Compressive Deformation Behavior Research Articles

Orientation Dependence of High Temperature Compressive Behavior of Textured Ti<sub>3</sub>SiC<sub>2</sub>

In order to clarify the orientation dependent deformation behavior of the MAX phase ceramics, compressive deformation behavior was examined in a textured Ti3SiC2 (TSC) at a high temperature of 1200°C. Depending on the relationship between the texture and loading directions, both the deformation behavior and microstructure were strongly influenced, and the resultant basal slip, kink formation and delamination affected the compression behavior of the textured TSC. When the stress was loaded parallel or perpendicular to the basal plane (0TSC and 90TSC), the stress-strain (S-S) curves showed higher peak stresses followed by the reduction in the flow stress. When the stress was loaded 45° to the basal plane (45TSC), the S-S curve showed strain hardening after yielding, but did not show peak stress. Although the strength was higher both in 0TSC and 90TSC than in 45TSC, both 0TSC and 90TSC showed the formation of cracks and delamination, resulting to the large drop in the flow stress. In contrast to 0TSC and 90TSC, although 45TSC did not exhibit the peak stress, it exhibited work hardening due to the kink boundary formation, irrespective of the formation of delamination. It is reasonable to conclude from the deformation behavior and the deformed microstructures that for the TSC, the kink boundary plays an important role for attaining both deformability and strength.

Effect of long-period ordered stacking on twinning behavior and mechanical properties of Mg-Al-Y alloy during uniaxial hot compression

Two alloys with (T4-4h) and without (T4-8h) long-period stacking ordered (LPSO) phase were obtained by solution treatment of as-cast Mg-1Al-12Y alloy at 540 ℃ for 4 h and 8 h, respectively. The compressive tests (300 – 450 ℃, ε=0.01s−1) showed that the strengthening effect of LPSO in T4-4h alloy gradually disappeared with temperature increase. In addition, the corresponding compression deformation behavior of the two alloys was also investigated by electron backscatter diffraction (EBSD). It was found that the twinning of the two alloys was dominated by {101¯2} extension twins, and the large amount of lamellar LPSO in T4-4 h alloy inhibited the activation and growth of twins. The [0001] // compression direction (CD) texture formed after deformation is mostly attributed to the activation and growth of extension twins. By analyzing the activated twin variants, it was found that the activation of twin variants mainly depended on Schmid factor (SF). For twin variants with smaller SF, they may be activated due to local stress concentration. Based on the analysis results of in-grain misorientation axis (IGMA) and SF, the deformation mechanism of the alloys at elevated temperature is dominated by basal slip and non-basal slip. The stronger mechanical properties of T4-4h alloy than those of T4-8h are attributed to the obstruction of non-basal slip movement by LPSO.

Effects of molybdenum on hot deformation behavior and microstructural evolution of Fe40Mn40Co10Cr10C0.5 high entropy alloys

ABSTRACT The remarkable properties of high-entropy alloys (HEAs) have resulted in their increased research interest and prompted the use of various strategies to enhance their mechanical properties. In this study, the effects of Mo on the hot compressive deformation behavior of carbon-containing FeMn40Co10Cr10 HEAs in the temperature range of 800–1000°C and strain rate of 0.001–0.1 s−1 was investigated. The microstructural evolutilon and phase structure were characterized by X-ray diffraction and electron backscattered diffraction. The effects of strain, strain rate, and deformation temperature on the thermally activated deformation restoration process of the Fe39.5Mn40Co10Cr10C0.5 and Fe38.3Mn40Co10Cr10C0.5Mo1.7 HEAs during hot compression were represented by the Zener–Hollomon parameter. Dynamic recrystallization was initiated at 800°C with the strain rate of 0.001–0.1 s−1. The precipitation of the M23C6 carbide along the grain boundaries and within the matrix exerted a strong pinning effect on the grain/subgrain boundaries and promoted dynamic recrystallization through the particle-stimulated nucleation of recrystallization. Moreover, the addition of Mo to the Fe39.5Mn40Co10Cr10C0.5 HEA changed the dynamic recrystallization mechanism by reducing the stacking fault energy and enhancing the reverse f c c ↔ h c p phase transformation. The heterogeneous microstructure composed of ultrafine, fine, and larger grains in the Fe38.3Mn40Co10Cr10C0.5Mo1.7 HEA could be obtained by the nucleation of new recrystallized grains at large deformed grain boundaries adjacent to the first necklace structures and shear bands.

