Room Temperature Deformation Behavior Research Articles

Ternary Mg-Sc-based TRIP alloys: Design strategy based on Sc-equivalent

This study addresses the transformation-induced plasticity (TRIP) effect observed in bcc single-phase Mg–Sc alloys, aiming to circumvent the strength-ductility tradeoff inherent in traditional Mg-based alloys. Introducing a third element (X = Zn, Y, Nd, Gd) significantly enhanced the strength of the binary Mg–Sc TRIP alloys, simultaneously preserving ductility due to the TRIP effect. Consequently, a ternary Mg–Sc–X TRIP alloy with a bcc single-phase, for instance, achieved an ultimate tensile strength of approximately 380 MPa and a fracture elongation of around 41%, surpassing the conventional tradeoff. Furthermore, we introduce the design strategy of Sc-equivalent (Sceq) to articulate the combined influence of Sc and X elements on the stability of the bcc phase. This novel approach demonstrates the room-temperature deformation behavior of the Mg–Sc–X ternary alloy can be predicted and modulated, showcasing superelasticity (17.5 < Sceq < 19.5) and TRIP effect (19.0 < Sceq < 21.0).

Heterostructure enables anomalous improvement of cryogenic mechanical properties in titanium

The pursuit of strong and ductile structures for cryogenic applications has fueled a persistent interest in the microstructure design of metals and alloys. While heterostructure design has recently demonstrated efficacy in achieving superior strength-ductility combinations at room temperature, its potential remains less explored in the cryogenic regime. In this report, we unveil anomalously improved cryogenic mechanical properties of a pure titanium with harmonic heterostructure that matches or even surpasses those of commercial titanium alloys. Through detailed comparison to room-temperature deformation behavior, we reveal that the superior performance of heterostructure at cryogenic temperature is fundamentally underpinned by the amplified inter-zone mechanical incompatibility and the suppression of dislocation cross-slip. The former promotes the generation of abundant geometrically necessary dislocations, and the latter optimally configures them. Collectively, these two factors culminate in the hetero-deformation-induced effect, delivering the anomalous improvement of cryogenic mechanical properties in titanium. These findings not only significantly advance our understanding of cryo-deformation behaviors in heterostructured materials but also offer the potential for developing high-performance materials for cryogenic applications.

Fabrication of Textured Ti&lt;sub&gt;2&lt;/sub&gt;AlC-MAX Phase Ceramic by Slip Casting under Strong Magnetic Field and Spark Plasma Sintering, and Its Crystal Orientation Dependence of Room Temperature Deformation Behavior

Fabrication of Textured Ti&lt;sub&gt;2&lt;/sub&gt;AlC-MAX Phase Ceramic by Slip Casting under Strong Magnetic Field and Spark Plasma Sintering, and Its Crystal Orientation Dependence of Room Temperature Deformation Behavior

Room-temperature deformation of single crystals of WC investigated by micropillar compression

The room temperature deformation behavior of single crystals of WC has been investigated as a function of crystal orientation and specimen size by micropillar compression tests. Plastic flow is successfully observed at room temperature by the operation of slip on {011¯0}〈21¯1¯3〉 when the specimen size is reduced to micrometer orders. This slip system is the only operative slip system in WC at room temperature, and thus plastic flow is not observed for crystal orientations close to the c-axis orientation. The bulk critical resolve shear stress (CRSS) is estimated to be 1.2 ± 0.3 GPa from the extrapolation of the size-dependent CRSS. The 1/3〈21¯1¯3〉 dislocation carrying slip on {011¯0} dissociates into two identical collinear partial dislocations separated by a stacking fault with the energy of 211∼264 mJ/m2. The preference of slip along 〈21¯1¯3〉 among possible directions (such as 〈21¯1¯0〉 and [0001]) on the {011¯0} prism plane is discussed in terms of dislocation self-energy based on anisotropic elasticity, stacking fault energy, dislocation dissociation and Peierls stress for dislocation motion. The lowest Peierls stress arising from the shorter Burgers vector (1/6〈21¯1¯3〉) of dislocations as a result of collinear dissociation of dislocations with b = 1/3〈21¯1¯3〉 on the {011¯0} slip plane is considered to be the main reason for the preference of the {011¯0}〈21¯1¯3〉 slip system.

