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 Nis0Ti30Hf20 alloy during isothermal aging at temperatures be-tween 450℃and 650℃for time to 75 h.The H-phase mean size and volume fraction were deter-mined 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 diffu-sion limited Lifshitz-Slyozov-Wagner coarsening for all considered temperatures.The coarsening rate con-stants 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 ki-netics and age hardening of H-phase precipitates in Ni50Ti30Hf20 alloy.
基金项目
国家自然科学基金(52050410340)
国家自然科学基金(51971072)
中央高校基本科研业务费专项(3072021CFJ1002)
维普
万方数据