Properties Evaluations of Topology Optimized Functionally Graded Lattice Structures Fabricated by Selective Laser Melting

Owning to their lightweight characteristic and high performance, functionally graded lattice structures (FGLSs) show great potential in orthopedics, automotive industries and aerospace applications. Here, two types of uniform lattice structures (ULSs) with RD = 0.50 and 0.20, and two types of FGLSs with RD = 0.30-0.50 and RD = 0.20-0.40, were designed by topology optimization and fabricated by SLM technology. Subsequently, their surface morphology, compressive deformation behavior and energy absorption abilities were evaluated by use of the finite element method (FEM) and compression tests. From these results, both elastic modulus and yield strength of specimens decreased with the lowering of the RD value. ULSs had a uniform deformation behavior with bending and bulking of struts, while FGLSs presented a mixed deformation behavior of different layers. Additionally, the energy absorption capability (Wv) of specimens was proportional to the RD value. When the value of RD increased from 0.20 to 0.50, the Wv of specimens increased from 0.3657 to 1.7469 MJ/m3. Furthermore, mathematical models were established successfully to predict the mechanical properties of FGLSs with percentage deviations < 10%. This work provides a comprehensive understanding regarding how to design and manufacture FGLSs with the properties desired for satisfying the demand of different application scenarios.

Experimental and Numerical Studies on Hot Compressive Deformation Behavior of a Cu-Ni-Sn-Mn-Zn Alloy.

Cu-9Ni-6Sn alloys have received widespread attention due to their good mechanical properties and resistance to stress relaxation in the electronic and electrical industries. The hot compression deformation behaviors of the Cu-9Ni-6Sn-0.3Mn-0.2Zn alloy were investigated using the Gleeble-3500 thermal simulator at a temperature range of 700-900 °C and a strain rate range of 0.001-1 s-1. The microstructural evolution of the Cu-9Ni-6Sn alloy during hot compression was studied by means of an optical microscope and a scanning electron microscope. The constitutive equation of hot compression of the alloy was constructed by peak flow stress, and the corresponding 3D hot processing maps were plotted. The results showed that the peak flow stress decreased with the increase in the compression temperature and the decrease in the strain rate. The hot deformation activation energy was calculated as 243.67 kJ/mol by the Arrhenius equation, and the optimum deformation parameters for the alloy were 740-760 °C and 840-900 °C with a strain rate of 0.001~0.01 s-1. According to Deform-3D finite element simulation results, the distribution of the equivalent strain field in the hot deformation samples was inhomogeneous. The alloy was more sensitive to the deformation rate than to the temperature. The simulation results can provide a guideline for the optimization of the microstructure and hot deformation parameters of the Cu-9Ni-6Sn-0.3Mn-0.2Zn alloy.

Characterizing the biaxial compressive deformation behavior of epoxy polymer through cruciform experiment and finite element analysis

The multiaxial deformation behaviors of amorphous epoxy polymers were characterized using planar biaxial compression tests and finite element (FE) analyses of cruciform specimens. The multiaxial limit of elastic deformation was investigated considering buckling instability of the planar biaxial compression tests. An offset-based yield criterion was proposed to determine the initial yield surface considering the nonlinear elastic deformation characteristics observed in the deformation tests. An FE analysis confirmed using the results of the tests revealed that the proposed method captured the initial multiaxial yielding in the central gauge of the specimen, demonstrating that existing pressure-dependent classical yield functions, such as the paraboloidal and conical yield functions, cannot appropriately describe the initial yield surface of the epoxy polymer. The yield function previously customized from molecular dynamics (MD) data exhibited a relatively good agreement with the initial yield surface. The determined shape of the initial yield surface and its agreement with the MD data–driven yield function were not consistently maintained during subsequent yielding. The results indicate that a new customized yield function properly describing the broader initial yield surface than those of the classical yield functions and its shape transition to plastic behavior is necessary to accurately reflect the entire multiaxial deformation behavior.