Revealing the dynamic recrystallization mechanism, extrusion deformation mechanism, and tensile deformation behavior of Mg–6Al–1Zn–1.1Sc alloy

In this study, extruded deformed billet and extruded rod of Mg–6Al–1Zn–1.1Sc (wt. %) alloy were characterized by optical microscopy (OM) and electron backscatter diffraction (EBSD). The room temperature tensile properties and deformation behavior of extruded alloy were investigated using a universal testing machine and the visco-plastic self-consistent (VPSC) model. The results indicated that the coarse deformed grains (DGs) progressively disappeared and the degree of dynamic recrystallization (DRX) of the alloy increased as the sampling position approached the outlet of the extrusion die. In addition, the grain boundary strengthening induced by DRX increased the corresponding Vickers hardness. DRX mechanisms during extrusion included discontinuous DRX, continuous DRX, twin-induced DRX, and particle-stimulated nucleation (PSN). The EBSD-based in-grain misorientation axes (IGMA) analysis revealed that the slip modes within DGs were dominated by prismatic slip in the early stages of extrusion and by multiple slip modes in the later stages. The yield strength, ultimate tensile strength, and elongation of the extruded alloy were 172.4 MPa, 290.1 MPa, and 26.9%, respectively. The combination of grain boundary strengthening, texture strengthening, and secondary phase strengthening resulted in the high yield strength. The VPSC model well simulated the tensile deformation of the extruded alloy with (0001)//ED (extrusion direction) fiber texture. The superior plasticity of the extruded alloy was ascribed to the high Schmid factor (SF) of the non-basal slip and the activation of the non-basal slip facilitated by the reduction in the ratio of the critical resolved shear stress (CRSS) between the non-basal slip and the basal slip.

Adjustable room temperature deformation behavior of Mg–Sc alloy: From superelasticity to slip deformation via TRIP effect

This study investigated the transformation-induced plasticity (TRIP) effect in Mg–Sc alloys with β single-phase (body-centered cubic) structure. A Mg-19.8 at% Sc alloy showed fracture strain of ∼53 % accompanied by necking propagation with increasing the tensile strain at room temperature. An X-ray diffraction analysis and transmission electron microscopy observations confirmed the existence of a hexagonal close-packed phase beside the β matrix phase during and after the tensile test; this indicates a strain-induced martensitic transformation, i.e., the TRIP effect induced superior ductility. Moreover, the study revealed a threshold Sc content of ∼19.5 at% Sc at which the deformation behavior at room temperature changes from superelasticity to TRIP. The TRIP Mg–Sc alloys exhibited fracture strain from 45 % to 66 % and ultimate tensile strength (UTS) above 220 MPa to overcome the tradeoff between the fracture strain and UTS of conventional Mg alloys.

Interstitial carbon content effect on the microstructure and mechanical properties of additively manufactured NiCoCr medium-entropy alloy

In this study, we manufactured the NiCoCr medium-entropy alloy (MEA) for the first time with controlled interstitial C content of 0.25 at% and 0.75 at% (0.25 C MEA and 0.75 C MEA) using a powder bed fusion-type additive manufacturing (AM) process. Moreover, we investigated the effect of interstitial C content on the microstructure, room temperature tensile properties and deformation behavior of MEA. The initial microstructure shows that both AM-built interstitial C-doped MEAs had a heterogeneous grain structure and epitaxial growth grains along the building direction. The analysis of electron channeling contrast images showed a large amount of nano-sized precipitates (in-situ precipitates) distributed at the sub-structure boundaries formed by a dislocation network, and a large number of stacking faults were simultaneously observed inside the sub-structure. The fraction of in-situ precipitates was higher in 0.75 C MEA than in 0.25 C MEA. A room temperature tensile test measured yield strengths (YS) of 747.5 MPa for 0.25 C MEA and 832.2 MPa for 0.75 C MEA, indicating the highest properties among additively manufactured MEAs reported to date. Considering the strengthening mechanisms, we compared the microstructural characteristics that affected YS, and identified that in-situ precipitates and high-dislocation density were major strengthening factors. On the other hand, deformation twin, which improves strain hardening rate and ductility was observed in both alloys. Based on the above results, we discuss the correlation of microstructure, mechanical properties, and deformation mechanism of AM-built interstitial NiCoCr MEA. • i-MEAs with different carbon contents were fabricated by additive manufacturing. • Mechanical and deformation behavior of AM-built i-MEAs were investigated. • Higher carbon addition lead to the enhanced tensile properties in AM-built i-MEA. • The predicted YS of i-MEAs corresponded well with the experimental data.

