Strain Rate Sensitivity Index Research Articles

Experimental constitutive relationships for high-temperature deformation of as-cast Al–Si binary alloys

ABSTRACT As-cast binary Al–Si alloys containing ∼2 to 30 wt.% Si were deformed by differential strain rate and differential temperature test techniques at 600–840 K and strain rates 10−4–10−2 s−1 to find the parameters of the constitutive relationships for high-temperature deformation. The maximum strain rate sensitivity index (m) of flow stress was found to be 0.28 in the eutectic Al-12Si alloy. The Arrhenius plot for activation energy for deformation (Q) exhibits bilinear behaviour, with Q being greater at higher test temperatures than at lower temperatures. The magnitude of Q varies as a function of Si content: 95.7 ± 9.8 kJ/mol for Al-2Si to 311.4 ± 98.1 kJ/mol for Al-12Si alloy. Also, the constant initial strain rate tests performed at selected strain rates and temperatures revealed flow hardening at small strains followed by flow softening. Deformation of Al–Si alloys is suggested to be controlled by the dislocation climb mechanism through the participation of both the grain interior and grain boundaries by consideration of effective stress instead of applied stress.

Understanding the hot deformation behavior of Mo[sbnd]42Re alloy: Insights from strain rate sensitivity, microstructure, and misorientation

Mo42Re alloy, as a high-temperature structural and functional material, has broad application prospects in the nuclear industry. In this study, the hot deformation behavior of Mo42Re alloy was systematically investigated using hot compression tests and electron backscatter diffraction (EBSD) techniques in the temperature range of 1200–1500 °C and strain rate range of 0.001–1 s−1. The results showed that the flow stress of Mo42Re alloy exhibited a strong dependence on temperature and strain rate. The strain rate sensitivity index (m-value) was high under the conditions of 1350–1450 °C and 0.001 s−1. With increasing deformation temperature and decreasing strain rate, dynamic recrystallization (DRX) was significantly promoted, and the recrystallized volume fraction increased from 2.79% at 1200 °C/1 s−1 to 20.3% at 1500 °C/0.001 s−1. Meanwhile, the occurrence of and DRX effectively reduced the grain reference orientation deviation (GROD) gradients and kernel average misorientation (KAM) levels within the grains. This study revealed the mechanisms of microstructural evolution during hot deformation of Mo42Re alloy, providing important guidance for optimizing its thermomechanical processing parameters.

Quantitative Insight into the Compressive Strain Rate Sensitivity of Polylactic Acid, Acrylonitrile Butadiene Styrene, Polyamide 12, and Polypropylene in Material Extrusion Additive Manufacturing

AbstractHerein, a research and engineering gap, i.e., the quantitative determination of the effects of the compressive loading rate on the engineering response of the most popular polymers in Material Extrusion (MEX) Additive Manufacturing (AM) is successfully filled out. PLA (Polylactic Acid), ABS (Acrylonitrile Butadiene Styrene), PP (Polypropylene), and PA12 (Polyamide 12) raw powders were evaluated and melt-extruded to produce fully documented filaments for 3D printing. Compressive specimens after the ASTM-D695 standard were then fabricated with MEX AM. The compressive tests were carried out in pure quasi-static conditions of the test standard (1.3 mm/min) and in accelerated loading rates of 50, 100, 150, and 200 mm/min respectively per polymer. The experimental and evaluation course proved differences in engineering responses among different polymers, in terms of compressive strength, elasticity modulus, toughness, and strain rate sensitivity index. A common finding was that the increase in the strain rate increased the mechanical response of the polymeric parts. The increase in the compressive strength reached 25% between the lowest and the highest strain rates the parts were tested for most polymers. Remarkable variations of deformation and fracture modes were also observed and documented. The current research yielded results with valuable predictive capacity for modeling and engineering modeling, which hold engineering and industrial merit.

