Compressive Plastic Research Articles

A particle-scale analysis of unload-reload hysteresis for normally consolidated kaolin

The mechanical behaviour of sands and clays subject to “normal” (plastic) compression are very similar, albeit at different stress levels, despite the differences in inter-particle interactions (Hertzian normal contact forces or similar for sand) and electro-chemical forces for clays. However the hysteretic behaviour of clay is very different to sand with clays exhibiting “springy” hysteresis loops and ratchetting volumetric compaction. This paper aims to show that whereas the “plastic” compression arises from degradation of macro particles, the “quasi-elastic” unload-reload behaviour is consistent with an increase in the number of platelet edge contacts as clay “stacks” rearrange and compact.

Effect of Strain Rate on Deformation Behaviors of Ti-12.1Mo -1Fe Metastable Beta Alloy

The addition of expensive elements to β titanium alloys, which are widely used in the aerospace and automobile industries, causes their price to increase. Low-cost, high-strength alloy (Ti-12.1Mo-1.0Fe) was designed in this study and the compressive behaviors of this alloy were evaluated for application to automobile parts, etc. As a result of ambient compression in the quasi-static and dynamic strain rate range (1×10<sup>-4</sup>/s~6×10<sup>3</sup>/s), twinning occurred at all strain rates, and in particular, adiabatic shear bands were observed, which cause cracks and fractures under dynamic strain rate conditions. In addition, when the relationship between these bands and mechanical characteristics was evaluated, an increase of compression strength and Vickers hardness was confirmed to occur, due to the strain rate hardening effect under compression loading. Some twins were formed by the deformation behavior during compression plastic deformation of the Ti-12.1Mo-1.0Fe alloy, and it exhibited excellent compression strength characteristics, showing a very high strain rate hardening effect at a high strain rate.

Dense lamellar scaffold based on collagen, silk fibroin and polyethylene glycol 400 produced by a novel plastic compression technique

Dense lamellar scaffold based on collagen, silk fibroin and polyethylene glycol 400 produced by a novel plastic compression technique

Ultrasonic solidification mechanism and optimized application performances of ternary Mg71.5Zn26.1Y2.4 alloy

One dimensional (1D) and three dimensional (3D) ultrasound sources were applied to the solidification process of Mg71.5Zn26.1Y2.4 alloy. The acoustic spectra were in-situ measured, based on which the cavitation intensities and dynamic solidification mechanism were further investigated. With the increase of ultrasonic dimension and amplitude, the primary Mg3Zn6Y phase was significantly refined from petals to nearly pentagonal shape. The sound field measurements showed that the transient cavitation played a decisive role in generating a high local undercooling, which facilitated the formation of icosahedral clusters and promoted the nucleation of primary Mg3Zn6Y phase. The morphological transition of (α-Mg+Mg3Zn6Y) eutectic from lamellar to anomalous structure occurred under 3D ultrasonic condition. The stable cavitation took the main responsibility because the high pressure excited by nonlinearly oscillating bubbles induced the preferential nucleation of α-Mg phase rather than Mg3Zn6Y phase. As compared with its static values, the tensile strength and compression plasticity of this alloy were increased by the factors of 1.9 and 2.1, and its corrosion resistance was also improved with the corrosion current density decreased by one order of magnitude.

Dynamic mechanical properties and microstructural evolutions of nanocrystalline Ni at 77 K and 298 K

Dynamic mechanical responses and microstructural evolutions of nanocrystalline Ni with an average grain size of 14 nm at both 77 K and 298 K were investigated by using Split-Hopkinson pressure bar in this work. Nanocrystalline Ni deformed at 77 K exhibited better dynamic compression strength and plasticity. Microstructural characterizations suggested that the deformation processes of Ni were jointly regulated by dislocation activities (such as full dislocations, stacking faults, twinning, and phase transitions) and grain boundary-dominant mechanisms (grain rotation) in the uniformly deformed regions, while dynamic recrystallization was the main feature in shear bands. The cryogenic temperature was conducive to suppressing grain coarsening and obtaining better dynamic mechanical properties. The work is beneficial to understanding dynamic deformation mechanisms and the service of nanocrystalline materials in extreme conditions, in addition to the development of high-performance nanocrystalline metallic materials.

