Microstructural Deformation Mechanisms Research Articles

Effect of Water Sensitivity on Microstructure Characteristics and Deformation Mechanism of Q3 Loess

Effect of Water Sensitivity on Microstructure Characteristics and Deformation Mechanism of Q3 Loess

Microstructure evolution and deformation mechanism along the thickness of heavy-wall ferrite-bainite dual-phase offshore pipelines by the progressive forming process

The progressive forming process of J-forming, C-forming, O-forming, and expansion (JCOE process) is an effective approach for manufacturing high-strength and high-strain offshore pipelines. However, the difference in microstructure of each layer along the thickness increases due to the strain accumulation and deformation direction during pipe forming, which affects the properties. In this study, the effects of the JCOE process on the microstructure evolution and deformation mechanism of heavy-wall ferrite-bainite dual-phase offshore pipeline steel along the thickness were investigated using a combination of simulation and experiment. The results revealed that the higher accumulated strains in the outer and inner layers increased localized microstrain and ferrite hardening and improved the overall strength. However, the pile-up of many dislocations at the ferrite-bainite interface promoted the generation of cleavage facets, increasing the plastic damage. The outer layer had a consistent deformation direction in the JCOE process, promoting dislocations to slip toward the phase interface. Dislocations in the inner layer slipped and annihilated in the opposite direction by back stress due to reverse deformation. The work-hardening behavior of each layer after JCOE process was divided into two stages and decreased with the increase of accumulated strain. Furthermore, the cyclic plastic deformation reduced the plastic damage and ensured the deformation capacity. This work is valuable for the development and control of microstructural characterization and forming fabrication of high-strength, high-strain offshore pipelines.

Cold deformation behavior and microstructure evolution of biomedical Cu-containing L605 alloy

The effect of copper (Cu) addition on the microstructure evolution and deformation mechanism of L605 (Co-20Cr-15 W-10Ni) alloy during cold deformation was investigated by using transmission electron microscopy (TEM), X-Ray diffraction (XRD) and electron backscatter diffraction (EBSD) analysis. The results indicated that the addition of Cu slightly decreased the yield strength and ultimate tensile strength, while it significantly increased the elongation. EBSD results revealed that hexagonal close-packed (HCP) martensite was generated during cold deformation and increased with increasing cold deformation level. The deformation microstructure of both alloys at different cold deformation levels shows that the stacking faulting was the primary deformation mechanism at early stage of cold deformation, in contrast, dislocation planar-slip and face-centered cubic (FCC) to HCP martensitic transformation were prevailed at both medium and late cold deformation level. Cu addition significantly suppressed the dislocation and stacking fault multiplication at early deformation stage and delayed the martensitic transformation at medium and late deformation stage, which could be ascribed to the relatively high stacking faulting energy by Cu addition, resulting in the low strain hardening behavior in the entire deformation process. These cumulative results and analyses could provide a solid foundation for the further development of this novel type of biomedical Cu-containing cobalt-based alloy.

Break the strength and ductility trade-off in novel NbC reinforced Fe40.5(CoCr)25Mn17.5Ni10Si5 high entropy alloy

In this study, a novel NbC reinforced Fe40.5(CoCr)25Mn17.5Ni10Si5 high entropy alloy (HEA) was designed, which exhibits high strength and ductility at room temperature. This alloy was prepared through hot forging and annealing treatments, which exhibited the FCC microstructure with NbC and discrete nano-sized M23C6 carbides precipitation. The studied HEA retained a tensile strength of 863 MPa, and an outstanding ductility of 58 %. The microstructure evolution and deformation mechanisms were further investigated. The deformation mechanism was mainly governed by nano-scale defect heterogeneity of stacking faults (SFs), deformation twins and dislocations. The improved strength-ductility synergy is attributed to the formation of multiple SFs, deformation twining, dislocation cells, and nano-sized NbC precipitation. Moreover, the TEM observation elucidates the presence of chemical short-range order (SRO) domain in the studied HEA, which also has a major contribution in strength and ductility increment. The present findings shed light on developing the HEAs through proper compositional design and heat treatments, resulting in the combine effect of precipitation strengthening, SFs mediated plasticity, twinning induced plasticity (TWIP), and SRO effect.

