高屈强比Ti-Nb-Cr-V-Zr系难熔高熵合金的组织与力学性能

Microstructure and mechanical properties of Ti-Cr-Nb-V-Zr refractory high entropy alloys with high specific yield strength

通过真空电弧熔炼法制备了Ti_(47-x)Nb_(23)Cr_(18)V_(12)Zr_(x)(x=0、4、8、12 at%)系难熔高熵合金,随后在1200℃下保温12 h对合金进行均匀化热处理。利用X射线衍射(XRD)、扫描电镜(SEM)、万能力学试验机和显微硬度仪等研究了铸态与均匀化热处理态合金的相组成、微观组织及力学性能。结果表明:Zr元素的添加使铸态合金在枝晶间析出C15结构的Cr_(2)(Ti,Nb,V,Zr)-Laves相,同时,Zr元素含量的增加增强了合金的压缩屈服强度和硬度,但使其塑性降低。均匀化热处理并未改变合金的相组成,但使合金的组织形貌发生了明显改变,并大大增加了析出相的体积分数。经过均匀化热处理后,合金的强度和硬度有所降低,但塑性得到改善。其中,Ti_(43)Cr_(18)Nb_(23)V_(12)Zr_(4)合金的压缩塑性由铸态时的29%提升至超过50%,同时具有1110 MPa的屈服强度和高达180 MPa·cm^(3)·g^(-1)的屈强比,表现出优异的强度-塑性匹配。此外,得益于细小弥散的Laves相,均匀化热处理后Ti_(39)Cr_(18)Nb_(23)V_(12)Zr_(8)合金的屈服强度和塑性均有小幅度增强。

Ti_(47-x)Cr_(18)Nb_(23)V_(12)Zr_(x)(x=0,4,8 and 12 at%)refractory high entropy alloys(RHEAs)were prepared by vacuum arc melting method,and then the as-cast alloys were subsequently homogenized at 1200℃ for 12 h.Phase constitution,microstructure and mechanical properties of the as-cast and homogenized alloys were investigated by means of X-ray diffraction(XRD),scanning electron microscopy(SEM),universal mechanical testing machine and microhardness tester.The results show that the addition of Zr element causes the precipitation of C15-structured Cr_(2)(Ti,Nb,V,Zr)-Laves phase between dendrites in the as-cast alloys.The increase of Zr element content enhances the compressive yield strength and hardness of the alloys,but reduces its plasticity.The homogenization heat treatment does not change the phase composition of the alloys,but significantly changes the microstructure and morphology of the alloys,greatly increasing the volume fraction of precipitates.After homogenization heat treatment,the strength and hardness of the alloys are reduced,but the plasticity is improved.Among them,the compressive plasticity of the Ti_(43)Cr_(18)Nb_(23)V_(12)Zr_(4) alloy increases from 29%in the as-cast to over 50% after homogenization heat treatment,with a yield strength of 1110 MPa and a specific yield strength of up to 180 MPa·cm^(3)·g^(-1),showing excellent strength plasticity matching.In addition,due to the fine dispersed Laves phase,the yield strength and plasticity of the Ti_(39)Cr_(18)Nb_(23)V_(12)Zr_(8) alloy after homogenization heat treatment have been slightly enhanced.