Effects of random and controlled irregularity in strut lattice structure of PA12 on compression anisotropy

Lattice structures have attracted significant attention as novel energy-absorbing structures; however, regular lattice structures have anisotropic energy-absorbing properties. To make the energy absorption properties isotropic, the irregularization of the lattice structures may be effective. However, the irregularity effect on the energy absorption amount is unclear. Therefore, in this study, irregularities were introduced into the lattice structures comprising struts, and the irregularity effects on the isotropy of the compressive properties and amount of energy absorption were investigated. The lattice structures were designed using a three-dimensional Voronoi partitioning method, and the irregularities of the structures were controlled by the Voronoi seed point distribution. The designed lattice structures were fabricated by powder bed fusion with recycled PA12 powder. In the compressive deformation behavior of the lattice structures with small irregularities, steep stress drops were observed with the generation of failure bands. However, local strut rupture occurred continuously in the lattice structure with large irregularities, and the flow stress undulated gently. From these behavioral characteristics, energy absorption was calculated and discussed concerning the irregularities, redefined quantitatively using the coefficient of variation (CV) for the cell volume distribution. The energy absorption anisotropy decreases sharply for CV above 0.1, and such lattice structures can be considered almost isotropic. Thus, even if the structure is incompletely random, it is isotropic with a certain level of irregularity. In contrast, the average energy absorption between structures with equivalent CV decreases monotonically until CV below 0.35 and then saturating. The results indicate that irregular lattice structures with controlled CV are isotropic and absorb energy more efficiently than random lattice structures designed without planning. Thus, irregularity control is evidently important in designing lattice structures with higher isotropic energy absorption.

Effect of interfacial damages on compressive deformation behavior of bonding components between auxetic structure and porous composite

Effect of interfacial damages on compressive deformation behavior of bonding components between auxetic structure and porous composite

Effect of fiber alignment on mechanical properties of chopped graphite fiber-reinforced copper-matrix composites: Designing fiber alignment in various stress conditions

Carbon-reinforced copper-matrix composites must provide improved mechanical properties if used as a structural part of machinery. However, little research has been conducted on the effect of the alignment of graphite fibers (GFs) with a high aspect ratio on the mechanical properties of composites. In this work, the effects of the alignment and volume fraction of GFs on the mechanical properties of GF/Cu composites subjected to tensile and compressive loading were analyzed and compared. The yield strength was highest when the composite with a GF volume fraction of 5% was subjected to compressive loading in the through-plane direction. The yield strength during tensile deformation was higher in the in-plane direction than in the through-plane direction. However, during compression testing, the yield strength was higher in the through-plane direction. Thus, the effects of the alignment and volume fraction of GFs on the tensile and compressive deformation behaviors of GF/Cu composites were revealed. These results are expected to provide a practical guide for optimizing the mechanical properties of GF/Cu composites subjected to various stress conditions as materials for the structural parts of machinery.

Characterization of Cr-Mo Alloyed Steel Foams Produced by Evaporative and Leachable Space Holder Techniques

Steel foams have attracted a lot of attention in both academia and industry with unique properties such as low density, high strength-to-weight ratio, operating temperature, good energy absorption, electrical conductivity, and large specific surface. The development of production methods will increase the use of steel foam. In this paper, Cr-Mo alloyed steel foams having porosities in the range of 46.8-71.3% were produced by evaporative and leachable space holder techniques in powder metallurgy. The effect on the properties of removing the carbamide used as a space holder material from the porous structure by different methods was compared. Microstructural evaluations of the pore wall, pore size, pore wall thickness, and the compressive deformation behavior of steel foam were evaluated. Steel foams produced by both routes have a rather similar macropore structure but differences in pore wall structure such as micropore ratio and pore wall thickness. The differences increase with increasing porosity content. The mechanical properties are higher in foams produced by the evaporative route as compared to the leachable route at similar porosity due to its stronger cell wall. The compressive stress and energy absorption of the leachable and evaporative process are in the range of 15-84 and 102 MPa and 1.91-6.03 and 2.98-7.83 J/mm2, respectively.

