Nb含量对铸造高铝TiAl合金室温拉伸性能的影响

Tensile Properties of High Al Containing Cast TiAl-Based Alloys at Room Temperature with Different Nb Contents

研究了Nb含量对铸造高铝Ti Al合金(%,原子分数)Ti-48Al-x Nb-2.5V-1.0Cr(x=2,4,7,9),以下分别简称2Nb,4Nb,7Nb和9Nb合金)组织和室温拉伸性能的影响。组织观察发现:不同Nb含量合金宏观组织均为柱状晶组织,微观组织均为有取向层片组织。经X射线衍射(XRD)分析表明,不同Nb含量合金均由γ相、α_2相和少量的B2相组成,其中,γ相体积分数随Nb含量的增加而增多;α_2相体积分数随Nb含量的增加而减少;B2相含量由于含量较少无法定量,但从XRD谱及扫描电镜(SEM)背散射(BSE)图可定性得知,其含量随Nb含量的增加而显著增多。合金室温抗拉强度随Nb含量的增加而降低:由2Nb合金的648.2 MPa降为9Nb合金的613.8 MPa;但屈服强度却随Nb含量的增加而升高:由2Nb合金的561.1 MPa增为9Nb合金的613.5 MPa。合金室温延伸率随Nb含量的增加呈线性下降:由2Nb合金的延伸率1.2%,降为9Nb合金的0.3%。γ相的晶格常数c/a随Nb含量的增加而增大,这对合金的室温塑性有不利的影响。

The influence of Nh content on macrostructure, microstructure and room temperature tensile properties of high Al containing cast TiAl-based alloys was investigated with Nb content varying from 2%-9% （atom fraction）. The results showed that all the alloys had the macrostructure with columnar crystals and microstructure with lamellar structure. There were three phases γ,α2 and B2 in the alloys by X-ray diffraction （XRD） analysis. With Nb content increasing, the volume fraction of 7 phases increased but the volume fraction of α2 phase decreased ; the volume fraction of B2 was too small to quantify, but it increased with Nb content increasing ob- served from XRD patterns and scanning electron microscopy （SEM） back scattered electron （BSE） images. With the Nb content in- creasing from 2% to 9%, the tensile strength of the alloys decreased from 648.2 to 613.8 MPa, but their yield strength increased from 561.1 to 613.5 MPa. The ductility of the alloys had a linear decrease from 1.2% to 0.3% with Nb content increasing from 2% to 9%. The axial ratio, c/a, of TiA1 phase which increased with the Nb content increasing was detrimental to the room temperature ductility.