Ultra-strong and ductile precipitation-strengthened high entropy alloy with 0.5 % Nb addition produced by laser additive manufacturing

Achieving a superior strength-ductility combination for fcc single-phase high entropy alloys (HEAs) is challenging. The present work investigates the in-situ synthesis of Fe49.5Mn30Co10Cr10C0.5 interstitial solute-strengthened HEA containing 0.5 wt.% Nb (hereafter referred to as iHEA-Nb) using laser melting deposition (LMD), aiming at simultaneously activating multiple strengthening mechanisms. The effect of Nb addition on the microstructure evolution, mechanical properties, strengthening and deformation mechanisms of the as-deposited iHEA-Nb samples was comprehensively evaluated. Multiple levels of heterogeneity were observed in the LMD-deposited microstructure, including different grain sizes, cellular subgrain structures, various carbide precipitates, as well as elemental segregation. The incorporation of Nb atoms with a large radius leads to lattice distortion, reduces the average grain size, and increases the types and fractions of carbides, aiding in promoting solid solution strengthening, grain boundary strengthening, and precipitation strengthening. Tensile test results show that the Nb addition significantly increases the yield strength and ultimate tensile strength of the iHEA to 1140 and 1450 MPa, respectively, while maintaining the elongation over 30 %. Deformation twins were generated in the tensile deformed samples, contributing to the occurrence of twinning-induced plasticity. This outstanding combination of strength and ductility exceeds that for most additively manufactured HEAs reported to date, demonstrating that the present in situ alloying strategy could provide significant advantages for developing and tailoring microstructures and balancing the mechanical properties of HEAs while avoiding conventional complex thermomechanical treatments. In addition, single-crystal micropillar compression tests revealed that although the twining activity is reduced by the Nb addition to the iHEA, the micromechanical properties of grains with different orientations were significantly enhanced.

Structural features of biobased composite foams revealed by X-ray tomography.

Polymer foams can have heterogeneous and complex internal structures, especially when material blends or particles have been integrated to create composites. It becomes even more challenging to probe and understand foam structure/properties when using non-uniform particles, such as biobased fillers. Optical or SEM imaging can only provide limited information as these are two-dimensional (2D) surface techniques. In this study, 3D X-ray tomography was applied to comprehensively analyze the structural features of biobased polyurethane foams containing porous rice hull fillers. The in-depth characterization at a wide range of length scale enabled us to quantify and obtain statistics of the unique trends in foam pore size and pore orientation corresponding to rice hull particle fraction and particle size. Rice hull particles were found to induce smaller cell formation. In addition, these biobased particles influenced cell expansion and caused cells to have less consistent orientation. Furthermore, after foam samples were subjected to cyclic compressive loading, X-ray tomography showed fractures in large (>100 μm) particles. This helps reveal the premature failing mechanism of composite foams with highly porous and coarse particles. The study elucidates novel microstructural evolution and deformation mechanisms using 3D X-ray tomography. The results offer new insights on internal structures for biobased composites and foams that are not previously possible through the conventional characterization tools.

