Microstructure evolution, strain-induced martensite transformation (SIMT) kinetics, tensile properties, deformation behaviors of UNS S32101 duplex stainless steel (DSS) with heterogeneous layered structure (HLS) were investigated. HLS composed of multiscale grains (spanning coarse, fine, and ultrafine grains) was prepared by direct cold rolling in combination with short-time annealing, being dominated by coarse-grained ferrite (CGed α) and fine-grained austenite (FGed γ). A quantitative SIMT kinetics model was established to predict the α′-martensite fraction at various strain/annealing parameters, indicating that increased average grain size (AGS) for γ not only contributed to the SIM formation but also promoted the monotonic increase of SIMT rate until annealing for 10 min. Relatively high stacking fault energy (SFE, 35.89∼39.34 mJ/m2) favored mechanical twinning as the dominant deformation mode of γ accompanied by SIMT and dislocation glide. And α deformation was mainly coordinated by wavy slip. Both SFE and Olson-Cohen parameters were strongly correlated with the γ AGS, which could reasonably interpret the dependence of SIMT on the AGS. The A and B values increased progressively with grain coarsening along with the rapid decline in SFE, facilitating the martensite formation. Further increasing the AGS beyond the peak region severely suppressed SIMT probably due to the low probability of martensite embryo generation at deformation twins (DTs) intersections, coinciding with the sharp decrease A value.

This study investigated the high-temperature tensile properties and deformation mechanisms of a solution treated Ni–Fe-based alloy ranging from 600 to 750 °C. The solution treated GH4070P (HT700P) alloy exhibits superior yield strength of 490 MPa and ultimate strength of 593 MPa at 700 °C. The major carbides in the alloy are the blocky MC and discrete-distributed M23C6. The MC and M23C6 carbides at the grain boundaries (GBs) can impede crack propagation, yet concurrently intensify the stress concentration. The transgranular and intergranular fractures are observed. Above 700 °C, micro-cracks emerge around M23C6 carbides at GBs and then are interlinked to form lengthy secondary micro-cracks, resulting in the intergranular fracture. The precipitation of γ′ precipitates during tension at 700 and 750 °C confers the alloy to a higher strength.

Titanium alloys produced by laser powder bed fusion (LPBF) are known to possess fine microstructures and multi-scale interfaces. Here, we introduce a high density of α'/β, α/β phase interfaces, {10 1¯1} twin boundaries, and basal stacking faults (BSFs) in a Ti–6Al–4V alloy through LPBF and annealing. The LPBF-fabricated alloy consists of fine acicular α′ martensite with numerous {10 1¯1} twins and BSFs, which results in ultrahigh strength (>1300 MPa), but very low ductility (<5%) due to the massive interface strengthening. Subsequent annealing treatments decrease the strength while increasing the ductility, as the α′ martensite partially or fully decomposes into a lamellar (α+β) structure. The 955 °C-annealed alloy possesses a good strength-ductility combination (yield strength of 1000 MPa, tensile strength of 1078 MPa, and total elongation of 20%). During the stages of uniform plastic strain (up to ∼12%), deformation occurs by dislocation slips, leading to significant dislocation accumulations around the α/β interfaces. At later stages (∼20% strain), when necking occurs, a high density of fcc-γ bands is observed in the hcp-α phase, indicating the onset of deformation-induced martensitic transformation (DIMT) from hcp-α to fcc-γ. The occurrence of DIMT may be attributed to the decreased stacking fault energy and the cohesive energy difference between the hcp and fcc phases, due to the segregation of Al elements in the hcp-α phase. Low-loss electron energy loss spectroscopy reveals that the deformation-induced fcc phase is not Ti-hydride, but a new allotrope of Ti.

