Lower Flow Stress Research Articles

Numerical investigation of flash formation and asymmetrical cooling in resistance projection welding

In resistance projection welding, the softened material is squeezed out from the joint area. The two workpieces being joined together often have different geometries, leading to asymmetrical cooling. The flash formation and asymmetrical cooling are not well quantified in the literature. This study developed a coupled electrical-thermal-mechanical model with adaptive remeshing and glued contact activation techniques for projection welding of steel fitting to a steel shell. The model was used to calculate the evolution of temperature distribution in the fitting and shell for welds made under two different hold times. The cooling rates were then inputted into a literature model to predict the joint hardness values, which correlated well with the experimental data. Additionally, the main factors for the accurate prediction of flash shape and size were the use of temperature-activated glued contact and high-temperature flow stress. Specifically, a combination of no glued contact and low flow stress can lead to an overprediction of the flash geometry.

Improved hot workability of TiAl composite with core-shell structure via in-situ synthesized multi-phases ceramic particles

TiAl composite with core-shell structure was in-situ synthesized incorporating BN nanosheets and graphene oxide into TiAl alloy using SPS, and the hot deformation behaviors were subsequently investigated on a Gleeble-1500D thermal simulation machine. The microstructural evolution and the influence of ceramic particles on hot deformation were revealed using OM, SEM, TEM, and EBSD. The results demonstrated a refined microstructure of TiAl composite induced by ceramic particles providing extra nucleation sites for DRX, contributing to lower flow stress, with peak stresses of 387 and 360 MPa for TiAl alloy and TiAl composite deformed at 1200 °C/1s−1, respectively. Moreover, dislocation slip was inhibited by ceramic particles leading to dislocation pile-up, facilitating the nucleation and growth of DRX at lamellar colony boundaries and α2/γ interfaces. Notably, the “shell” composed of TiB2 and Ti2AlN nanoparticles coordinated the deformation of lamellar colonies with different orientations, improving the hot workability of TiAl composite.

Deformation behavior and microstructure of pure Mg during hot shear-compression

In this study, the deformation behavior and microstructure evolution of pure Mg under hot shear-compression deformation conditions are investigated using the “Shear-Compression Specimen” as a model, which provides theoretical guidance for the investigation of the principles of surface defects in the hot extrusion process. The results showed low flow stress corresponded to a high temperature and a low strain rate, temperatures between 350–450 °C and strain rate at 5 s−1 are the perfect hot deformation parameters. The deformation generates a special texture that is bent by 45° along the extrusion direction, weakening the strong basal texture structure created by extrusion. The deformed microstructure is fine and uniformly distributed. In summary, the surface of the material is forced to undergo a complex shear-compression deformation during the hot extrusion process, while the core belongs to a simple uniaxial extrusion deformation. In some specific deformation conditions, the difference between these two may produce some defects.

Processing Techniques and Metallurgical Perspectives and Their Potential Correlation in Aluminum Bottle Manufacturing for Sustainable Packaging Solutions

This study explores the potential of aluminum wine bottles as a sustainable alternative to traditional glass bottles, emphasizing their recyclability and environmental advantages. It reviews the potential use of Al-Mn-Mg 3xxx alloys in beverage can bodies and examines various applications of aluminum containers in packaging, including recyclable beverage containers. The manufacturing processes for aluminum bottles, including casting, rolling, punching, and deformation techniques, are discussed in detail, with a particular focus on their impact on mechanical properties and microstructure. The preference for 1xxx aluminum alloys in impact extrusion is explained, highlighting their lower flow stress and higher formability compared to 3xxx alloys, and the microstructural changes induced by various processing steps are analyzed. Challenges related to using recycled aluminum and their effects on mechanical properties and microstructure during aluminum bottle production are also addressed. One objective is to increase the proportion of recycled alloyed material used in aluminum bottle manufacturing. Depending on the technique employed, the fraction of alloyed recycled material can vary. The percentage of recycled alloyed material (3xxx series Al alloys) in cold backward impact extrusion could be raised by 60%. High-speed blow forming could facilitate the production of aluminum bottles with a recycled alloyed material ranging from 50 to 100% of the 3xxx series aluminum can body alloys. The high-speed drawing and ironing (DWI) process can produce large-format aluminum bottles (up to 750 mL), utilizing at least 90% of the recycled 3xxx series can body stock. Furthermore, the paper discusses the importance of optimized heat treatment designs in enhancing mechanical properties and controlling microstructural evolution in alloyed aluminum materials, such as 3xxx series alloys. The study concludes with a need for further research to deepen our understanding of the metallurgical aspects of aluminum bottle manufacturing and to optimize the use of recycled aluminum in packaging solutions, with a specific focus on improving mechanical properties and microstructural integrity. This comprehensive review aims to contribute to the development of more sustainable packaging practices in the beverage industry by providing insights into the interplay between manufacturing processes, mechanical properties, and microstructure of aluminum bottles.