Effects of size, geometry, and testing temperature on additively manufactured Ti-6Al-4V titanium alloy

This article presents a comprehensive study concerning size and geometry effect on the ambient and high-temperature mechanical behavior of additively manufactured laser powder bed fusion Ti-6Al-4V alloy. Key mechanical property metrics are presented, including strain hardening rate, yield strength, and Young’s modulus as a function of thickness and testing temperature (ambient, 250 °C, and 450 °C). The effect of specimen size on manufacturing-induced microstructural feature formation is demonstrated and discussed. A detailed analysis regarding Young’s modulus, yield strength, and strain hardening rate variation at elevated temperatures is also presented. Size effect and temperature-sensitive deformation mechanisms are linked to the underlying microstructural deformation mechanisms activated at respective temperatures. Counter-intuitively, this study determined that irrespective of the geometry, strain hardening rates increased as temperature increased. An in-depth microstructural examination is presented to explain the stated observation. The texture of Interrupted tensile test samples examined for ambient, 250 °C, and 450 °C post-yield was observed to be unchanged, indicating the strain hardening behavior was not texture dependent. Schmid factor analysis, coupled with experimental findings from previous work, was implemented to generate a hypothesis. This hypothesis suggests that the drop in critical resolved shear stress for basal and pyramidal slip systems, as temperature increases, paired with the high dislocation density of laser powder bed fusion Ti-6Al-4V, leads to dislocation entanglement and results in increased strain hardening at elevated temperatures.

High strain rate mechanical behavior of Ti-6Al-4V with micro–macro correlation under compressive loading

The application of Ti6Al4V in lightweight structures subjected to impact loads necessitates a comprehensive understanding of its dynamic response under high strain rates to ensure the safety and reliability of these components. In this paper, the macroscopic compressive mechanical behavior of Ti6Al4V under high strain rates was investigated through the split-Hopkinson pressure bar (SHPB) technique at both room temperature and 200 °C, followed by microstructure analysis of the compressed specimens, carried out employing a combination of optical microscopy (OM) and electron backscatter diffraction (EBSD), and elastic modulus and hardness measurements, performed by a nanoindentation instrument. At room temperature, both the modulus and strain hardening exponent of Ti6Al4V exhibited an initial increase before the strain rate reached 1000s-1, after which they decreased at 3400s-1. Meanwhile, the flow stress continued to rise with increasing strain rate. Microscopic observations revealed that twinning played a substantial role in the strain hardening effects. Notably, the basal slip system of the hcp (hexagonal close packed) α phase did not display a more favorable trend, while the c+a type slip systems became more active. Under a strain rate of 5000s-1, discontinuous dynamic recrystallization emerged as the dominant mechanism, resulting in an increased frequency of low-angle grain boundaries, as well as a reduction in grain size and dislocation density. These results provide a basis for explaining the mechanical behavior of Ti6Al4V under high strain rates and offer insights for the establishment of material models that take into account microstructure deformation mechanisms.

Crafting high-strength and ductile powder metallurgy Ti6Al4V alloy with a multi-scale microstructure

In this work, a novel multi-scale microstructure of Ti6Al4V duplex alloy with nano-sized β particles was designed based on powder metallurgy. The common lamellar structure was carefully adjusted to reveal the complex effects of microstructure on mechanical properties. The ideal microstructure transforms into a composition dominated by sparse equiaxed primary α, lots of β-nanoprecipitates, and traces of secondary acicular α′ by heat treatment. The uniform nucleation of nano-sized β particles, driven by intragranular element concentration difference and local distortions, is a pivotal reason for high yield strength by dispersion strengthening. More phase boundaries also act as sustainable sources for geometrically necessary dislocations. An uncoordinated phase interface relationship from variant selection improves strain-hardening ability. The intragranular misorientation causes the value inhomogeneity of the Schmid factor in primary α, resulting in an auxiliary slip effect that benefits ductility. Therefore, the fabricated Ti6Al4V alloy displays an ultrahigh ultimate tensile strength of 1329 MPa, yield strength of 1223 MPa, and reasonably large elongation of 8.5 %, respectively. This work underscores the intricate interplay of microstructure evolution and deformation mechanisms in powder metallurgy duplex titanium alloys, offering valuable insights into enhancing the mechanical properties.

