Dislocation Deformation Research Articles

Mechanical Responses and Deformation Mechanisms of Low-Cost High-Entropy Alloy AlCrFe2Ni2 with Heterogeneous Structure Subjected to High-Strain Rate Deformation

Introducing heterogeneous structures into metallic materials through composition design is a promising strategy for simultaneously improving the strength and ductility of the materials. In this work, a novel dual-phase low-cost AlCrFe2Ni2 high-entropy alloy (HEA) was designed and prepared. Its phase constitution, microstructure, dynamic mechanical responses at strain rates ranging from 1100[Formula: see text]s[Formula: see text] to 4800[Formula: see text]s[Formula: see text] as well as deformation mechanisms were investigated. It was found that the HEA consists of FCC, B2 and BCC phases and has a heterogeneous microstructure containing dual-phase alternate lamellar and high-density precipitates. The HEA displays the optimal mechanical properties at the strain rate of 4800[Formula: see text]s[Formula: see text], of which the yield strength, maximum flow stress and strain are 1222.9[Formula: see text]MPa, 2340.8[Formula: see text]MPa and 30.5[Formula: see text]%, respectively, better than that of most single-phase FCC or BCC HEAs, dual-phase HEAs and traditional alloys. The deformation mechanism of the HEA at the strain rate of 4800[Formula: see text]s[Formula: see text] involves both dislocation slip and deformation twinning, with the former dominating. This work could provide guidance and insights for designing metallic materials with excellent mechanical properties at high strain rates.

Study on high temperature tensile constitutive behavior and deformation mechanism of Ti-47.5Al-2.5 V-1.0Cr-0.2Zr alloy

The high temperature tensile test of Ti-47.5Al-2.5 V-1.0Cr-0.2Zr alloy was carried out by electronic universal testing machine under the condition of 750–900 °C/10−5–10−3 s−1. The hot tensile stress-strain curves were analyzed, and the constitutive model under hot tensile conditions was established. The microstructure transformation rule and deformation mechanism during tensile process were determined. The results show that the hot tensile curve is longer in the steady-state flow stage corresponding to lower strain rate and higher tensile temperature, the true stress declines and the elongation at break increases. The constitutive equation was established based on the tensile curve data, and the corresponding thermal activation energy was 310.3 kJ/mol. As the rise of tensile temperature and the decline of strain rate, the proportion about cross-layer fracture in the tensile fracture morphology decreases, the number of dimples increases, more lamellar structures change into recrystallized structures, and the softening effect of the alloy is more obvious. The dislocation deformation mechanism mainly includes the existence of dislocation slip and climb, dislocation intersection and dislocation ring or dislocation network formation. Twinning deformation is also another important mechanism of high temperature tensile deformation of TiAl alloy. Twins are formed in parallel with each other, so that the deformation can be further carried out. The dislocations and twins in the deformed microstructure will provide nucleation conditions for recrystallized grains. The dynamic recrystallization(DRX) grains are preferentially formed around the grain boundary and the vicinity of dislocation and twin is also preferred nucleation site for DRX. The DRX behavior is the main softening mechanism, and DRX size and volume fraction corresponding to lower tensile rate and higher tensile temperature are larger.

Enhanced strength-ductility synergy in a Ni–W–Co–Ta medium-heavy alloy via cryogenic supersonic fine particle bombardment

This study explores the influence of cryogenic supersonic fine particle bombardment (CSFPB) on a Ni–W–Co–Ta medium heavy alloy (MHA), and focus on the effect of gas pressure and impact time on the surface integrity, microstructural evolution, and mechanical properties of the MHA. CSFPB treatment creates a gradient structure, including surface layer with nanograins down to 9.0 nm due to severe plastic deformation, subsurface layer with high density dislocation structures and deformation twins due to weakened impact energy, and undeformed matrix. A key advantage of CSFPB is seen to be the cryogenic environment, which promotes superior surface integrity by reduced roughness. As the impact duration and gas pressure increase, the depth of deformation layer, surface hardness and strength of the MHA progressively rise. The optimal combination of strength and ductility is achieved at a gas pressure of 1.0 MPa for a duration of 90 s. This setting results in a maximum ultimate tensile strength of 1351 MPa and yield strength 796 MPa, with uncompromising elongation. However, excessively long treatment durations or high gas pressures can lead to the formation of surface microcracks, ultimately reducing the MHA's strength. Therefore, CSFPB offers the benefit of improved surface integrity through the cryogenic environment while maintaining a desirable balance between enhanced strength and ductility.

