颗粒增强钛基复合材料大塑性变形组织演变与性能研究

Microstructural Evolution And Properties Of Particle Reinforced Titanium Matrix Composites Processed By Severe Plastic Deformation

摘要:

本研究采用大塑性变形实现了难变形微纳米颗粒(TiB+La₂O₃)复合增强Ti-6Al-4V钛合金等通道挤压变形(ECAP),深入研究了大塑性变形温度对复合材料组织演变的影响规律和超细晶形成机制。结果表明,材料经ECAP大变形后易于在基体形成超细晶,变形温度对超细晶形成机制有显著影响。变形温度较低时,易于在基体产生位错塞积和位错缠结；变形温度较高时,发生动态再结晶实现细晶强化,经800 ℃变形后抗拉强度可达1128 MPa,相比未加工时提升了18%。且增强体在界面微区诱发连续动态再结晶,实现晶粒的进一步细化。变形后TiB增强体平均长径比随变形温度的增加而减小,使得增强体与基体极易发生脱粘,无法有效承载,最终造成变形温度对强度影响并不明显；且增强体的脱粘,在基体中形成的孔洞易引发应力集中,造成裂纹萌生,降低材料塑性。

Abstract:

Micro TiB and nano La₂O₃ particles hybrid reinforced difficult-to-deformation Ti-6Al-4V TMCs were processed by severe plastic deformation of equal-channel angular pressing (ECAP). The effect of ECAP temperature on microstructure, formation mechanism of ultrafine grains and mechanical properties was studies by SEM, TEM and room temperature tensile in detail. The results show that ultrafine-grained (UFG) structure has formed in ECAPed matrix, and ECAP temperature have significant impact on the formation mechanism. Plenty of dislocation pile-ups and tangling contribute to cell structures of hundreds of nanometers in matrix at lower ECAP temperature, while dynamic recrystallization occurs at higher ECAP temperature, which promotes the formation of a large number of new ultrafine grains (100~500 nm). The ultimate tensile strength of ECAPed TMCs at 800℃ is up to 1128.01MPa, which is 18% higher than unECAPed ones. In addition, micro-nano reinforcements induce continuous dynamic recrystallization in the interface microdomain, resulting in further refined grains. However, the average aspect ratio of ECAPed TiB whiskers decreases with the increase of ECAP temperature, which makes TiB tend to debond with matrix and be disabled to play a load-bearing role. It results in the inapparent effect of ECAP temperature on ultimate tensile strength. And the voids in matrix formed by debonding induce stress concentration, cause crack easily and reduce ductility of TMCs.