Shear Punch Test Research Articles

Enhanced mechanical behavior and texture development of Al/Al2O3 composites produced by spark plasma sintering (SPS) and vacuum hot pressing (VHP) followed by simple shear extrusion (SSE)

Green compacts of Al-3vol% Al2O3 composites were produced by powder metallurgy (PM) and subsequently processed by spark plasma sintering (SPS) and vacuum hot pressing (VHP). The manufactured samples were then processed by the simple shear extrusion (SSE) process. Three SSE dies with the distortion angles (α) of 8°, 10° and 22.5° were used in this study. The SPS-ed/SSE-ed specimens for α = 10° were successfully deformed up to sixteen passes, while the VHP-ed/SSE-ed samples failed after six passes. In addition, the SPS-ed sample for α = 22.5° only underwent one pass of SSE. The SPS-ed/SSE-ed composites resulted in the highest shear punch test (SPT) load, modified porosity amount and the best reinforcement redistribution, as compared to the vacuum sintering and stir-casting manufacturing methods, which was confirmed by microstructure evaluation and porosity measurements. The crystallographic texture of the SPS-ed/SSE-ed composites for α = 10° was investigated in the sixteenth pass using the X-ray method. The results of texture development showed the very low intensity of shear and cube texture with {100} <011> and {001} <100> components, subsequently.

Shear mechanical properties of AISI 316L stainless steel processed by unidirectional/cross rolling and annealing treatment

The effects of cold rolling routes followed by annealing on the mechanical properties of AISI 316L stainless steel were characterized. Both unidirectional and cross rolling methods were applied and the evolutions of shear mechanical properties by shear punch testing (SPT) and hardness during reversion/recrystallization annealing were systematically investigated. It was revealed that cross rolling promotes strain-induced martensitic transformation during rolling and also enhances grain refinement during annealing, leading to improved hardness and ultimate shear strength (USS). The variation of USS with annealing time was similar to that of Vickers hardness (HV), so that the simple and useful equation of USS = 0.196HV was derived. Moreover, by relating the USS to the ultimate tensile strength (UTS) via von Mises criterion, the finalized equation of HV = 2.95UTS was obtained, confirming the empirical formula of HV = 3UTS for steels. Accordingly, this work can shed light on the application of SPT for investigating the mechanical properties of austenitic stainless steels.

Enhancing mechanical and microstructural properties of Pb composite anode by the addition of W-Co3O4 ceramic particles fabricated by Accumulative Roll Bonding

In this research, the accumulative roll bonding (ARB) technique was employed as a severe plastic deformation method to manufacture a unique bi-metal Pb/W composite reinforced by Co3O4 ceramic oxide. For this purpose, composites with different amounts of reinforcement particles (0.25, 0.5, 1, 1.5, and 2 wt%) were successfully produced using the ARB process (up to 10 cycles). Also, the mechanical properties were evaluated using microhardness, tensile, and shear punch tests. For microstructural investigations, the X-ray diffraction method (XRD), transmission electron microscopy (TEM), and fractography analysis by scanning electron microscopy (SEM) were employed. The Pb-0.5%W/Co3O4 following 10 ARB cycles exhibited optimal mechanical and microstructural properties. For this composite, the tensile strength showed a markable increase of 2.17 times, yield strength by 4.7 times, shear strength by 3.6 times, and hardness by 4.2 times compared to the pure Pb sample subjected to the same ARB cycles. However, the strain was reduced by 3.85 times. These enhanced properties are also followed by increased stiffness and improved anode dimensional stability, creep resistance, and operational lifespan.

Microstructure and Microhardness Evolution of Mg-8Al-1Zn Magnesium Alloy Processed by Differential Speed Rolling at Elevated Temperatures.