Research on low flow stress and quantitative DRX analysis in B4C/Al composites with interfacial amorphous B2O3 layer

Hot deformation plays a crucial role in strengthening and toughening of aluminum matrix composites, but the high hot deformation resistance and the microstructure defects generated after deformation need to be solved urgently. In this paper, a new material, B4C@B2O3/Al composites, with the low melting point B2O3 phase at the interface, has been successfully prepared and the hot deformation behavior was studied in detail. By comparison, the hot deformation resistance and activation energy of the B4C@B2O3/Al composites is significantly lower than that of the B4C/Al composites. The softening mechanism of the B4C@B2O3/Al composites is mainly dynamic recrystallization (DRX) and the critical stress of DRX is much lower for the B4C@B2O3/Al composites than for the B4C/Al composites, while the volume fraction of DRX is higher than for the B4C/Al composites. Compared with the B4C/Al composites with similar particle content, the hot deformation temperature of the B4C@B2O3/Al composites decreases, but with high strength-plasticity compatibility (with tensile strength of 560 MPa and elongation of 4.2 %). This work provides an effective method to reduce the hot deformation resistance of the B4C/Al composites and explains the micro mechanism, guiding low-stress forming of the B4C/Al composites with high volume fraction and good mechanical properties.

Investigation of grain size and geometrically necessary dislocation density dependence of flow stress in Mg-4Al by using nanoindentation

Models for grain size dependence of flow stress typically ignore contributions from geometrically necessary dislocations (GNDs) in the grain boundary regions. Ashby had proposed the following equation for flow stress (τ) as a function of grain size (d) and effective plastic strain (ε¯): τ=τ0+C′Gbε¯d using an unknown empirical coefficient, C’, In this study, the coefficient, C’, and equation for the grain size dependence of flow stress were investigated in Mg-4Al using nanoindentation. C’ ranges from 1.4 to 7.11 that is related to the hardness difference (∆H0) between the adjacent grains as C′=0.62ΔH0. Ashby equation was used to predict uniaxial stress-strain curves in grain sizes of 55 µm, 187 µm, and 333 µm. The results showed lower flow stress and lower hardening rate compared to experimentally measured tensile stress-strain response. The discrepancy seems to be a result of hardening effect of SSDs. We propose a modified Ashby equation that takes into account the hardening effect of SSDs and GNDs separately, resulting in a better agreement between calculated and experimentally measured values. This analysis demonstrates estimation of uniaxial stress-strain response using nanoindentation measurements that captures effects of grain size, and strain hardening from SSDs and GNDs. The combination of the revised equation and nanoindentation method will enable rapid exploration of stress-strain response of a diverse range of single-phase polycrystalline alloys.

Effects of starch–fatty acid complexes with different fatty acid chain lengths and degrees of saturation on the rheological and 3D printing properties of corn starch

The effect of corn starch-fatty (CS-FA) complexes from varying carbon chain length and degree of unsaturation on the rheological and 3D printing properties of corn CS–FA complex gels. The CS-FA complexes with longer carbon chain lengths and lower saturation enhanced the ability of gels to bind water, promoting the formation of intermolecular hydrogen bonds. The CS-FA complexes inhibit retrogradation and increase the amount of bound water, thereby reducing the structural integrity and transforming the original skeleton structure into a flake-like structure. These changes in gel structure led to lower flow stress and storage modulus for CS-FA gels containing FAs with shorter carbon chain lengths and lower saturation, resulting in reduced “extrusion swelling” of the material and facilitating its extrusion. The decreased “extrusion swelling” of gel improved print line width and printing performance. The CS-FA complex gel-printed product with a 12-carbon chain FA has the greatest printing accuracy, thanks to its moderate G', flow stress, and viscosity. This study provides important information for the CS-FA complexes for the preparation of starch-based 3D printing materials.

