Compressive Deformation Behavior Research Articles

Intrinsic stacking fault energy and mechanism for deformation twin formation of solid solution matrix in Ni-based superalloys

Molecular dynamics simulations were used to calculate the equilibrium lattice constant and intrinsic stacking fault energy (γISF) of binary, ternary, and quaternary Ni-based solid solution alloys formed by substituting Ni atoms in the matrix with Cr, Co, and Al. Molecular dynamics simulations were also used to monitor the compression deformation behavior of Ni-based alloys with different γISF values at room temperature. The results show that the relative ability to reduce the γISF is Co < Cr < Al when equal content of Cr, Co, and Al added to the Ni matrix to form binary Ni-based alloys. The γISF decreases with an increase in the alloying element content. The γISF of Ni–Cr–Co alloys is a linear combination of the content of Cr and Co. The addition of Al, complicated the chemical interaction between Ni and the alloying elements, and the γISF of some Ni–Cr–Al, Ni–Co–Al, and Ni–Cr–Co–Al solid solution alloys fluctuate up and down with an increase in alloying element content. The formation of deformation twins resulted from the sequential expansion of stacking fault planes. The process of alloying with elements with a lower γISF means that it is easier to form deformation twins.

Selective laser melted high Ni content TiNi alloy with superior superelasticity and hardwearing

• High quality Ti 47 Ni 53 alloy is fabricated by the SLM for the first time. • The microstructure of SLM-Ti 47 Ni 53 alloy has been systemically studied. • Compressive deformation behavior is explored by the in-situ HE-XRD. • Synergy relationship between transforming matrix and elastic Ni 4 Ti 3 is revealed. • This work is a favorable reference for preparing other high Ni content TiNi alloys. TiNi alloys with high content Ni (52–55 at.%) are perfectly suitable for preparing wear- and corrosion-resistant parts that service on the space station, spacecraft, and submarine, because of their superior superelasticity, high strength, and hardwearing. However, the fabrication of complicated Ni-rich TiNi parts by the traditional machining method often faces problems of poor precision, low efficiency, and high cost. In this work, we succeed in preparing an excellent Ti 47 Ni 53 alloy by selective laser melting (SLM), and thus, open a new way for the efficient and precise formation of complicated Ni-rich TiNi parts with superelasticity and hardwearing. An optimized processing window for compact parts without defects is reported. The elaborately fabricated Ti 47 Ni 53 alloy exhibited a breaking strain of 11%, a breaking stress of 2.0 GPa, a superelastic strain of 9%, and a better hardwearing than that of casting and quenched Ti 47 Ni 53 alloy. Besides, the microstructure, phase transformation, and deformation, as well as their influence mechanisms are investigated by in situ transmission electron microscope (TEM) and high-energy X-ray diffraction (HE-XRD). The results obtained are of significance for both fundamental research and technological applications of SLM-fabricated high Ni content TiNi alloys.

Hot compression deformation behavior and processing maps of Al–0.5Mg–0.4Si–0.1Cu alloy

To improve the hot working stability of Al–0.5Mg–0.4Si–0.1Cu alloy, isothermal compression tests were performed at the temperature range of 350–500 °C and strain rate of 0.001–10 s−1. Strain-compensated Arrhenius constitutive equation containing Zener–Hollomon parameters was established to describe the hot deformation behavior. Its accuracy was evaluated within the whole strain range and the established constitutive equation can well predict the flow behavior. In addition, intrinsic machinability was further analyzed by constructing processing maps under different true strains based on dynamic material models. Microstructures are in fine agreement with processing maps and flow instability occurred mainly in high strain rate regions due to the presence of adiabatic shear bands and flow localization. Dynamic softening mechanism of the alloy mainly stems from dynamic recovery and partial dynamic recrystallization. Based on processing maps and microstructure observations, optimal process parameters of alloy were obtained, which are beneficial to optimize its hot working parameters.