Hot isostatically pressed AA6061 cladding is an important structural component of the high performance, Zr-laminated U-10Mo monolithic fuel system for the application in research and test reactors. In this study, the mechanical behavior of two diffusion bonded aluminum alloy, AA6061, was examined using tensile testing. Solid-to-solid diffusion bonding between two pieces of AA6061 was performed by isothermal annealing at 560 °C for 1.5 h, and diffusion couples were subsequently cooled via three different cooling methods: furnace cooling, air cooling, and water quenching. Dog-bone shaped tensile specimens, with 10 mm in gauge length (with diffusion bonded interface in the middle), and 1.5 × 1.5 mm2 gauge cross-sections, were fabricated from the diffusion bonded AA6061 by electro-discharge machining. Yield strength (% EL at failure) of furnace cooled, air cooled and water quenched tensile specimens determined was 82–89 MPa (10–30%), 112–116 MPa (10–14%), and 149–164 MPa (10–17%), respectively. This variation in mechanical behavior was examined with cooling-rate dependent, concentrated precipitation of Mg2Si at the diffusion bonded interface, with due respect for mechanical properties of the AA6061 alloy that inherently vary as a function of cooling rate from 560 °C. Finite element analysis using ABAQUS was employed to augment experimental findings with the appropriate microstructural constituents and alloy properties. Results suggest that the strength is dominated by matrix/bulk properties of AA6061, while ductility is strongly influenced by the cooling method dependent presence of Mg2Si precipitates at the interface.

In this work, cast Mg-1Zn-0.2Ca (wt%) was thermomechanically processed using a two-step procedure to identify the impact of both processing steps on the resulting microstructure and mechanical properties. Samples were first preprocessed via rolling or conventional extrusion (at 400 °C), followed by Equal Channel Angular Extrusion (ECAE), utilizing routes A or Bc. ECAE was performed at 300 °C for the first pass, followed by 275 °C, 250 °C, and 225 °C for passes 2–4. Subsequent microstructures, textures, and quasi-static tension test results are presented to illuminate the effect of preprocessing and ECAE route on grain size refinement and mechanical behavior. Preprocessing via rolling yielded a smaller, more homogeneous initial grain size than the conventionally extruded material. After the second processing step, ECAE, the microstructural differences due to the preprocessing methods are reduced, but not eliminated, and mechanical properties show little variation between rolling and extrusion. The ECAE route did not impact the microstructural refinement, however, the 4Bc route did lead to enhanced ductility (>36%) and higher average ultimate tensile strengths, compared to the 4A route, when tested in the normal direction (perpendicular to the ECAE extrusion direction). The relative importance of texture alteration versus grain refinement and homogeneity is highlighted herein. Lastly, we comment on the influence of processing routes on inclusions and voids.

In the present work, hot compression deformation behavior and microstructure evolution in a homogenized Al–6Mg–0.8Mn alloy with nano-sized Al6Mn phase particles were investigated under the temperature ranging from 300 to 500 °C with the strain rate of 0.001–1 s−1. The constitutive equation of the Al–6Mg–0.8Mn alloy was established and the average deformation activation energy was calculated to be 167.07 kJ/mol. The flow stress of the alloy decreased with increasing the compression temperature and raised with increasing the strain rate, which was closely associated with the competitive relationship between work hardening and dynamic recovery (DRV). The low compression temperature accelerated the formation of shear bands in the alloy. The low strain rate was beneficial for the generation of low-angle grain boundaries (LAGBs), and the high compression temperature and strain rate promoted dynamic recrystallization (DRX). The interaction between the nano-sized Al6Mn phase particles participating near the initial grain boundaries and mobile dislocations facilitated the generation of LAGBs. Discontinuous DRX through grain boundary bulging mechanisms and continuous DRX with the LAGBs transforming to HAGBs led to the preferred formation of recrystallized grains along the initial large-sized grains. Furthermore, this interaction also resulted in the dissolution of Al6Mn phase particles.

Niobium alloys are widely applied in aerospace technologies. Traditional niobium alloys suffer from insufficient high-temperature strength or limited room-temperature plasticity. Here, we develop novel Nb2Mo0.5W0.5Cx eutectic niobium alloys by introducing refractory alloying elements and carbide inspired by design concept of multiprincipal alloy and carbide eutectic alloys. The Nb2Mo0.5W0.5Cx alloys contain numerous eutectic structures consisting of body-centered cubic (BCC) solid solution and carbide phases, in which the carbide phase transfers from Nb2C to NbC with the increase of C addition. By optimizing the composition, a Nb2Mo0.5W0.5C0.25 niobium alloy consisting of BCC and Nb2C with strong bonded semi-coherent interface exhibits a high yield strength of 1.27 GPa, compressive strength of 2.03 GPa, and good plasticity with a fracture strain of 17.8%. Solid solution strengthening from alloying elements and second phase strengthening from carbide phases contribute to the high strengths, while the plasticity is improved mainly from fine grain strengthening and strong bonding of phase interface by reducing the interfacial energy and slowing down the crack propagation. This study offers a strategy for designing the high-performance refractory alloys to bypass the content limitation of alloying elements and enhanced ceramics that generally reduce plasticity.