Investigation on hot deformation behavior and quenching precipitation mechanism of 2195 Al-Li alloy

Al-Li alloys suffer from a narrow processing window. The hot deformation behavior of the ramp heating homogenized 2195 Al-Li alloy was investigated by hot compression test in the temperature range of 300–500 °C and strain rate range of 0.01–10 s−1, and the strain compensated Arrhenius constitutive relationship model and processing map of the alloy were established. The laws of Zener-Hollomon parameters on the age-hardening response and quenching sensitivity of the deformed alloy were analyzed. The quenching precipitation mechanism of the deformed alloy were revealed. The results showed that the hardness of the aged alloy tends to increase first and then decrease with increasing Z parameter, while the quenching sensitivity tends to decrease first and then increase. The quench-induced phases are precipitated under the induction of incoherent Al3Zr dispersoids within recrystallized grains. The boundary angle would affect the quenching precipitation behavior. It was also found that the types and amounts of second phases are significantly different between the homogenized and hot-deformed samples under slow cooling rate. The ramp heating homogenized 2195 Al-Li alloy after hot deformation at temperatures of 455–500 °C and strain rates below 1 s−1 possesses a lower flow stress, higher age-hardening response and smaller quenching sensitivity.

Dynamic phase transformation driven microstructure and texture development during deformation of Zr-2.5wt.%Nb in α+β phase field

This work demonstrates and explains how, during the hot deformation of a Zr alloy in the two-phase field, the texture developed in the α phase is influenced by that developed in the β phase. For this Zr-2.5wt.%Nb alloy was hot compressed in the α+β phase field (700, 750 and 800°C) at 0.1 s−1 to a true strain of 1.1. The microstructure and texture were characterized using scanning electron microscopy and electron backscatter diffraction. The flow curves showed a sharp drop in flow stress at ε≈0.01 due to plastic deformation induced α→β phase transformation. At 700°C, α-Zr developed 〈21¯1¯3〉 parallel to compression axis (||CA) (as is commonly observed in α-Zr system), whereas at 750 and 800°C 〈21¯1¯0〉||CA formed. At all studied temperatures, β-Zr developed {001}〈110〉 and {111}〈110〉 texture components that were shown to be dependent on the elongated morphology of the α-Zr grains and not on the α-Zr texture. From experimental observations and thermodynamic calculations of the free energy changes in absence and presence of stress, it was shown that the formation of 〈21¯1¯0〉α−Zr||CA occurred by migration of β-Zr into 〈21¯1¯3〉α−Zr followed by the reverse β→α transformation (through Burgers orientation relationship) driven by low flow stress in 〈21¯1¯0〉α−Zr and low Nb content in the transforming β-Zr. It was concluded that the presence of β-Zr with 〈001〉||CA and 〈111〉||CA is a necessary condition for the formation of 〈21¯1¯0〉||CA in α-Zr. In addition, temperature promotes the development of 〈21¯1¯0〉α−Zr through enhanced boundary mobility of β-Zr into harder α-Zr.

Investigation of the mechanisms on the abnormal features observed in thermal-mechanical testing of AA6061 under extrusion conditions

Hot extrusion is the most common forming technology for aluminium alloy AA6061 due to its good extrudability, and thus it is important to study its high-temperature deformation characteristics. In this study, three abnormal features are observed in thermal-mechanical testing under extrusion conditions of AA6061 specimens from one billet: 1) Two types of specimens with grey-coloured surface or silver-coloured surface appear after solution heat treatment (SHT); 2) The silver-coloured specimens show orange peel surface after hot compression tests; 3) The silver-coloured specimens have lower flow stresses than the grey-coloured specimens. This paper investigates the mechanisms behind the above abnormal features. A laser scanning confocal microscope is employed to examine the surface roughening, and electron back scatter diffraction is used to characterise microstructural changes. It is found that the main causes of the above behaviour are due to different initial grain morphologies and the evolution of dislocation density after SHT. The silver-coloured specimens initially have smaller columnar grains which undergo recrystallisation and extensive growth during SHT, and the dislocation density decreases significantly, leading to orange peel defect and low flow stress during compression tests, respectively. The grey-coloured specimens have larger columnar grains. After SHT, some grains undergo recrystallisation, but others still maintain the shape of the large columnar grains, and the dislocation density does not change significantly, resulting in surface oxidation with smooth surface after thermal-mechanical testing and 10–25 MPa (30–50%) higher flow stress compared to the silver-coloured specimens in compression tests.