Mg-8Al-1Zn magnesium alloy was successfully processed using deferential speed rolling (DSR) at temperatures of 400 and 450 °C for thickness reduction of 30, 50, and 70% with no significant grain growth and dynamic recrystallization. Using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), the rolled microstructures were examined. Although the results indicate a slight reduction in grain size from the initial condition, the DSR processing of alloy at an elevated temperature was associated with a significant number of twins and a distribution of the fine particles of the second phase. The strength in terms of microhardness measurements and strain hardening in terms of shear punch testing was significantly improved in the rolled microstructure at room temperature. The existence of twins and widely distributed second-phase fine particles at twin boundaries reflected positively on the extent of the elongations in terms of shear displacements when microstructures were tested at elevated temperatures in the shear punch testing.

Tribological and magnetic properties of AlCrCuFeNi high entropy alloy fabricated by MA-SPS

In this study, the AlCrCuFeNi high entropy alloy (HEA) with two FCC and BCC crystalline phases was successfully synthesized through 60 h of mechanical alloying (MA) followed by spark plasma sintering (SPS). After the sintering process, these solid solutions underwent further transformation, resulting in the coexistence of FCC, BCC, and σ phases. This highlights the considerable significance of considering mixing enthalpy in the context of determining phase formation in HEAs. The mechanical properties of the bulk specimen were assessed using nano-hardness, micro-hardness, and shear punch tests, yielding mean values of 781 ± 10 Vickers for nano-hardness and 762 ± 10 Vickers for micro-hardness. Additionally, the alloy exhibited a yield tensile strength of 367 ± 4 MPa and an ultimate tensile strength of 445 ± 5 MPa. Examination of fracture surface of the sintered HEA illustrated cleavage fractures, likely attributed to the presence of the BCC phase. Furthermore, the tribological behavior of the alloy was investigated through pin-on-disk wear tests at different temperatures (ambient, 250 °C, and 500 °C). The results indicated a shift in the wear mechanism and an increase in the coefficient of friction with rising temperature. These changes correlated with the temperature-dependent increase in the volume fraction of the FCC phase, as observed in XRD patterns, suggesting its potential influence on altering the wear mechanism. Eventually, the magnetic behavior of the alloy was analyzed using vibration sample magnetometer (VSM) analysis, confirming its ferromagnetic behavior.

Microstructure and properties of ZrB2-reinforced aluminum matrix composites consolidated by ECAP process

In this research work, the effects of mechanical alloying and subsequent compaction by ECAP on the microstructural, physical, and mechanical properties of Al-ZrB2 metal matrix composites (MMCs) were evaluated. To prepare composite powders, a mixture of Al and ZrB2 particles was mechanically alloyed at various times of 1, 6, 12, 18 and 24 h. SEM micrographs indicate that the size of the obtained particles decreases by increasing the time of mechanical alloying up to 18 h. However, after this time, increasing the time of mechanical alloying has led to an increase in the size of the particles. By means of mechanical alloying for 18 h, the average size of fine particles reached 823 nm, while coarse particles were 8 μm. The calculation via the use of XRD examination implies that the mean crystallite size of powder decreased from about 68 nm to 31 nm and 26.8 nm, for Al and Al-5%ZrB2 samples, respectively, while lattice strain increased from 0.25% to 0.64% and from 0.3% to 0.73% after 1 h to 24 h milling of same samples, respectively. However, the rate of crystallite size reduction after 12 h of mechanical alloying is gradually reduced, and that is reached its lowest level after 18 h. After that, increasing the time of mechanical alloying has led to a saturation in the lattice strain. In continue, the resulting composite powder was heated, consolidated and turned into bulk material by warm equal channel angular pressing (ECAP) at the temperature of 250 °C. The resultant optimum composite has been characterized by EDS elemental mapping. Microhardness measurements and shear punch tests were performed to evaluate the mechanical properties of the unreinforced and composite samples after the ECAP process. The Al-ZrB2 MMC bulk samples subjected to ECAP, with a ZrB2 amount of 5 wt%, had a relative density, hardness, and ultimate shear strength of 99.3%, 170 HV, and 151 MPa, respectively, using powders which have been mechanically alloyed up to 24 h.