Enhancing wear resistance of CoNiCrMo medium entropy alloy through cold working and aging: Tradeoffs with corrosion performance

This study investigates the wear behavior and corrosion resistance of MP35 N alloy under various conditions, including annealed, cold-worked, and aged states. The microstructure was characterized using optical microscopy, X-ray diffraction, and transmission electron microscopy. Results indicated that cold rolling induced a dislocation structure and deformation features such as mechanical twins, stacking faults, and slip bands. The presence of non-homogeneous strain and planar defects in the cold-rolled samples led to broader diffraction peaks compared to the annealed samples. The microstructure of the cold-rolled and artificially aged samples exhibited deformation features, dislocation structures, and ultra-fine precipitates. High-angle annular dark field imaging and energy-dispersive X-ray spectroscopy revealed that these precipitates were Ti-rich particles, which, along with molybdenum segregation in stacking faults, contributed to the highest hardness observed. X-ray diffraction analysis confirmed the segregation and depletion of alloying elements from the lattice during aging. Wear and corrosion tests demonstrated that while cold working and aging enhanced the wear performance of the annealed CoNiCrMo alloy, they adversely affected its corrosion resistance. Specifically, the volume loss for cold-worked and aged samples was approximately 2.7 and 2.1 times smaller than that of the annealed specimen, respectively. However, the annealed alloy exhibited a lower corrosion current density (icorr) of 70 nA cm−2 compared to the cold-worked and aged samples, which had icorr values of 130 and 200 nA cm−2, respectively.

Microstructure and dynamic deformation mechanism of laser powder bed fusion of 316L-containing Ti–6Al–4V with dual-phase heterostructure

In this paper, 316L-containing Ti–6Al–4V alloy was fabricated by laser powder bed fusion (LPBF) through mixing Ti–6Al–4V and 4.5 wt% 316L powders, and the dynamic compressive mechanical properties and deformation mechanism at different strain rates were studied. The results show that the volume fraction of β phase sharply increases from 1.8% (in TC4) to 61.4% (in HST), and micro- and submicron-sized grains coexist in the HST alloy, producing heterostructure in the form of bimodal grain size distribution. The presence of the heterostructure led to superior heterogeneous deformation induced stress, thus facilitating the additional strain hardening and deformation coordinating ability, thus made the HST alloy achieved ultimate compressive stress of ∼1750 MPa and fracture strain of ∼17%, showing excellent comprehensive mechanical properties. Under quasi-static load, the deformation mode of HST alloy is mainly attributed to progressive deformation-induced martensitic transformation. However, at high strain rates, the impact loading inhibited the activation of progressive DIMT, and thus the deformation mode changed to combination of dislocation slipping and deformation twinning.

Dual effects of pre-deformation and shape recovery process on martensitic transformation behavior in NiTi-Nb composite wire

The martensitic transformation behavior of NiTi-Nb composite wire following the pre-deformation and shape recovery (PD&SR) process was investigated. The wire drawing process significantly decreased the martensitic transformation start temperature (Ms) of NiTiNb alloy. Interestingly, the PD&SR process exhibited dual effects on the initial Ms temperature, depending on the annealing temperature. When the composite wire was annealed at higher temperature, the PD&SR process decreased the Ms temperature. In contrast, when the composite wire was annealed at lower temperature, the PD&SR process raised the Ms temperature. These dual effects can be attributed to the competition between the hindering effect of deformation dislocation and the promoting effect of stress coupling near the interface between the β-Nb phase and the NiTi matrix. At lower annealing temperature, the stress coupling generated by the β-Nb nanowires and the NiTi matrix is stronger, leading to an increase in the Ms temperature. Furthermore, the pre-deformation strain and shape recovery temperature influenced the dislocation density and the strength of stress coupling, thereby regulating the Ms temperature within a certain range.