Rewilding and the water cycle

AbstractRewilding is a radical approach to landscape conservation that has the potential to help mitigate flood risk and low flow stresses, but this remains largely unexplored. Here, we illustrate the nature of hydrological changes that rewilding can be expected to deliver through reducing or ceasing land management, natural vegetation regeneration, species (re)introductions, and changes to river networks. This includes major changes to above‐ and below‐ground vegetation structure (and hence interception, evapotranspiration, infiltration, and hydraulic roughness), soil hydrological properties, and the biophysical structure of river channels. The novel, complex, uncertain, and longer‐term nature of rewilding‐driven change generates some key challenges, and rewilding is currently relatively constrained in geographical extent. Significant changes to the water cycle that benefit people and nature are possible but there is an urgent need for improved understanding and prediction of rewilding trajectories and their hydrological effects, generation of the knowledge and tools to facilitate stakeholder engagement, and an extension of the geography of rewilding opportunities.This article is categorized under: Science of Water > Hydrological Processes Science of Water > Water Extremes Water and Life > Conservation, Management, and Awareness

MANIFESTATION OF SUPERPLASTICITY AT LOWER TEMPERATURES OF 1565CH ALLOY OF THE Al−Mg SYSTEM IN ULTRAFINE-GRAIN AND NANOSTRUCTURAL STATES

In this work, homogeneous nanostructured and ultrafine-grained (NS and UFG) states with an average grain size of 95 nm and 200 nm, respectively, are formed in the 1565ch alloy of the Al-Mg system. In both states, the microstructure is formed by a network of predominantly high-angle grain boundaries. It has been shown that an alloy with an NS and UFG structure formed at room temperature by high-pressure torsion (HPT) and at 200°C by equal-channel angular pressing according to the Conform scheme (ECAP-С) exhibits similar signs of superplastic (SP) behavior at low temperatures 250 …300 °С in the range of strain rates 5×10-4 s-1…10-2 s-1: elongation values were 170…560%, the rate sensitivity coefficient (m) was 0.3-0.73 at low flow stresses . The temperature range of stability of the strength characteristics of the 1565ch alloy in the NS and UFG states was established, both after thermal and deformation-thermal treatment. It is shown that the material in both studied structural states retains a high level of strength after deformation under SP conditions. The deformation relief formed on the working part of the NS and UFG samples of the 1565ch alloy at the stage of a steady-state SP flow is analyzed.

Low-Temperature Superplasticity of the 1565ch Al–Mg Alloy in Ultrafine-Grained and Nanostructured States

—Homogeneous nanostructured and ultrafine grained (NS, UFG) states with mean grain sizes of 95 and 200 nm, respectively, have been formed in a 1565ch Al–Mg alloy (Al–5.66Mg–0.81Mn–0.67Zn–0.09Zr–0.07Cr–0.04Ti–0.001Be–0.3(Fe + Si) wt %). Microstructure of both states is represented by grain boundaries with predominantly high-angle misorientations. The alloy, produced both by high pressure torsion at room temperature and equal channel angular pressing at 200°C using the Conform approach, exhibits superplasticity at low temperatures in the range 250–300°C and strain rates in the range of 5 × 10–4–10–2 s–1. Elongation values range 170–560%, while the rate sensitivity coefficient (m) varies from 0.3 to 0.73 at low flow stress for both NS and UFG structures. The temperature range for the stability of strength properties of the 1565ch alloy in NS and UFG states after thermal and thermal mechanical treatments has been determined. The material in both structural states maintains a high level of strength after undergoing deformation under SP conditions. The deformation relief formed on the gage surface of the NS and UFG specimens of the 1565ch alloy during the established SP yield stage has been analyzed.

