Microstructure and hardness of W-25Re alloy processed by high-pressure torsion

The evolution of microstructure and microhardness was studied in a commercial tungsten-25%rhenium(mass fraction)(W-25Re)alloy processed by the high pressure torsion(HPT)procedure under a pressure of7.7GPa up to10revolutions at different temperatures.The results show that the samples processed by10revolutions at room temperature could have the smallest grain size at around0.209μm.High saturation hardness(HV^1200)could be achieved after the rapid strengthening stage for samples processed by10revolutions both at room temperature and at573K.Microstructural observation and analysis from Hall-Patch relationship could reveal that grain refinement and grain boundaries strengthening are the main factors of hardening mechanism in W-25Re alloy.It is also demonstrated that sintered W-25Re sample may have brittle phase separation phenomenon after HPT processing.

2219-O铝合金声软化效应建模与预测

超声振动辅助加工技术目前已广泛应用在金属的塑性成形过程中,已有研究表明超声振动的引入会令塑性成形过程出现声软化效应。对超声辅助拉伸条件下的形变材料进行电子背散射衍射(EBSD)观测时发现其晶粒尺寸有所增大。针对此现象推导了与超声振幅相关的应变-晶粒尺寸关系式,并基于Hall-Patch关系建立了晶粒尺寸变化对应力-应变曲线影响的模型,使用粒子群算法开展参数识别,利用所建模型对高超声振幅拉伸过程的声软化效应进行预测。通过2219-O铝合金的超声拉伸试验及EBSD微观结构组织观测验证了模型的正确性,进一步分析表明随应变增加,拉伸过程形变材料会出现硬化现象,而超声能量的引入会在一定程度上抵消拉伸过程中出现的硬化,且抵消的效果强度与超声振幅大小正相关。随超声振幅升高,晶粒尺寸增大的趋势更为显著,且在相同的应变条件下流动应力会随晶粒尺寸增大而降低。通过模型预测定量分析发现相同应变条件下,超声振幅每提高3μm,拉伸应力下降约6.5%。