Hot deformation behavior, superplasticity and microstructure evolution of a new hot isostatic pressed nickel-based superalloy

The new hot isostatically pressed (HIP) superalloy has demonstrated remarkable superplastic characteristics, as evidenced by studying the compression and tensile deformation behavior. To identify the superplastic deformation zone, the instability regions at various strain variables were overlaid onto the strain rate sensitivity index (m) distribution map at a strain of 0.6, resulting in the acquisition of a new hot working map. The tensile test results showed that under the conditions of 1080 °C-10−2.5 s−1 (0.35 < m < 0.43) and 1030 °C-10−3 s−1 (0.66 < m < 0.74) which located in the superplastic deformation zone in the new hot working map, the new HIPed superalloy exhibited superplasticity, and the elongation was 395 % and 410 %, respectively. Considering the hot working map and the microstructure evolution, the suitable hot working window was further optimized to be 1030–1080 °C and 0.001–0.005 s−1. At high strain rate and low temperature conditions, continuous dynamic recrystallization (CDRX) was the primary mechanism for dynamic recrystallization (DRX), while with the gradual decrease of strain rate, discontinuous dynamic recrystallization (DDRX) tended to occur and dominate the process. DDRX dominated under high temperature deformation condition.

Compressive Flow Behavior and Microstructural Evolution of Friction Stir Processed A356-5% B4C Composite

Abstract An Al-7Si-0.3Mg (A356) alloy reinforced with 5 % boron carbide (B4C) particulates was produced through squeeze casting technique at a temperature of 710°C. Friction stir processing (FSP) was employed on an A356-5% B4C composite with optimized parameters, viz., tool advancing speed of 15 mm/min and tool rotation speed of 250 r/min for one pass and two passes. High-temperature flow behavior of the FSPed A356-5% B4C composite was investigated by strain rate jump (1 × 10−3 to 5 × 10−1 s−1) compression tests using a thermomechanical simulator at temperatures of 470°C and 500°C. Strain rate jump tests revealed superplastic region with strain rate sensitivity index m = 0.4 in the lower strain rate regime of 1 × 10−3 to 5 × 10−2 s−1. However, the value of m reduced to 0.3 upon two-pass FSP. The reduction in m is attributed to the more uniform redistribution of hard Si particles throughout the composite, as examined by microstructure evolution in scanning electron microscopy, linked with energy-dispersive spectroscopy and electron-backscattered diffraction facility.

Superplastic behavior of a fine-grained Mg−Gd−Y−Ag alloy processed by equal channel angular pressing

An extruded Mg−6Gd−3Y−1.5Ag (wt%) alloy was processed by 6 passes of equal channel angular pressing (ECAP) at 553 K using route Bc to refine the microstructure. Electron back-scattered diffraction (EBSD) analysis showed a fully recrystallized microstructure for the extruded alloy with a mean grain size of 8.6 µm. The microstructure of the ECAP-processed alloy was uniformly refined through dynamic recrystallization (DRX). This microstructure contained fine grains with an average size of 1.3 µm, a high fraction of high angle grain boundaries (HAGBs), and nano-sized Mg5Gd-type particles at the boundaries of the DRXed grains, detected by transmission electron microscopy (TEM). High-temperature shear punch testing (SPT) was used to evaluate the superplastic behavior of both the extruded and ECAP-processed alloys by measuring the strain rate sensitivity (SRS) index (m-value). While the highest m-value for the extruded alloy was measured to be 0.24 at 673 K, the ECAP-processed alloy exhibited much higher m-values of 0.41 and 0.52 at 598 and 623 K, respectively, delineating the occurrence of superplastic flow. Based on the calculated average activation energy of 118 kJ mol−1 and m-values close to 0.5, the deformation mechanism for superplastic flow at the temperatures of 598 and 623 K for the ECAP-processed alloys was recognized to be grain boundary sliding (GBS) assisted by grain boundary diffusion.

