitation sequence of Laves and NiAl phases was related to aging time, and precipitated after 20 h and 100 h in this work, respectively. The average particle diameter of precipitates continuously increased with aging time. And the coarsening rate of the precipitates decreased at 1000 h due to the exhaustion of Nb atoms in matrix. The precipitation of NiAl and Laves phases plays an important role in mechanical properties. The hardness and the work hardening rate continuously increased. In contrast, the elongation gradually decreased. The above results indicated that the effect of aging strengthening. The room-temperature yield strength firstly sluggish increased and then gradually decreased, finally increased significantly due to the increase in σ gb , the decrease in σ dis and σ ss , and the change in σ ppt. [ABSTRACT FROM AUTHOR]

Abstract The micro-plastic deformation behavior of Al-Zn-Mg-Cu alloy subjected to cryo-cycling treatment was investigated experimentally in the present work. Micro-plastic deformation was produced by continuous loading-unloading method with applied stress far below the yield strength of this alloy, and the deformation characteristics of grains were detected by Optical Microscope (OM) and Scanning Electron Microscope (SEM). The results showed that cryo-cycling treatment reduced the residual strain (ε p) after each cycle of loading-unloading, and the degree of grain deformation was decreased apparently, which indicated that cryo-cycling treatment enhanced the capacity of resistance to micro-plastic deformation. Transmission Electron Microscope (TEM) was employed to reveal the mechanisms of cryo-cycling treatment on Al-Zn-Mg-Cu alloy. The results showed that higher content of homogenous η phases precipitated in the matrix and grain boundaries of Al-Zn-Mg-Cu alloy after cryo-cycling treatment. Meanwhile, no clear precipitate-free zones (PFZs) can be observed in the microstructure of cryo-treated specimen. The changes of microstructure had great contribution to improve the pinning effect of dislocations during micro-plastic deformation. Internal stress was released by the cryo-cycling treatment which was demonstrated by the in-suit cryogenic X-Ray (XRD) measurement, as a result, the stability of dislocation was improved. Cryo-cycling treatment had no obvious influence on the tensile strength and yield strength of Al-Zn-Mg-Cu alloy, while elongation and fracture toughness were improved by the extent of 7% and 10.3% respectively, compared to those of the untreated specimen. [ABSTRACT FROM AUTHOR]

Abstract High-Energy Diffraction Microscopy (HEDM) was employed to measure and compare the evolving micromechanical state of two alloys, an austenitic stainless steel (316 L) and nickel-based alloy (Inconel 625) fabricated by both conventional methods and powder metallurgy with hot isostatic pressing (PM-HIP) during in situ uniaxial tensile testing. Each of the four materials was tested through the elastic regime to just beyond yield. HEDM was performed at room temperature in the far-field (ff) configuration at the Cornell High Energy Synchrotron Source to measure grain-average elastic strains and subsequently derive stress tensors. The evolution of the normal stress component along the loading direction in individual grains as a function of macroscopic deformation is presented. Initially, grain-scale stresses in the loading direction are more heterogeneous in the wrought alloys than in the PM-HIP alloys. Notably, many peripheral grains in the wrought specimens are near yield even before load is applied. With increased loading, grain-scale stresses tend to homogenize in all specimens. Orientation fields measured using electron back scatter diffraction (EBSD) are used to determine grain morphologies and interpret the ff-HEDM data. The PM-HIP grains tend to be finer and rounder in shape than the wrought grains, potentially explaining the grain-scale stress distributions. Finally, yield strength and modulus of elasticity are measured for the four alloys and correlated to the resultant grain size and morphology from the fabrication processes. Graphical abstract fx1 Highlights • Grain-level mechanical response is studied using HEDM. • In situ tensile straining for wrought and PM-HIP 316 L and IN625. • Wrought specimens exhibit more heterogeneous initial grain-scale stress distributions. • Grain-scale stresses homogenize during loading. • More homogeneous stress distribution in PM-HIP alloys due to grain size and shape. [ABSTRACT FROM AUTHOR]