Acoustic softening – investigation of the volume effect and introduction of amplitude strain parameter

Acoustic softening is a phenomenon where metals exhibit a lower flow stress when excited by a vibration at ultrasonic frequencies. This softening effect has been well documented in the literature, however, there are two areas that require further in-depth analysis. The first relates to the wide range of reported softening responses for the same alloy. The second relates to the use of coefficients and compensation factors when modeling the acoustic softening phenomenon in a complex forming processes. This study investigates the changes in softening response when altering specimen dimensions in ultrasonic assisted compression tests. Aluminum alloys (AA) 2024-O and AA7075-O were machined to different dimensions and compressed with ultrasonic assistance, to investigate the relationship between specimen volume and softening response. An inverse relationship between softening magnitude and sample volume was found. When relating this to acoustic energy density and stress, the values are invariant because the standard acoustic equations cannot account for changes in specimen height. The amplitude strain parameter, amplitude divided by the current specimen height, is introduced, and shown to account for changes in specimen dimensions. In addition, the softening effect diminishes relative to the state of strain. The results suggest acoustic softening is a function of the amplitude strain parameter and strain history.

Carbon-induced negative strain-rate sensitivity in a quenching and partitioning steel

The present work reports an abnormal negative strain-rate sensitivity (SRS) in a room-temperature quenching and partitioning (RT-Q&P) steel. The mechanisms responsible for such negative SRS were systematically investigated. Continuous and interrupted tensile tests at quasi-static (10− 3s − 1) and high strain rate (600 s − 1) were performed. It is found that the flow stress after yielding exhibits abnormal negative SRS. Interestingly, similar martensitic transformation occurs at both 10− 3s − 1 and 600 s − 1, implying that transformation induced plasticity (TRIP) effect is not responsible for the negative SRS. The designed interrupted rate-change tests and interrupted high-strain-rate load-unload-load tests were performed to reveal the significant effect of interstitial carbon atoms on the negative SRS. Moreover, the Cottrell atmospheres with carbon atoms segregated at dislocations were further confirmed by atom probe tomography (APT). The Cottrell atmosphere can be continuously rebuilt during deformation at quasi-static strain rate, but cannot be rebuilt at high strain rate since there is no sufficient time for carbon atoms to diffuse to the high-velocity dislocations. The lack of Cottrell atmospheres at high strain rate results in (1) absence of extra carbon dragging force and (2) a lower dislocation density, both of which contribute to a lower flow stress at high strain rate and therefore the negative SRS.

Hot deformation behavior and processing map development of Mg/Al2O3 composite: A case study of extrusion ratio effects

The hot deformation behavior of 2.5 wt.% submicron alumina reinforced magnesium composite manufactured by a new casting method was examined to assess the impact of extrusion ratio and initial microstructure on the hot workability of Mg/Al2O3 composite. The thermomechanical experiments were performed at strain rates from 0.001 s−1 to 0.05 s−1 and the temperature ranging from 523 K to 673 K. The processing map was developed using power dissipation efficiency in terms of temperature and strain rate. Results revealed that the higher extrusion ratio yields finer grain size and a more homogenous distribution of alumina particles resulting in lower flow stress and activation energy. Stable regions with more power efficiency (57%) and less instability were observed in materials that experienced higher strain. Based on the microstructural observation, dynamic recrystallization as the main restoration mechanism occurred at composite with a higher extrusion ratio and finer grains in all conditions. It was deduced that the enhanced workability of fine-grain material is confirmed by steady flow stress and safe zones of the processing map. It was also revealed that twinning–twinning intersection and flow localization are the main reasons for unstable flow in both samples with unlike grain sizes.

A strategy to promote formability, production efficiency and mechanical properties of Al–Mg–Si alloy

To enhance the formability, production efficiency and mechanical properties of Al–Mg–Si alloy, the 6063 Al alloy was extruded from as-cast, furnace-cooling and air-cooling homogenized billets and followed by online quenching, respectively. The effects of initial billet states, extrusion parameters and online quenching process on the formability, microstructure and mechanical properties of the profile were investigated. It was found that the second phases in as-cast and furnace-cooling homogenized billets not only brought no brittle crack during extrusion, but also refined the grain size. The online quenching of the 6063 Al alloy profiles with complex sections prevented the abnormal grain growth occurring in offline solid solution treatment, so as to improve production efficiency. The strengths of the profiles extruded from as-cast and air-cooling homogenized billets were equivalent. Therefore, most of 6063 Al alloy profiles could be directly extruded from as-cast billet without homogenization treatment, which improved the production efficiency. The furnace-cooling homogenized billet had the lowest flow stress, indicating lower break-through force to activate extrusion. The strength of the profile extruded from furnace-cooling homogenized billet was higher than that of air-cooling homogenized billet. Therefore, the furnace-cooling homogenized billet was recommended for the profile with complex section or higher performance requirement.