The effects of pre-existing dislocations on the mechanical properties of iron

In atomistic simulations, pre-existing dislocations have been reported to reduce the yield stress compared to the ideal crystals. However, the underlying physics behind yield stress reduction is still unrevealed, which hammers the design of advanced materials. Here, large-scale molecular dynamics simulations are carried out to investigate the influence of pre-existing dislocations on the mechanical properties of body-centered cubic Fe crystals with dislocation, twinning, and phase transformation-dominated deformation mechanisms. The results suggest that the overestimated yield stress of all the crystals is significantly reduced by increasing dislocation numbers and obtaining closer flow stress on the uniform plastic deformation stage. This reduction in yield stress can be attributed to the lower thermo-dynamical driving force required to activate existing dislocations in pre-existing dislocation crystals than that to nucleating new dislocations in ideal crystals. Furthermore, pre-existing dislocations inhibited the phase transformation-dominated deformation process, but the twinning/dislocation-dominated deformation process still exhibited its original deformation mechanism.

Mechanical characterization of nanocrystalline Cu-Ag alloys subjected to shear deformation

ABSTRACT This study investigates the mechanical behaviour of nanocrystalline Cu-Ag alloys using molecular dynamics simulations combined with detailed analyses of dislocation densities, atomic populations, and deformation characteristics. Shear tests were conducted across three different atomic compositions at temperatures ranging from 10 K to 500 K. The influence of temperature and Ag impurities on the mechanical properties of nanocrystalline Cu is explored. Elevated temperatures are found to promote plastic deformation by increasing atomic mobility, resulting in reduced dislocation densities and flow stresses. Increasing Ag content correlates with lower dislocation densities, highlighting enhanced plastic activity between grain and grain boundaries. Structural population analysis underscores the significant impact of Ag species on the mechanical response of nanocrystalline Cu. Further investigations are warranted to explore additional deformation mechanisms. These findings contribute to a deeper understanding of nanocrystalline Cu-Ag alloys, informing the design of novel materials with tailored mechanical properties.

The deformation mechanism of low symmetric Ti–Pt intermetallic compounds containing high density of planar defects

Intermetallic compounds typically exhibit limited plastic deformation capacity due to challenges in activating dislocation slip and deformation twinning, coupled with a lack of alternative deformation mechanisms. Ti–Pt alloys are a prevalent type of intermetallic compound utilized in high-temperature shape memory alloys and as materials for energy applications in electric fields. However, they often exhibit poor deformation capability. Here, we prepared a low-symmetry intermetallic phase, Ti4Pt3, which demonstrates significant plastic deformation capability. This phase features a high density of parallel planar defects, resulting in an exceptionally large lattice periodicity perpendicular to these defects. Through in-situ scanning electron microscope compression tests, we observed substantial plastic deformation in this new phase. Analysis of the deformed Ti4Pt3 phase revealed that the dense planar defects create uniformly distributed sites of internal stress concentration, enabling a rapid increase in back stress within crystals. This phenomenon leads to notable lattice rotation and localized order-disorder transitions, both crucial mechanisms facilitating plastic deformation and enhancing deformation capacity. Our research underscores the potential of leveraging structural asymmetry to enable unconventional deformation mechanisms, thereby enhancing the plasticity of intermetallic materials.

Electronic descriptors for dislocation deformation behavior and intrinsic ductility in bcc high-entropy alloys

Controlling the balance between strength and damage tolerance in high-entropy alloys (HEAs) is central to their application as structural materials. Materials discovery efforts for HEAs are therefore impeded by an incomplete understanding of the chemical factors governing this balance. Through first-principles calculations, this study explores factors governing intrinsic ductility of a crucial subset of HEAs—those with a body-centered cubic (bcc) crystal structure. Analyses of three sets of bcc HEAs comprising nine different compositions reveal that alloy chemistry profoundly influences screw dislocation core structure, dislocation vibrational properties, and intrinsic ductility parameters derived from unstable stacking fault and surface energies. Key features in the electronic structure are identified that correlate with these properties: the fraction of occupied bonding states and bimodality of the d-orbital density of states. The findings enhance the fundamental understanding of the origins of intrinsic ductility and establish an electronic structure–based framework for computationally accelerated materials discovery and design.