Abstract Interfaces and their interactions with other microstructural features, such as grain boundaries or twin structures, have been widely viewed as parameters for designing metallic nanolayers. These interfaces could play a role in hindering cracks from propagating across the nanolayers while in operation. To date, many studies have focused on the roles of interfaces in affecting the plasticity mechanisms and thus the deformability of nanolayers. However, no studies have investigated on the subsequent mechanisms of fracture leading to the final failure. In this study, in situ microfracture bending tests inside a scanning electron microscope (SEM) were performed on the notched clamped beams of Cu/Nb nanolayers with a similar layer thickness using two different fabrication processes: physical vapor deposition (PVD) and accumulative roll bonding (ARB). Due to the columnar grains of the Cu/Nb PVD beams, a sudden catastrophic linear elastic, brittle fracture phenomenon was observed; in the Cu/Nb ARB beams, fracture events of notch widening phase and crack initiation and fracture along the shear instability were observed. Detailed examinations showed the presence of competing mechanisms between the multilayered interface, columnar grain boundary, and experimental factors of beam geometry and the position of the tip. With this newfound knowledge, new types of metallic nanolayers can be designed with enhanced strength and fracture resistant properties. [ABSTRACT FROM AUTHOR]

Abstract We compared deformation twinning activity and twin structure development of pure Ti at cryogenic temperature and room temperature by conducting unidirectional rolling at 77 K and 293 K. Twinning activity was significantly higher in rolling at 77 K than in rolling at 293 K. This was because lowering the deformation temperature increased the necessity for twinning operation to compensate for reduced accommodation of strain along the c -axis of the crystal structure, caused by inhibition of < c + a > slips. Twin structure was also entirely different between the two rolling temperatures. Compared to the case of rolling at 293 K, rolling at 77 K generated thin and numerous individual twins in the twinned grains, thereby giving rise to the development of a totally different twin structure. The differences in twin structure were caused by the combined effect of significant local stress concentration at grain boundaries and a reduction in stacking fault energy by rolling at 77 K. The twin structure strongly contributed to severe twinning-induced grain refinement that occurs at cryogenic temperature. [ABSTRACT FROM AUTHOR]

Abstract The creep behavior, creep damage and creep life of 718Plus alloy were investigated at temperatures ranging from 650 to 750 °C in air. The fracture surface, microstructure evolution and deformation mechanisms were studied by optical, scanning and transmission electron microscope (SEM and TEM). The results show that creep curves of 718Plus alloy consist of primary stage and tertiary stage without steady-state region. The Monkman-Grant relationship of 718Plus alloy can be described by t r = 9.32E-2/( ε ̇ min)0.75 and apparent creep activation energy of 718Plus alloy is about 572.7 kJ/mol. Further investigation shows creep damage of alloy at 650 °C can be mainly ascribed to the effect of grain boundary sliding (GBS) and microtwinning. The alloy shows transgranular fracture at high stress, while it presents ductile fracture at low stress due to the nucleation, growth and linkage of creep voids. At 750 °C, the alloy failed in the form of ductile fracture mainly due to the microstructure instability and dislocation glide. At higher stress of 700 °C, the effect of GBS is mainly responsible for the creep damage of 718Plus alloy, while GBS, dislocation glide and microstructure instability work together and lead to the creep damage of alloys at lower stress of 700 °C. The fracture mechanism map and fracture models for 718Plus alloy were constructed. Remaining life assessment of 718Plus alloys was also evaluated by Larson-Miller parameter method. [ABSTRACT FROM AUTHOR]

Abstract For precipitation-strengthened heat-resistant steels, property degradation resulted from phase coarsening is always one of the most critical challenges, and therefore, knowledge regarding the long-term influence of temperature on mechanical properties and microstructure is prerequisite for their applications. In this work, long-term thermal aging up to 10,000 h of typical alumina-forming austenitic (AFA) stainless steels was conducted, and evolution of microstructure and mechanical properties of these promising heat-resistant alloys were studied systematically. It was found that mechanical performance of the steel strengthened by secondary nanosized NbC showed not only much enhanced creep resistance, superior to that of most traditional heat-resistant steels, but also stable high-temperature strength even after long-term aging. The spheroidal secondary NbC particles showed extreme coarsening resistance with a low coarsening kinetic constant (almost six orders of magnitude smaller than that of the Laves Fe 2 Nb phase). The low interfacial energy of nanosize NbC, which was resulted from the cube-on-cube orientation relationship and semi-coherent interfacial structure with the matrix, gave rise to its sluggish coarsening kinetics. Our current findings not only confirm that the AFA alloys strengthened by dense precipitated, nanosized semi-coherent NbC is a promising structural material for long-term high-temperature applications, but also sheds new insights into understanding precipitation hardening mechanism for high-temperature materials in general. [ABSTRACT FROM AUTHOR]