Super plasticity of bulk metallic glasses at room temperature: A friction self-locking state

This study examines the compressive deformation and fracture characteristics of Fe74Mo6P13C7 bulk metallic glasses (BMGs) with aspect ratios ranging from 1.0 to 2.5. The compressive plastic strain of BMGs exhibits a consistent upward trend as the aspect ratio decreases. As the aspect ratio decreases, the influence of the surrounding friction becomes increasingly pronounced. The finding was made that the exceptional ability of BMGs to exhibit super plasticity at ambient temperature is attributed to the phenomenon of friction self-locking occurring within the shear planes. The deformation behavior of brittle BMGs is significantly influenced by the applied stress conditions. However, it is worth noting that even brittle BMGs can display ductile characteristics when subjected to multiaxial constraints. This finding is not only essential for comprehending the deformation and fracture of amorphous materials, but it can also serve as a valuable reference for rock mass control, structural stability, earthquake mitigation, and disaster reduction engineering.

Spinodal decomposition induced brittleness of Zr-Ta containing medium-entropy alloys

Spinodal decomposition, originating from the miscibility gap, plays an important role in the mechanical properties of alloys. In this work, the correlations between the development of spinodal substructure and mechanical properties are investigated by a comparative study on TiZrTa and TiZrHfTa medium-entropy alloys (MEAs). The results indicate that Hf addition in TiZrTa alloy can reduce the spinodal decomposition propensity. Besides, compared to the arc-melt process, the fast-cooling rate of the drop-cast process dramatically freezes the spinodal separation at this initial stage with a small misfit and inhibits the brittle ω phase formation, which in turn increases the compression plasticity of the TiZrHfTa alloys. In short, this work clarifies the spinodal decomposition induced brittleness of the Zr-Ta refractory MEAs and would contribute to the design and preparation of high-ductile refractory multicomponent alloys.

The Effect of Electroplating Nickel on the Mechanical Properties of Brittle Mg-Based Bulk Metallic Glasses

Magnesium-based bulk metallic glasses (BMGs) are typical intrinsic brittle lightweight BMG alloys, and their improvement in plasticity has attracted widespread attention in the field of BMGs. We used the electroplating method to modify the surface of Mg59.5Cu22.9Ag11Gd6.6 BMGs and investigated the geometric confinement effect of the Ni coating on the mechanical properties of the BMG. The results show that under the plating conditions of adding 1 g/L nano Al2O3 to the plating solution, adjusting the plating temperature to 50 °C, and plating time to 3 h, a smooth and dense nickel coating with a thickness of about 150 μm can be formed on the surface of the Mg-based BMG. The uniaxial compression tests showed that the average fracture strength of the BMG was increased from 565 MPa to 598 MPa by a 50 μm Ni coating, and the fluctuation range of strength was decreased from 429 MPa to 265 MPa, a reduction of 36%. The Weibull analysis showed that the Weibull modulus m was increased from 4.3 to 4.8 by the coating, and the safety stress was increased from 54 MPa to 235 MPa, indicating that electroplating nickel could improve the reliability of the Mg-based BMG alloy. However, no significant improvement of the compression plasticity was found, which indicated that improving the room temperature plasticity of brittle Mg-based BMG alloys by the geometric confinement of electroplating Ni was limited. The influence of the thickness of the Ni coating on the maximum stress level and stress distribution in the BMG samples was analyzed by ANSYS finite element simulation. It was found that when the thickness of the coating was 30% of the radius of the cylindrical compressed sample, the stress distribution caused by the Ni coating was the most uniform, and the maximum stress level was relatively reduced, which is beneficial for improving the geometric confinement effect. As a result, the Mg-based BMG sample coated with a Ni coating of 150 μm thickness exhibited ~0.3% macroscopic compressive plasticity. This is of great significance for understanding the plastic deformation mechanism of brittle BMGs improved by geometric confinement.

