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The effect of prior plastic deformation on the discontinuous precipitation in a supersaturated binary Ni-Cr alloy (42 wt pct Cr) was investigated. Solutionised samples were cold rolled to different extents of reduction (20, 50 and 70 pct) and then subjected to aging heat treatments in the temperature range of 923 K to 1123 K (650 °C to 850 °C) for different time periods, resulting in the precipitation of α-Cr in various morphologies. The α-Cr precipitates were in the form of lamellar discontinuous precipitation, acicular continuous precipitation along the deformation bands, globularization and equiaxed precipitation concurrently with matrix recrystallization. The volume fraction of each morphology varied according to the heat treatments. Overall, the prior plastic deformation had a retarding effect on the kinetics of discontinuous precipitation and accelerated the kinetics of continuous precipitation. The retardation of discontinuous precipitation was attributed to the loss of supersaturation of the matrix due to the other competing modes of precipitation supported by deformation. Plastic deformation prior to aging is shown to be a possible route for engineering the microstructure in this alloy.

In the present work the commonly stated but not explicitly demonstrated association between the chemical composition of a material, its stacking fault energy (SFE) and dynamic recrystallization (DRX) behaviour, is established using thermo-mechanical testing, microstructural characterization and thermodynamic calculations on a Fe-Cr-Ni-Mo model alloy with varying interstitial content (0.1

The chemical reactivity of the uranium oxide prepared by thermal denitration is not as good as that of the ADU precipitation route due to lower specific surface area (SSA) of the former. In the present study, the chemical reactivity of the above uranium oxide towards hydro-fluorination has been enhanced by employing a reduction-oxidation–reduction cycle. This resulted in an increase in the SSA from 0.24 to 2.35 m2/g leading to enhanced reactivity towards hydro-fluorination. The oxides at each step were characterized for particle size, SSA, phase, crystallite size and morphology. The mechanism behind the increase in specific surface area was investigated through morphological analysis of the oxides at each step of the process by FESEM and a physical model was proposed for the same.

A dilute Zr alloy containing 0.3% Sn (a potential material for liner applications of composite fuel claddings of thermal nuclear power reactors) was subjected to controlled uniaxial compression over a wide range of strain rates and temperatures in a thermo-mechanical simulator. The evolved microstructures were characterized using SEM based EBSD technique and the texture evolution was analysed by bulk X-ray diffraction method. The study had brought out the systematic changes brought out in microstructure and texture as a function of temperature and strain rate. The results indicate that a temperature of 750 °C is the optimum temperature for hot deformation of this alloy in terms of achieving a homogenous and well recrystallized microstructure.

The deformation and recrystallization behaviour with associated microstructural and textural evolutions, precipitation formation and dissolution behaviour, and structure-property correlations have been investigated in V–Ti–Ta alloy system. Recrystallization temperature in this system was found to be in the range of 1250–1300 °C, 200 °C higher than reference V–4Ti–4Cr alloy. Substitutional solid solution strengthening by Ta was found to be the dominant strengthening mechanism. In addition, Ta was also found to influence the precipitation behaviour of V–Ti–Ta alloys. Synchrotron XRD and TEM-EDS results indicated the composition of precipitate to be (Ti,Ta)CON in contrast to V–Ti–Cr system where no Cr is found in the precipitates. Theoretical calculations based on thermodynamics and experimental evidence are presented which indicate desirable enhanced precipitate stability in this system due to presence of Ta. Deformation texture of the alloy was found to exhibit prominent θ-fibre, whereas the recrystallized texture had shown predominant γ-fibre texture.

The present study investigated the microstructural evolution in α + βZr regime of Zr-2.5 wt% Nb (a dual phase alloy with α (hcp) and β (bcc)) as a function of heat treatment temperature and holding time. The microstructures were studied in terms of composition and phase fraction evolution and the morphological changes of the constituent phases. The composition and quantification of phases revealed that, they significantly deviated from the corresponding equilibrium values for all the temperatures and holding times employed in the present study. In addition, an anomalous behavior was noticed in the time evolution of the phase fraction. The observed anomaly was rationalized by suggesting a possible sequence in attaining the equilibrium as: the crystal structure transformation of α to β phase followed by Nb enrichment in the β phase. Widmanstatten and ω phase transformations were exhibited by β phase at certain heat treatment conditions. The critical temperature for the widmanstatten transformation was found to be 750 °C, below which the high temperature β phase retained to room temperature. Despite wide variations in the microstructures, flow curves were characteristically similar for all the heat treatment conditions. However, yield strength was found to be more sensitive to the β phase morphology and the transformations associated with it. The presence of fine transformed products inside the β phase was observed to promote higher extent of deformation twinning.

The role of pre-strain on hydrogen embrittlement susceptibility of Indian Reduced Activation Ferritic Martensitic Steel was investigated using constant nominal strain-rate tension test. The samples were pre-strained to different levels of plastic strain and their mechanical behavior and mode of fracture under the influence of hydrogen was studied. The effect of plastic pre-strain in the range of 0.5–2% on the ductility of the samples was prominent. Compared to samples without any pre-straining, effect of hydrogen was more pronounced on pre-strained samples. Prior deformation reduced the material ductility under the influence of hydrogen. Up to 35% reduction in the total strain was observed under the influence of hydrogen in pre-strained samples. Hydrogen charging resulted in increased occurrence of brittle zones on the fracture surface. Hydrogen Enhanced Decohesion (HEDE) was found to be the dominant mechanism of fracture.