Dynamic compression deformation behavior of laser directed energy deposited α + β duplex titanium alloy with basket-weave morphology

Duplex titanium alloy with basket-weave morphology made by laser directed energy deposition (LDED) technique, has a bright application prospect in the armor protection field attributed to its excellent specific strength and bulletproof performance. In this research, the dynamic compressive deformation mechanisms of LDEDed TC11 titanium alloy under a strain rate of 3000/s are systematically investigated by investigating the dislocation slipping and twinning behavior. Meanwhile, this work gives explanations of the microstructure evolution of subsequent heterogeneous shear localization. The results indicate that TC11 alloy with basket-weave morphology possesses huge improvement in the average dynamic flow stress, uniform plastic strain, and impact absorption energy in contrast to that of titanium alloys with an equiaxed microstructure, which is known as the optimum prepared via traditional forming methods. The loading direction to α laths is largely responsible for slip modes manifestation under dynamic compression, which is illustrated in the unit triangle. When loading along < 0001 > at the vertex of the unit triangle, both basal slip and prismatic slip systems could not be motivated. When loading along directions within the unit triangle, either or both basal slip and prismatic slip systems could be activated, causing α lath twisting, rotation, or even refinement. Meanwhile, the Schmid factors reduction caused by α laths rotation results in the twinning, which will reduce the slip mean free path. During the heterogeneous shear localization, the adiabatic shear bands (ASB) formation finally leads to shear failure. The α laths within the transition zone in ASB are compressed to less than 200 nm in thickness. Ultrafine nanoscale equiaxed grains with few defects in the center zone of ASB are generated under dislocations pile-up and sub-grain rotation.

Study on thermal compression deformation behavior and constitutive model of homogenized Mg–5Zn–1Mn alloy

The thermal compression deformation behavior of homogenized Mg–5Zn–1Mn (wt.%) alloy was systematically investigated over the temperature and strain rate ranges of 285–345 °C and 0.001–1 s−1, respectively. The constitutive model and thermal processing diagrams were established. The microstructure evolution process and dynamic recrystallization (DRX) mechanisms were analyzed. The results demonstrate that the flow stress curves of the ZM51 alloy exhibit prominent DRX characteristics. The peak stress can be improved by decreasing the deformation temperature or increasing the strain rate. A finite element simulation is performed, and the Arrhenius constitutive model can accurately depict the plastic flow process of the alloy with strain correction, and the average activation energy is about 143.821 kJ/mol. Both the percentage DRX and the DRX grain size are found to be sensitive to the applied deformation conditions, including temperature, strain rate, and true strain. The formation of DRX grains promotes the weakness of the texture and the refinement of the grains. Grain boundaries nucleation (including discontinuous and continuous DRX) and particle-stimulated nucleation (PSN) are the main DRX mechanisms. Based on the processing map, ZM51 alloy is suitable for large plastic deformation by multi-pass forging. The optimum processing temperature is 345 °C, and as the degree of plastic deformation increases, the strain rate can be suitably increased. Local plastic flow and microcracking at grain boundaries are the primary instability mechanisms of the alloy.

Compressive strength and deformation behavior of the hybrid S phase layer under micro-pillar compression

Austenitic stainless steel of medical grade was subjected to low-temperature thermochemical heat treatment process which forms a distinctive layer on the surface of the material. The distinctive layer is commonly known as ‘S phase’, and resulted due to diffusion of elemental species present in the heat treatment atmosphere. A cross-sectional microstructural investigation confirms that the layer thickness increases with the increase of methane (CH4) contents in the carrier gas and the microstructure contain abundance of structural defects like slip bands, stacking faults, twins, and dislocations. Subjected to micro-pillar compression, the ultimate compressive strength of this layer was up to 190% more than that of bulk material which comes in expense of limited strain accommodation of such layer. Consequently, the critically resolved shear stress of the S phase layers were higher than that of the bulk material and microstructural defects contribute up to 83.17 MPa on that. On course of the micro-pillar compression, the S phase layers show catastrophic cleavage type brittle fracture in contract of progressive ductile fracture of the bulk material.