Development and characterization of a low-density TiNbZrAlTa refractory high entropy alloy with enhanced compressive strength and plasticity

A new refractory high entropy alloy (RHEA) is designed by combining refractory elements Nb and Ta with Ti, Zr, and Al, resulting in a (TiNbZr)89(AlTa)11 alloy composition with a low-density of 6.0 g/cm3. The novel RHEA features a BCC matrix with B2 and Zr5Al3 nano precipitates, exhibiting a compressive yield strength of ∼890 MPa and specific yield strength of ∼148.3 MPa g−1 cm3. Remarkably, the alloy demonstrates excellent compressive plasticity of ∼70% at 298 K. As the temperature increases to 873 K, 1073 K, and 1273 K, the yield strength of the RHEA gradually decreases to ∼610 MPa, ∼ 210 MPa, and ∼ 60 MPa, respectively. These results indicate that this novel RHEA showcases a combination of good specific strength and plasticity. Post-compression, B2, and Zr5Al3 phases are observed. The second-phase particles dispersed throughout the grains hinder dislocation motion and contribute to the formation of sub-grain boundaries during hot compression.

A method locating Cu-Ti-based glass formers using Ni-Zr binary clusters

Formation abilities and mechanical properties are essential for the application of amorphous alloys. In this work, the concept of similar elements has been expanded to similar clusters. Firstly, taking the topologically dense packed clusters Ni-Ni6Zr6 from the Ni-Zr system as the basic structural unit, a series of Cu-Ti-based alloy compositions with high formation ability are parsed and designed. The best composition is Cu46.15Ni7.69Ti32.70Zr13.46 with the cluster expression of Ni-Cu6Zr1.75Ti4.25. Then, the amorphous formation abilities are analyzed from the perspective of the packing degree of clusters and the mixing entropies. Secondly, the crystallization activation energies for characteristic temperatures deduced by Kissinger's approach are analyzed. Finally, the plasticity of Cu-Ti-based amorphous alloys is investigated and Cu46.15Ni7.69Ti32.70Zr13.46 exhibits outstanding fracture strength of 2168 MPa. The results in this paper lay the foundation for further exploration of amorphous alloys with high formation ability, good thermal stability, and high compressive plasticity.

Improving low-cycle fatigue life of ZK61 magnesium alloy via basal texture weakening by the compression-extrusion process

In response to the problem that intense basal texture seriously affects the low-cycle fatigue life of magnesium alloys, the compression-extrusion process for basal texture weakening was implemented in ZK61 magnesium alloys. The low-cycle fatigue life under uniaxial symmetrical tension-compression cyclic loading was dramatically improved by basal texture weakening, up to 1.5∼3 times that in an intense-textured state. Basal texture weakening promoted basal slip to dominate the cyclic deformation, thus significantly reducing the cyclic tension-compression asymmetry caused by the {10–12} twinning-detwinning. Further, the suppression of {10–12} twinning and the decrease of compressive plastic strain slowed down dislocation accumulation inhibiting the cyclic hardening and fatigue crack initiation. The Manson-Coffin equation was feasible to predict the fatigue life of the intense-textured and weak-textured ZK61 magnesium alloys. The promotion of basal slip arising from basal texture weakening led to the decrease of fatigue ductility coefficient and the increase of fatigue ductility exponent contributing to the higher fatigue life.