Two types of welding processes，with double-side friction stir welding (DS-FSW) and single-side friction stir welding (SS-FSW)，were used for dissimilar welding between AM60 and AZ31 Mg alloys in this study. The evolution of texture and microstructure, deformation behavior and mechanical properties of both joints were investigated. The microstructure observation indicated that the microstructure of the joint nugget zone (NZ) under both processes was refined after welding and their grain size was relatively close. The two joints exhibited approximately symmetrical local strong texture distribution characteristics from the advancing side to the retreating side. However, the DS-FSW joint had a larger processing volume and a symmetrical macroscopic weld structure. Due to the symmetry distribution characteristics of texture in NZ, the Schmidt factors for basal slip of the joints from the vicinity of the NZ side to the NZ center showed a decreasing trend, resulting in severe strain localization in both DS-FSW and SS-FSW joints during the tensile process. The tensile tests revealed that the DS-FSW joint exhibited excellent mechanical.properties compared with the SS-FSW joint. This was attributed to its large processing volume, lower volume proportion of the stirring zone and symmetrically distributed weld zone structure improved the deformation coordination of the joint, thereby delaying its premature fracture and exhibiting better mechanical properties.

Many unremitting pursuits have been paid on designing microstructures to enhance the strength-ductility synergy of metallic materials. In this work, laminated bimodal heterostructure and dislocation source limitation were introduced together into pure Ni with various laminate thicknesses by electrodeposition and subsequent annealing to circumvent the limitations of the strength-ductility trade-off. The specimen, composed of alternative fine-grained and ultrafine-grained laminates with the optimized laminate thickness, had a combination of 601 MPa yield strength which was 4.8 times its Hall-Petch yield strength (124 MPa), and 24.5% reasonable ductility. The combination went beyond the range established by the reported pure Ni. When the fine-grained laminates started dislocation slip first and ultrafine-grained ones remained elastic, incompatible deformation between the two different laminates resulted in a high density of piled-up geometrically necessary dislocations (GNDs) against the interfaces, increasing the yield strength. Deformation incompatibility was also present in each of the individual laminates exhibiting bimodal structure, which further facilitated strengthening and strain hardening. Plentiful dislocation cells and walls were found to form inside the fine-grained laminates during work hardening, which could contribute to the production of GNDs. The carefully constructed heterostructures maximized the role of GNDs. Besides, dislocation source limitation induced further hardening, in the form of the yield-point behaviour, and ductilization which resulted from more room inside grains for the accumulation and interaction of dislocations. The superior strength-ductility synergy here paves a promising paradigm for designing high-performance structural metallic materials.

Here, cold-drawing was applied to melt-extracted Cu47.5Zr47.5Al5 amorphous alloy (AA) microwires. The structural observations and tensile deformation behaviors were studied before and after cold-drawing. The drawn wire still possesses amorphous structure. Less surface defects, higher local order degree, and greater compressive residual stress induced by cold-drawing lead to a higher tensile fracture strength and a higher reliability of the drawn wires than those of melt-extracted one. The results obtained in this paper demonstrate that the cold-drawing processing is an effective method to improve the mechanical performance of the AA wires.

