Evolution of Ti3Ni4 precipitates in Ti49.2Ni50.8 alloy during equal channel angular pressing
(1. Institute of Materials Processing and Intelligent Manufacturing, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China;
2. Center of Testing and Analysis, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China)
2. Center of Testing and Analysis, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China)
Abstract: The evolution of Ti3Ni4 precipitates in Ti49.2Ni50.8 alloy during equal channel angular pressing (ECAP) and intermediate annealing was investigated by transmission electron microscopy. The solution-treated Ti49.2Ni50.8 alloy was aged at 450 °C for 10 to 60 min to obtain Ti3Ni4 precipitates ranging from 37 to 75 nm. After ECAP at 450 °C for one pass, Ti3Ni4 precipitates introduced by aging for 10 and 30 min totally dissolve into the matrix; however, those produced by aging for 60 min become smaller. The critical size of Ti3Ni4 precipitates to totally dissolve into matrix is determined to be in the range of 37-68 nm. The dislocation density of ECAP-processed samples depends on the initial size of Ti3Ni4 precipitates after aging. With increasing the duration of initial aging from 10 to 60 min, the dislocation density firstly increases and then decreases.
Key words: TiNi shape memory alloy; equal channel angular pressing; dislocation; precipitation; Ti3Ni4 phase