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The effect of deformation temperature (77, 298 and 573 K) on the evolution of slip and twinning modes in Zircaloy-4 was studied. Samples of Zircaloy-4 were uniaxially compressed to different strains at a nominal strain rate of 10 −3 s −1 . The compression direction was chosen so as to activate twinning. Microstructural examination was carried out using electron backscatter diffraction to relate the evolution of microstructure and texture to the micro-mechanics and work-hardening behaviour. In conjunction with experiments a visco-plastic self-consistent crystal plasticity model was used to determine the evolution of deformation modes. Extensive twinning was observed at all the test temperatures. Twinning activity at 298 and 573 K was comparable, but was lower than that at 77 K. A strong basal texture parallel to the compressive direction was found at 298 and 573 K. The VPSC model predicted well the texture evolution at 298 and 573 K. The basal texture developed at 77 K was found to have partially reoriented back to the initial texture due to secondary twinning. Prism slip was the dominant deformation mode with secondary slip becoming more active at higher temperatures. [ABSTRACT FROM AUTHOR]

High temperature tensile creep tests were conducted on AZ31 Magnesium alloy at low stress range of 1–13 MPa to clarify the existence of grain boundary sliding (GBS) mechanism during creep deformation. Experimental data within the GBS regime shows the stress exponent is ~2 and the activation energy value is close to that for grain boundary diffusion. Analyses of the fracture surface of the sample revealed that the GBS provides many stress concentrated sites for diffusional cavities formation and leads to premature failure. Scanning electron microscopy images show the appearances of both ductile and brittle type fracture mechanism. X-ray diffraction line profile analysis (based on Williamson-Hall technique) shows a reduction in dislocation density due to dynamic recovery (DRV). A correlation between experimental data and Langdon's model for GBS was also demonstrated. [ABSTRACT FROM AUTHOR]

Portevin−Le Chatelier (PLC) effect has been observed in HT-9 steel. The present study involves different types of tensile testing to characterize the features of PLC effectin HT-9 steel. Stress serrations observed during tensile tests are analyzed using different statistical analysis techniques to investigate the underlying nature of the effect. Peaked type of stress drop distribution indicated occurrence of type B serrations in the steel. Multiscale entropy analysis of the stress serrations indicated substitutional solute atoms to be responsible for the PLC effect in HT-9 steel. [ABSTRACT FROM AUTHOR]

Due to their significant role in automobile industries, high temperature deformation of Mg–Al–Zn alloys (AZ31) at constant stress (i.e. creep) were studied at a wide range of stresses and temperatures to characterize underlying deformation mechanism, dynamic recrystallization (DRX) and dislocation density evolution. Various microstructures (e.g. grain growth & DRX) are noted during steady-state creep mechanisms such as grain boundary sliding (GBS), dislocation glide creep (DGC) and dislocation climb creep (DCC). Although a combination of DRX and grain growth is characteristic of low stacking fault energy materials like Mg alloys at elevated temperatures, observation reveals grain growth at low strain-rates (GBS region) along with dynamic recovery (DRV) mechanism. X-Ray Diffraction (XRD) analysis revealed a decrease in dislocation density during GBS region while it increased under dislocation based creep mechanisms which could be related to the possible DRV and DRX respectively. Scanning Electron Microscopic (SEM) characterization of the fracture surface reveals more inter-granular fracture for large grains (i.e. GBS region with DRV process) and more dimple shape fracture for small grains (i.e. DGC & DCC region with DRX). [ABSTRACT FROM AUTHOR]

Neutron irradiation effects on ultra-fine grain (UFG) low carbon steel prepared by equal channel angular pressing (ECAP) have been examined. Counterpart samples with conventional grain (CG) sizes have been irradiated alongside with the UFG ones for comparison. Samples were irradiated in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) to 1.37 dpa. Atom probe tomography revealed manganese and silicon-enriched clusters in both UFG and CG steel after neutron irradiation. Mechanical properties were characterized using microhardness and tensile tests, and irradiation of UFG carbon steel revealed minute radiation effects in contrast to the distinct radiation hardening and reduction of ductility in its CG counterpart. After irradiation, micro hardness indicated increases of around 9% for UFG versus 62% for CG steel. Similarly, tensile strength revealed increases of 8% and 94% respectively for UFG and CG steels while corresponding decreases in ductility were 56% versus 82%. X-ray quantitative analysis showed that dislocation density in CG increased after irradiation while no significant change was observed in UFG steel, revealing better radiation tolerance. Quantitative correlations between experimental results and modeling were demonstrated based on irradiation induced precipitate strengthening and dislocation forest hardening mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: Addition of boron in small quantities to various titanium alloys have shown significant improvement in mechanical behavior of materials. In the present study, electron back-scatter diffraction (EBSD) techniques have been applied to investigate the deformation microstructure evolution in boron modified two-phase titanium alloy Ti–6Al–4V. The alloy was hot compressed at 750°C up to 50% height reduction at two different strain rates (10−3 s−1 and 1s−1). The EBSD analyses indicated significant differences in deformed microstructure of the base alloy and the alloy containing boron. A strong subgrain formation tendency was observed along with inhomogeneous distribution of dislocations inside large α colonies of Ti64. In contrast, α colonies were relatively strain free for Ti64+B, with more uniform dislocation density distribution. The observed difference is attributed to microstructural modifications viz. grain size refinement and presence of TiB particles at grain boundary produced due to boron addition. [Copyright &y& Elsevier]