The present study is concerned with the twinning behaviour of Zr–Sn alloys at low temperature as a function of Sn content and starting texture. Zr–Sn samples, with Sn contents in the range of 0.33–2.9 wt. % and with different initial textures were subjected to uniaxial compression tests at −80 °C. Sn was found to enhance the { 10 1 ¯ 2 } 10 1 ¯ 1 ¯ type of deformation twinning and the extent of its effect on promoting this type of twinning was observed to be texture dependent. The influence of Sn in promoting twinning was seen to be stronger when the texture of the samples was relatively less favourable for the twinning.

Zircaloy-2 was deformed by cryorolling (CR) and room-temperature rolling (RTR) with different true strains, and the effects of true strains on microstructural characteristics, texture, and mechanical properties of the alloy were investigated in the current study. The alloy was subjected to rolling at liquid nitrogen temperature and room temperature with the maximum true strain of 1.89 after the initial heat treatment of the alloy at 800 °C in inert atmosphere followed by quenching in mercury. The hardness and tensile properties of the CR, RTR, and annealed alloy upon rolling were systematically measured in rolling and transverse directions. The tensile strengths were found to be 891 and 679 MPa, while hardness values were found to be 282 and 269 VHN for the CR and RTR alloys, in the rolling direction, respectively. Texture results showed the activation of basal slip at higher strains in RTR zircaloy-2. In CR zircaloy-2, only activation of prism slip was observed. Grain refinement, substructures, and texture in the deformed alloy contribute to the improved mechanical properties observed in the current study.

Effect of change in strain path by cross rolling up to a true strain of 1.89 has been studied in the present work. The Zircaloy-2 was subjected to solutionising heat treatment at 800 °C in argon environment for 2 h and subsequently quenched in mercury prior to cross rolling at room temperature. The fragmentation of near basal grains due to change in strain path is evident from the EBSD micrographs. The dislocation density in the crossrolled alloy increases with true strain as calculated from the XRD and EBSD data and it is found to be 2.806453 × 1016/m2. $$ \left\{ {10\bar{1}2} \right\} $$ extension twins are observed initially up to 25% reduction, with the further reduction in thickness, near basal grains are oriented toward the normal direction. These basal grains undergone fragmentation due to changes in strain path upon cross-rolling as observed from KAM and EBSD images. TEM results of the cross-rolled sample confirm the formation of ultrafine and nanograins in the alloy due to orientation of incidental dislocation boundaries in the direction of macroscopic plastic flow and post-annealing treatment of the deformed alloy. A tensile strength of 991 MPa with 7.5% ductility is observed in the 85% cross-rolled alloy. The cross-rolled alloy upon annealing at 400 °C for 30 min improves ductility to 11%.

The mechanical properties and microstructural characteristics of ultrafine grained Zircaloy-2 processed by cryorolling (CR) were investigated in the present work. The solutionised Zircaloy-2 was rolled at liquid nitrogen temperature (77 K) with different thickness reductions (25–85%). The dislocation density 〈ρ〉 in the cryorolled Zircaloy-2 increases with increasing true strain due to the suppression of dynamic recovery. EBSD analysis of CR Zircaloy-2 revealed initial strain hardening, which has occurred due to activation of { 10 1 ¯ 2 } 〈 1 ¯ 011 〉 tensile and { 11 2 ¯ 2 } 〈 1 ¯ 1 ¯ 23 〉 compressive twins during deformation of samples up to 50% strain. The prismatic and basal slips were activated during subsequent deformation. The fraction of low angle boundaries has increased with increasing true strain up to 50% thickness reduction but the fraction of high angle grain boundaries has increased for CR85% alloy. The CR 85% alloy showed hardness and yield strength values of 282 HV and 891 MPa, respectively. The annealed CR 85% alloy showed higher ductility (9.5% and 11.2% in rolling and transverse direction, respectively) as compared to CR 85% alloy. The annealed Zircaloy-2 showed heterogeneous microstructure consisting of ultrafine grains and nanograins.

The hot extrusion of Zr-2.5Nb alloy has been simulated using an FEM based software and validated by the experimental measurements during real extrusion process. The flow stress data for Zr-2.5Nb alloy at different temperatures, strain and strain rates were generated by hot compression testing on Gleeble Machine. The flow stress data, obtained both below β transus temperature in two phase α+β region as well as above β transus temperature in β phase region, were directly used in the FEM simulation of extrusion process, eliminating the need for any assumptions regarding material plastic flow law. Two important extrusion parameters, viz. included die angle and reduction ratio, were varied and for each set of conditions, temperature, strain and strain rate at different nodal points of the tube at different stages of extrusion were calculated. The extrusion parameters were optimized to obtain minimum variation in the force, temperature, strain and strain rate in the extruded product. A fair agreement has been found between the measured values of the applied ram force and the temperature profile at the die landing area in a 3780 ton horizontal extrusion press and those obtained through simulations. The effect of the friction and heat transfer coefficient between the die chamber and work piece was also investigated in this study.