Superplasticity of a hot rolled Mg–3Zn–0.5RE–0.5Zr (ZEK300) alloy

Superplasticity of a hot rolled fine-grained Mg–3Zn–0.5RE–0.5Zr (ZEK300) alloy was assessed via shear punch testing (SPT). The deformation behavior of the alloy having a grain size of 4.5 μm exhibited regions I, II and III, typical of superplastic materials. In region II, the strain rate sensitivity indices of ZEK300 alloy were obtained as 0.51, 0.48 and 0.41 at 350, 400 and 450 °C, respectively. The average activation energy of 87.6 kJ mol–1 implies that the principal mechanism of deformation is grain boundary sliding (GBS) facilitated by grain boundary diffusion.

Strain rate sensitivity of low-temperature superplastic cold-rolled medium Mn steel with ultrafine equiaxed dual-phase microstructure

This study reports the evolution of strain rate sensitivity (SRS) a novel 3.6Al Medium Mn steel (MMS) with an ultrafine equiaxed dual-phase structure. By varying temperature and strain rate, a new bidirectional reciprocating strain rate jump experiment was conducted to evaluate the effect of strain rate on the SRS index m. Tensile tests were conducted at high-temperature deformation to obtain the maximum m-value, and microstructure were characterized. The results demonstrate that at temperatures ranging from 700 °C to 750 °C and strain rates from 2.5 × 10−4 to 1.6 × 10−2 s−1, the m-value decreases monotonously with increasing strain rate, and the decreasing trend slows down. During high-temperature deformation, the m-value is more sensitive to changes in strain rate. At 700 °C, the grain refinement increases the m-value with the increase in strain. Interestingly, MMS exhibited new γ fiber and brass texture during deformation at 750 °C, with a larger m-value and better superplasticity (∼1295%).

Mechanical behavior of nanorubber reinforced epoxy over a wide strain rate loading

Nanorubber/epoxy composites containing 0, 2, 6 and 10 ​wt% nanorubber are subjected to uniaxial compression over a wide range of strain rate from 8 ​× ​10−4 s−1 to ∼2 ​× ​104 s−1. Unexpectedly, their strain rate sensitivity and strain hardening index increase with increasing nanorubber content. Potential mechanisms are proposed based on numerical simulations using a unit cell model. An increase in the strain rate sensitivity with increasing nanorubber content results from the fact that the nanorubber becomes less incompressible at high strain, generating a higher hydro-static pressure. Adiabatic shear localization starts to occur in the epoxy under a strain rate of 22,000 s−1 when the strain exceeds 0.35. The presence of nanorubber in the epoxy reduces adiabatic shear localization by preventing it from propagating.

Superplasticity in a coarse-grained as-cast magnesium alloy

Superplasticity of a coarse-grained cast Mg–2.5Gd–0.5Zr alloy was investigated by assessing the strain rate sensitivity index (m-value) through the shear punch testing (SPT) method in the temperature range of 623–748 K and shear strain rate range of 2.8 × 10−3–2.2 × 10−2 s−1. The initial as-cast grain size of about 150 μm was reduced to about 3.5 μm at the end of the test. This severe grain refinement caused by dynamic recrystallization (DRX) facilitated superplasticity in the studied cast alloy. According to the respective m-values of 0.51 and 0.53 obtained at 698 and 723 K, and the activation energy of 80 kJ mol−1, the prevailing mechanism of deformation was suggested as grain boundary sliding (GBS) controlled by grain boundary diffusion.