Nb-1wt.%Zr was subjected to severe plastic deformation at room temperature using multi-axial forging (MAF) in a closed channel die to an effective strain of 4.6. Separate such MAF samples of Nb–1Zr were subsequently annealed for 1 h at 450, 550, 600 and 700 °C to study the thermal stability of the microstructure after severe deformation. Electron backscatter diffraction measurements were used to characterize the microstructure in terms of grain size, local misorientations within grains and the fraction of recrystallization after annealing using the criteria of grain orientation spread. MAF increased the strength of Nb–1Zr to 540 MPa as compared to 120 MPa in the initial coarse grained condition. Subsequent annealing resulted in regions of recrystallized grains and an overall reduction in local misorientations. Annealing at 700 °C showed a bimodal grain size distribution with large recrystallized grains surrounded by deformed regions. The tensile strength reduced with increasing annealing temperature. The as-MAF and the 450, 550 and 600 °C annealed conditions showed low ductility (16%), whereas the 700 °C annealing condition showed a moderate ductility of 28% as compared to the coarse grained condition which showed a 44% ductility. It was estimated that the contribution of strength increase after MAF was more due to increase in dislocation density as compared to the reduction in grain size. [ABSTRACT FROM AUTHOR]

HANA-4 (High Temperature Alloys for Nuclear Applications) is Zr-1.5 Nb alloy developed by the Korea Atomic Energy Research Institute for advanced nuclear fuel cladding applications. In this work, the effect of hydriding on the biaxial creep behavior of HANA-4 alloy was studied through internal pressurization of closed end tubes by applying a range of hoop stresses (27 MPa–156 MPa) at two temperatures: 400 °C and 500 °C. Test specimens included two HANA-4 tubes hydrided using an electrolytic method with 387 ppm and 715 ppm of hydrogen, respectively, and non-hydrided HANA-4 tubes as the control sample. To understand the effect of hydriding on creep, steady state creep rates and stress exponents of the specimens were determined from the creep data. Furthermore, in situ X-ray diffraction (XRD) experiments were conducted on the hydrided HANA-4 specimens during heating to detect the dissolution limit of the hydride phase. On examining the results of the creep tests and the XRD experiments collectively, it is concluded that hydrogen while being fully dissolved into the solid solution enhances the creep rate of HANA-4 tubes. On the other hand, hydrogen present, even partially, as hydride phase at the creep test temperature lowers the creep rate. The rate controlling mechanisms of creep in HANA-4, however, remained unchanged as noted from similar stress exponents of the hydrided and non-hydrided specimens. The rationale behind these observations is explained based up on models predicting the interaction of dislocations with hydrogen and hydride phase. [ABSTRACT FROM AUTHOR]

This study attempts to identify the type of dynamic recrystallization (DRX) occurring in hot deformed zirconium. For this, samples of Zr were uniaxially compressed at 800 °C and 0.1 s −1 to varying strains. Microstructural characterization was done using electron back scatter diffraction (EBSD). The flow stress showed an initial hardening followed by softening to a steady state value. DRX grains were identified as those with a grain orientation spread of less than 2°. Fine recrystallized grains were observed along grain boundaries at low to intermediate strains (0.15 and 0.6). The grain size decreased with increasing strain up to a strain of 0.6, beyond which it showed no further decrease. The degree of misorientation of boundaries was used to distinguish between discontinuous and continuous dynamic recrystallization (dDRX and cDRX, respectively). Most recrystallized grains had their boundaries of very high misorientation (> 50°) suggesting that dDRX was prevalent. The evidence of cDRX was weak, although it cannot be ruled out at higher strains. It was concluded that Zr undergoes dDRX when deformed at 800 °C and 0.1 s −1 . [ABSTRACT FROM AUTHOR]

Tailoring the strength and ductility of metals through microstructural design has been a longstanding endeavour. Here, we report the development of a hierarchical ultrafine twinned microstructure in zirconium via a novel multi-axial cryo-forging (MACF) process. MACF of Zr resulted in the formation of dense and fine tensile twins, { 10 1 ¯ 2 } < 10 1 ¯ 1 > (T-1) and { 11 2 ‾ 1 } ⟨ 1 ‾ 1 ‾ 26 ⟩ (T-2) within coarse and equiaxed grains. This microstructure exhibited a remarkable combination of enhanced strength, strain-hardening rate, and ductility, compared to its coarse-grained counterpart. The yield strength and ultimate tensile strength increased by up to 26 % and 30 %, respectively, without compromising material ductility. The improved strength and strain-hardening stemmed from the activation of the harder slip system and its consequent interaction with the fine twin boundaries. Notably, the growth of fine T-2 twins during ambient temperature deformation, absent in coarse-grained zirconium, contributed to additional ductility. Crystal plasticity simulations reveal that the activity of pyramidal slip within T-2 twins is twice that of prismatic slip, leading to an enhanced strain-hardening rate contributed by the T-2 twins. Subsequent heat treatment of MACF Zr at 500 °C relieved the elastic distortions around twin boundaries, and hence tensile straining led to stress-assisted easier migration of pre-existing twin boundaries. This resulted in a lowering of the strain-hardening rates. It was shown that the dislocation substructure around these typically incoherent tensile twins in hcp metals plays a crucial role in their strain-hardening behaviour. [ABSTRACT FROM AUTHOR]