Microscopic segregation of chemical elements results in the banded microstructure of finished steel products, and the harmful effect of banded microstructure on toughness is well recognized. However, typical industrial hot work processing, such as hot rolling and forging, cannot erase the banding, and eliminating it with homogenization heat treatment is also challenging and uneconomical. In this study, the impact energy of a 12%Cr tempered martensitic steel with the banded microstructure was significantly improved from 74 J to 154 J by employing thermal cycling and tempering as the final heat treatment to meet the service performance requirement. Compared to conventional quenching and tempering (Q + T), thermal cycling and tempering (TC + T) simultaneously refined the effective grain size of tempered martensite matrix and coarse M23C6 carbides that were continuously distributed along the δ-ferrite/matrix phase boundaries. As a result, more high angle grain boundaries (HAGBs) were introduced and acted as obstacles in retarding the propagation of microcracks. Additionally, finer carbides precipitated at the banding boundary during tempering, owing to the increasing triple junctions between δ-ferrite and tempered martensite. These finer carbides prevent the initiation of microcracks. The results demonstrate the potential of TC + T as a final heat treatment to remove the detrimental effect of banded microstructure on impact toughness.

The microstructure, room-temperature deformation mechanisms, and weldability of the medium-entropy alloy (MEA) NiCoVAl0.2 have been investigated. Defect-free welded joints have been produced with good mechanical properties, indicating excellent weldability. The microstructure consists of f.c.c. grains containing many b.c.c. Ni2VAl (Ni26.1Co33.5V27.8Al12.6) and few σ-type precipitates (Ni15.5Co21.3V62.7Al0.5). Decreasing the aging temperature from 1100 °C to 900 °C, produced a higher area fraction of Ni2VAl precipitates (8 → 25%), much smaller L21 precipitates (7.2 → 1.4 μm), finer grains (17.1 → 2.4 μm), and presence of σ-type precipitate, resulting in simultaneous improvements in both the strength and ductility for both the thermo-mechanically treated (TMT) and electron beam welded (EBWed) MEA. The TMT MEA shows an excellent combination of strength (YS∼993 MPa, UTS∼1478 MPa) and ductility (30.3%), while the EBWed MEA shows slightly lower strength (YS∼822 MPa, UTS∼1194 MPa) and significantly reduced ductility (12.3%), i.e. a YS, UTS, and ductility of 83%, 81%, and 41%, respectively, of those of the TMT MEA. With increasing strain, both low-angle grain boundaries and geometrically-necessary dislocation (GND) densities increased. The TMT MEA has a higher GND density (1.6 × 1015 m−2) than the 9.1 × 1014 m−2 of EBWed MEA after strained to fracture. For both the TMT and EBWed MEA aged at 900 °C, the deformation was accommodated by dislocation slip, dislocation looping around precipitates, and nano-twinning. However, for both the TMT and EBWed MEA aged at 1100 °C, more abundant deformation twinning and an fcc→hcp shear transformation appeared, which may originate from a lower stacking fault energy due to differences in the f.c.c. matrix composition.

Quasi-static tensile and stress-controlled high cycle fatigue tests of solution heat-treated (SHT) Hastelloy X manufactured by electron beam powder bed fusion (PBF-EB) and laser-based power bed fusion (PBF-LB) process were performed at room temperature and 750 °C. Post-fabrication SHT was ineffective in overcoming the microstructural anisotropy observed within as-built specimens, with the grains still maintaining its columnar architecture along the build direction. A significant drop in ductility was observed in tensile specimens tested at 750 °C, which was attributed to the carbide precipitation and grain boundary sliding. Upon investigating the influence of microstructural evolution as a function of test duration, a significant increase in precipitation was observed with an increase in test duration. A notable decrease in the fatigue strength was observed at elevated temperature. The long columnar grain structure within vertically build PBF-EB specimens was found to offer higher resistance against fatigue at 750 °C, owing to its reduced grain boundary area perpendicular to the loading direction. The corresponding fatigue damage mechanisms were investigated via fractographic analysis of the fracture surfaces and longitudinal cross-sections of the fractured specimens. Irrespective of the build orientation and test conditions, the fatigue cracks that resulted in final failure were found to initiate from the specimen surface. Also, the grain boundary precipitates were found to result in intergranular cracking during elevated temperature fatigue tests.