Bi-directional freezing to fabricate freeze-cast ceramics with orientation gradient and uniaxial compressive deformation behavior of infiltrated composites

Structural orientation gradient in living organisms is attributed to their enhanced surface protection to penetration and deformation, providing bioinspiration to fabricate engineering materials with gradient in mechanical properties. Freeze-casting is a promising technique to fabricate bioinspired materials. However, in the conventional freeze-casting process, due to the applied unidirectional temperature gradient, all the material layers are also unidirectional, oriented in the direction of applied gradient. While bi-directional freezing conditions have been used but still preserving the characteristic unidirectional alignment. The main objective of this work was to demonstrate that bi-directional freezing conditions could be employed to create and control orientation gradient in freeze-cast materials and thereby develop multilayered composites with orientation gradient. Bi-directional freezing conditions were used to generate both horizontal freezing front (HFF) and vertical freezing front (VFF), where the ice crystals associated with VFF tilted the ice crystals associated with HFF, resulting in orientation gradient. 4 different bi-directional freezing conditions were achieved to change gradient microstructure. In situ studies were performed to investigate different growth front movements and calculate the velocities. Porous ceramics were infiltrated to develop bi-directionally freeze-cast composites. While the current literature sheds invaluable insights into the mechanical behavior of freeze-cast composites with unidirectional orientation, this investigation characterized uniaxial compressive mechanical response and damage characteristics of bi-directionally freeze-cast composites, which is another objective of this work. It was revealed that bi-directional freezing conditions can tune material layer orientation throughout freeze-cast microstructure, strongly influencing compressive mechanical response and damage characteristics in the resulting composite materials.

Compression deformation behavior of silicide coating on Nb-Si based alloy

The aim of this work is to investigate the compression deformation behavior of the Nb–Si based alloy with an Al–Y modified silicide coating at different conditions, including the height reduction, deformation temperature, strain rate and oxidation. The results showed that the silicide coating and substrate have a good coordinated deformation at a higher temperature or at a lower strain rate. While at a lower deformation temperature (1100 °C, 1200 °C) or a higher strain rate (0.005 s−1), the silicide coating shows a barrier effect on the deformation of substrate. At 1350 °C, the grains of NbSi2 phase in the coating were coarsened significantly. During the high temperature compression process, the coating can undergo a certain degree of plastic deformation, and NbSi2 phase in the coating would form sub-grain and a small amount of recrystallized grains. The crack initiation and propagation in the coating and substrate during compression deformation have also been discussed. The big cracks produced in the process of oxidation can be pressed gradually with the increase of the height reduction. The oxidation of the coating has no significant effect on the compressive properties of the alloy.

Compression and Deformation Characteristics of Hydrate-Bearing Sediments under High Effective Confining Pressure

The depressurization method that is used to produce methane gas can increase the effective stress in hydrate-bearing sediments and induce deformation and settlement of reservoirs, which has adverse effects on safe and stable exploitation. A series of isotropic consolidation and depressurization dissociation tests under high effective confining pressures on methane hydrate-bearing specimens were conducted to investigate compressive characteristics and deformation behaviors. Isoconsolidation test results demonstrated that the rise in effective confining pressure-induced increasing compressibility and particle crushing of sediment, while the presence of hydrates can suppress compressibility and crushing. The compression index tends to increase with increasing effective stress but decrease with increasing hydrate saturation. Dissociation test results suggested that higher effective stress during dissociation and higher deviatoric stress led to more significant deformation and particle breakage. A specimen can exhibit serious deformation (ɛv ≈ 20%) after dissociation when the effective stress is extremely high (17 MPa), even if the stress state is in the stable zone. During water recovery after dissociation, axial and volumetric strains may further increase under the combined effect of deviatoric stress and high effective confining pressure.

Observation of compressive deformation behavior of Al-12%Si alloy lattice structures additive-manufactured by laser powder bed fusion using mechanical stress-induced luminescent material

Observation of compressive deformation behavior of Al-12%Si alloy lattice structures additive-manufactured by laser powder bed fusion using mechanical stress-induced luminescent material

In-situ synchrotron diffraction study on compressive deformation behavior of Mg92Y5Ni3 alloy mostly composed of LPSO

The compressive deformation behavior of the as-cast and as-extruded Mg92Y5Ni3 (at.%) alloy mostly composed of long period stacking ordered (LPSO) phase was studied by in-situ synchrotron radiation combined with the analysis of deformation traces after compression at different applied stress. The as-cast alloy has random texture, while the as-extruded alloy has a typical basal texture with basal plane parallel to extrusion (compression) direction. Prior to macro-yielding, some softly oriented grains are preferentially plastically deformed, leading to micro-yielding. The micro-yielding behavior of both as-cast and as-extruded alloys is controlled by basal slip, the as-extruded alloy has higher micro-yielding strength than the as-cast alloy. The activated deformation mode near the macro-yielding point is prismatic slip in both as-cast and as-extruded alloys, and as the hard oriented grains dominate in the as-extruded alloy, the compressive yield strength of the alloy is increased from 217 MPa to 535 MPa after extrusion. The kinking activated following the prismatic slip can introduce a large number of dislocations in the as-extruded alloy, resulting in high strain-hardening rate of 3000 MPa, high ultimate compressive strength of ∼800 MPa and plastic strains above 10%.

