Microstructural Deformation Mechanisms Research Articles

Investigation of the Microstructure Characteristics and Deformation Mechanisms of the Carbonaceous Slate under Hydromechanical Coupling

Carbonaceous slate inevitably possesses microscopic pores, microcracks, cleavages, and bedding planes in complex geoenvironment during the diagenesis processes. The microstructure of carbonaceous slate changes apparently under the effects of underground water infiltration, tectonic stress, and engineering disturbance, which induces the large deformation of rock mass and influences the stability of geotechnical engineering projects. To investigate the microstructure characteristics and reveal deformation mechanisms of carbonaceous slate under the influence of water pressure and stress, the variations of the pore size distribution(PSD), connectivity of pores, and porosity of samples during water injection and triaxial compression were studied using multiple methods. The results indicated that voids include plate-like micropores and microcracks, which are discontinuous without external stress. The micropores with a size of less than 1 μm dominate in number. The flaky particles were extruded and bent at a confining pressure, which caused the intermediate pores to form and altered the PSD of the samples. Hence, the connectivity dramatically improved and resulted in increased permeability. Water with dissolved clay minerals and small particles could move between micropores and microcracks during the water injection process. The elastic deformation of the particles recovered, and the intermediate pores disappeared when the imbalanced forces on two sides of the particles were narrowed. Pore water pressure affected the effective stress state and decreased the cohesion and stiffness of the rock. In the lower stress state, the porosity had a certain range of decrease (about 0.2%) mainly due to micropore compression, while the microcrack sprouted and expanded with the increase of compressive stress, resulting in the extension of porosity. The interaction of the stress and water seepage on the slate reduced the rock strength and favored the deformation, leading to a large macrodeformation of the soft rock in the long run.

Effects of post annealing on the microstructure, precipitation behavior, and mechanical property of a (CoCrNi)94Al3Ti3 medium-entropy alloy fabricated by laser powder bed fusion

• The (CoCrNi) 94 Al 3 Ti 3 medium-entropy alloys with different strength-ductility combinations were fabricated by laser powder bed fusion and subsequent annealing processes. • Cr-rich σ-phase precipitates formed after 1073 K and then gradually dissolved at 1373 K, while fine L1 2 coherent precipitates were formed at 1373 K. • Precipitation and grain boundary strengthening both markedly increased owing to the formation of precipitation particles and recrystallization-induced grain refinement after annealing at 1073 K. The additive manufacturing of multi-principal element alloys has remarkable potential for industrial applications. In this study, a (CoCrNi) 94 Al 3 Ti 3 medium-entropy alloy (MEA) with adequate strength-ductility synergy was prepared via laser powder bed fusion. The microstructural evolution, mechanical property, and deformation mechanisms of the MEA were investigated after post annealing for a short period (0.5 h) at a temperature range of 773-1373 K using various microstructural characterization techniques and quantitative analysis. The static recrystallization temperature of the (CoCrNi) 94 Al 3 Ti 3 MEA ranged from 973 to 1073 K. The average grain size first decreased and then increased, while the dislocation density persistently decreased and texture gradually weakened with increasing annealing temperature. Cr-rich σ-phase precipitates formed after 1073 K and then gradually dissolved at 1373 K, while Ni, Al, and Ti elements were aggregated to form a small amount of fine L1 2 coherent precipitates with an average diameter of approximately 70 nm at 1373 K. The evolution of the dislocation density, grain size, and precipitates significantly influenced the propensity of deformation twins and stacking faults, which consequently affected the strain hardening behavior and mechanical properties. The quantitative calculation of strengthening mechanisms showed that dislocation strengthening played a dominant role at annealing temperatures below 1073 K, and it significantly weakened at 1373 K. Precipitation and grain boundary strengthening both markedly increased owing to the formation of precipitation particles and recrystallization-induced grain refinement after annealing at 1073 K.