High-strain-rate superplasticity and microstructural evolution in ECAP-processed Mg–6.5Y–1.2Er–1.6Zn–0.5Ag alloy

A warm equal-channel angular pressing (ECAP) procedure was applied to a new Mg–6.5Y–1.2Er–1.6Zn (WEZ612)–0.5Ag alloy with a long-period stacking ordered (LPSO) phase. The microstructure, superplasticity, and deformation mechanism of the WEZ612–0.5Ag alloy were then systematically investigated. Three different precipitation phases formed in the alloy with trace Ag addition, namely LPSO, γ, and nanoprecipitate phases. A remarkable elongation of 726% was attained at 623 K and a strain rate of 0.01 s−1. The strain rate sensitivity index (m) and activation energy (Q) under these deformation conditions were 0.461 and 133.08 kJ mol−1, respectively. These m and Q values confirm that the primary deformation mechanism of the WEZ612–0.5Ag alloy at 623 K was grain boundary sliding assisted by lattice diffusion. The highly stable LPSO phases, γ precipitates, and nanoprecipitates synergistically improved the superplasticity of the alloy by retarding crack propagation and grain growth and by promoting the basal plane slip.

Revealing hot deformation behavior and optimizing process parameters of as-cast Ti–5Al–5Mo–5V–1Cr–1Fe alloy

Hot compression tests are carried out at temperatures ranging from 900 °C to 1050 °C, strain rates ranging from 0.001s−1 to 1s−1 and deformation degree ranging from 60% to 70% on the Gleeble-3500 thermal simulator. Strain-compensated Arrhenius constitutive model, activation energy maps, hot processing maps and microstructure evolution are used to analyse the flow behavior of as-cast Ti-55511 alloy. At low temperature (≤950 °C), the flow softening behavior is mainly related to cracks, deformation bands (DBs) and DRV at high temperature (≥1000 °C) and high strain rate (≥0.1s−1), and DRV at high temperature (≥1000 °C) and low strain rate (≤0.01s−1). DBs and cracks are the main forms of hot deformation instability. There is a competitive relationship between DRV and DBs. Under high strain rate (≥0.1s−1), DBs are more likely to occur. Under low strain rate (<0.1s−1), the DBs are restrained by DRV. The simultaneous activation of different slip systems causes the rotation of different areas in the grains to form DBs. The DRX grains in the DBs are produced by continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX), but the DRX grains in the sample without DBs are produced by CDRX. The analysis of hot activation energy (Q), strain rate sensitivity index (m), power dissipation efficiency (η), flow instability parameter (ξ(ε˙)) and microstructure analysis showed that 1000°C–1050 °C/0.001s−1–0.01s−1 are an optional processing window. And the proportion of recrystallization is the highest at strain of 1.2 and 1000 °C/0.01s−1, so it can be considered as the optimal processing parameter.

Hot Tensile Deformation Behavior and Constitutive Models of GH3230 Superalloy Double-Sheet.

In this paper, the hot tensile deformation of a GH3230 superalloy double-sheet was conducted under deformation temperatures ranging from 1123~1273 K and strain rates ranging from 0.001~0.2 s-1. The flow behavior of the GH3230 superalloy double-sheet was analyzed in detail. The hot tensile deformation process of the GH3230 superalloy double-sheet includes four stages of elastic deformation, strain hardening, steady state and fracture. The true stress decreases with the increasing deformation temperature and decreasing strain rate. The variation of the strain rate sensitivity index and strain hardening index with processing parameters were discussed. The average apparent activation energy for hot tensile deformation is 408.53 ± 46.96 kJ·mol-1. A combined Johnson-Cook and Hensel-Spittle model considering the couple effect of strain hardening, strain rate hardening and thermal softening was established to describe the hot tensile behavior of the GH3230 alloy double-sheet. Compared to Johnson-Cook model and Hensel-Spittle model, this model has the highest predicting accuracy. The average absolute relative error of true stress between the experimental and the predicted is only 2.35%.