Room temperature compressive superplasticity of low density steel

The present work deals with the room temperature compressive deformation behavior of a low density steel holding an apparent density of 6.8 gr/cm3. Surprisingly, it was found that the experimented materials tolerated a high amount of compressive true strain (∼2.5) without the occurrence of any micro-cracking or macro-localized shearing. Step by step study of the interrupted microstructures indicated the continuous and progressive development of the substructure in the course of room temperature compressive deformation. The extended dynamic recovery was justified considering the high stacking fault energy of the material and was followed by the occurrence of continuous dynamic recrystallization where the final microstructure was composed of ultrafine and equiaxed grains. Interestingly, the corresponding flow behavior was greatly affected by such specified microstructure evolution and an appreciable strain softening was obtained over a wide range of strain.

Study on the compressive deformation behavior of a basal textured AZ31 magnesium alloy from the perspective of local strain

For basal textured magnesium alloy subjecting to in-plane compression, the deformation is complicated since twinning, dislocation slipping and their intersecting are involved. In this work, a high-resolution digital image correlation (HR-DIC) technique combined with electron backscatter diffraction (EBSD) was used to quantitatively study the deformation behavior of AZ31 alloy in in-plane compression. Grain-scale local strain characteristics were emphasized. It is found that the local strain in the twined region is homogeneous and will not continuously increase with the applied nominal compression strain if no dislocation slipping is activated. When twinning is accompanied by dislocation slipping in the deformation of magnesium alloys, which is actually the common case, the strain contribution by the twinning can be calculated by transferring its shear from the twin frame to the sample frame. The results of this work can be beneficial for further understanding of deformation mechanism of magnesium alloy and the development of physics-based simulation models.

Effects of sample diameter, aspect ratio, and strain rate on compressive deformation and fracture behavior of Zr50Cu34Al8Ag8 metallic glass

In this paper, Zr50Cu34Al8Ag8 metallic glass bars with diameters of 2, 3, and 4 mm were prepared by copper mold suction casting. The compressive mechanical properties of metallic glass samples having different diameters, aspect ratios, and strain rates were tested by a universal testing machine. The microstructure of metallic glass samples was analyzed by X-ray diffractometer, scanning electron microscope, and transmission electron microscope. The experimental results show that the mechanical properties of Zr50Cu34Al8Ag8 metallic glass improve with decreasing sample diameter, aspect ratio, and strain rate. The maximum compressive strength, ultimate strain, and plastic strain of 1991.2 MPa, 7.95%, and 4.99% were respectively achieved for the metallic glass sample of φ = 2 mm. The main reason for the metallic glass's superior mechanical properties is its higher free volume content. For the metallic glass samples with the same diameter and different aspect ratios, the compressive strength and ultimate strain of the metallic glass with φ = 3 mm and aspect ratio = 1 is the largest, which are 2052.8 MPa and 15.2%, respectively, and the plastic strain is 11.09%. The improvement of mechanical properties of metallic glass samples is primarily attributed to the change of stress state. When the strain rate is 3 × 10−4 s, the compressive strength and ultimate strain of the sample are 1851.2 MPa and 4.09% respectively. This study will help to improve our understanding of the compression deformation and fracture behavior of metallic glasses, as well as promote their application.

Deformation mechanisms in the directionally solidified nickel-based CM247LC at room temperature

ABSTRACT After solutionizing and aging at 980°C for various durations, the compressive deformation behaviour and mechanisms of the directionally solidified nickel-based superalloy CM247LC are investigated at room temperature. Experimental results show that the yield strength decreases gradually from 991 ± 1.2–672 ± 7.5 MPa with increasing the γ′ precipitate size from 145 ± 2–604 ± 19 nm. Transmission electron microscope observations on the slightly deformed specimens reveal that, in contrast to previous researches, plastic deformation of all the specimens is controlled by strongly coupled dislocations cutting through γ′ precipitates. Based on these experimental results, the relationship between the yield strength and precipitate size is discussed.

Compression Performance and Deformation Behavior of 3D-Printed PLA-Based Lattice Structures.