Microstructure evolution, strengthening mechanisms and deformation behavior of high-ductility Mg−3Zn−1Y−1Mn alloy at different extrusion temperatures

Hot extrusion was performed on as-cast Mg−3Zn−1Y−1Mn alloy to further improve the mechanical properties and investigate its microstructure evolution and deformation mechanism at different thermal deformation temperatures. The experimental results suggested that the alloy at the extrusion temperature of 330 °C had the optimal mechanical properties, and the tensile strength and elongation of the alloy were 270 MPa and 16.8%, respectively. The strength improvement of the as-extruded alloy primarily arose from three aspects, including fine-grain strengthening due to dynamic re-crystallization (DRX), dislocation strengthening not offset by DRX, and second phase strengthening. Continuous dynamic re-crystallization (CDRX) and dynamic recovery (DRV) occurred simultaneously at the extrusion temperature of 300 °C. The discontinuous dynamic re-crystallization (DDRX) occurred at the extrusion temperature of 330 and 360 °C. However, the contribution of {0001} basal plane slip, {1010} prismatic type I and {1120} prismatic type II slips to plastic deformation was significantly affected by the extrusion temperature. The {1120} prismatic type II slip was found to be the most difficult one to initiate among the three slip systems.

Heterogeneity of deformation, shear band formation and work hardening behavior of as-printed AlSi10Mg via laser powder bed fusion

The deformation heterogeneities and micro-to macro-structural evolution of shear bands were thoroughly characterized and assessed in correlation with the work hardening behavior of laser powder bed fused as-built AlSi10Mg using compression testing at 78 and 293 K in a wide range of constant strain rates. Using the Kocks-Mecking model, work hardening behavior was correlated with the evolved microstructure and rate-controlling deformation mechanisms. It was found that initial work hardening (athermal hardening rate) is dependent on the strain rate at both 78 and 293 K, where it increases by a transition from shearing to looping of nano-precipitates in the 10−2-10−1 s−1 strain rate range. Stages II (hardening stage) and Stage III (dynamic recovery stage) of work hardening were also observed and their dependence on temperature and strain rate was assessed. The former includes the dislocation-obstacle interactions resulting in work hardening, whereas the latter consists of recovery processes where density of dislocations decreases. Shear banding was reported for higher strain rates manifesting in micro- and then evolving into macro-shear bands with deformation, which led to the increase in the dislocation recovery rate in Stage III of work hardening. Compressive work hardening mechanisms were discussed for both 78 and 293 K temperatures.

Exploring microstructure refinement and deformation mechanisms in severely deformed LPBF AlSi10Mg alloy

An additively produced AlSi10Mg aluminium alloy was post-processed by Equal Channel Angular pressing at 150ºC. This resulted in a fabrication of the novel submicrometer-grained (SMG) microstructure, which was subsequently characterised by optical microscopy, scanning electron microscopy, and transmission electron microscopy. In addition, the deformation mechanisms were also studied in detail at different scales. The post-deformation studies show that the predominant deformation mechanism of the alloy matrix was dislocation slip. However, the heterogeneous microstructure also activated another important mesoscale deformation mechanism - the plastic deformation gradient (incompatible deformation) that existed between the boundaries of the melt pools and their interiors and the Al/Si interfaces. More importantly, the TEM analysis provided evidence for the deformation twinning of the hard Si phase as well as for the deformation-induced amorphisation of the Si phase. The revealed synergy of different deformation modes sheds light on the good balance between strength and ductility and opens a new horizon for the development of the next generation of structural materials.

In-situ surface study of the mechanism of high temperature deformation in an Al-Cu-Li alloy

The 2195 Al-Cu-Li alloy is able to obtain an elongation of 203% by high temperature stretching. The microstructure evolution and deformation mechanism of non-recrystallized Al-Cu-Li alloy after high temperature stretching were studied. The results show that the inhomogeneous grain structure is the main factor affecting the elongation. High resolution surface studies with focus ion beam show that intragranular dislocation slip provides up to 57% of the total strain and grain boundary sliding plays an accommodating role.