Study on the organization and properties of high-strength Ti-Zr-Mo-Al alloys

This work investigated the effect of the heat treatment mechanism on the mechanical properties and microstructure of the metastable β titanium alloy (Ti-16.3Zr-13.6Mo-6Al-1.6Cu-0.6Ni). The results reveal that the α phase morphology at the grain boundary of the as-cast changes from continuous distribution to discontinuous distribution after heat treatment at 900°C/12 h. When the solution temperature is raised to 1200°C/12 h, the α phase shows spherical distribution at the grain boundary. At this moment, the yield strength reaches about 1009 MPa, and the tensile strength reaches about 1188 MPa. In addition, the elongation is about 2.3%. Then the alloys were aged at 450°C from 4 h to 8 h after solution at 1200°C/12 h. In the aging process, the plastic deformation capacity is further reduced because a point-like α phase was precipitated in the alloy. However, the compressive strength was improved. From aging treatment at 450°C/6 h, the compressive yield strength reached about 1584 MPa, and the compressive strength reached about 2034 MPa. However, the compressive plasticity strain is only 2.1%.

Research on the Elastoplastic Theory and Evolution Law of Plastic Zone Contours of Horizontal Frozen Walls under Nonuniform Loads

The study of the changes in stress and deformation of frozen walls during excavation has always been a hot topic in underground freezing engineering, and the size of the plastic zone is an important basis for evaluating the stability of frozen walls. In response to the shortcomings in the current design of horizontal frozen walls, based on the internal excavation unloading conditions of the frozen wall in artificial ground freezing, an elastoplastic mechanical model for the interaction between a circular horizontal freezing wall and unfrozen soil mass is established under nonuniform loads to obtain the corresponding solutions for stress and displacement in the system. In this study, considering the shear stress of the plastic zone, the method for solving the traditional plastic zone contour equation is modified; consequently, the modified solution of the contour equation of the plastic zone for the frozen wall is obtained. Using this theoretical solution, the influence of the external load p0 and the lateral pressure coefficient λ on the contour line of plastic zone and tensile stress zone are analyzed by combining the project case, the calculation results show that: the λ=0.485 is the critical point where the inner edge of the frozen wall just happens to have tensile stress. When λ<0.485, the tensile stress zone is inevitable in the inner edge of the frozen wall vertical direction, and its range is only related to λ and increases with the decrease of λ. The p0 only affects the magnitude of tensile stress in the region, but does not affect its range. At this time, the frozen wall compression plastic zone contour evolves from crescent shaped to ear shaped with the increase of p0. When 0.485<λ<0.61, there will be no tensile stress zone, the frozen wall compression plastic zone contour also evolves from crescent shaped to ear shaped with the increase of p0. When λ>0.61, there will be also no tensile stress zone, with the increase of p0, the compression plastic zone contour evolves from the crescent shaped in the horizontal direction to the elliptical shaped, and there is no ear-shaped plastic zone in the whole evolution process. Based on our results, we show that our method can be used to provide a theoretical basis for the stability evaluation and parameter (thickness) design calculation of horizontal frozen walls under nonuniform loads.

High compression strength pure tungsten fabricated by plasma arc additive manufacturing

Pure W were fabricated by wire plasma arc additive manufacturing technology (WPAAM) and systematically investigated in terms of the microstructure and mechanical property. The as-fabricated W exhibits large-size columnar grains along the deposition direction, and it has extremely few microcracks, compared with that fabricated by laser powder bed fusion (LPBF). The compression strength and compressive plastic deformation capability of WPAAM W are significantly improved compared to the widely studied LPBF W and the fine grained W fabricated by other processes. In particular, the strength of WPAAM W is comparable to that of ultrafine grained W. A microstructure-based predictive model of compressive strength is developed to understand the strength performance of AM W. The proposed model correlates the manufacturing process, microstructure and mechanical property of additive manufactured W. This study is expected to shed light in the development of additive manufacturing technology of refractory metals.