Understanding room-temperature deformation behavior in a dilute Mg–1.52Zn–0.09Ca (mass%) alloy sheet with weak basal texture

The deformation behavior of a weakly textured Mg–1.52Zn–0.09Ca (mass%) alloy sheet during room-temperature uniaxial tensile and bending tests was thoroughly investigated using the electron backscattered diffraction technique and crystal plasticity finite-element method. The sheet exhibited a high elongation to failure of 46.1% along the transverse direction because of the easy activation of basal slips, prismatic slips, and tensile twinning. Although the activities of the basal slips and tensile twinning were suppressed during the tensile deformation along the rolling direction, the sheet showed a satisfactory elongation to failure of 28.2% owing to the activation of the prismatic slips. Notably, the sheet exhibited excellent stretchability with a limiting dome height of 10.1 mm. This was attributed to a small fraction of the basal texture component, which facilitated the basal slips during the stretch formation. However, during the bending deformation, the prismatic slips and tensile twinning became less active than during the uniaxial tension, affording inferior bendability to that of automotive-grade Al alloy sheets. This may help to establish microstructural design guidance for the development of room-temperature formable Mg alloy sheets.

Deformation mechanism and inverse Hall – Petch behavior in nanocrystalline materials

Abstract It is widely accepted that for the very smallest grain sizes (typically below 20 – 30 nm), dislocations play no significant role in the deformation of nanocrystalline materials. However, the grain-boundary mechanisms responsible for the reported decrease in strength with decreasing grain size in this regime (the ‘inverse Hall–Petch effect’) remain unclear. Here, we demonstrate by molecular-dynamics simulation that, in the absence of both grain growth and any dislocations, nanocrystalline fcc metals deform via a mechanism involving an intricate interplay between grain-boundary sliding and grain-boundary diffusion. By quantitatively reproducing the well-known Coble-creep formula for coarse-grained materials, we show that the ‘inverse Hall–Petch effect’ arises from sliding-accommodated grain-boundary diffusion creep. Previous, apparently contradictory, suggestions that GB sliding, on the one hand, or GB-diffusion creep, on the other, are responsible for this behavior can thus be reconciled as originating from one and the same deformation mechanism. We discuss the reasons why we believe that these simulations also capture the room-temperature deformation behavior of nanocrystalline fcc metals in the absence of dislocation nucleation and microcracking.

Room-temperature deformation of single crystals of transition-metal disilicides (TMSi2) with the C11b (TM = Mo) and C40 (TM = V, Cr, Nb and Ta) structures investigated by micropillar compression

The room-temperature deformation behavior of single crystals of transition-metal (TM) disilicides with the tetragonal C11b (TM=Mo) and hexagonal C40 (TM = V, Cr, Nb and Ta) structures has been investigated by micropillar compression as a function of specimen size, paying special attention to the deformation behavior of the equivalent slip ({110}<1¯11> and (0001)<21¯1¯0>, respectively for the two structures). In contrast to bulk single crystals, in which high temperature at least exceeding 400 °C is usually needed for the operation of the equivalent slip, plastic flow is observed by the operation of the equivalent slip at room temperature for all these TM disilicides in the micropillar form. The critical resolved shear stress (CRSS) value exhibits the ‘smaller is stronger’ behavior following an inverse power-law relationship for all these TM disilicides. The bulk CRSS values at room temperature estimated from the specimen size dependence are 620 ± 40, 240 ± 20, 1,440 ± 10, 640 ± 20 and 1,300 ± 30 MPa for MoSi2, VSi2, CrSi2, NbSi2 and TaSi2, respectively. Transmission electron microscopy reveals that the equivalent slip at room temperature occurs by a conventional shear mechanism for all TM disilicides, indicating the change in deformation mechanism from synchroshear in bulk to conventional shear in micropillars occurs in CrSi2 with decreasing temperature.

Effects of Zr addition on lattice strains and electronic structures of NbTaTiV high-entropy alloy

The room-temperature (RT) deformation behavior for two single-phase body-centered-cubic (BCC) refractory high-entropy alloys (RHEAs), NbTaTiV and NbTaTiVZr, has been comprehensively investigated via in-situ neutron-diffraction experiments. Our work shows that the addition of Zr leads to the transition of mechanical response from ductile to brittle behavior. The results of lattice-strain evolutions obtained from in-situ neutron diffraction for the ductile NbTaTiV RHEA exhibit atypical plastic-deformation behavior, i.e., the reduced plastic-anisotropic deformation, leading to an even distribution of the applied stress amongst the grains with different orientations rather than forming stress concentrations in {200}-oriented grains during plastic-deformation. Density functional theory (DFT) analysis shows that NbTaTiVZr has a lower electron density at the Fermi level, larger lattice distortion, and stronger charge transfer, as compared to NbTaTiV, suggesting higher strength and lower ductility in NbTaTiVZr, which are consistent with the current experimental results.