Effects of pre-aging on microstructure evolution and deformation mechanisms of hot extruded Mg–6Zn–1Gd–1Er Mg alloys

Abstract The influence of pre-aging treatment on the microstructure, texture and mechanical properties of the Mg–6Zn–1Gd–1Er (wt.%) alloy was investigated. The microstructure analysis shows that the presence of pre-aging is beneficial to { 10 1 ¯ 2 } twin nucleation at the early stage of extrusion and inhibits the growth of twins and promotes the formation of [ 10 1 ¯ 0 ] -fiber texture components, thus accelerating the complex process of recrystallization. In the middle stage of extrusion, the extruded samples under the condition of solid solution were subjected to dynamic precipitation during severe shear deformation. The precipitation of the second phase particles followed the particle stimulating nucleation (PSN) mechanism, which increased the volume fraction of DRX grains during extrusion. In the extruded samples under the peak-aged condition, the particles appear dissolved during the severe shear deformation strain, which slows down the DRX process. In the later stage of extrusion, the small rod-shaped particles followed the PSN mechanism, and finally formed the strong fiber texture. The extruded alloy exhibits the strongest mechanical properties under the peak-aged state, with ultimate tensile strength (UTS) of 346 MPa, tensile yield strength (TYS) of 217 MPa, and elongation to failure (EL) of 13.6%. The improvement of mechanical properties is mainly attributed to the existence of strong fiber texture, small rod-shaped and block-shaped phases.

Unraveling process-microstructure-property correlations in powder-bed fusion additive manufacturing through information-rich surface features with deep learning

A machine learning (ML)–based framework has been developed to optimize the process parameters and unravel the paramount process–microstructure–property (PMP) relationships rapidly and precisely, which is demonstrated using electron beam melting (EBM®)-processed Ti–6Al–4V alloy. The process maps are constructed using ML to discover the optimal process window based on the three criteria: fully dense (≥ 99.5% in relative build density), flat fusion surface and highest possible strength, without which the optimization outcome will be deficient. By using the ML-optimized process parameters, Ti–6Al–4V parts were fabricated with ultimate tensile strength ∼5% higher and ∼80% faster than the classical parameter setting developed by the original machine manufacturer. The α/β dual-phase microstructure and tensile deformation mechanism are further studied to understand the superior mechanical properties obtained in the ML-optimized sample. In addition, the information-rich top fusion surface is found to be an alternative route to implicitly materialize the microstructure-to-property relationships with a prediction accuracy of ∼98%. The full-scope surface and microstructure maps are then generated from the process parameters. Surface features that reflect superior and poor mechanical properties are particularly identified. Finally, the implications of the ML-based PMP framework with surface feature correlation are discussed in the context of improving resources utilization efficiency.

Effect of Initial Microstructure on the High-Temperature Formability of STS 321 Alloy Using a Dynamic Material Model

General austenitic stainless steel has a problem with intergranular corrosion due to volatilizing chromium, which forms chromium carbide in a high temperature environment. By adding titanium as an alloying element, STS 321 stainless steel has excellent creep resistance and intergranular corrosion resistance at high temperatures, because the formation of chromium carbide is suppressed. It is important to find the optimal process conditions for STS 321 stainless steel used in the aerospace field, because high temperature processing is mainly applied, and defects or inhomogeneity of materials that occur during high temperature processing lowers the yield of products. In this study, to investigate the effect of the initial microstructure on the high-temperature deformation behavior of STS 321 stainless steel, a high-temperature compression test was performed on two types of STS321 alloys with different initial microstructures. The temperature range was set at 50°C intervals from 800°C to 1100°C, and the strain rate was set at 10-1/sec intervals from 1 × 100/ sec to 1 × 10-3/sec. Based on the experimental results, the thermal activation energy, which differed depending on differences in the initial microstructure, was calculated. In addition, by deriving flow stress and processing maps, the difference in energy dissipation efficiency depending on temperature and strain rate was explained, along with the initial microstructure and high-temperature deformation mechanism.