Characterization of a copper matrix composite reinforced with nano/submicron-sized boron fabricated via spark plasma sintering

The addition of various reinforcing phases can improve the mechanical properties of copper. This study investigates the enhancement of the mechanical properties of copper by adding boron, focusing on overcoming the challenges associated with the homogeneous distribution of submicron/nanoscale secondary phases in metal matrix composites. Employing a combination of mechanical alloying and spark plasma sintering, a copper-boron composite containing 3 wt% boron was prepared. Scanning electron microscopy equipped with an electron backscatter diffraction detector and energy-dispersive X-ray spectroscopy was utilized to characterize the structure of the sintered samples and mechanically alloyed powder. A two-phase structure containing nano/submicron-sized boron distributed uniformly in the copper matrix was formed in the sintered sample. Instrumented micro-indentation tests were performed to characterize the mechanical behavior of the samples. The sintered composite sample exhibits significantly higher hardness than the sintered copper. The enhanced mechanical performance of the composite is primarily attributed to grain boundary strengthening and microstructural refinement, where nano/submicron-sized boron particles prevent grain growth and refine the microstructure, enhancing hardness and strength. Additionally, dispersion strengthening from hard boron particles and the presence of a high density of twin boundaries within the copper matrix increase resistance to dislocation motion and deformation, and further improving the material's mechanical properties. On the other hand, the composite sample exhibits increased electrical resistivity due to the boron’s role as electron scattering centers. Overall, this study provides a valuable strategy for the design and optimization of advanced copper-based composites with tailored mechanical and electrical properties.

Influencing laser shock peening treatment of the mechanical, tribological, corrosion, and microstructural characteristics on AA5052 alloy

This study examines the effects of laser shock peening parameters on the structural, mechanical, tribological, and corrosion properties of AA5052 aluminum alloy. The LSP process uses specific parameters, detailed in Table 2, to induce ultra-high plastic strains and strain rates in the material. The research demonstrates significant improvements in both surface hardness (48.29% increase) and tensile strength (24.63% increase) for the optimized LSP conditions. The treatment results in a maximum compressive residual stress of 231.02 MPa near the surface, concentrated within a depth of 100 μm. X-ray diffraction analysis reveals the formation of Mg2Al3 (β) precipitates on the LSP surface, along with peak broadening and shifting indicative of residual stress. These precipitates, along with the high dislocation density caused by severe plastic deformation during LSP, are contributed to the enhanced mechanical properties. Electron backscatter diffraction and transmission electron microscopy observations on the LSP-treated AA5052 confirm the introduction of dislocation shifts, deformation twins, and refinement of grain structure. Additionally, the LSP treatment (1.046 × 10−3 mm/N-m3) significantly improves wear resistance compared to unpeened alloy (4.482 × 10−3 mm/N-m3), with a wear rate reduction of over 76.6% during the linear reciprocating tribometer. Finally, electrochemical corrosion tests demonstrate superior corrosion resistance in LSP-treated AA5052 (corrosion rate of 0.0116 mm/yr) compared to the unpeened alloy (0.0551 mm/yr). This study demonstrates that LSP significantly enhances the mechanical performance and corrosion resistance of AA5052 alloy, establishing it as a valuable candidate for shipbuilding applications that require superior durability.