Abstract Cu/CuZr nanolaminates with varying individual layer thickness and CuZr layer structure were prepared by magnetron sputtering on single-crystalline Si (100) and polyimide film substrates. Nanoindentation and uniaxial tension tests were conducted to evaluate the hardness and plasticity of these nanolaminates, while morphologies of indentation and tensile cracks were examined with scanning electron microscope (SEM). Combined with high resolution transmission electron microscopy (HRTEM), the deformation mechanisms of Cu/CuZr nanolaminates were explored. The hardness of Cu/CuZr nanolaminates was found to be dominated by both the Cu layer and the CuZr layer. Varying the Cu layer thickness induced different size-dependent effects of the CuZr layer. For Cu/CuZr nanolaminates having the same layer thickness but different CuZr layer structures, the deformation mechanisms were closely related to the interface structure rather than the whole amorphous layer. [ABSTRACT FROM AUTHOR]

The Fe macrosegregation during casting and the limited sample size of the traditional powder metallurgy methods are challenges for the application of Cu-Fe composite. In this work, a powder rolling strategy is developed to fabricate fully dense Cu-10Fe billet by consolidating pure Cu and Fe powders. This method can solve the above problems. The microstructure evolution at different processing stages was characterized in detail by scanning electron microscope (SEM), electron probe microanalysis (EPMA) and transmission electron microscope (TEM). The Fe macrosegregation was avoided and good metallurgical bonding quality between powders was achieved after cold rolling. Ordered clusters were formed in the Fe phase, and three different types of Fe precipitates were found in the Cu matrix. The formation mechanisms of ordered structure and precipitates were analyzed. The variation of mechanical and electrical properties with aging process was discussed. • Bulk dense Cu-10Fe composite was prepared by direct consolidating pure Fe and Cu powders. • Macrosegregation of Fe phase was eliminated and metallurgical bonding was realized. • Three types of Fe precipitates were found in the Cu matrix. • Superior mechanical and electrical properties were obtained. [ABSTRACT FROM AUTHOR]

This study focuses on the influence of porosities present in the stainless steel 17-4 PH made by material extrusion additive manufacturing (MEAM) process. A comparison is made at the sub-micron scale between an as-fabricated sample and a H900 post-fabrication heat treatment sample. To achieve such observations, gold nanoparticles (NPs) are used as markers in order to capture the evolution of the material behavior during an in-situ mechanical tensile test under a scanning electron microscope. The obtained strain maps allow to evidence strain concentrations and their evolutions regarding the microstructure and the applied post-treatment. The heat-treated sample reveals a change in size and number of porosities. The displacements of NPs during the test highlight the quantitative evolution of the crack initiations and the porosities growth, exposing a more homogenized strain evolution for the H900 sample compared to the as-fabricated one. [ABSTRACT FROM AUTHOR]