Research progress on microstructure evolution and hot processing maps of high strength β titanium alloys during hot deformation

High strength β titanium alloys are widely used in large load bearing components in the aerospace field. At present, large parts are generally formed by die forging. Different initial microstructures and deformation process parameters will significantly affect the flow behavior. To precisely control the microstructures, researchers have conducted many studies to analyze the microstructure evolution law and deformation mechanism during hot compression. This review focuses on the microstructure evolution of high strength β titanium alloys during hot deformation, including dynamic recrystallization and dynamic recovery in the single-phase region and the dynamic evolution of the α phase in the two-phase region. Furthermore, the optimal hot processing regions, instability regions, and the relationship between the efficiency of power dissipation and the deformation mechanism in the hot processing map are summarized. Finally, the problems and development direction of using hot processing maps to optimize process parameters are also emphasized.

Microstructure evolution and deformation mechanism of α+β dual-phase Ti-xNb-yTa-2Zr alloys with high performance

• Microstructure of the alloys is more sensitive to Nb rather than Ta. A slight difference in Nb content will affect the morphology of martensite and even induce ω phase transformation, resulting in completely different mechanical responses of the alloy. • The as-cast Ti-3Nb-13Ta-2Zr alloy shows the highest compressive strength (227 ±10 MPa), and compressive strain (74.3% ± 0.4%). • Nb and Ta content strongly affects Young's modulus and tensile properties of the alloys after rolling. The as-rolled Ti-3Nb-13Ta-2Zr alloy exhibits much lower modulus due to lower Nb content as well as more α"-martensite and β-phase, and a good combination of low modulus and high strength among all the designed alloys. Biomedical β-phase Ti-Nb-Ta-Zr alloys usually exhibit low elastic modulus with inadequate strength. In the present work, a series of newly developed dual-phase Ti- x Nb- y Ta-2Zr (wt.%) alloys with high performance were investigated in which the stability of β-phase was reduced under the guidelines of ab initio calculations and d-electronic theory. The effects of Nb and Ta contents on the microstructure, compressive and tensile properties were investigated. Results demonstrate that the designed Ti- x Nb- y Ta-2Zr alloys exhibit typical characteristics of α+β dual-phase microstructure. The microstructure of the alloys is more sensitive to Nb rather than Ta. The as-cast alloys exhibit needle-like α′ martensite at a lower Nb content of 3 wt.% and lamellar α′ martensite at an Nb content of 5 wt.%. Among the alloys, the Ti-3Nb-13Ta-2Zr alloy shows the highest compressive strength (2270 ± 10 MPa) and compressive strain (74.3% ± 0.4%). This superior performance is due to the combination of α+β dual-phase microstructure and stress-induced α" martensite. Besides, lattice distortion caused by Ta element also contributes to the compressive properties. Nb and Ta contents of the alloys strongly affect Young's modulus and tensile properties after rolling. The as-rolled Ti-3Nb-13Ta-2Zr alloy exhibits much lower modulus due to lower Nb content as well as more α" martensite and β phase with a good combination of low modulus and high strength among all the designed alloys. Atom probe tomography analysis reveals the element partitioning between the α and β phases in which Ta concentration is higher than Nb in the α phase. Also, the concentration of Ta is lower than that of Nb in the β phase, indicating that the β-stability of Nb is higher than that of Ta. This work proposes modern α+β dual-phase Ti- x Nb- y Ta-2Zr alloys as a new concept to design novel biomedical Ti alloys with high performance.

