The significance of strain weakening and self-annealing in a superplastic Bi–Sn eutectic alloy processed by high-pressure torsion
The significance of strain weakening and self-annealing in a superplastic Bi–Sn eutectic alloy processed by high-pressure torsion
复制标题
DOI：
10.1016/j.actamat.2019.11.064
复制
发表时间：
2020-02
期刊：
影响因子：
9.4
通讯作者：
Chuan Ting Wang;Yong He;T. Langdon
中科院分区：
文献类型：
--
作者：
Chuan Ting Wang;Yong He;T. Langdon
对一种铸造的铋锡共晶合金进行了常温高压扭转处理，并在室温下存放91d，以研究自退火的影响。HPT处理产生了晶粒细化，但硬度测量表明，存在应变软化，显微硬化值低于初始铸态材料，硬度值随施加的扭转应变量的增加而下降。这种软化归因于在加工过程中锡和铋相中析出物的损失。在室温自退火过程中，由于再析出，显微硬度显著增加，随着存放时间的延长，晶粒度也略有增大。拉伸试验表明，经高温高压处理的铋锡合金在储存35天后表现出超塑性，延伸率可达>；1000%，应变速率灵敏度接近∼0.5。晶界滑移在超塑性流动中起着重要的作用，滑移的最大值出现在铋-铋界面上，这与对铋锡合金晶界扩散系数的估算是一致的。
A cast Bi–Sn eutectic alloy was processed by high-pressure torsion (HPT) at room temperature and stored at room temperature for durations of up to 91 days in order to investigate the effect of self-annealing. The HPT processing produces grain refinement but hardness measurements show there is strain softening with lower microhardness values than in the initial as-cast material and with hardness values that decrease with increasing amounts of imposed torsional strain. This softening is attributed to a loss of precipitates within the Sn and Bi phases during the processing operation. In self-annealing at room temperature, the microhardness increases significantly due to reprecipitation and there is also a minor increase in grain size with increasing time of storage. It is demonstrated by tensile testing that the HPT-processed Bi–Sn alloy exhibits superplastic behavior with elongations of up to >1000% after storage for 35 days and with an associated strain rate sensitivity close to ∼0.5. Grain boundary sliding plays an important role in superplastic flow and it is shown that maximum sliding occurs on the Bi–Bi interfaces where this is consistent with estimates of the coefficients for grain boundary diffusion in the Bi–Sn alloy.