Twinning engineering of high-entropy alloys: An exercise in process optimization and modeling

In a bid to improve the mechanical properties of high-entropy alloys, particularly, their strain hardening capability, we adapted the time-proven concept of ‘twinning engineering’, developed in the context of TWIP steels, to twinning-assisted high-entropy materials. The strategy chosen involved a two-step thermomechanical processing that consisted of low-temperature pre-straining and subsequent annealing. This approach was trialled on CoCrFeMnNi as an exemplary high-entropy alloy. The annealing conditions selected ensured that the deformation twins generated under low-temperature deformation were retained, whilst the dislocation density was recovered. The viability of this strategy was convincingly confirmed for room temperature deformation of the alloy. A constitutive model accounting for the effect of the pre-straining induced deformation twins was proposed. It was shown to provide a reliable description of the low-temperature and room-temperature deformation behavior of CoCrFeMnNi when deformation twins are involved.

Mechanical response and microstructure evolution of commercially pure titanium subjected to repetitive bending under tension

The aim of this work was to study the cold formability of commercially pure Titanium alloy (Grade 2) by a testing methodology known as repetitive bending under tension (R-BUT). A dedicated test rig to perform the test was designed and fabricated to analyse the room temperature deformation behaviour of Ti-50A alloy sheet of 1.2 mm thickness. Samples from three different orientations were tested to investigate the effect of mechanical anisotropy on deformation behaviour. The results confirmed a significant increase in elongation to failure in samples subjected to R-BUT as compared to those subjected to standard tensile tests under similar conditions. This may be due to a delay in localised necking during R-BUT. Finite element analysis (FEA) suggested that a decrease in stress triaxiality in R-BUT could be the reason for enhanced formability of the materials compared to the conventional tension. Furthermore, electron backscatter diffraction (EBSD) study of the microstructure confirmed the development of highly strained regions that eventually lead to the formation of fine grains in the samples subjected to R-BUT. This could be due to a strain induced dynamic recovery process occurring during the test.

The microstructure and the mechanical property of AZ91D solidified under GPa-grade high-pressure

ABSTRACTHigh-pressure (2–4 GPa) solidified AZ91D alloy was prepared and the microstructure was investigated by X-ray energy diffraction and scanning electronic microscopy. The room-temperature compression deformation behaviour was also studied. The results showed that the high-pressure solidified AZ91D alloy was composed of nanometre β-Mg17Al12 and equiaxed α-Mg dendrites. The average size of α-Mg grains decreased from 395 ± 5 µm (atmosphere pressure) to 12 ± 3 µm (4 GPa) and the solubility of Al in α-Mg increased to 6.25 wt-% at 4 GPa. The compression strength of 402 MPa and the relative compression ratio of 27% (4 GPa) were 50% and 93% higher than the original AZ91D. Meanwhile, high pressure can also decreased the corrosion rate from 0.0675 mA/cm2 (atmosphere pressure) to 0.0122 mA/cm2 (4 GPa).

The effect of Mo on load partitioning and microstrain evolution during compression of a series of polycrystalline Ni-Based superalloys

The room temperature deformation behaviour of a series of model polycrystalline Ni-based superalloys with varying Mo content has been studied in compression using in situ neutron diffraction. Initially, it was found that intergranular load partitioning was operative, followed by interphase partitioning at higher applied loads, with yield of the γ phase and associated strain redistribution to the γ′ phase. The initiation of interphase load partitioning was found to be dependent on the lattice misfit, occurring at lower applied stress in alloys with larger lattice misfit, and was influenced by the sign of the lattice misfit. Notably, deformation behaviour was found to be contingent on the complex relationship between lattice misfit and the strength of each phase.

Room Temperature Compressive Property and Deformation Behavior of Microporous STS 316L Stainless Steel Tube Manufactured with Powder Sintering Process.

This study investigated the room-temperature compressive property and deformation behavior of microporous STS 316L stainless steel tube for catalyst manufactured with powder sintering after two-way compression molding. The microporous tube was manufactured using STS 316L powder stocks with an outer diameter of 30 mm, inner diameter of 25 mm and length of 120 mm. In initial microstructure observed from different directions and locations, the porosity was measured as 32%, and the relative density obtained using micro-computed tomography was 0.54. Phase analysis did not identify phases other than γ-Fe. In a room temperature compression test, compressive yield strength measured 32 MPa. Observation of fractpgraphy after compression test revealed that dimples were formed at the powder-powder interface during the process where necks were disconnected. Based on the above findings, this study attempted to identify the deformation behavior of microporous STS 316L material manufactured with powder sintering after two-way compression molding and powder sintering process.

