Effect of Solution-Hardening on the Evolution of Nanostructure in Ni-Fe alloys during Severe Plastic Deformation by High Pressure Torsion

Khan, N (2014) Effect of Solution-Hardening on the Evolution of Nanostructure in Ni-Fe alloys during Severe Plastic Deformation by High Pressure Torsion. Masters thesis, Indian Institute of Technology, Hyderabad.

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Abstract

Solid solution hardening via alloying addition could be used to control the microstructure, texture and properties of a range of alloys. However, solution-hardening due to alloying should be generally accompanied by change in stacking fault energy (SFE).Thus, the evolution of microstructure and microtexture during severe plastic deformation (SPD) could be affected by both solution-hardening and change in SFE. However, the extent of their individual effect should be isolated for better understanding of these parameters. In the present work Ni-Fe alloys were studied as a model system to evaluate the effect of solid solution hardening on microstructure and texture evolution during SPD processing by High Pressure Torsion (HPT). This alloys system was particularly suitable for the present study as alloying of Fe with Ni resulted in solution-hardening but no significant change in the SFE. A series of Ni-Fe alloys with composition Ni-10%Fe, Ni-20%Fe and Ni-30%Fe were SPD processed by HPT at room temperature to different number of rotations (N), namely, N=1/12, 1/4, 1/8, 1/2, 1, 3, 5 and 10 under an applied load of 5GPa. It was observed that homogenous equiaxed microstructure with grain size ~160 nm and large fraction of high angle boundaries (~80%) are achieved in both Ni-20%Fe and Ni-30%Fe after 10 revolutions but hardness value(~ 470Hv) was uniform throughout the disk only in Ni-30%Fe after 10 whole revolutions. The microtexture of these alloys were found to be similar indicating that texture evolution was not significantly influenced by solid-solution hardening. A comparison with a series of Ni-Co alloys (where the SFE was decreased systematically with alloying addition) obtained from previous studies revealed that increased solution-hardening was also an equally effective strategy as decreasing SFE in achieving nanostructure during SPD processing.

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