Characteristic Flow Behavior and Processing Map of a Novel Lean Si Spring Steel for Automotive Stabilizer Bars

The spring steel for automotive stabilizer bars has a great responsibility in that its quality directly affects the stability, safety, and comfort of vehicle operation. The isothermal thermal compression behavior of a novel lean Si spring steel that was used to manufacture an anti-roll bar was investigated with a DIL805A/D quenching thermal dilatometer in this research. A hyperbolic sine type of constitutive model was established, and hot processing maps were produced to evaluate the experimental steel’s hot workability properties. The experimental results suggest that dynamic recrystallization (DRX) preferentially occurs at a low strain rate and high thermal processing temperature, while the processing maps of the experimental steel are susceptible to strain. The instability regions increase as the strain increases. The processing maps’ stable and instable domains should be decided upon comprehensive analysis of the instability criterion, power dissipation efficiency, and strain rate sensitivity index. The optimum parameters of hot processing for the experimental steel at various strains are that the deformation temperature of 1000–1150 °C and the strain rate of 0.1, approximately.

Study on the Microstructure Evolution and Mechanical Properties of Cu/Cu41Sn11/Cu Solder Joint During High-Temperature Aging

Abstract The paper focused on the changes in microstructure and mechanical properties of the full Cu41Sn11 solder joint (Cu/Cu41Sn11/Cu) during isothermal aging at 420 °C. It was motivated by potential applications of Cu–Sn intermetallic compounds (IMCs) solder joint in third-generation wide bandgap semiconductor devices. Experimental results revealed that the Cu41Sn11 phase was unstable under high-temperature conditions, the full Cu41Sn11 joint transformed into the full α(Cu) joint (Cu/α(Cu)/Cu) joint at 150 h during thermal aging. The formed α(Cu) phase was a Cu solid solution with inhomogeneous Sn atomic concentration, and its crystal structure and orientation were consistent with the original Cu plate. The conversion of the Cu41Sn11 to α(Cu) was accompanied by the formation of voids due to the volume shrinkage effect, predominantly near the middle of the solder joint interface. The α(Cu) solder joint presented a decrease in strength but an increase in strain rate sensitivity index compared to the Cu41Sn11 solder joint. Furthermore, the strain rate sensitivity index of α(Cu) and Cu41Sn11 is lower than that of ordinary Sn solders. After the shear test, the fractures that occurred in Cu41Sn11 grains were brittle, while the fractures in α(Cu) grains were ductile.

Strain Hardening Exponent and Strain Rate Sensitivity Exponent of Cast AZ31B Magnesium Alloy

The flow curves of as-cast AZ31B magnesium alloy during high temperature deformation were obtained with a thermal compression test, and the effects of deformation amount, grain size, strain rate, and deformation temperature on the flow stress, strain rate sensitivity index, and strain hardening index were analyzed. The results showed that deformation and grain size were negatively correlated with both the strain rate sensitivity index and strain hardening index. The increase in strain rate increased the strain hardening index but made the strain rate sensitivity index show an opposite trend. Increasing temperature reduced the strain rate sensitivity index and strain hardening index but, when the temperature exceeded 700 K, the strain rate sensitivity index was no longer affected by temperature. Since the strain rate sensitivity index m and strain hardening index n are important parameters for measuring the plastic deformation of metal materials, this study has great significance for guiding the selection of process parameters in the plastic processing of as-cast AZ31 magnesium alloy.

Indentation creep deformation behavior of local zones for X70 girth weld

Creep failure of in-service pipes is a fundamental engineering issue. Since the girth weld joint is a weak link in the pipeline, the creep deformation behavior of the girth weld must be carefully researched. This research sheds light on determining the local creep properties of girth welds. The creep deformation behavior of local zones for the X70 girth weld was studied using nanoindentation creep experiments with maximum nano-indenter loads of 10 mN, 50 mN, and 100 mN. The load dependency and creep mechanism of local zones for the X70 girth weld were investigated through creep properties such as creep strain rate, creep stress, creep stress index, and strain rate sensitivity index. In addition, the microstructures of base material (BM), root welding zone (RWZ), and heat-affected zone (HAZ) were studied to determine the differences in creep properties for the girth weld's local zones. The creep displacement of BM, RWZ, and HAZ follow the RWZ > BM > HAZ sequence as the maximum load increases. The creep stress, on the other hand, exhibits HAZ > RWZ > BM sequence. Furthermore, RWZ and HAZ have a higher load dependency of creep stress index and strain rate sensitivity than BM.