Correction to: A review on the effect of various rolling regimes (cryo, cold, warm, hot) and post-annealing on high-entropy alloys: microstructure evolution, deformation mechanisms, and mechanical properties

Correction to: A review on the effect of various rolling regimes (cryo, cold, warm, hot) and post-annealing on high-entropy alloys: microstructure evolution, deformation mechanisms, and mechanical properties

A review on the effect of various rolling regimes (cryo, cold, warm, hot) and post-annealing on high-entropy alloys: microstructure evolution, deformation mechanisms, and mechanical properties

A review on the effect of various rolling regimes (cryo, cold, warm, hot) and post-annealing on high-entropy alloys: microstructure evolution, deformation mechanisms, and mechanical properties

Microstructure evolution and deformation mechanism with comparison of Ta-2.5 W and Cu under detonation load

The comparison of microstructure evolution of Cu and Ta-2.5 W liner during explosively formed projectile (EFP) formation was studied. The electron backscatter diffraction method (EBSD) was used to statistically characterize the microstructure of the liner before and after deformation. Both recycled EFPs show strong fiber texture and different degrees of recrystallization. The center of the recycled Cu EFP has strong <001> and <111> preferred orientations along the EFP axis, and the density of the texture changes with the deformation strain. Cu EFP has extensive dynamic recrystallization, up to 88%, which is considered to be a traditional dynamic recrystallization mechanism, the temperature is the main controlling factor in the refinement process. On the contrary, the recycled Ta-2.5 W EFP has a strong <101> fiber preferred orientation, and almost no dynamic recrystallization occurs, large strain deformation is the main factor for the microstructure fragment.

Ultra-low stress triaxiality ring-roller spinning: microstructure, plastic behavior, and cumulative large deformation mechanism

Spinning is a common processing method for ultra-thin-walled tube. However, it is susceptible to surface ruptures in the deformation zone due to point-by-point contact, which affects the quality of products. In response to this issue, a ring-roller spinning (RRS) process is proposed, where the spinning roller makes tangential inner contact with the tube blank. This expands the triaxial compressive region, reducing ruptures tendency. And the tangential compressive stress is strengthened on the basis on triaxial compression of the conventional spinning (CS) process, which provides shear stress state in deformation zone. This paper conducts a comprehensive investigation into the RRS for thin-walled tubes made of 304 austenitic stainless steel. The study combines theoretical and experimental approaches and employs the finite element method (FEM) to evaluate the stress state within the tangential region. Various characterization methods are applied to examine the microstructural evolution under ultra-low stress triaxiality (ULST). The results confirm that the deformation zone is primarily characterized by tangential pressure under ULST, which significantly influence the metal microstructure, plastic behavior, and cumulative large deformation. This innovative process facilitates the continued deformation of the tubes, even under the saturated conditions of work hardening with the martensitic plasticising behaviour promotes grain refinement to 124 nm, resulting in an increase in the yield strength of the tubes from -1060 MPa to 1550 MPa. Continuous processing of ultra-thin-walled tube with a cumulative thinning rate of 90% was achieved by conducting RRS five-pass spinability experiments.

Microstructure evolutions and deformation mechanisms of a Ni-based GH3536 Superalloy during loading at 293 K and 77 K

In this study, tensile tests and interrupted experiments at different true strain levels were performed at 293 K and 77 K to reveal the deformation mechanisms of GH3536 superalloy during loading. The microstructure evolutions of the alloy with strain at both temperature were studied via Transmission electron microscopy (TEM), and dislocation densities were calculated by X-ray diffraction (XRD) for quantifying the forest hardening contribution to the flow stress. Deformation twins were rarely observed in the GH3536 superalloy specimens deformed at 293 K, where deformation occurred solely by dislocation slip. While twinning was initially found at a strain of ∼7% at 77 K, and the corresponding stress at which twinning occurs is 808 ± 46 MPa. The twin volume fractions, their widths and spacings were determined by electron backscatter diffraction (EBSD), which is used to investigate the twin evolution of GH3536 alloy at 77 K. The deformation mechanisms of GH3536 alloy, as well as its twinning behaviors, depend on the competition between the maximum flow stress and critical stress for twinning. The maximum flow stress is large enough to activate twinning at cryogenic temperature, resulting in the transition of deformation mechanisms for GH3536 alloy as SLIP (dislocation slip) at 293 K and TWIP+SLIP (deformation twinning and dislocation slip) at 77 K, and the improved combination of ductility and strength at 77 K compared to 293 K is derived from additional deformation mode provided by twinning during the process of deformation.