Room temperature compression deformation behavior of a Cr–Nb alloyed high manganese steel

The strain hardening behavior and microstructure evolution of a newly developed Cr–Nb alloyed high manganese steel were investigated in the present study. The investigated steel demonstrated good combination of yield strength (425.6 MPa) and impact toughness (372.5 J/cm2) after solution treatment. Room temperature compression test was conducted to investigate the strain hardening behavior during the practical performance condition. The investigated steel exhibited a long continuous strain hardening stage. The ultimate true stress could be higher than 5000 MPa. No obvious phase transformation was activated during the deformation process. The deformation behavior was dominated by planar dislocation slip, dislocation walls, formation of mechanical twinning and inhabitation of nano size NbC carbide precipitations. The formation of mechanical twinning and dislocation cell played a dyanamic grain refinement effect, which contributed to the upward trend of the strain hardening rate. Precipitation strengthening would also help improving the strain hardening rate.

Compressive deformation behavior of AZ31 alloy at 21K: an in-situ neutron diffraction study

Deformation behavior during uniaxial compression at 21 K and 298 K in a commercial AZ31 magnesium alloy was studied by in-situ neutron diffraction. Decreasing the deformation temperature resulted in a slight increase in yield stress (115 MPa →139 MPa), but a remarkable enhancement in both the fracture stress (365 MPa → 551 MPa) and fracture strain (12.8%→16.5%). The low temperature sensitivity of the {101¯2} extension twinning which governed the macroscopic yielding led to the slight increase in yield stress. At 21K, basal slip was suppressed, while the extension twinning was promoted resulted in higher twin volume fraction. In the late stage of deformation, the {101¯1}-{101¯2} double twinning was suppressed, which is considered to be the reason to delay the fracture at 21 K.

Compressive properties and deformation behaviors of sintered W-m-ZrO2 alloy under different temperature

The compressive properties of sintered tungsten alloys with different m-ZrO2 weight percentage (0, 0.5, 1.0%) were tested at room temperature and high temperature, and the hot deformation behaviors of the three metals were investigated under different temperature (1300–1600 °C) and strain rate (0.005–1 s−1). The room temperature strengthening model of zirconia particle reinforced tungsten alloy was established, and the hot deformation activation energy and constitutive equation of the three metals were calculated. Characterized by field emission scanning electron microscopy (FE-SEM) and the electron back scattering diffraction (EBSD) technique, the results show that zirconia doping can significantly refine the tungsten grain size, improve sintering densities, and uniformly disperse in the boundaries and inside of tungsten grain. The room temperature compression results show that the ultimate compressive strength and strain-to-failure of W-1.0 m-ZrO2 increase by 51.94% and 96.69%, respectively compared with pure tungsten. The main contribution to the room temperature strength of tungsten alloys is the fine grain strengthening caused by zirconia doping, about 60% for W-1.0 m-ZrO2，while the strengthening of the secondary phase particles accounts only for about 5%. High-temperature compression results show that zirconia doping increases the dislocation density of the alloy and significantly improve the ultimate compressive strength under high-temperature compression, but the influence of zirconia content on the strength will be weakened at high temperature. The doping of zirconia reduces the hot deformation activation of tungsten alloys and improves the hot processing behavior of tungsten alloy.

A Variable-Order Fractional Constitutive Model to Characterize the Rate-Dependent Mechanical Behavior of Soft Materials

Building an accurate constitutive model for soft materials is essential for better understanding its rate-dependent deformation characteristics and improving the design of soft material devices. To establish a concise constitutive model with few parameters and clear physical meaning, a variable-order fractional model is proposed to accurately describe and predict the rate-dependent mechanical behavior of soft materials. In this work, the discrete variable-order fractional operator enables the predicted stress response to be entirely consistent with the whole stress history and the fractional order’s path-dependent values. The proposed model is further implemented in a numerical form and applied to predict several typical soft materials’ tensile and compressive deformation behavior. Our research indicates that the proposed variable-order fractional constitutive model is capable of predicting the nonlinear rate-dependent mechanical behavior of soft materials with high accuracy and more convinced reliability in comparison with the existing fractional models, where the fractional order contains a constant initial order to depict the initial elastic response and a linear variable-order function to account for the strain hardening behavior after acrossing the yield point.