The aim of this study is to fabricate biodegradable PLA-based composite filaments for 3D printing to manufacture bear-loading lattice structures. First, CaCO3 and TCP as inorganic fillers were incorporated into a PLA matrix to fabricate a series of composite filaments. The material compositions, mechanical properties, and rheology behavior of the PLA/CaCO3 and PLA/TCP filaments were evaluated. Then, two lattice structures, cubic and Triply Periodic Minimal Surfaces-Diamond (TPMS-D), were geometrically designed and 3D-printed into fine samples. The axial compression results indicated that the addition of CaCO3 and TCP effectively enhances the compressive modulus and strength of lattice structures. In particular, the TPMS-D structure showed superior load-carrying capacity and specific energy absorption compared to those of its cubic counterparts. Furthermore, the deformation behavior of these two lattice structures was examined by image recording during compression and computed tomography (CT) scanning of samples after compression. It was observed that pore structure could be well held in TPMS-D, while that in cubic structure was destroyed due to the fracture of vertical struts. Therefore, this paper highlights promising 3D-printed biodegradable lattice structures with excellent energy-absorption capacity and high structural stability.

4D-XCT and Digital Volume Correlation of Flax Fibre Composites Under Compressive Load After Relaxation

In-situ testing capabilities of lab-scale industrial computed tomography are rapidly improving. In the present study, the compressive deformation behaviour of a flax fibre-reinforced epoxy composite is studied in an in-situ compression test with stepwise loading, during 3D imaging with X-ray Computed Tomography (XCT). The 3D volumes are processed with Digital Volume Correlation (DVC) to identify the deformation of each loading step. The natural variability of the flax texture served as an adequate speckle pattern for DVC. The precision and accuracy of the DVC were investigated prior to the analysis of the deformation volumes by digitally deforming the reference undeformed volume with a known strain of 2 %. The calculated global strain was in good agreement with the digitally applied strain. Subsequently, DVC was applied to the acquired reference and deformed volumes and the analysis was focused on the 3D strain field evolution between the consecutive loading steps. Strain localization regions were observed in the axial strain εzz and the in-plane strain εxx. In the subsequent loading steps, the onset of compressive fibre-kinking is observed as a rotating fibre inside the magnified strain region. The 3D strain field evolution allows for a better understanding of the deformation and failure mechanisms at the meso/micro-scale in natural fibre reinforced composites under compressive loads.

Compressive deformation behavior and energy absorption characteristic of additively manufactured sheet CoCrMo triply periodic minimal surface lattices

CoCrMo sheet triply periodic minimal surface (sheet-TPMS) lattices with two different topologies (Neovius, IWP) were fabricated by laser power bed fusion (LPBF). Compressive behavior and energy absorption characteristic for each topology and direction were investigated. The unique pore channel structures of the fabricated Neovius and IWP lattices were well formed. The microstructural observation revealed that fine cellular substructures existed inside the sheets, and most of their constituent phases were confirmed to be the FCC phase. The results of the compression tests demonstrated that Neovius lattice had higher yield strength and first peak strength than IWP lattice, regardless of the compressive direction. As for the stress–strain curves of the lattices, an abrupt stress drop was found in neither of the two topologies. A comparison of the energy absorption characteristics confirmed that Neovius lattice had higher energy absorption efficiency and ideality than IWP lattice. The deformed structures showed that Neovius lattice displayed a gradual collapse mode, whereas a layer-by-layer compaction mode was indicated in IWP lattice. After the deformation, Neovius showed an evenly distributed and high fraction of the HCP phase caused by strain-induced martensitic transformation. The topology of lattice and strain-induced martensitic transformation effects on the compressive mechanical responses of the LPBF-built TPMS lattices were also discussed.

Compressive deformation behaviour and toughening mechanisms of spark plasma sintered NiAl-CNT composites

Carbon nanotube (CNT)-reinforced NiAl intermetallic composites were produced via powder metallurgy, particularly spark plasma sintering. The aim of this study was to evaluate the room temperature compressive behaviour of the sintered NiAl-CNT composites with a focus on the toughening mechanisms of the CNT reinforcement and the resulting microstructures. Remarkably, the NiAl-0.5 wt% CNT composites exhibited a balanced combination of strength and toughness despite a trade-off tendency, due to the presence of both coarse and fine bimodal grains in its microstructure. Mechanical properties of 831 MPa, 429 MPa and 360 HV were recorded for the ultimate compressive strength (UCS), compressive yield strength (CYS) and microhardness of the NiAl-0.5%CNT intermetallic composites, respectively, along with a compressive strain of 12% being higher than the unreinforced NiAl.