The load partitioning between inter-phases and intragranular of austenite, their dislocation density evolution, and mechanical behavior were investigated in two medium Mn steels by in-situ high-energy synchrotron x-ray diffraction during tensile loading. The investigated steels were produced with different hot rolling parameters resulting in different initial microstructures. The initial microstructures were characterized using scanning electron microscope and electron backscatter diffraction analysis. Transmission electron microscope with high angle annular dark field technique was furthermore used to provide the fine microstructural features of deformed specimens in order to supplement the in-situ analysis. Despite the differences in the initial microstructure, the load partitioning from the softer ferrite to the stronger α '-martensite (α ') was observed; while different degrees of load partitioning for intragranular of γ occurred. The sample with a relatively low degree of load partitioning exhibits the intersection of two bundles of stacking faults (SF), one with high density SF, and the other with low density and limited SF, as well as the occurrence of α′ in the intersecting region. The secondary SFs and the relatively intermediate density of primary SFs bundle are characterized in γ for the sample with relatively high degree of load partitioning. The load partitioning between intragranular of γ is found to have a coordination relationship with the dislocation density evolution of γ ; after the load partitioning, dislocation density of γ rapidly rises. The sample with intersection of two bundles SFs and the occurrence of α′ , exhibits the higher transformation rate of γ into ε -martensite/ α ', resulting in the larger work hardening rate. In addition, the early load on α ' is found to contribute to a higher yield strength. These results reveal the importance of assessing both phase-specifc strain/stress and the dislocation density evolution in order to predict the macroscopic mechanical properties of medium Mn steels. [ABSTRACT FROM AUTHOR]

The (TiTaCrMoNb)N x films with nitrogen content were prepared on the surfaces of TC4 by magnetron sputtering. The effects of nitrogen content on the microstructures and mechanical properties of (TiTaCrMoNb)N x films were investigated by x-ray diffractometer (XRD), scanning electron microscope (SEM), nanoindentation, high-resolution transmission electron microscope (HRTEM), electron probe microanalysis (EPMA), and laser confocal microscope. The results show that the deposition rates of the films decrease with the increase of the nitrogen flow. Besides, when N element is intoduced, the structures of the films change from the body-centered-cubic (BCC) to face-centered-cubic (FCC) phase composed of Me–N (metal nitride), which are preferentially oriented in the (111) crystal plane. Meanwhile, with increasing nitrogen flow, the hardness of the films shows a trend of first increasing and then decreasing. When the ratio of Ar and N 2 flows is 25:25, the hardness and elastic modulus reaches the maximum value of 26.1 GPa and 311.8 GPa, respectively. The increase of hardness is mainly attributed to the formation of saturated Me–N and the solid solution strengthening. Meanwhile, the film behaves the best tribological performance, which presents a lowest friction coefficient and excellent wear resistance. [ABSTRACT FROM AUTHOR]

The additive manufacturing (AM) of α + β titanium alloys using electron beam (EB) and laser directed energy deposition (DED) processes has been widely characterized in both the as-deposited and post processed conditions. Fine basket weave α lath structures are commonly observed in both the as-deposited and post processed hot isostatically pressed (HIP) conditions for both laser and EB DED processes, but more in-depth knowledge of the crystallographic texturing and variant selection of the α laths growing from the primary β-grains across the height of EB DED Ti-6Al-4V structures is not well established. At locations near the substrate in both conditions, microtexturing is weak, but EB DED builds exhibit a strong microtexture and pronounced variant selection with increasing build height. On the other hand, the laser DED builds displayed weak texturing and no prominent variant selection across all heights. With the addition of HIP post processing, there was no change in microtexturing of the coarsened α laths for both the laser and EB structures, and the same variant selection observed in the as-deposited EB DED builds was present. [ABSTRACT FROM AUTHOR]

Dynamic strain aging (DSA) has a noticeable impact on low cycle fatigue behavior of Cr-Mo tempered martensitic steel at elevated temperatures. At 350 °C, the stress response presented evidently secondary hardening phenomenon, and the fatigue life is significantly higher than room temperature which is contrary to the usual understanding. The analysis shows that the reason for the secondary hardening is mainly because of DSA which affects the evolution of dislocations. The influence process of the DSA effect on the dislocation evolution in low-cycle fatigue was first observed, which is from lath substructure to a smaller cell substructure at high temperature. Fracture observation indicates that the new dislocation structure promotes the crack propagation resistance of the material. The effect of DSA on the low cycle fatigue properties of high temperature provides a new idea for the study of fatigue resistance of materials. [ABSTRACT FROM AUTHOR]

