温度和应变率对原位合成钛基复合材料动态压缩性能及破坏机制的影响

Effects of temperature and strain rate on dynamic compressive property and failure mechanism of in-situ synthesized titanium matrix composites

使用分离式Hopkinson压杆（SHPB）系统,在温度293~973K、应变率6 000~10 000s^-1下,对原位合成TiC颗粒和TiB晶须混合增强钛基复合材料（TMCs）的动态压缩性能进行了研究。试验结果表明：在373~573K、673~773K和873~973K范围内TMCs流变应力随温度的增加而显著减小;在较低温度（低于373K）和较低应变率（6 000~8 000s^-1）下,TMCs呈现小幅的应变率硬化特征,而在较高温度（573K及以上）时各应变率下TMCs均存在应变率软化特征,且温度越高材料应变率软化效应越明显。材料失效/断裂机制分析表明：应变率软化机制主要是绝热软化及其产生的绝热剪切带（ABS）中微裂纹的形成和扩展的综合作用;在较高的应变率和较大应变下ABS中会产生微裂纹,温度较低时TMCs塑性不足以抑制或阻碍微裂纹的扩展,从而导致TMCs在宏观上迅速破坏;材料破坏时以钛合金基体塑性断裂为主,但在局部伴随部分增强相脆性断裂。

Split Hopkinson pressure bar（SHPB）system was used to investigate the dynamic compressive properties of in situ synthesized TiC particles and TiB whisker mixing reinforced titanium matrix composites（TMCs）at the temperature range 293-973 Kand the strain rates range 6 000-10 000s^-1.The test results show that the flow stress of TMCs significantly decreases with the temperature increasing when the temperature is in the range of 373-573 K,673-773 Kand 873-973 K.At relatively low temperature（lower than 373K）and low strain rate（6 000-8 000s^-1）,TMCs exhibit a slight strain rate hardening characteristic.However,at high temperature（573Kor higher）,TMCs present obvious strain softening feature at all strain rates used and the strain rate softening effect is more significant under higher temperature.The analysis on the failure/fracture mechanisms shows that the combined effect of the adiabatic softening and the behavior of the micro cracks generation and development in the adiabatic shear band（ABS）are the mechanisms for the strain softening.Under high strain rate combined with high strain,micro cracks initiate in the ABS and will cause the rapidly damage or fracture of TMCs on the macro when the ductility of the TMCs is not high enough to suppress or hinder the development of the micro cracks under relative low temperature.Titanium alloy matrix plastic fracture is the main material damage mode but local brittle fracture also presents around the reinforcement phase.