铸态Ti-43Al-6Nb-1Mo-1Cr-0.2TiB_(2)合金高温蠕变行为研究

Creep Behavior of As-cast Ti-43Al-6Nb-1Mo-1Cr-0.2TiB_(2) Alloy at Elevated Temperature

通过XRD与SEM分析铸态Ti-43Al-6Nb-1Mo-1Cr-0.2TiB_(2)合金组织,并进行760~840℃、240~300 MPa范围内的蠕变测试,利用SEM、EBSD和TEM方法观察蠕变变形后的显微组织及断口形貌,以探究温度和应力对试验合金高温蠕变变形与断裂行为的影响。结果表明,该铸态合金为近片层组织,硼化物弥散分布在基体中。根据蠕变数据计算可得合金在测试范围内的应力指数n和蠕变激活能Q_(c)分别为6.64和388.37 kJ/mol。结合TEM观察可推知,合金的变形速率主要由位错攀移控制。结合蠕变变形后的显微组织及断口形貌可知,该合金的蠕变断裂模式主要为韧脆混合型断裂。随着温度升高,局部韧断区域增加;随着应力增大,萌生裂纹数量增多。根据EBSD和TEM分析可知,晶界处的B2相和γ相的界面存在较大的应力集中,容易萌生裂纹。此外,在蠕变过程中,硼化物不仅可以阻碍位错运动,还可促进动态再结晶。

The microstructure of as-cast Ti-43Al-6Nb-1Mo-1Cr-0.2TiB_(2) alloy was analyzed by XRD and SEM,and the creep tests were carried out at 760~840℃ under 240~300 MPa.The deformed microstructure and fracture morphology were observed by SEM,EBSD and TEM to explore the effects of temperature and stress on creep deformation and fracture behavior at elevated temperature.The results reveal that the as-cast alloy exhibits nearly lamellar structure,and the borides are dispersed in the matrix.According to the creep data,the stress exponent n and apparent activation energy Q_(c) of the alloy in the test range are 6.64 and 388.37 kJ/mol,respectively.Meanwhile,it can be inferred that the creep deformation rate of the alloy is mainly controlled by dislocation climb combined with TEM observation.Deformed microstructure and fracture morphology demonstrate that the creep fracture mode of the alloy is dominated by ductile-brittle mixed fracture.With the increase of temperature,the local ductile fracture area is expanded.With the increase of stress,the quantities of crack are increased.EBSD and TEM analysis indicate that great stress concentration occurs at the interface between B2 phase and γ phase at the grain boundary,leading to crack initiation.In addition,borides can hinder dislocation movement and promote dynamic recrystallization during creep.