Grain refinement is one of the most effective methods for strengthening steels, but grain refinement to 1 µm or less deteriorates the ductility considerably. To evade the strength-ductility trade-off, a lamellar-structured (LS) ultrafine-grained (UFG) dual-phase (DP) ferrite/martensite (F/M) steel was produced by warm rolling an intercritical annealed low-carbon martensite and subsequent air cooling in this paper. The microstructure is similar to a short fiber reinforced composite, and the highest strength (1432 ± 15 MPa) combined with a decent ductility (16.5 ± 0.5% elongation) is achieved in DP steel. Compared with conventional equiaxed coarse-grained (CG) and UFG DP counterparts, the LS martensite in UFG DP steel can produce extra strengthening effect and is also beneficial to ductility. And the short fiber theory can predict the strength very well. [ABSTRACT FROM AUTHOR]

In the present research, the hot deformation microstructure of AISI 321 austenitic stainless steel was studied by performing hot compression tests in the temperature range of 800–1200 °C and strain rates of 0.001–1 s−1. Microstructural evolutions were studied using transmission and scanning electron microscope equipped with EBSD camera. Results show that the main restoration process in the temperature range of 800–950 °C is dynamic recovery and dynamic recrystallization is the prevailing softening mechanism in the temperature range of 1000–1200 °C. TEM observations confirm the occurrence of dynamic recovery and recrystallization at the specified temperatures. Increasing deformation temperature leads to the increase in the fraction of high angle boundaries and simultaneous decrease in the fraction of low angle boundaries. Also, deformation at 800 and 850 °C is accompanied by the formation of M 23 C 6 precipitates at austenite grain boundaries that increases the deformation activation energy and results in grain boundary sensitization detected using scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Two quite different primary Mn-rich phases were observed by optical microscope and scanning electron microscope in the surface and central parts of Al-12 wt%Si-4 wt%Cu-2 wt%Mn heat-resistant alloy casting. Deep-etching observation reveals that one is as highly developed 3D-dendrites and the other is as simple 2D-laths. The results of SEM-EDS show the constituents of these two Mn-rich phases are quite different too. The results of TEM-EDS verify it further. By selected area electron diffraction pattern, the lath-shaped Mn-rich phase is identified as: Al 13 Mn 4 Si 8 , simple tetragonal, a = b = 1.240 nm, c = 0.489 nm. The tension test indicates the contribution to strength from dendritic Al 15 Mn 3 Si 2 phase is larger than Al 13 Mn 4 Si 8 phase whether at room temperature or at high temperature. The reason for it is thought to be tied with the much larger difference in elastic modulus of Al 13 Mn 4 Si 8 phase with aluminum matrix than that of Al 15 Mn 3 Si 2. [ABSTRACT FROM AUTHOR]

Two quite different primary Mn-rich phases were observed by optical microscope and scanning electron microscope in the surface and central parts of Al-12 wt%Si-4 wt%Cu-2 wt%Mn heat-resistant alloy casting. Deep-etching observation reveals that one is as highly developed 3D-dendrites and the other is as simple 2D-laths. The results of SEM-EDS show the constituents of these two Mn-rich phases are quite different too. The results of TEM-EDS verify it further. By selected area electron diffraction pattern, the lath-shaped Mn-rich phase is identified as: Al 13 Mn 4 Si 8 , simple tetragonal, a = b = 1.240 nm, c = 0.489 nm. The tension test indicates the contribution to strength from dendritic Al 15 Mn 3 Si 2 phase is larger than Al 13 Mn 4 Si 8 phase whether at room temperature or at high temperature. The reason for it is thought to be tied with the much larger difference in elastic modulus of Al 13 Mn 4 Si 8 phase with aluminum matrix than that of Al 15 Mn 3 Si 2 . [ABSTRACT FROM AUTHOR]