A scheme for achieving strength-ductility trade-off in metallic glasses

The strength-ductility paradox in structural materials remains a long-standing dilemma in advanced materials synthesis. Metallic glasses (MGs) that are structural materials of remarkably high-strengths are not exclusive in structural applications due to their inherently poor plasticity. This study addresses this conundrum by presenting a scheme for achieving excellent strength-ductility synergy in MGs from structural and energetic standpoints. By applying a two-step pathway of mechanical rejuvenation and cyclic stress loadings upon a Zr2Cu as-constructed MG model, deformation behavior was analyzed by molecular dynamics simulations. As higher energy states of the MG characterized by enhanced compressive plasticity was found by mechanical rejuvenation due to internal stress accumulation accompanied with an unusual increase in free volume and atomic energy, cyclic stress loading upon rejuvenation annihilated loosely-packed regions to advance a more stable state with less energy to enhance structural stability with an improvement in elastic strain limit and strength. By theoretical modelling, strength-ductility trade-off was demonstrated by the delay in shear transformation zone activities that orchestrated the generation and intersection of multiple shear bands. As a result, a two-step scheme in which soft regions are aggregated to a concentered mass intensified to higher potential energy followed by dissipating the consolidated mass into randomly dispersed soft regions is the key to achieve the strength-ductility trade-off in MG materials. The outcome of this study will further advance structure-property characterization in amorphous solids.

Ductile Ni-based bulk metallic glasses at room temperature

In this work, a series of new Ni76-xCoxNb4P16B4 (x = 5, 10, 15, in at.%) bulk metallic glasses (BMGs) with the maximum diameter in the range of 1.2–1.6 mm were prepared by combining fluxing and J-quenching technology. The effects of Co content on glass forming ability (GFA), thermal stability, mechanical properties, serrated-flow behaviors and corrosion performance of the present Ni-based BMGs were systematically investigated. The ranges of Tg and ΔTx are 664–668 K and 21–31 K, respectively. Uniaxial compressive tests revealed that the present Ni-based BMGs have the compressive plastic strain (εp), yield strength (δy), and fracture strength (δf) that range from 16% to 27%, 2.1–2.6 GPa, and 2.2–3.6 GPa, respectively. The unprecedented mechanical properties originate from more icosahedral-like clusters (ILCs) and crystal-like clusters (CLCs) in the present Ni-based BMGs. It is found that the serrated-flow behaviors of the present Ni-based BMGs transition self-organized critical state (SOCs) into chaotic state (Cs) as plasticity decreases. The stick-slip dynamics were used to calculate the average shear-band velocity (ASBV), which shows an increasing trend as the Co content rises from 5 at.% to 15 at.%. Electrochemical measurements in 3.5 wt.% NaCl solution showed that the Ni71Co5Nb4P16B4 BMG has a self-corrosion current density of 3.30 × 10−8 A/cm2 and significantly stronger corrosion resistance than austenite 316L and 304L stainless steel. The present Ni-based BMGs have excellent comprehensive performance, which has great potential for industrial applications.

Psidium guajava L. phenolic compound-reinforced lamellar scaffold for tracheal tissue engineering

The aim of this work was to develop a dense lamellar scaffold, as a biomimetic material with potential applications in the regeneration of tracheal tissue after surgical tumor resection. The scaffolds were produced by plastic compression technique, exploiting the use of total phenolic compounds (TPC) from Psidium guajava Linn as a potential cross-linking agent in a polymeric mixture based on collagen (COL), silk fibroin (SF), and polyethylene glycol 400 (PEG 400). Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) confirmed the chemical interactions between the polymers and the cross-linking of TPC between COL and SF. Morphological analyses showed scaffolds with porosity, interconnectivity, and a porous surface structure with a gyroid-like geometry. The analysis of the anisotropic degree resulted in anisotropic structures (0.1% TFC and 0.3% TFC) and an isotropic structure (0.5% TFC). In the mechanical properties, it was evidenced greater resistance for the 0.3% TFC formulation. The addition of TPC percentages did not result in a significant difference (p > 0.05) in swelling capacity and disintegration rate. The results confirmed that TPC were able to modulate the morphological, morphometric, and mechanical properties of scaffolds. Thus, this study describes a potential new material to improve the regeneration of major tracheal structures after surgical tumor removal.Graphical