Effect of Repetitive Bending and Straightening Process on Microstructure Properties and Deformation Mechanism of a Ti-Al-Cr-Mo Alloy.

In this research, a repetitive bending and straightening process was carried out on the Ti-3Al-4Cr-Mo alloy for 20 passes. The changes in mechanical properties of the titanium alloy before and after repetitive bending and annealing were studied. The microstructure evolution and deformation mechanism were analyzed. The results show that after the repetitive bending and straightening process, the microstructure of the Ti-3Al-4Cr-Mo alloy is obviously refined, and, simultaneously, the yield strength is significantly improved. After annealing at 850 °C, the plastic ductility of the material was improved. The combined effects of grain refinement and dislocation behavior were the main reasons for the improvement in mechanical properties of the Ti-3Al-4Cr-Mo alloy. Twinning rarely occurred during plastic deformation of the Ti-3Al-4Cr-Mo alloy. The fine grains strongly inhibited the formation of twins. In addition, a small amount of α to β phase transformation was observed during the repetitive bending and straightening process of the material, which may have been induced by strain accumulation.

Microstructure Evolution and Deformation Mechanism of Ti‐55531 Alloy During Hot‐Rolling Process

Ti‐55531 alloy is a novel near‐β‐Ti alloy, which has promising application potential as critical aircraft components due to its outstanding mechanical properties. In this work, it is aimed to tailor the microstructure and mechanical properties of Ti‐55531 alloy by hot‐rolling in α + β‐phase field. In experimental results, it is indicated that an increasing number of α lamellae becomes globular or ellipsoidal shape with the increase of rolling reduction. As a result, the strength and elongation of the rolled samples continually increase. Lath‐like substructures are observed inside some residual lamellar α after 20% rolling reduction. Nearly all lath‐like substructures have their habit plane corresponding to (100)α and exhibit the orientation relationship (OR) of [0001]HCP //[001]FCC, [20]HCP //[]FCC, and (100)HCP //(FCC with α phase. At high rolling reductions, the face‐centered cubic (FCC) substructures disappeared. Instead, {101} twin structures are frequently observed in lamellar α grains, indicating that both {101} twinning and martensitic transformation can be activated in Ti‐55531 alloy to accommodate the applied rolling deformation. To the authors’ knowledge, such stress‐induced martensitic transformation has not been reported before in Ti‐55531 alloy. Therefore, the findings in this work should advance the understandings on the deformation behavior and mechanism in this alloy.

Development of high-performance nanostructured aluminum and its constitutive modeling

A new technique, an in-situ hot-extrusion-based synthesizing process, is proposed to develop high-performance nanocrystalline aluminum (nc-Al) with an optimally tuned strength-to-ductility ratio suitable for various technologically relevant applications. Comprehensive investigations are conducted by characterizing mechanical and microstructural properties to realize the influence of various synthesizing variables on the properties of the bulk nc-Al. Furthermore, a continuum-scale constitutive modeling approach is proposed based on dominant microstructural mechanisms of plastic deformation and implemented into a finite element solver using a user-defined material interface. It is shown that the proposed theory can provide a versatile platform to predict the nanocrystalline aluminum mechanical response quite well.