In the present research, the hot deformation microstructure of AISI 321 austenitic stainless steel was studied by performing hot compression tests in the temperature range of 800–1200 °C and strain rates of 0.001–1 s −1 . Microstructural evolutions were studied using transmission and scanning electron microscope equipped with EBSD camera. Results show that the main restoration process in the temperature range of 800–950 °C is dynamic recovery and dynamic recrystallization is the prevailing softening mechanism in the temperature range of 1000–1200 °C. TEM observations confirm the occurrence of dynamic recovery and recrystallization at the specified temperatures. Increasing deformation temperature leads to the increase in the fraction of high angle boundaries and simultaneous decrease in the fraction of low angle boundaries. Also, deformation at 800 and 850 °C is accompanied by the formation of M 23 C 6 precipitates at austenite grain boundaries that increases the deformation activation energy and results in grain boundary sensitization detected using scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Effects of the zinc, copper and brass interlayers were studied on the microstructure evolution and mechanical properties of the wrought aluminum friction stir welds. Optical and scanning electron microscopes (SEM) as well as X-ray diffraction (XRD) analysis were used for investigation of the distribution, dissolution and reactions of the interlayers, grain structure in the stir zone and fracture surfaces. Longitudinal and transverse tensile and microhardness tests were also carried out in order to evaluate the mechanical properties of the welds. The results showed that without insertion of the interlayer, the joint efficiency (ratio of the weld strength to the aluminum base metal strength) was ~60%. While zinc and copper interlayers had no significant effect on the joint efficiency, insertion of the brass interlayer increased the joint efficiency up to ~90%. Microstructural observation indicated that brass interlayer was relatively well distributed inside the stir zone and Al 2 Cu and Al 4 Cu 9 intermetallic compounds were formed due to the solid-state reactions between the aluminum matrix and brass particles during welding leading to the increase in the weld strength. In the case of the zinc interlayer, no intermetallic compound was detected inside the weld zone and zinc was dissolved in the aluminum matrix to form a solid solution. Moreover, the joint welded using copper interlayer suffered from lack of distribution of the detached copper particles. Fracture analysis after tensile test showed that insertion of the interlayers generally changed the fracture location from the advancing side towards the retreating side due to the formation of a composite structure and increase in the strength of the advancing side. [ABSTRACT FROM AUTHOR]

Effect of parameters such as current density, welding time, electrodes force and holding time after welding on tensile-shear strength of dissimilar joint were analyzed. Taguchi method was used to design the experiments and Minitab software was used to analyze the effect of parameters and obtain an optimum condition. The microstructure of the optimum condition was analyzed by Scanning Electron Microscope (SEM). The strength of the join was analyzed by tensile-shear test. Fracture mode was assessed by optical microscope. Results showed that current density, holding time after welding, welding time and electrodes force were the most effective parameters hierarchically. Optimum current density of 8 Kamp, holding time after welding of 40 cycle, 16 cycle welding time and 5 kN electrode force were defined as the optimum parameters to join the sheets. Weld nugget (WN) had a martensitic structure containing a relatively high strength and hardness. Its fracture mode was pullout failure. [ABSTRACT FROM AUTHOR]

In order to understand the mechanism of substitution for nickel with manganese in metastable austenitic stainless steels 14Cr10Mn and 16Cr6Mn, the transformation behavior of ε- and α′- martensite and the corresponding mechanical properties were investigated in this study. The microstructures and tensile and hardness properties of the cold-rolled steels under different rolling reductions at ambient temperature were measured using X-ray diffraction (XRD), scanning electron microscope (SEM) together with an electron back scatter diffraction (EBSD) and transmission electron microscope (TEM). The results show that α′- martensite is not easy to be transformed from austenite, and the martensite transformation γ → ε → α′ in 14Cr10Mn and 16Cr6Mn metastable stainless steels is found during cold rolling. The results also reveal that ε- martensite acts as an hardness reinforcing phase, and high total martensite volume fraction and ratio of ε- and α′- martensite content are helpful to achieve higher tensile strength with sigmoidal shape stress-strain curves. In addition, a model considering cold rolling reduction was developed to predict the contents of ε- and α′- martensite in the steels. [ABSTRACT FROM AUTHOR]

The effect that twin activity in Magnesium alloys has in both local and global strain is investigated in this article. The need to investigate this effect is related to difficulties in associating the spatially varying twinning with both plasticity and failure of this particular class of alloys. To address this need, mechanical testing both inside and outside the Scanning Electron Microscope was conducted and it was coupled with Digital Image Correlation (DIC) deformation and Electron Backscattered Diffraction (EBSD) texture measurements. In addition volume recordings of Acoustic Emission (AE) and surface measurements of microstructural changes were used to further complement the in situ tracking of twinning activity throughout monotonic and cyclic mechanical loading experiments. The definition of appropriate monitoring regions allowed the direct correlation of evolving twin activity with associated deformation in Magnesium alloys, for the first time to the authors’ best knowledge, from which twinning contributions to strain localizations were computed. [ABSTRACT FROM AUTHOR]