Processing by high-pressure torsion (HPT) was applied to a cold-pressed mixture of Al and Cu (4%wt) powders to successfully synthesise a high-strength nanocomposite. The powder consolidation and redistribution of second phases involved the stretching and fragmentation of the Cu domains into shorter strips and submicrometre particles. After 1 turn, the Al+4 wt%Cu alloy was not fully consolidated and exhibited numerous microvoids at the disc centre. For this reason, the material displayed comparatively low microhardness at this location which triggered early metal cracking during testing through plane strain compression. An adequate consolidation was achieved after 30 HPT revolutions as the composite exhibited a homogenous distribution of Cu fragments without any visible microcavities. This is consistent with the high flow stresses achieved during plane strain compression without incipient metal cracking. At this processing stage, there is evidence of partial dissolution of Cu into the Al–Cu solid solution followed by dynamic precipitation of Al2Cu nanoprecipitates. Additional straining up to 100 turns promoted further hardening up to 270 Hv and grain refinement down to ∼48 nm. However, this occurs concurrently with the coalescence and loss of coherency of the Al2Cu precipitates with the Al matrix.

As base metals (BMs), plates of 5-mm-thick low-alloyed ultra-high-strength carbon steel (LA-UHSS) with a tensile strength of 1.3 GPa and 5-mm-thick 316L austenitic stainless steel were laser-welded at two different energy inputs (EIs; 60 and 100 J/mm). The microstructural characteristics of the fusion zones (FZs) in the welded joints were examined using electron backscattering diffraction (EBSD) and transmission electron microscopy. The fine microstructural components, such as the prior austenite grain size (PAGS) and effective grain size of the fresh martensite promoted during welding, were analysed by processing the EBSD maps using MATLAB software. The micromechanical performance of the weldments was investigated using microindentation hardness (HIT) to display the mechanical responses of different zones. Uniaxial tensile testing was conducted to explore the joint strength and plasticity failure. The dominant phase structures promoted in the FZs at low and high EIs were similar, that is, martensite with a small fraction of austenite. The HIT values displayed a distinct variation in strength between different zones. The HIT values of 316L, LA-UHSS, and FZ were 1.95, 5.55, and 4.63 GPa, respectively. The PAGS increased from 45 to 70 μm with an increasing EI, and a finer martensitic grain structure with an average size of 2.62 μm was observed at high EIs. The mechanical tensile properties of the dissimilar joints at the studied EIs closely matched those of the BM 316L, demonstrating comparable yield and tensile strengths of 225 MPa and 650 MPa, respectively. This similarity can be attributed to the localized plastic tensile deformation occurring primarily within the relatively softer BM 316L, ultimately resulting in joint failure. The flow behaviour of the dissimilar joints under uniaxial tensile testing was analysed using finite element modelling to determine the stress and strain distributions. The plastic strain was mainly localised within the soft metal 316L owing to enhanced dislocation-mediated plasticity.

In this paper, 7055 Al composites reinforced by Al2O3 and ZrB2 nanoparticles were fabricated by in-situ reaction. The adhesion (Wad) of the ZrB2/Al interface was 3.91 J/m2 while the adhesion at the Al2O3/Al interface was 3.69 J/m2. At room temperature and high temperature up to 523 K, yield strength (YS), ultimate tensile strength (UTS), and elongation (EI) in (Al2O3+ZrB2)/7055 Al composites reached up to 595 MPa, 710 MPa, 19% and 371 MPa, 435 MPa, 24%, respectively. The combined strengthening effect produced by Al2O3 and ZrB2 nanoparticles was found to be stronger than that of the individual ZrB2 particles and the matrix. In addition, the steady creep rate of the (Al2O3+ZrB2)/7055 Al composites were the lowest, constituting only 3∼14% of the matrix and 5∼68% of the ZrB2/7055 Al composites. The true stress exponents in the matrix and composites were 5, indicating a dominative dislocation climbing mechanism. Both the promotion of precipitation nucleation and the precipitation-coarsening inhibition during the creep process at the interfaces between the matrix and nanoparticles were discussed. Additionally, deformed and fragment mechanisms and the creep resistance mechanism were elucidated.