Plastic deformation mechanism and interaction of B2, α2, and O phases in Ti[sbnd]22Al[sbnd]25Nb alloy at room temperature

In this work, quasi-in situ tensile unloading and electron backscatter diffraction (EBSD)-based slip trace analysis were applied to study the room-temperature deformation behaviour of Ti22Al25Nb alloys with three different microstructures and the plastic deformation mechanism of the B2, α2, and O phases. In addition, the interaction model of the three phases was presented. The results showed obvious B2 slip deformation in the necking region of the B2+α2 microstructure and the B2 texture+α2 samples. The cracks expanded along the regions with low grain boundary density, and the fracture mode was transgranular fracture. The B2 texture improved the harmony and uniformity of the slip deformation between different grains, obviously improving ductility. Owing to the obstruction of the O phase to the B2 phase slip, the B2+O+α2 sample generated an obvious deformation strengthening effect, had no necking phenomenon, and it was also transgranular fracture. The B2 phase slip deformation mode included single system, double system, tri-system, and cross slips. The B2 phase induced a small number of the α2 phases to experience basal slip ((0001) [11–20]) and cracking. The O phase had two deformation modes: (001) plane slip and twin that had (021) as a twinning plane. Two of the 24 slip systems of the B2 phase {110} <111> and {112} <111> can induce an O phase (001) plane slip, 12 systems whose <111> slip direction formed a 54.7° angle with the (001) plane can induce an O phase twin, and other 10 systems cannot induce O phase deformation.

Cold deformation of dezincification resistant yellow brass for plumbing applications

ABSTRACTIn the present work, the room temperature deformation behavior of dezincification-resistant (DZR) brass was performed by varying strain rates (1 × 10−4 s−1, 0.55 × 10−3 s−1, 1 × 10−3 s−1, 0.55 × 10−2 s−1, 1 × 10−2 s−1) and percent cold works (15 to 65% with step of 10%). These parameters are important to plumbing parts of its forming. Room temperature deformation workability map was developed that provides the selection of safe deformation parameters without cracking. The as-received and deformed DZR brass samples were carefully characterized by various microscopes. The results revealed that more dislocations lines and twinning were observed through transmission electron microscope images as the strain rate (SR) increases which led to early failure of the sample before reaching the set height reduction. It was determined that more amount of strain hardening with designed height reduction was achieved at lower SR whereas less amount of strain hardening was achieved at higher SR due to strain mismatching phenomenon and various deformation mechanisms.

Microstructure and Room Temperature Compressive Deformation Behavior of Cold-Sprayed High-Strength Cu Bulk Material

This study investigated the room temperature compressive deformation behavior of Cu bulk material manufactured by cold spray process. Initial microstructural observation identified a unique microstructure with grain size of hundreds of nm in the particle interface area and relatively coarse grains in all other areas. Room temperature compressive results confirmed cold-sprayed Cu to have a yield strength of 340 MPa, which is similar to materials manufactured by severe plastic deformation process such as equal channel angular press. In addition, strain softening phenomenon, which is rarely found in room temperature compressive deformation, was observed. According to such unique characteristics, continuous microstructure evolution and surface fractures according to the strain (e t = 0.3/0.6/0.9) of the material were observed, and considerations were made for deformation and fracture behavior. Microstructural observation after compressive deformation confirmed that average grain size decreased as the strain increased, and the fraction of the low-angle boundary, which has an indirect relationship with dislocation density, showed a tendency to decrease in e t = 0.3-0.6 region where the strain softening phenomenon occurs. Based on the results described above, this study was able to identify the possibility of manufacturing cold-sprayed Cu bulk material for structural material and its room temperature deformation behavior.

Stress-induced phase transformation and room temperature aging in Ti-Nb-Fe alloys

Room temperature deformation behavior of Ti-17Nb-1Fe and Ti-17Nb-2Fe alloys was studied by synchrotron X-ray diffraction and tensile testing. It was found that, after proper heat treatment, both alloys were able to recover a deformation strain of above 3.5% due to the Stress-induced Martensite (SIM) phase transformation. Higher Fe content increased the beta phase stability and onset stress for SIM transformation. A strong {110}β texture was produced in Ti-17Nb-2Fe compared to the {210}β texture that was observed in Ti-17Nb-1Fe. Room temperature aging was observed in both alloys, where the formation of the omega phase increased the yield strength (also SIM onset stress), and decreased the ductility and strain recovery. Other metastable beta Ti alloys may show a similar aging response and this should draw the attention of materials design engineers.