Effect of laser shock peening on tribological properties of 55SiMoVA bearing steel

Wear is an important factor limiting the service life of 55SiMoVA bearing steel. In this work, laser shock peening (LSP) technology is used to improve the tribological properties of 55SiMoVA bearing steel, and the corresponding underlying mechanism is systematically discussed. After LSP, the kurtosis (Sku) of surface roughness asperities reduced from 10.355 to 5.488, and no new phase was generated. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analysis suggested LSP induced the generation of dislocation structures and deformation twins, leading to a decrease in the average grain size and an increase in the fraction of high-angle grain boundaries. Due to the work-hardening and fine-grain strengthening, the microhardness increased by 16.6 %, the maximum residual compressive stress amounted to −793.1 MPa, and the coefficient of friction (COF) and wear volume were significantly reduced. Scanning electron microscopy (SEM) results indicated that the wear mechanism of 55SiMoVA bearing steel before and after LSP was not transformed. However, the abrasive wear and delamination wear of the LSPed specimens were significantly improved, which was mainly attributed to grain refinement, increasing microhardness and constructing a residual compressive stress layer in the subsurface layer of 55SiMoVA bearing steel. During the sliding process, the increase in microhardness limits micro-plowing on the wear surface, and the residual compressive stress inhibits the crack formation and expansion, improving the wear resistance of 55SiMoVA bearing steel.

Twinning behavior and variant selection mechanism of b.c.c tantalum during dynamic plastic deformation

In this paper, the microstructure and twinning behavior of tantalum (Ta) during dynamic plastic deformation (DPD) were jointly analyzed in combination with impact experiments and molecular dynamics simulations, with a focus on the mechanism of variant selection for twinning. The results indicated that twins nucleate at grain boundaries and gradually grows with increasing deformation until it penetrates the entire grain. Due to the difference of grain boundary dislocation density, strain rate and deformation temperature have significant impacts on the quantity and distribution of twins. In addition, at room temperature, nearly half of the twin variants in DPD samples do not conform to Schmid law, and almost all the twin variants in liquid nitrogen samples do not follow to Schmid law. The activation of these non-Schmid variants is mainly affected by the strain coordination. Through this study, we have deepened our understanding of the dynamic microstructural response of Ta under high-speed deformation conditions.

Research on the shear band suppression mechanism in strut-based lattice structures by oblique graded design

Under compressive loads, shear band formation in lattice structures can lead to stress fluctuations, resulting in a decrease in energy absorption capacity. To specifically suppress shear bands, it is necessary to expound the formation mechanisms. This study used theoretical analysis, experiments, and finite element (FE) simulations to elucidate the mechanism underlying shear band formation in strut-based lattice structures. It was determined that stress concentration at strut joints along the 45° diagonal plane induced shear deformation. Shear bands were most pronounced along the four body diagonals, and their existence diminished as the distance from the diagonal increased. Therefore, a design of oblique graded lattice structure (OGLS) was proposed, and quasi-static compression experiments were performed using FE method. The results showed that the main internal stress of OGLS is combined with the original 45° shear stress and the annular staggered stress produced by the oblique graded design, which constrains each other and avoids mutual dislocation deformation, thus realizing shear band suppression. However, an excessively large graded coefficient excessively weakens the 45° shear stress and results in the appearance of an annular compact band. By optimizing the graded coefficient based on the deformation consistency of the outer contour, the optimized OGLS exhibited significant improvements in yield strength, plateau stress, and energy absorption, which are increased by 36.06%, 39.29%, and 34.41%, respectively. This research offers novel perspectives on how lattice structures can attain stable compression deformation and a high energy absorption capacity.

Effect of Co-content on microstructure, phases, and mechanical properties of laser additive manufactured Cox(CrNi)100-x alloy

