粉末冶金态与铸态Ti-5553合金高温不连续屈服行为和绝热温升效应对比研究

Comparison of Discontinuous Yielding Phenomenon and Adiabatic Temperature Rising of Ti-5553 Alloy Prepared by Powder and Ingot Metallurgy Approaches during Hot Compression

摘要:

本文系统地研究了粉末冶金态与铸态Ti-5553合金在温度为700 ℃~1100 ℃、应变速率为0.001 s_^-1~10 s_^-1条件下的高温不连续屈服行为和绝热温升效应,并对这两种同名义成分不同制备工艺的钛合金进行了对比研究。结果表明：两种合金不连续屈服的幅度均与应变速率呈正相关关系,并与温度呈近似负相关关系, 两种合金中出现的不连续屈服现象符合动态理论。在相同变形条件下,铸态合金中不连续屈服的幅度更大,其原因是相对于粉末冶金态合金,铸态合金中的起始位错密度低,这更有利于晶界处可动位错的突然增殖与扩展。两种合金在热变形中绝热温升的大小均随应变速率的升高而逐渐增大,并随着变形温度的升高而逐渐降低。在相同变形条件下,粉末冶金态合金的绝热温升效应相比与铸态合金较弱,这是因为粉末冶金态合金具有较低的变形抗力和较高的协调变形能力。

Abstract:

Discontinuous yielding phenomenon (DYP) and adiabatic temperature rising (ATR) effect have been investigated in this paper for Ti-5553 (Ti-5Al-5Mo-5V-3Cr) alloys manufactured by powder metallurgy (PM) and ingot metallurgy (IM) approaches based on hot compression testing conducted at the temperature range of 700 °C to 1100 °C and the strain rate range of 0.001 s_^-1 to 10 s_^-1. The results show that the magnitude of yield drop exhibits a positive correlation to strain rate but nearly a negative correlation to deformation temperature for both PM and IM alloys, and the occurrences of DYP in the alloys are elucidated by the dynamic theory. IM alloy shows a higher degree of yield drop than PM alloy at the same condition because of low initial dislocation density at as-cast state and the subsequently promoted newly-generated mobile dislocation from grain boundary. Strong positive correlation between ATR effect and strain rate but intensive negative correlation when it subjected to deformation temperature are uncovered for the two alloys. PM alloy shows a lower degree of ATR effect at the same processing condition than IM alloy as a result of its lower deformation resistance and higher deformation compatibility.