Effect of solution cooling rate on the microstructure and creep deformation mechanism of a rhenium-free second-generation single crystal superalloy

• The cubic degree and size of γ′ phases were inversely proportional to the solution cooling rate. • Air cooling method significantly improved the creep lifetime at 800 °C/750 MPa and 1100 °C/137 MPa. • Air cooling facilitated the formation of dislocation locks and retarded γ′ phases to coarsen at 800 °C/750 MPa. • The influence mechanism that air cooling facilitated the denser interface dislocation networks was explored in combination with the long-term ageing test. • The nucleation and precipitation of secondary γ' phase might well be influenced by the solution cooling rate. Various cooling scenarios (water, oil, air and furnace) were employed to study the impacts of the solution cooling rate (SCR) on the microstructure and creep behavior of a novel single-crystal (SX) superalloy. The results showed that the cubic degree and size of the γ′ phases were inversely proportional to the SCR. The creep life first increased and then dropped dramatically with a reduction in the SCR. The creep life of the sample cooled with air cooling (AC) was the highest, up to 144.90 h at 800 °C/750 MPa and 160.15 h at 1100 °C/137 MPa. During creep at 800 °C/750 MPa, the improved creep life of the AC sample was mainly attributed to the fine cubic γ′ phases, which decreased the rate of γ′-phase coarsening and favoured plastic deformation by promoting the active movement of dislocations. The AC helped the γ′ phases become rich in Al, Ti and Ta while depleted in Co and Cr, which enhanced its stacking fault energy, thus promoting the formation of dislocation locks. Meanwhile, the largest negative lattice misfit caused by AC induced denser γ/γ′ interface dislocation networks at 1100 °C/137 MPa, which efficiently reduced the minimum creep rate. The calculated average dislocation spacing results indicated that the smallest density of excess dislocations corresponded to the AC sample, proving its greatest creep resistance. Interestingly, the size of the secondary γ′ phases first decreased and then increased sharply with decreasing SCR during creep at 1100 °C/137 MPa, when fine secondary γ′ phases had a positive role in the blockage of dislocation movement in the matrix. Eventually, the comprehensive SCR effect was explored to provide more guidance in the design of Re-free SX superalloys.

An investigation on microstructure evolution and deformation mechanism of Ti–5Al–5Mo–5V–1Cr–1Fe alloy during in-situ tensile

The effect of volume fractions of α phase and β phase on the microstructure evolution and deformation mechanism of as-forged Ti–5Al–5Mo–5V–1Cr–1Fe alloy during in-situ tensile was investigated. The morphologies, low angle grain boundaries (LAGBs), textures, geometrically necessary dislocation (GND) densities and Schmid factors (SFs) of α phase and β phase during deformation were analyzed. The results showed that the volume fractions of β phase decreased from 42.7% to 28.8% while those of α phase increased from 57.3% to 71.2% when the stresses reached the critical induced stress. The microstructure evolution of α phase is more obvious than that of β phase with the variation about volume fractions of α phase and β phase. Besides, the number of LAGBs in α phase was increased with the increasing of volume fractions of α phase. The texture intensities of α phase were decreased with the increasing of volume fractions of α phase and those of β phase were increased with the decreasing of volume fractions of β phase. The effect of volume fractions of α phase and β phase on dislocation density and deformation mechanism was unobvious.

Deformation mechanism of commercially pure titanium under biaxial loading at ambient and elevated temperatures

Commercially pure (CP) titanium is thermally processed and subjected to biaxial stress. However, the evolution of the microstructural deformation mechanisms under such circumstances is not adequately understood. In this study, the mechanical responses and microstructural deformation mechanisms of TA2 CP titanium sheets under equi-biaxial loading at room temperature (RT), 300 °C, and 400 °C were studied. The activated slip and twinning systems were investigated by transmission electron microscopy (TEM) after polished cruciform specimens were biaxially tensile-tested at RT and elevated temperatures. The results show that {112¯2} contraction twinning and {101¯2} extension twinning are the main deformation mechanisms of RT biaxial deformation, while dislocation glide is predominant in biaxial deformation at 300 °C and 400 °C. This difference yields varied work-hardening behaviors at RT and elevated temperatures. In biaxial deformation at 400 °C, the main slip trace type is multiple slip. The interaction of different slip systems in multiple slip created shear deformation concentration areas and further induced cross-slip. However, in biaxial deformation at 300 °C, the amounts of simplex and multiple slip were significantly reduced compared to those at 400 °C because the lower temperature increased the critical resolved shear stress and insufficient activated slip systems were available for grain deformation. Therefore, several stress-concentration areas were generated with the activation of cross-slip.