Implementing shear-punch test for the assessment of mechanical properties of cast and selective laser melted AlSi10Mg alloys

Implementing shear-punch test for the assessment of mechanical properties of cast and selective laser melted AlSi10Mg alloys

Optimization of insert roughness and pouring conditions to maximize bond strength of (Cp)Al-SS304 bimetallic castings using RSM-GA coupled technique

The integration of ferrous and non-ferrous materials represents a breakthrough in materials technology, enabling the fabrication of functionally graded lightweight components with enhanced properties. In this study, a Box-Behnken design of experiments was employed to investigate the effects of pouring temperature, insert temperature, insert thickness, and surface roughness on the bond strength of bimetallic components. Shear punch tests were conducted to assess the maximum loads before fracture, with the highest bond strength of 17.04 MPa achieved under specific processing conditions. The presence of intermetallic compounds, including Fe2Al5, FeAl2, and Fe4Al13, contributed to the observed increase in reaction layer thickness. Response surface methodology revealed concentric responses for pouring temperature and surface roughness with an optimal predicted bond strength of 18.02 MPa. Further optimization using Genetic Algorithm resulted in a maximum bond strength of 19.20 MPa. These findings demonstrate the potential for producing high-performance bimetallic components tailored for applications in various industries.

Effect of processing environment during friction stir processing of AZ31/(ZrO2+CuO)p surface composite on the mechanical and tribological performance

In this work, the AZ31 Mg alloy was subjected to friction stir processing (FSP) by adding CuO and ZrO2 particles. The main aim of this study was to increase the tribological and mechanical behavior of AZ 31/(CuO + ZrO2)p surface composite in air and water. The influence of the processing media on the microstructural modification and mechanical properties of the developed composites is assessed via optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), shear punch testing (SPT) and Vickers hardness testing. It had been found that finer grains are produced in the stir zone due to the reduction in heat input for the water-cooled composite relative to the air-cooled composite. Indeed, the water-cooling system acted as a hamper and suppressed grain growth, which consequently resulted in the enhancement of the mechanical and tribological behavior of the AZ 31/(CuO + ZrO2)p surface composite.

Influence of Gd and Li additions on the microstructural evolution and mechanical properties of hot-rolled AZ31 alloy

Thermomechanical processing and alloying are two common approaches to enhance the mechanical properties of Mg. Thus, the effects of Gd and Li elements, as two elements with various properties, on the microstructure and mechanical properties of a hot-rolled and consequently annealed AZ31 alloy were analyzed. The microstructure and texture was analyzed by scanning electron microscopy and electron back scattered diffraction. Accordingly, the mean grain size of 46 μm in the AZ31 alloy was reduced to 41 and 26 μm in the AZ31–2.9Gd and AZ31–2.3Li alloys, respectively. Grain refinement occurred due to continuous dynamic recrystallization and twinning-induced recrystallization in all of the alloys. Textural evolution showed that neither Gd nor Li could inhibit the occurrence of basal texture. Room temperature mechanical properties were assessed by using the shear punch test (SPT) method. The results exhibited that the strength of the AZ31 alloy was improved from 116 MPa to 139 MPa and 141 MPa by respective additions of Gd and Li. Strength enhancement was mainly attributed to the grain boundary strengthening and second-phase particles hardening. One promising observation was the simultaneous enhancement of shear strength and ductility by the addition of Gd and Li. This observation was ascribed to the more uniform distribution of second-phase particles and lower volume fraction of twins as potential sites for crack initiation. As long as mechanical strength is concerned, results favor the use of Li as alloying element in Mg, especially due to the more noticeable lightweighting potential compared to Gd.

