W和Cr微合金化高Nb-TiAl合金组织演变及性能

Microstructure Evolution and Properties of W and Cr Microalloying High Nb-TiAl Alloy

采用真空感应悬浮熔炼法制备了W和Cr微合金化高Nb-TiAl合金材料,利用光学显微镜、扫描电镜和MTS810万能试验机等手段研究了合金的铸态组织及室温拉伸性能,并分析了其凝固相变路径和偏析的形成原因。结果表明,W和Cr扩大了Ti_(46.55)Al_(45)Nb_8W_(0.2)Cr_(0.25)合金的β相区,减小了α相区,合金晶粒尺寸为(230±10)μm。合金的凝固路径为L→β+L’→β+L’+α_(β)→β+α→α→α+γ→α_(2)+γ+B_(2),室温组织以γ和α_(2)相为主,同时含有少量残余的β(B_(2))相,主要分布在晶界或层片内部。合金室温铸态抗拉强度约为600MPa,伸长率为0.44%,断裂方式为穿晶解理脆性断裂与沿晶脆性断裂的混合断裂模式。

W and Cr microalloying high Nb-TiAl alloy was prepared by vacuum induction suspension melting.The as-cast microstructure and tensile properties of the alloy at room temperature were investigated by means of optical microscopy,scanning electron microscopy and MTS810 universal testing machine,and solidification phase transition path as well as forming mechanism of segregation were analyzed.The results indicate that the W and Cr can enlarge theβ-phase region and decrease theα-phase region of Ti_(46.55)Al_(45)Nb_8W_(0.2)Cr_(0.25)alloy,where the grain size is(230±10)μm.The solidification path is L→β+L'→β+L'+α_(β)→β+α→α→α+γ→α_(2)+γ+B_(2),and microstructure is dominated byγandα_(2)phase,accompanied with a small amount of residualβ(B_(2))phase,which are mainly distributed at the grain boundary or internal layer.The tensile strength and elongation of as-cast alloy at room temperature is 600 MPa and 0.44%,respectively.The fracture mode is a mixture characteristics of transgranular cleavage fracture and intergranular brittle fracture.