The microstructure evolution and deformation mechanism in a casting AM80 magnesium alloy under ultra-high strain rate loading

Ultra-high strain rate impact tests were conducted by Split-Hopkinson pressure bar to investigate the microstructure evolution and impact deformation mechanism of a solution treated casting AM80 Mg alloy at 25, 150 and 250 °C with a strain rate of 5000 s −1 . The microcrack and dynamic recrystallization (DRX) preferentially nucleate at grain boundary (GB) and twin boundary (TB), especially at the intersections between GBs and TBs, and then propagate along twin direction. In contrast, the adiabatic shear bands preferentially occur at high-density twined regions. At 25 °C, the dominated deformation mechanisms are basal slip and twinning. As deformation temperature increases to 150 and 250 °C, the deformation gradually shifts to be dominated by a coordinated mechanism among non-basal slip, twinning and DRX. The flow stress behavior and deformation mechanism indicate that the degree of decrease in flow stress with temperature is associated with the change of deformation mode.

Microstructure evolution, tensile properties and deformation mechanism of Fe-6.5 wt.% Si steel doped with yttrium

Fe-6.5 wt.% Si steels doped with different contents of yttrium were fabricated by vacuum induction melting (VIM), forging, hot rolling and annealing. The microstructure evolution, ordered degree, tensile properties and deformation mechanism were investigated. The results showed that the amount of high-melting precipitates enriched in yttrium increased with the content of yttrium increasing. The solidification, hot rolling and annealing microstructures were refined due to the elevated nucleation rate and the effect of microstructure heredity. The steel containing the highest content of yttrium exhibited the highest tensile ductility and the most developed dimple patterns. Deformation bands appeared in the tensile microstructures at 400 °C. Most of the deformation bands in the steels without yttrium and doped with the intermediate content of yttrium possessed the special {112}<111> twinning mis-orientation with the matrix, implying the cooperation of the deformation twinning mechanism. Nevertheless, the smooth stress-strain curves and the absence of the deformation bands indicate the predominance of the dislocation sliding mechanism during the tensile test at 500 °C. The present work manifested that the doping of yttrium in Fe-6.5 wt.% Si steel could be utilized to raise the intermediate-temperature tensile ductility through purifying the matrix, refining the microstructure and reducing the ordered degree.

Origin, parameters, and underlying deformation mechanisms of propagating deformation bands in irradiated 316L stainless steel

Lüders-type propagating deformation bands were observed in specimens of irradiated 316L stainless steel samples removed from Spallation Neutron Source target vessels after service. Mechanical testing with digital image correlation (DIC) and in-situ tensile testing with scanning electron microscopy electron backscatter diffraction showed that the observed Lüders-type behavior was not related to the known transformation-induced plasticity or twinning-induced plasticity behavior. Instead, the phenomenon occurs at small local strain values before a significant amount of martensite or deformation twins appear in the microstructure. Microstructural analysis and in-situ mechanical test results suggest Lüders-type band formation and propagation were related to the appearance and evolution of defect-free channels—analogous to slip bands. A modified Swift equation with a Ludwigson-like component was offered to rationalize the phenomenon and model the strain-softening processes at small strain values. The results indicate complex microstructural processes and deformation mechanisms were active at small strain values and underline the benefits of advanced mechanical test approaches such as DIC.