This study describes the combination of mechanical properties of the CoCrNi medium entropy alloy system by tailoring its non-equiatomic compositions. The Laser Directed Energy Deposition (LDED) based Additive Manufacturing (AM) technique is deployed to fabricate the Cox(CrNi)100-x (x=40, 50, 60) alloy system. All compositions exhibit the formation of solidification substructures, with the refinement of subgrain size correlated with an increase in Co-content. The Co40 alloy exhibited a single-phase FCC structure, while Co50 (3.1 % ε-martensite) and Co60 (53.6 % ε-martensite) exhibited dual FCC+HCP structure during deposition. The combined effect of dislocation slip, deformation twinning, and deformation-induced HCP ε-martensite transformation strengthened the Co40 alloy during deformation. However, the Transformation-Induced Plasticity effect (TRIP) resulted in greater HCP ε-martensite transformation during deformation. Due to limited slip systems in the HCP structure, the Co60 alloy showed lower strength. The TRIP effect is highly dominant in Co60 alloy due to the prevalent HCP phase fraction in the initial samples. This led to stress concentration at FCC grain boundaries and ε-martensite, resulting in early failure of the alloy. With the increase in Co-content, the deformation mechanism changed from dislocation slip to deformation twinning to HCP ε-martensitic transformation. The LDED-built Cox(CrNi)100-x alloy system showed a good combination of strength and ductility. The study suggests that additive manufacturing is an easier and more suitable technique for obtaining compositions with the desired combination of mechanical properties.

Effects of strain rate and low temperature on dynamic behaviors of additively manufactured CoCrFeMnNi high-entropy alloys

With the increasing demand for high-performance alloys in extreme environments, there has been an active development of new materials. High-entropy alloys (HEAs) are considered a promising choice due to their exceptional properties. Even though HEAs exhibit remarkable mechanical properties, only a limited number of studies have explored the mechanical properties and microstructures of additively manufactured HEAs under extreme conditions. In this work, the dynamic mechanical properties at high strain rates and different temperatures (i.e., 293 K and 77 K), as well as quasi-static mechanical properties for the CoCrFeMnNi HEAs fabricated by selective laser melting (SLM) are investigated. Microstructure observations have demonstrated that the as-printed sample displays a single face-centered cubic (FCC) phase with a columnar dendrite feature. Within dendrites, a large number of dislocations and substructures appear due to the applied high cooling rates during the SLM process. The as-printed sample exhibits a significant strain rate dependence from quasi-static to dynamic loading during deformation. Compared to the quasi-static mechanical properties, the as-printed HEA reveals higher dynamic yield strength (e.g., ∼1081 MPa and ∼1020 MPa along the build and scanning directions under 2800 s−1, respectively), more pronounced strain-hardening behavior, and larger remarkable plasticity under dynamic loading at cryogenic temperatures. When subjected to increasing strain rates ranging from 0.001 s−1 to 3500 s−1 at 293 K, the yield strength of the as-printed HEAs exhibits a notable enhancement, increasing from ∼517 MPa to ∼723 MPa along the BD direction, and from ∼545 MPa to ∼667 MPa along the SD direction. The corresponding variation in the strength of the BD samples is more pronounced than that of the SD samples. The enhancement in strength should be attributed to the differences in the features of grain orientation and dislocation distribution along different build directions, as well as the strain rate dependence. During plastic deformation, the dominant mechanisms of dislocation slips and deformation twins (DTs) are transformed into multi-stage-twin-controlled ones at cryogenic temperatures, which is beneficial to improve the strain hardening rate and plasticity. The present studies provide a deep understanding of the deformation mechanism of HEAs under extreme conditions and help promote the application of HEAs in the future.

Kyanite microstructural and microchemical characteristics reveal differences in growth, deformation and chemical modification: A case study from the Paleoproterozoic suture zone of South Harris, NW Scotland

