Precipitation and coarsening kinetics of H-phase in NiTiHf high temperature shape memory alloy. (1st July 2022)

• Record Type: Journal Article
• Authors: Shuitcev, A.; Ren, Y.; Sun, B.; Markova, G.V.; Li, L.; Tong, Y.X.; Zheng, Y.F.
• Is Part Of: Journal of materials science & technology. Volume 114(2022)
• Page Start: 90
• Page End: 101
• Publication Date: 2022-07-01
• Subjects: High temperature shape memory alloys -- NiTiHf -- Time-temperature-transformation diagram -- Coarsening kinetics -- H-phase; Metals -- Periodicals; Materials science -- Periodicals; Materials science; Metals; Periodicals; 620.1105
• DOI: 10.1016/j.jmst.2021.11.011
• Languages: English
• ISSNs: 1005-0302

Abstract

Highlights: Aging induced precipitation in Ni50 Ti30 Hf20 alloy was investigated. Activation energy for the precipitation and coarsening of the H-phase was determined. TTT and TTH diagrams were constructed for Ni50 Ti30 Hf20 alloy. Critical size for breaking down the coherency was determined. Abstract: Precipitate hardening is the most easiest and effective way to enhance strain recovery properties in NiTiHf high-temperature shape memory alloys. This paper discusses the precipitation, coarsening and age hardening of H-phase precipitates in Ni50 Ti30 Hf20 alloy during isothermal aging at temperatures between 450 °C and 650 °C for time to 75 h. The H-phase mean size and volume fraction were determined using transmission electron microscopy. Precipitation kinetics was analyzed using the Johnson-Mehl-Avrami-Kolmogorov equation and an Arrhenius type law. From these analyses, a Time-Temperature-Transformation diagram was constructed. The evolution of H-phase size suggests classical matrix diffusion limited Lifshitz-Slyozov-Wagner coarsening for all considered temperatures. The coarsening rate constants of H-phase precipitation have been determined using a modified coarsening rate equation for non-dilute solutions. Critical size of H-phase precipitates for breaking down the precipitate/matrix interface coherency was estimated through a combination of age hardening and precipitate size evolution data. Moreover, time-temperature-hardness diagram was constructed from the precipitation and coarsening kinetics and age hardening of H-phase precipitates in Ni50 Ti30 Hf20 alloy. Graphical abstract: Image, graphical abstract