Effect of DCT with post-tempering on impact toughness and tensile strength of nimonic-90 superalloy

Abstract

The present work focusses on the effect of Deep Cryogenic Treatment on impact toughness and tensile strength of Nimonic-90 super alloy. Significant improvement in tensile strength and impact toughness has been recorded due to the evolution in microstructure at cryogenic temperature (−196 °C) which includes grain size, micro voids and dimples. Out of 24 h and 36 h soaking period, best results in impact toughness, tensile strength and yield strength were obtained corresponding to 36 h soaking period. The maximum percentage improvement in impact toughness, tensile strength and yield strength was 46.32 %, 19.34 % and 17.16 % respectively when compared with untreated sample. The maximum percentage elongation was observed for the sample which was soaked for 24 h. In 36 h soaking period, the amount of dimples was more as compared to 24 h soaking period. The brittle fracture zone decreased in the Charpy impact samples with the increase in the soaking time from 24 h to 36 h. This was due to the formation of coarse and deeper dimples which absorbed more energy during fracture. The tensile strength and yield strength were found higher for 36 h soaking period than 24 h soaking period because in 24 h soaking period, the presence of voids and small number of carbides made the matrix of Nimonic-90 weaker than 36 h soaking period samples.