Improving the tolerance to fatigue damage for bulk metallic glass (BMG) is of vital importance for its industrial applications during long-term mechanical service. In this work, the composition dependence of structure stability against thermal and mechanical stimuli are studied with Zr–Ni–Al BMGs from the perspective of atomic topological packing and chemical affinity. Large atomic size disparity and strong interactions between component elements facilitate the stability of glass structure, which impart BMGs with relatively higher glass transition temperature and yield strength. Fatigue failure of BMG initiates from the accumulation of inelastic shear transformation events on the sample surface under cyclic loading. The fatigue endurance limit of Zr–Ni–Al BMG is effectively improved by tailoring the chemical composition with increased structure stability, which is characterized by high mismatch entropy and mixing enthalpy. Aluminum plays a role in enhancing the fatigue tolerance of Zr–Ni–Al BMGs, which presumably arises from the covalent-like bond character of aluminum that promotes the formation of rigid atomic packing motifs with great resistance to shear rearrangement, and consequently mitigates the fatigue crack initiation process.

The stress-controlled creep-fatigue test was conducted to investigate the damage mechanism for the CrMoV steel welded joint by introducing tensile holding and tensile-compressive holding respectively. It was found that the final fracture mode changed from creep void-induced fracture inside the over-tempered zone (OTZ) to fatigue crack-induced fracture in the fine-grain heat-affected zone (FGHAZ) as the stress amplitude decreased to 250 MPa and compressive holding of 180 s was introduced. Simulation results based on the local miniature tensile test indicated that the strain mainly concentrated inside the OTZ because of the low strength, while the stress concentrated on the surface of the FGHAZ and inside the OTZ due to the constraint of high-strength weld metal (WM) on the radial deformation. The distribution of strain and stress demonstrated the competitive failure between OTZ and FGHAZ with different modes of damage. The crack initiation on the surface of FGHAZ was promoted in the oxide due to compressive holding, then the sharpened tip of cracks induced sufficient propagation during numerous cycles under low stress amplitude, resulting in the fracture of fatigue crack-induced mode.

The high brittle-to-ductile transition temperature (DBTT) of tungsten is a significant concern that hinders its use as a structural material. This study employs small punch testing over a broad temperature range to investigate the anisotropic mechanism of DBTT in as-hot rolled W-2%wt Y2O3 specimens. RD-TD specimen exhibits the highest EUS(0.75/J), highest ELS(0.08/J) and lowest TSP (∼336 °C) in three oriented materials. Multiple factors were conducted individually, revealing that the similar dislocation density, and fraction of LAGBs are not the primary determinant of the observed variations in DBTT performance. RD-TD specimen with strong {111} γ-fiber texture exhibits the highest Fm that is nearly twice as high as that of RD-ND specimen and almost three times as high as that of TD-ND specimen. The relationship between the grain morphology, such as aspect ratio present on the DBTT as well as fracture mode of the material is apparent. RD-TD specimen boasts superior plastic properties, which displays an annular crack with the dome-like structure at the core and small incisions at the periphery. While, the plasticity of TD-ND and RD-ND specimens are deemed inadequate, as evidenced by the emergence of multiple lengthy and linear cracks in a particular orientation upon initial cracking. The utilization of numerous superimposed loads and the sandwich configuration of Y2O3 particles in tungsten matrix have been discovered to promote the occurrence of delamination in the thickness direction of the RD-TD specimens. The stratified structure, texture, screw dislocations, and grain aspect ratio have been identified as the pivotal factors influencing the anisotropy on DBTT and fracture analysis.

In this work, the exceptional strength-ductility synergy of a dual-phase high entropy alloy (HEA) is achieved by architecting complex microstructures. The HEA rolled at 700 °C shows the yield strength and tensile strength as high as 1580 MPa and 1854 MPa with ductility of ∼18.4%. Different flow stress regions (face-centered cubic (FCC) and body-centered cubic (BCC) phases) divided by complex microstructures lead to strong hetero-deformation-induced strain hardening. The dispersed micro-strain band and the precipitates buffering the dislocation in front of the heterogeneous phase boundary also help to improve the ductility. In addition, utilizing the sensitivity difference between FCC and BCC phases for dislocation accumulation, more dislocations are accumulated in FCC phase to reduce the mechanical incompatibility with BCC phase and fully release the strain hardening ability. The strategy of architecting complex microstructures and selectively modifying phases will be beneficial to the development of high-performance dual-phase alloys.