Dynamic recrystallisation and constitutive equation in hot deformed AISI H10 tool steel

ABSTRACT The compression deformation behavior of AISI H10 (DIN 32CrMoV12-28) hot work tool steel was investigated at temperatures ranging from 900°C to 1200°C and strain rates from 0.01 to 1 s−1. True stress-strain curves showed that a decrease in strain rate or increase in deformation temperature can promote the occurrence of DRX. It was found that the characteristic strains and stresses decrease with an increase in temperature or decrease in strain rate. The σc/σp ratio takes an average of 0.94; and the ϵc/ϵp ratio lies in range of 0.48-0.65 (average of 0.53). This suggests that DRV in H10 is not extensive and DRX starts at strains about half of the peak strain. However, the extensive softening by DRX keeps σp close to σc. Using the hyperbolic-sine constitutive equation, the deformation activation energy was calculated to be about 435.76 kJ mol−1.

Developing harmonic structure in CoCrFeMnNi high entropy alloy to enhance mechanical properties via powder metallurgy approach

The FCC structured CoCrFeMnNi high entropy alloy (HEA) has attracted great attention due to its excellent ductility and strain hardening ability, but the lowest yield strength is insufficient for structural applications. To achieve high strength and ductility, we developed a new strategy called harmonic structure (HS) consisting of soft coarse and hard fine grains via controlled mechanical milling time. The SEM and EBSD microscopic characterizations reveal that the formation of HS from surface to the interior of powder is due to a difference in the degree of plastic deformation. The hardness of HS HEAs increased with increasing distance from center to surface regions due to a reduction in grain size. Compared with the homogeneous HEA, the yield strength of HS HEAs increased from 370 MPa to 730 MPa and 760 MPa due to grain boundary strengthening, dislocation strengthening, and twin boundary strengthening effects. While HS HEAs exhibited enhanced strain hardening ability due to gradient structure with their mechanical incompatibility provide back stress strengthening. Furthermore, the compressive deformation behavior of homogeneous and HS HEAs was analyzed by microstructural evolution.

Investigation of conventional and asphaltic underlayment track behaviors subjected to freight train load: Mechanistic approach

The load characteristics in terms of the carrying capacity and the train operation speed limit Indonesia's conventional track capability. In this study, the behaviors of Indonesia's conventional tracks and the proposed asphaltic underlayment tracks under cyclic loading conditions of the low-speed Babaranjang (long-chain coal) freight trains have been evaluated using the finite element package Abaqus/CAE considering linear elastic behavior of materials. The numerical modeling was applied on three different layer thicknesses of sub-ballast in Indonesia's conventional tracks and three different layer thicknesses of asphalt in asphaltic underlayment tracks to investigate the vertical compressive stress, horizontal-vertical-maximum strain, and deformation behaviors. According to the numerical simulation, the measurements indicate that the asphaltic underlayment tracks are superior to Indonesia's conventional tracks. Furthermore, a 15 cm of asphalt layer in the asphaltic underlayment tracks demonstrates promising performance in the future of Indonesia's railway systems. The asphaltic underlayment tracks are expected to serve the heavier and higher speed Babaranjang freight trains with longer service life and lower life cycle cost than Indonesia's conventional tracks.

Compressive deformation and electrochemical analysis of Ti4AlxCo alloy

Ti4AlxCo (wt%) (x = 0%, 2%, 4%, and 6%) were synthesized via powder metallurgy route. Effect of Co content on the phase formation, microstructural transformation, compressive deformation and electrochemical behaviour of the alloy were investigated. Phase formation and microstructural analysis were done with the help of XRD and FESEM respectively. Compression test was performed to investigate the yield strength and modulus of elasticity of the alloy. Synthesized alloys were analyzed by electrochemical method to probe their resistance to corrosion in the Hank’s solution. XRD test confirms the formation of Ti2Co phase in the alloy which volume fraction increases with the increment of Co content. Leafy columnar structure of Ti2Co phase was clearly observed in the microstructure of the alloy containing Co. Compressive yield strength (σy) and elastic modulus (E) of Ti4Al sample are about 45% and 25% lower than the sample made of commercially pure (CP) Ti. Addition of Co content improves σy as well as E. However, alloys containing more than 2 wt% of Co have higher elastic modulus than Ti6Al4V which may be a concern to use them as a bone scaffold. In Tafel plot, corrosion current density (Icorr) shifts towards the higher value with the increment of Co content causing the reduction of corrosion resistance.