Grain size dependent mechanical properties of CoCrFeMnNi high-entropy alloy investigated by shear punch testing

The effect of grain size on the mechanical properties of an equiatomic CoCrFeNiMn high-entropy alloy (HEA) was investigated by shear punch testing (SPT) as a miniature test method and Vickers hardness measurements. A Hall–Petch relationship was developed for the dependency of shear yield stress (SYS) on the average grain size (D). The correlation of the SYS and ultimate shear strength (USS) to the tensile yield stress (TYS) and ultimate tensile strength (UTS) values were also studied. A wide range of grain sizes was obtained by the thermomechanical processing of cold rolling and annealing at hot temperatures, where the primary recrystallization and grain growth phenomena were used for grain refinement and grain coarsening, respectively. Based on the obtained results and literature data, the Hall–Petch relationships of SYS = 88.9 + 301.1/√D and TYS = 167 + 520/√D were proposed, respectively. Moreover, the correlation of tensile test properties with those predicted by the shear punch test was also investigated. Accordingly, the relationships of TYS = 1.76 × SYS and UTS = 1.33 × USS were obtained, where the former is in excellent agreement with the von Mises yield criterion based on the plasticity theory, and the latter is influenced by the work-hardening behavior of the material and dynamic phenomena during plastic deformation.

3D Printing of Bone Scaffolds Based on Alginate/Gelatin Hydrogel Ink Containing Bioactive Glass 45S5 and ZIF‐8 Nanoparticles with Sustained Drug‐Release Capability

Herein, 3D printing coupled with drug‐release systems introduces many advantages to bone‐regenerative medicine. In this research, hydrogel‐based nanocomposite inks comprising alginate/gelatin (Alg/Gel) matrix supplemented with mesoporous bioactive glass (MBG) and zeolite‐imidazole framework‐8 (ZIF‐8) nanoparticles are presented. A fixed wt% of mixed nanoparticles at MBG/ZIF weight ratios of 85:15 and 70:30 is added to Alg/Gel to prepare nanocomposite inks. All inks have shear‐thinning behavior, facilitating scaffolds’ 3D printing via extrusion. Scaffolds’ 3D spatial and nanocomposite microstructures are confirmed using field‐emission scanning electron microscope and energy‐dispersive X‐ray (FESEM/EDX) and Fourier transform infrared (FT‐IR). Shear punch testing indicates an enhanced shear strength of 85:15 samples in both dry (9.49 ± 0.23 MPa) and wet conditions (1.19 ± 0.16 MPa). After 1 month, nanocomposite scaffolds have a higher degradation rate (65%) than Alg/Gel (50%) in phosphate‐buffered saline. In vitro drug‐release study using UV–visible spectrophotometry exhibits a similar prolonged release profile for 85:15 and 70:30 nanocomposites compared to Alg/Gel. Due to its better mechanical performance, 85:15 is used for bioactivity and cellular tests. MBG provides bioactivity in simulated body fluid by the rapid development of hydroxyapatite validated by FESEM/EDX, XRD, and FT‐IR. Nanocomposite scaffolds exhibit significantly higher MG‐63 cell viability (&gt;90%) than Alg/Gel. Finally, these scaffolds provide a potential additive‐manufacturing solution to bone tissue regeneration.

Microstructural evolution in shear-punch tests: A comparative study of pure Cu and Cu-Cr alloy

Understanding the mechanisms behind microstructural evolution during shear deformation has been a long-standing area of interest. However, establishing a connection between microstructure, mechanical properties, and the extent of shear deformation is challenging and requires refined experimental approaches. Shear-punch testing (SPT) provides a controlled method to introduce shear into small volumes of material that later can be subjected to detailed microstructural characterization. In this study, we utilize an SPT device to induce shear deformation to pure copper (Cu) and a binary copper-chromium (Cu-Cr) alloy. Electron backscatter diffraction and transmission electron microscopy were used to study the mechanisms of plastic deformation after SPT. Our results indicate that shear deformation of pure Cu produces a dense network of intercepting microshear bands upon sustained deformation. Twin boundaries in annealed Cu undergo transformation into high-angle grain boundaries due to simultaneous deviation from the axis-angle pair condition of 60° misorientation on [111] direction. The presence of 50 vol% Cr particles in the soft Cu matrix altered the shear deformation mechanism. Preferential deformation of the Cu matrix in Cu-Cr alloy led to accelerated shear-induced formation of low and high-angle grain boundaries and subsequent grain refinement. Comparatively, insignificant grain refinement occurred in pure Cu samples even at a strain ∼10 times larger (ε = 4.73) than that of the Cu-Cr case (ε = 0.42). This study sheds light on the microstructural evolution of Cu during shear deformation and highlights the significant influence of a hard second phase in modifying the microstructural response mechanisms of a softer matrix.