The hot compressive deformation behavior of cast Mg-Gd-Y-Zn-Zr alloys with and without LPSO phase in their initial microstructures

Samples of Mg-8.2Gd-3.8Y-1.1Zn-0.4Zr alloy with and without an intragranular lamellae-shaped long period stacking ordered (LPSO) phase were prepared through heat treatment and a series of hot compression tests on these materials were conducted to examine and evaluate the influence of LPSO on the hot compressive deformation behavior and deformation mechanisms at a given alloy composition. The values of activation energy for plastic flow (Q c ) of the solution treated (without LPSO phase) and annealed alloys (with intragranular LPSO phase) were larger than that for pure Mg, indicating that the presence of a high amount of rare earth (RE) elements and LPSO in the Mg matrix significantly increases Q c . The Q c value of the annealed alloy was larger than that of the solution treated alloy at all the strain levels (223.3 vs. 195.5 kJ/mol in average) and the largest difference in Q c between the two alloys was recorded at the smallest strain of 0.1 where precipitation of LPSO during deformation was limited in the solution treated alloy. These observations imply that the formation of LPSO phase out of the RE-rich solid solution matrix during deformation increases Q c , but the increment is not so large. Analysis of the hot compressive data of the alloys with LPSO phase and the alloys with RE-rich solid solution matrix in literatures indicates the similarity of the effect of the LPSO and RE-rich solid solution matrix phases on Q c and high-temperature strength.

Hot Compression Deformation Behavior and Microstructure of As-Cast and Homogenized AA2195 Al-Li Alloy

To understand the effect of the initial state of AA2195 Al-Li alloy on the forming process, as-cast and homogenized ingots were compressed by using a Gleeble-3150 thermo-mechanical simulator at different temperatures (360–480 °C) and strain rates (0.01–10 s−1). The hot compression deformation behaviors and microstructural characteristics of the two types of ingots were systematically investigated. The as-cast alloy possessed a better hot compressibility with higher power dissipation efficiency and lower rheological stress than the homogenized alloy under the same deformation conditions. When the temperature was increased above 450 °C, all the alloys showed similar rheological curves. Based on the rheological stress curves, processing maps for the as-cast (AC) and homogenized (HG) alloys were established, and optimal processing domains were identified. In addition, the homogenized alloys were dominated by a fibrous microstructure during deformation, whereas the as-cast alloy produced fine crystals at low temperature (360 °C) and equiaxed crystals at high temperature (480 °C). Our results show that it is possible to use the as-cast 2195 Al-Li alloy as the initial billet to get complicated components. This is attributed to the dispersed eutectic phases, which can provide more nucleation sites for Dynamic Recrystallization (DRX) and Dynamic Recovery (DRV) during hot deformation.

Optimized hot working parameters of Fe2.5Ni2.5CrAl multi-principal element alloys

The hot compressive deformation behavior of Co-free Fe2.5Ni2.5CrAl multi-principal element alloys (MPEAs) was investigated in the temperature and strain rate ranges of 800–1100∘C and 0.001 s−1 and 1 s−1, respectively. Microstructural observations were carried out by optical microscopy (OM) and electron backscatter diffraction (EBSD). A constitutive model based flow-stress analysis was carried out, the activation energy (Q) was obtained as 315.9 kJ/mol at steady state. The strain rate sensitivity (m), the power dissipation (η), and instability parameter (ξ) were utilized to construct the processing maps. Power-law breakdown and unstable flow occurred at the high strain rates at which strain hardening was pronounced. The optimal condition for successful hot working was determined to be at strain rates in the range of 10−2–10−3 s−1 and a temperature range of 850 ~ 1020∘C. FEM simulations revealed the strain and stress distribution during hot deformation and predicted instabilities during hot forming. The main deformation mechanism was dislocation climb with a stress exponent n > 5. The Q value for plastic flow in the power-law creep regime was calculated considering the effect of lattice diffusion of atoms and was in accordance with the measured Q value. Thus, our study revealed the hot working characteristics and the optimum processing parameters for successful hot working of Fe2.5Ni2.5CrAl MPEAs.