Dynamic Recrystallization Mechanisms of As‐Extruded GH4151 Alloy during Hot Deformation

Different degrees of deformation, as an important forming method in the machining process, which has an important influence on the dynamic recrystallization (DRX) behavior. In this study, we investigated the effect of different deformation strains on the microstructure evolution and deformation mechanism of as‐extruded GH4151 nickel‐based superalloy using isothermal hot compression. As a result, the average grain size decreased with the increase of deformation, and the proportion of Σ3 boundaries tended to decrease and then increase with the increase of DRX grain volume fraction, indicating that the presence of twins had a facilitating effect on the nucleation of DRX. In addition, discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) coexisted during hot deformation, and DDRX was the main nucleation mechanism. CDRX was easy to occur at middle strain of 50%, and its nucleation mode was subgrain rotation nucleation. And there were two types of nucleation for DDRX: grain boundary bulging nucleation and twin‐assisted nucleation.

Hot compression behavior and recrystallization mechanism of 1.5 wt% Ti3AlC2 ceramic-enhanced Mo alloys with two-dimensional layers

Improving the high temperature strength of Mo alloys is a key problem to expand the application range of Mo alloys. In this study, the Mo-1.5 wt%Ti3AlC2 alloy was designed by introducing new two-dimensional (2D)-layered ceramic particles Ti3AlC2 into Mo. The peak flow stress of the Mo-1.5 wt%Ti3AlC2 alloy reaches 308 MPa at 1200 °C. The diffusion activation energy Q of the Mo-1.5 wt%Ti3AlC2 alloy is as high as 533.38 kJ/mol, which is higher than that of pure Mo (480 kJ/mol). Sintering in the reducing atmosphere of hydrogen at high temperature, the Ti3AlC2 consumes a large amount of energy to form AlTi3 and Ti5O9, which leads to an increase in the diffusion activation energy. We have established the constitutive equation of the Mo-1.5 wt%Ti3AlC2 alloy, and studied the microstructure evolution and deformation mechanism under hot compression. The results show that the stress index of n1 > 3 indicates that the plastic deformation mechanism was a dislocation mechanism. With the addition of Ti3AlC2, a large number of dislocations were produced in the alloy at the early stage of hot deformation. With increasing temperature, the dislocation entanglement gradually cancels out, resulting in the decrease of dislocation density. With the increase of temperature and deformation rate, the dynamic recrystallization (DRX) mechanism of the Mo-1.5 wt%Ti3AlC2 alloy was mainly continuous dynamic recrystallization (CDRX) at 1200 °C/0.01 s−1 and discontinuous dynamic recrystallization (DDRX) at 1600 °C/10 s−1. This work provides a new research direction for designing high performance Mo alloys.

In-situ investigate on the microstructure evolution, deformation and fracture mechanism of Mg-Gd-Zn-Mn alloy with varies of LPSO volume fraction

The induction of long-period stacking ordered (LPSO) phase through heat treatment was an effective method to strengthen magnesium alloys. In this study, the volume fraction of lamellar LPSO in the Mg-4Gd-1Zn-0.5Mn alloy was controlled by optimizing the heat treatment process. The research findings showed that with increasing heat treatment time, the volume fraction of LPSO initially increased then decreased until disappearing. The alloy treated at 500 °C for 2 h exhibited the highest volume fraction of lamellar LPSO, increasing from 1.64% to 13.68%. Further in-situ tensile tests were conducted on two types of alloys contain higher LPSO fraction (HL) and lower LPSO fraction (LL) at ambient temperature. The increased critical shear stress (CRSS) and obstacle effects on dislocations caused by LPSO effectively enhanced the strength of the alloy. The dominant deformation mechanisms of both HL and LL alloys are basal slip and twinning during tensile deformation. However, the HL alloy activated more non-basal slip significantly, which was ascribed to the activation of non-basal slip by LPSO kinking during deformation. Additionally, the bending and kinking of LPSO effectively restricted crack initiation and propagation, thereby enhancing the plasticity. The HL alloy exhibited fewer twin boundaries after deformation, which was attributed to the hindrance of twinning extension by LPSO.