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.

Investigation of the strain rate sensitivity of CoCrFeMnNiTix (x = 0, 0.3) high-entropy alloys using the shear punch test

High entropy alloys (HEAs) are a novel class of metallic materials that exhibit a unique blend of properties due to their chemical composition and atomic arrangement. This research aims to investigate the strain rate sensitivity (SRS) of two HEA CoCrFeMnNiTix (x = 0, 0.3) alloy compositions through the use of shear punch testing. This method has been proven to provide reliable results for both HEA materials, including the CoCrFeMnNiTi0.3 HEA composition which was found to be inherently brittle and contained both σ-phase and Laves phase compounds with a hardness close to 14 GPa and a soft FCC phase. Among all the testing temperatures (room temperature to 400 °C) and deflection rates (0.2, 2 and 10 mm.min−1) used, only the CoCrFeMnNi HEA alloy was found to exhibit SRS at room temperature (m = 0.0333), while for the other HEA alloy variant and testing conditions, the SRS was found to be zero. From empirical correlations and finite element analysis (FEA), the calculated value for m ranged from 0.0333 to 0.0359, thus evidencing that the FEA simulations provide an accurate and suitable means of capturing the deformation behaviour of such alloys when subjected to shearing.

Shear punch testing for evaluation of mechanical properties of post heat-treated Inconel 718 nickel-based superalloy fabricated by additive manufacturing

Shear punch testing, as a cost-efficient miniature testing technique for investigating the mechanical properties under shear loading conditions, was utilized for the first time to elucidate the effect of post heat-treatment on the mechanical properties of additively manufactured Inconel 718 superalloy. Homogenization heat treatment was performed for the dissolution of undesirable Laves phase; while the aging treatment was performed on both as-built and homogenized superalloys for age hardening by precipitation of strengthening phases such as γ˝ phase. Better aging response and consequently superior shear properties were obtained by aging from the as-built condition, which were ascribed to the high dislocation density and more homogeneously dispersed precipitates in the microstructure. Moreover, by comparing the shear yield stress (SYS) with the tensile yield stress (TYS) and ultimate shear strength (USS) with ultimate tensile strength (UTS), the relationships of TYS = 1.71 × SYS and UTS = 1.72 × USS were obtained, which reveal that the experimental data points follow the von Mises criterion. Accordingly, these simple and useful formulae are consistent with the general expectations from the plasticity theory, and hence, it is possible to estimate the tensile or shear properties by performing one of these tests.

Punching shear failure behavior of fine-grained ZK60 Mg alloy processed by a novel forward shear normal extrusion process at room and elevated temperatures

The shear punch test (SPT) of ZK60 Mg alloy hot deformed by a novel sever plastic deformation technique called the forward shear normal extrusion (FSNE) was carried out at room and elevated temperatures, and the influence of FSNE process temperature on shear deformation behavior was clarified. FSNE of Mg alloy was carried out at temperatures of 200 °C, 250 °C, 300 °C and 350 °C and then SPT behavior of deformed samples was studied at temperature range of 25–250 °C. The results demonstrated that the deformation behavior and mechanical properties during SPT were significantly affected by the initial microstructure owning to different temperatures of the FSNE process. The microstructures in 200 °C, 250 °C and 300 °C FSNE processed specimens were composed of coarse deformed grains and ultra-fine DRXed grains with a near fully DRXed structure in the highest temperature (350 °C). Basal plane intensity was the maximum value in the 200 °C FSNE processed specimen, whiles with increasing FSNE process temperature, the random crystallography orientation was gradually dominated. Mechanical properties results showed that the 350 °C processed specimen presented the superior RT shear properties with the ultimate shear strength (USS) of ∼ 159 MPa and peak shear strain (PSS) of 81% as well as the highest thermal stability. Shear failure surface was mainly composed of rollover, burnished, fractured and burr areas. The percentage of burnished area in punching-out specimens was affected by initial microstructure and strength and for the specimens having high strength, the percentage of this area was low. In each SPT process temperature, higher peak strain postponed rapture and resulted in higher burr area.