Temperature-dependent microstructural evolutions and deformation mechanisms of (Ni2Co2FeCr)92Al4Nb4 high-entropy alloys

Precipitation-strengthened high-entropy alloys (HEAs) with tailored phase structures are expected to possess excellent strength-ductility combinations for advanced structural applications. In this work, we systematically studied the microstructural evolutions and mechanical behaviors of (Ni 2 Co 2 FeCr) 92 Al 4 Nb 4 HEAs at different aging temperatures (700–900 ℃). It was revealed that only spherical L1 2 phase existed in the specimen peak-aged at 700 °C without other precipitates, while in the specimen peak-aged at 800 °C, irregular precipitation of ε phase appeared on the grain boundaries in addition to the intragranular L1 2 phase. In strong contrast, upon peak aging at 900 ℃. the fine interleaving Widmanstätten-type ε phase with an ordered hexagonal structure (D0 19 ) became the dominated precipitate. We further revealed that the coherent L1 2 phase provided a more effective strengthening effect than that of the ε phase, leading to the highest yield strength of ~950 MPa in the alloy peak-aged at 700 °C. The stacking faults shearing of L1 2 phase and the planar dislocations shearing of ε phase were identified as the main deformation mechanisms of the specimens peak-aged at 700 and 900 °C, respectively. Interestingly, the ε phase was determined to have certain plastic deformability, enabling the 900 °C peak-aged alloy to exhibit excellent tensile ductility. These findings would provide valuable guidelines for the design of precipitation-strengthened HEAs with optimized microstructures and superior mechanical properties. • Temperature-dependent microstructural transformation of precipitation strengthened high-entropy alloys was established. • The L1 2 phase dominated the precipitation behaviors at low temperature, while the ε phase dominated at higher temperatures. • The L1 2 phase sheared by the stacking faults was the main deformation mechanism of the specimen peak-aged at 700 ℃. • The precipitation strengthening efficiency provided by the ε phase was lower than that of the L1 2 phase. • The ε phase in this HEA was shearable and deformable in contrast to many other brittle phases.

Microstructure evolution, deformation mechanism, and mechanical properties of biomedical TiZrNb medium entropy alloy processed using equal channel angular pressing

Equal channel angular pressing (ECAP) was applied to a biomedical TiZrNb medium entropy alloy (MEA) with an equal atomic ratio at 480 °C with 1, 2, 4, and 6 deformation passes in route C to enhance the mechanical properties and exploit the plastic deformation mechanism of the MEA. As the applied strain increased, dendritic grains first tended to merge and form equiaxed grains, which eventually elongated and formed coarse grains. Simultaneously, many straight dislocations and dislocation loops occurred and coalesced into a line during the early stages. Then, they rearranged to construct highly dense dislocation walls (HDDWs) and evolved into shear bands, maintaining the continuity of the deformation. After a 6-pass deformation, the TiZrNb MEA exhibited a yield strength of 1170 ± 21 MPa, higher than that of the as-cast sample of 830 ± 21 MPa, and a maximum hardness of 389 ± 11 HV0.2, which enhanced its wear resistance.

Hot deformation behavior and constitutive modeling of a cost-effective Al8Cr12Mn25Ni20Fe35 high-entropy alloy

In this study, a new non-equiatomic and cost-effective high-entropy alloy (HEA), Al8Cr12Mn25Fe35Ni20, was designed using thermodynamic parameters and prepared by arc melting. The alloy was subjected to homogenization at 1200 °C and a hot-rolling reduction of 50%. The hot deformation behavior and deformation mechanism were studied at varying strain rates ranging from 0.01 to 10 s−1 and temperatures ranging from 900° to 1100°C via plane strain compression tests using a Gleeble 3800 thermo-mechanical simulator. The phase structure of the rolled alloy was studied using electron backscattered diffraction (EBSD), X-ray diffraction, and differential thermal analysis to detect phase transformation. The constitutive model was implemented to predict the high-temperature flow stress using the Zener-Holloman parameter (Z), which correlated well with the experimental values. The studied HEA exhibited a relatively high activation energy for hot deformation of 389.5 kJ.mol−1, i.e., comparable to those of equiatomic HEAs in the literature. The hot-deformed microstructural features and deformation mechanism were studied using EBSD, which revealed discontinuous dynamic recrystallization as the main softening mechanism. Dynamic recrystallization (DRX) showed the formation of fine grains along the initial grain boundaries, accompanied by Al-Ni-rich B2 precipitates at the recrystallized grain boundaries.