Enhancing the tensile properties of Sn-Zn-Ag lead-free solder alloy by loading MgO nanoparticles and irradiation

Lead-free composite solders has attracted more attention as they are required in the microelectronics industry to assure good electrical connections and the best mechanical response between integrated circuit devices and the substrate. The mechanical mixing technique was used to prepare the plain (Sn-5.3 wt% Zn-1 wt% Ag, SZA531) and composite solder (SZA531/0.5 wt% MgO), while MgO nanoparticles were synthesized by sol-gel technique. The aim to investigate the effects of loading 0.5 wt% MgO NPs and [Formula: see text]-irradiation doses (0–2.0 MGy) on the tensile properties of plain solder at different strain rates (ε•). The microstructural properties revealed that MgO was pure, crystalline, and had a nanoparticle-like morphology with an average crystallite size of 9.61 nm. Plain and composite solders contained β-Sn, Zn, and Ag, as well as some intermetallic compounds, Ag3Sn and AgZn. Loading MgO refined [Formula: see text]-Sn and Ag3Sn, while AgZn particles were partially dissolved. The thermal analysis reported that the melting point slightly increased from 206.1°C with SZA531 to 208.7°C when loaded which confirms the good solderability of composite solder. The tensile properties revealed that ultimate tensile strength and the tensile toughness increased with increasing ε•, dose of γ-rays, and MgO loading, while ductility decreased. The strain rate sensitivity index ( m) decrease with increasing the dose and MgO loading because of the decrease in the resistance to necking. These results were interpreted based on Orowan strengthening and dislocation strengthening.

Structural Performance of Fusion Weld Based on Weld Parameters and Strain Rate in High-Density Polyethylene

Abstract Use of high-density polyethylene (HDPE) material has increased considerably in the last few decades to form long installation lengths of buried infrastructure such as water mains, sewers, and gas pipelines. These pipes are available in standard length sections and joined together to get customized length using fusion-welding techniques. The strength of welds highly depends on welding parameters such as temperature, heat, and soaking time. The structural performance also varies with respect to strain rate. In this paper, the strength of fusion-welded HDPE material is analyzed under different welding parameters and variable strain rates of welded and unwelded samples. An additional important aspect of the present research is to study the structural performance of fusion welds made between extruded HDPE pipes and injection molded HDPE fittings, i.e., elbows, Tee joints and closed-end cap connections. The strain-rate sensitivity index is measured with variable strain rates during tensile testing. The findings of this research can help in understanding and improving the structural performance of HDPE fusion-welded joints in various applications.

Flow behavior and microstructure evolution of Al-3.65Cu-0.98Li (wt%) alloy during hot deformation

The phenomenological constitutive model, processing map and microstructure evolution of Al-3.65Cu-0.98Li (wt%) alloy were studied by means of isothermal compression tests conducted on a Gleeble-3500 isothermal simulator in the temperature range of 350 °C−500 °C and strain rate range of 0.01 s−1–10 s−1 and EBSD. The strain compensated Arrhenius model describes the flow curves accurately with a relative error of 0.9898 and an average absolute relative error of 4.70%. The plastic capability was characterized by strain rate sensitivity index, and it has the positive relation with temperature and negative relation with strain rate. The processing map was constructed, the instable deformation window and optimal hot working window of this alloy was identified to be 350 ∼ 455 °C & 0.37 ∼ 10s−1 and 440 ∼ 500 °C & 0.01 ∼ 0.368s−1, respectively. Moreover, the dynamic recrystallization occurs more violently at lower strain rate, and most portion were transformed into substructure with increasing strain rate, which was nearly vanished at the strain rate of 10 s−1. The geometric necessary dislocation distributions under different temperatures and strain rates were analyzed. More uniform distributed dislocation cell structures were observed at high temperature with low strain rate conditions and intensive dislocation and more pileups occurs at the contrary conditions.