Dissociation of edge and screw pyramidal I and II dislocations in magnesium

Pyramidal dislocations in magnesium (Mg) and other hexagonal close-packed metals play an important role in accommodating plastic strains along the c-axis. Bulk single crystal Mg only presents very limited plasticity in c-axis compression, and this behavior was attributed to out-of-plane dissociation of pyramidal dislocations onto the basal plane and resulted in an immobile dislocation configuration. In contrast, other simulations and experiments reported in-plane dissociation of pyramidal dislocations on their slip planes. Thus, the core structure and mode of dissociation of pyramidal dislocations are still not well understood. To better understand the dissociation behavior of pyramidal dislocations in Mg at room temperature, in this work, atomistic simulations were conducted to investigate four types of pyramidal dislocations at 300 K: edge and screw Py-I on {101¯1}, edge and screw Py-II on {112¯2} by using a modified embedded atom method (MEAM) potential for Mg and anisotropic elasticity dislocation model. The results show that when energy minimization was performed before relaxation, in-plane dissociation of edge dislocations on respective pyramidal plane could be obtained at room temperature for all four types of dislocation. Without energy minimization, the edge dislocations dissociated out-of-plane onto the basal plane. Calculations of potential energy and hydrostatic stress of individual atoms at the edge dislocation core show that the extraordinarily high energy and atomic stresses in the as-constructed dislocation structures caused the out-of-plane dissociation onto the basal plane. The core structures of all four types of pyramidal dislocation after in-plane dissociation were analyzed by computing the distribution of the Burgers vector.

Elucidating the evolution of long-period stacking ordered phase and its effect on deformation behavior in the as-cast Mg-6Gd-1Zn-0.6Zr alloy

Herein, the evolution of long-period stacking ordered (LPSO) phases in the as-cast Mg-6Gd-1Zn-0.6Zr (wt.%) alloy are investigated via transmission electron microscopy (TEM) and atom probe tomography (APT). The TEM results reveal that two types of LPSO phase (a bulky interdendritic phase and a plate-like matrix LPSO phase) are formed in the as-cast sample. Most of the LPSO phases are confirmed to be of the 14H type, with a smaller proportion being of the 18R LPSO. Further, the APT results reveal that the composition of the interdendritic LPSO phase is closer to that of the ideal 14H phase compared to the matrix LPSO phase, and both the interdendritic and matrix LPSO phases exhibit a Gd/Zn ratio of 2.5, thereby indicating a deficient Zn content compared to the ideal 14H phase (i.e., 1.3). In addition, the influence of the LPSO phases on the deformation behavior is investigated at different compressive plastic strains using electron backscatter diffraction (EBSD) analysis to reveal twinning and slip behavior during deformation. The results indicate that the LPSO phase induces additional work hardening in the late stage of deformation via the suppression of {101¯1} compressive twinning and the activation of non-basal slip systems.

Oxide dispersion strengthening mediated ultra-high strength at wide temperature range in NbTaTiV refractory high-entropy alloys

The NbTaTiV-based refractory high-entropy alloys (RHEAs) show promising high-temperature properties and excellent processability. However, achieving ultra-strong strengths while maintaining room-temperature processability is still a challenge. In this work, a new ultra-strong NbTaTiV RHEA reinforced with 0.35 wt% Al2O3 was successfully designed and synthesized. The characteristics of oxides and their effects on mechanical properties were systematically studied. It was found that the Al2O3 will fully disperse and reacted with NbTaTiV RHEA after milling and sintering at 1600 °C, leading to the in-situ formation of dispersive Ti-(O, N) particles and the dissolving of Al atoms. The dual-phase RHEA exhibited a superior combination of yield strength (2075 MPa) and compressive plasticity (15%) while keeping high strength at a wide temperature range (25–1000 °C). The ultra-strong strength of the present dual-phase RHEA is mainly attributed to the particle strengthening caused by the high dispersion of Ti-(O, N) submicron particles and the solid solution strengthening from the dissolved Al and interstitial atoms. It is revealed that RHEAs can be remarkably enhanced through oxide dispersion strengthening and solution strengthening, which provides a new sight for designing high-performance RHEAs.