Based on petrological association, cathodoluminescence (CL), trace element signatures and orientation relationships, two generations of kyanite are distinguished in a high temperature, high pressure garnet-biotite-aluminosilicate bearing migmatite of South Harris, NW Scotland. The migmatite shows a garnet and biotite rich domain (Grt-Bt domain) which is cut at a low angle by a dominantly coarse-grained plagioclase-quartz leucosome. In addition, a fine-grained plagioclase-quartz-kyanite domain (Plag-Qtz-Ky domain) is present intercalated with the Grt-Bt domain and subparallel to the plagioclase-quartz domain. Type 1 kyanite is coarse grained and associated with Bt clusters and garnet within the Grt-Bt domain. It grew relatively early, syn- to post-garnet growth, in a suprasolidus environment resulting in crystallographically determined oscillatory CL and trace element zoning. Grains record evidence of progressive deformation in the crystal plastic regime, where deformation is accommodated by dislocation glide, climb and deformation twinning. The dominant activated slip system is (100)<001> with minor component of <100>, while deformation twins show a ∼ 180° rotation around ∼<001> axis and a twin plane near (001). Grains appear to be impervious to deformation induced diffusion with all zoning remaining sharp despite crystal plastic deformation. Grains in direct contact with the Plag-Qtz-Ky domain show late modification of the CL and trace element signature suggesting melt-mediated interface-coupled dissolution-precipitation reaction. This modification resulted in crosscutting lobate high trace element regions and irregular rims with low Cr and V content. These rims show similar CL and trace element characteristics as Type 2 kyanite which are exclusively seen within the Plag-Qtz-Ky domain suggesting that Type 2 grains are cogenetic with Type 1 rims. Type 2 grains are finer grained than Type 1 grains and show near uniform CL and trace element distributions with rare oscillatory zoned and relatively higher Cr & V bright cores. Type 2 show either no or very localized internal deformation features. However, they exhibit a clear shape preferred orientation which coincides with a crystallographic preferred orientation where the longest shape axis is parallel to <001>. We propose that Type 2 kyanite grains underwent melt-present deformation by rigid body rotation in an externally derived melt with different trace element chemistry than the host rock. This melt thus interacted chemically by melt-mediated interface-coupled dissolution-precipitation reactions with the surrounding rocks forming the Type 1 rims.Our study shows detailed analysis of kyanite is an important tool for giving constraints on the deformation, P–T and melting history of high-grade metamorphic rocks and migmatites.

Tuning mechanical behavior of an FCC high entropy alloy: Insights from roll deformation and texture

Severe plastic deformation (SPD) is introduced as a significant approach in designing and tailoring the mechanical characteristics of high entropy alloys (HEAs). This research focuses on investigating the microstructure evolution, deformation mechanisms, and their influence on texture components and mechanical behavior in a single solid solution Ni1.5FeCrCu0.5 HEA subjected to cold rolling. For this purpose, microstructure evolution and texture expansion were studied in 25, 45, 65, and 85 % thickness reductions using electron backscatter diffraction (EBSD) as well as transmission electron microscopy (TEM). The finding illustrates that alongside dislocation density, deformation twins and shear bands increase with higher strain; in particular, nanotwins with a thickness of approximately 50 nm were observed in the 85 % cold rolled (85 % CR) alloy. Bulk texture analysis indicates that the presence of shear bands and twins leads to the Goss {110}<001> and Brass {110}<112> texture orientations in the cold-rolled samples, which is ascribed to the low SFE of the alloy. With increased strain, the alloy's hardness and yield strength increased from ∼150 Hv and ∼236 Mpa (As-cast sample) to ∼467 Hv and ∼1097 Mpa (85 % CR), respectively, while the elongation decreased by ∼66 %. By examining the alloy's strengthening mechanisms, it has been determined that increasing the dislocation density and the presence of twins are the two main strengthening mechanisms of the alloy.

Transformation pattern of shape-memory NiTi alloy during stress-biased thermal cycling

Despite the superelastic deformation of NiTi has been documented and analyzed elaborately, its shape-memory behavior during stress-biased thermal cycling has not been thoroughly unveiled. This paper examines the evolution of transformation pattern in NiTi upon thermal cycling over a wide range of biasing stress. For the present shape-memory NiTi, both forward and reverse transformations proceed via the growth of localized deformation band (LDB) under low biasing stress (σbias ≤ 150 MPa), while LDB only appears during forward transformation and reverse transformation is uniform under high biasing stress (σbias ≥ 200 MPa). This is the first time that delocalization (conversion of deformation mode from localization to homogeneity) is observed during stress-biased thermal cycling. We clarify that the intrinsic undercooling/overheating of martensitic transformation results in unstable thermomechanical response, and it is the origin of localization in shape-memory NiTi. It is found that transformation-induced plasticity (TRIP), which is dominated by dislocation slip and deformation twining, not only causes irreversibility in the present shape-memory NiTi but also leads to delocalization through stabilization of intrinsic thermomechanical response of reverse transformation.