Anisotropy of mechanical properties and hardness homogeneity in the three orthogonal directions of a multi-directionally forged ZK60 Mg alloy

An extruded ZK60 Mg alloy was processed by multi-directional forging (MDF) for up to 9 passes at a temperature of 473 K. The microstructure, hardness homogeneity, texture, and mechanical properties of the alloy were examined on the transverse and longitudinal sections of the extruded and MDF-processed samples. Microstructural observations revealed that a fine-grained and homogeneous microstructure was achieved after 9 passes of MDF in all three mutually perpendicular planes (A, B, and C) of the processed billet. Mechanical properties were determined using the shear punch testing (SPT) method, and hardness homogeneity was studied by Vickers microhardness measurements. The ultimate shear strength (USS) decreased from 186.8 MPa in the as-extruded condition to 154.7 MPa after 3 MDF passes, due to the overcoming of texture softening to the strengthening by grain refinement. The ZK60 alloy showed anisotropic behavior in terms of USS and hardness, measured on the three A, B, and C planes after 3 and 6 MDF passes. The observed differences in the measured properties, however, almost vanished after 9 MDF passes because of homogeneity in the microstructure and texture. Vickers microhardness measurements revealed that the material has excellent uniformity in hardness throughout the billet after 9 MDF passes in all planes, due to a fully recrystallized homogeneous microstructure.

Toward understanding the effects of solution heat treatment, Ag addition, and simultaneous Ag and Cu addition on the microstructure, mechanical properties, and corrosion behavior of the biodegradable Mg–2Zn alloy

In this study, the effects of adding silver (0.2 and 0.6 wt%) and copper (0.1 wt%) antibacterial elements, on the microstructure, mechanical properties, and degradation behavior of the as-cast Mg–2Zn alloy were investigated. The obtained results indicate that both Ag and Cu showed significant grain refinement effects in the as-cast condition. The MgZn precipitates were formed in the as-cast Mg–2Zn–0.2Ag alloy, which contained a small amount of Ag. Increasing the Ag content to 0.6 wt% resulted in formation of the Mg54Ag17 phase. Simultaneous addition of 0.2 wt% Ag and 0.1 wt% Cu to the Mg–2Zn alloy caused the ternary Mg(Zn,Cu) precipitates to form. Solution-treated Mg–2Zn and Mg–2Zn–0.6Ag alloys had a single-phase microstructure, while some Mg(Zn,Cu) precipitates remained in the Mg–2Zn–0.2Ag–0.1Cu alloy after solution treatment. Shear punch test showed 15, 12, and 23% increases in ultimate shear strength values of the as-cast Mg–2Zn–0.2Ag, Mg–2Zn–0.6Ag, and Mg–2Zn–0.2Ag–0.1Cu alloys compared to the Mg–2Zn alloy, respectively. The hydrogen evolution rate of the as-cast Mg–2Zn–0.2Ag, Mg–2Zn–0.6Ag, and Mg–2Zn–0.2Ag–0.1Cu alloys were found to be 38, 90 and 70% higher than the as-cast Mg–2Zn alloy, respectively. However, the solution treatment reduced the degradation rate significantly. Hence, it was found in this investigation that adding Ag and Cu elements would be so effective for improving different properties of the Mg–Zn alloys by using appropriate solution heat treatment.

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.