The microstructure of Sn-11Sb-6Cu Babbitt consists of a soft solution matrix and hard particles (SnSb and Cu 6 Sn 5 ). The soft solution matrix acts as solid lubrication and embedability provider, and the hard particles provide the sufficient load carrying capacity. In the present study, the effects of Ag micro-addition on the structure and mechanical properties of Sn-11Sb-6Cu Babbitt were investigated by optical microscopy, vickers microhardness tester, X-ray diffractometer, scanning electron microscope and servo-hydraulic materials testing system. The results indicate that a new intermetallic compound Ag 3 Sn is formed after Ag is added to Sn-11Sb-6Cu, which increases the microhardness and improves the strength and ductility of Sn-11Sb-6Cu Babbitt. It is also found that the addition of 1.0 wt% Ag to Sn-11Sb-6Cu Babbitt has the potential to improve the load carrying capacity without sacrificing the embedability. [ABSTRACT FROM AUTHOR]

To characterize the plastic deformation behavior and globularization in multistage primary hot working, isothermally interrupted compression was carried out for a TA15 titanium alloy with initial colony structure at temperature of 900 °C and strain rate of 0.1 s −1 . Through-process microstructural developments were examined by Electron Backscattered Diffraction (EBSD) and Scanning Electron Microscope (SEM). The globularization efficiency was analyzed via the evolution of intra-α boundaries, α/β interfaces and α grain size. The analyses show that the globularization efficiency is greatly enhanced by short time holding after a true strain of 0.73. The acceleration in globularization is associated with the formation of transverse intra-α boundaries across the α lamellae, the loss of α/β interfacial coherency, the change in deformation mode and the improvement of deformation homogeneity. Thus, the globularization efficiency increases with interrupted strain, holding time and loading pass. The results can be used to optimize the primary hot working of titanium alloys. [ABSTRACT FROM AUTHOR]

In this study, the effect of friction stir processing (FSP) by various transverse welding speeds of 50–150 mm/min on mechanical properties and microstructure of Fe-24Ni-0.3C TRIP steel was investigated. The results showed that defectless FSPed specimen was obtained at the transverse speed of 100 mm/min. Microstructural analysis was carried out by scanning electron microscope equipped with electron backscattered diffraction (EBSD) detector. It was found that by increasing the transverse speed, more significant grain refinement was observed in the stir zone. Furthermore, deformation induced martensite was not observed in the area subjected to FSP. Significant grain refinement resulted from dynamic recrystallization was found to be responsible for hindering formation of deformation induced martensite in the weldment section after tensile deformation test. Tensile test results showed that yield strength (YS) was increased from 145 MPa to 210 MPa in the FSPed specimens. However, tensile elongation was restricted in the FSP processed specimens which may be due to limitation of TRIP phenomenon. [ABSTRACT FROM AUTHOR]

In this study, fully dense Ti-6Al-4V alloy parts were successfully fabricated by an in-situ tooling (skin or shell) via a novel hybrid process of selective laser melting (SLM)/hot isostatic pressing (HIP). In this hybrid process, the in-situ tooling of Ti-6Al-4V parts was prepared via selective laser melting, then filled with Ti-6Al-4V powder, and finally consolidated by hot isostatic pressing to build fully dense complex parts without the need of removal of anything. The interface between tooling and consolidated powder was investigated in detail using scanning electron microscope (SEM) and electron backscattered diffraction (EBSD), and the bond strength was evaluated by tensile and fatigue testing. It was found that there was no obvious element diffusion around the interface, but the pronounced difference in microstructure type and gain size could be seen. Regardless of HIP temperatures, the tensile and fatigue samples preferentially failed on the tooling side due to the coarser Widmanstatten microstructure. Compared with the as-SLMed parts, the samples prepared by this hybrid SLM/HIP process exhibited higher mechanical properties such as superior strength and outstanding ductility, and became more competitive, even than wrought Ti-6Al-4V parts. [ABSTRACT FROM AUTHOR]