Achieving superior superplasticity in CoCrFeNiCu high entropy alloy via friction stir processing with an improved convex tool

The investigation of the superplastic behavior of HEAs is significant since superplastic forming shows a great potential in fabricating complex components of HEAs. In this study, the superplastic behavior of the CoCrFeNiCu HEA fabricated by friction stir processing (FSP) was first time investigated at the temperature range of 900–950 °C and strain rate range of 3 × 10−4–3 × 10−2 s−1. The ultrafine grained structure with 320 nm in grain size and 91% of high angle grain boundaries (HAGBs) was achieved by FSP with the improvement of stirring tool based on the characteristics of HEAs, which exhibited a good thermal stability when annealing at 900 °C. The FSP CoCrFeNiCu HEA exhibited a largest elongation of 620% and a low flow stress of 5 MPa at 950 °C and 3 × 10−3 s−1. The flow stress in this study is the lowest in all the HEAs reported during superplastic deformation, which shows the great potential in the practical superplastic forming application. This is the first time to report the excellent superplasticity of dual-phase FCC HEAs. The superplastic deformation mechanism was mainly dominated by grain boundary sliding (GBS), accommodated by the diffusion of Cu-rich second phase. The failure mechanism was related to the aggregation of cavities. The excellent superplastic property was attributed to the stable equiaxed ultrafine microstructure, the high HAGB ratio, and soft Cu-riched second phase, which promoted the occurrence of GBS and its accommodation behavior. This study provides a way for fabricating superplastic HEAs and theoretical basis for superplastic forming of HEAs.

Effect of stress state on adiabatic shear banding in Al2024-T351

Cubic uniaxial compression and angled cubic biaxial shear-compression specimens are a preferable choice in the context of developing empirical data for models such as the Generalized Incremental Stress State Dependent Damage Model (GISSMO), with a strain-rate dependent extension. The angled cubic specimens introduce a multiaxial stress state of combined shear and compression. Al2024-T351 specimens have been impacted using a direct impact Hopkinson bar coupled with Digital Image Correlation (2D-DIC). 2D-DIC has been used to track the full-field strain evolution of all specimens and obtain the fracture strains for fractured specimens. The shear strain evolution related to failure along the shear planes can be acquired using 2D-DIC, and a quantitative measurement of fracture initiation is acquired from the DIC data. It is also highlighted that the transverse displacement contours can offer qualitative information about the effects of friction on proportional loading during uniaxial compression. Interrupted tests using stop rings are conducted for angled cubic specimens to identify the critical strains for the initiation of adiabatic shear bands (ASBs), which can be defined as the GISSMO instability strains. ASBs are confirmed using the optical microscope, and it is found that for a constant impact momentum, the specimens with a greater shear to compressive stress state exhibit a higher tendency to form ASBs at lower major axial strains. It is also found that ASBs are observed using the optical microscope with no loss of flow stress, and that angled specimens exhibit a lower flow stress than uniaxial compression specimens at higher strain rates. Lastly, pre-impact and non-fractured post-impact Vickers microhardness tests have been conducted, and it is found that for all specimens, the material is on average about 20% harder after impact in regions away from the ASB, and further that regardless of stress-state, the ASB is consistently about 30% harder than the pre-impact microstructure.

The role of stress-state on the low cycle fatigue resistance of non-hydrided beta-treated Zircaloy-4

Reactor operation results in cyclic stresses that produce fatigue. Increased strain to failure under monotonic loading has been observed for Zircaloy-4 under a stress-state of shear defined by a low triaxiality. Triaxiality (η) is defined as the ratio of hydrostatic stress to von Mises stress and typically ranges from values of -0.33 for compression, to 0 for torsion loading and to 0.9 for notched, axial loaded specimens. Low Cycle Fatigue (LCF) testing of Zircaloy-4 was performed under uniaxial and torsion loading in air at room-temperature. Both smooth and notched specimens were tested to vary the value of positive triaxiality. An increase in LCF resistance with less notch sensitivity is observed under torsion loading. Cyclic stress-strain curves are developed that show a higher strain to failure and lower flow stress under torsion loading. This suggests a lower triaxiality produces increased strain to failure capability under both cyclic and monotonic loading that is shown to generally follow a Rice-Tracey model for void nucleation, growth and coalescence. Fractography examinations are used to understand the mechanism for crack extension.