等离子表面渗Nb对γ-TiAl合金扩散焊接性能的影响

Effect of plasma surface metallizing Nb on diffusion welding performance of γ-TiAl alloy

采用双辉等离子表面渗金属技术在名义成分为Ti-45Al-8.5Nb (W, B, Y)的γ-TiAl合金表面制备了Nb涂层。使用SEM、EDS、XRD等手段研究了不同渗Nb温度、焊接温度对γ-TiAl合金扩散焊接接头微观组织及性能的影响。结果表明,在800~950℃的渗Nb温度范围内均可以在γ-TiAl合金表面形成致密的Nb涂层,随着渗Nb温度的升高,Nb涂层晶粒尺寸和表面粗糙度均不断增大。典型的接头组织从基体向焊缝中心可分为4层:Ⅰ层(Nb涂层与基体间扩散层)、Ⅱ层(含有少量AlNb;的Ti-Nb互溶层)、Ⅲ层(富Ti-TiNi层)、Ⅳ层(近等原子比TiNi层)。接头的剪切强度随渗Nb温度和焊接温度的升高均呈先增大后减小的趋势。渗Nb温度为850℃,焊接温度为900℃时获得的接头剪切强度最高,达到82.0 MPa。

Double glow plasma metallizing technology was used to prepare Nb coating on the surface of γ-TiAl alloy with a nominal composition of Ti-45 Al-8.5 Nb(W, B, Y). Effect of Nb depositing temperature and welding temperature on microstructure and properties of the γ-TiAl alloy diffusion welded joints was studied by SEM, EDS, XRD, etc. The results show that dense Nb coating can be formed on the γ-TiAl alloy at the Nb depositing temperature range of 800-950 ℃. The grain size and roughness of the Nb coating increase continuously with the increase of Nb depositing temperature. The typical joint structure from the substrate to welded center can be divided into 4 layers: layer Ⅰ(diffusion layer between substrate and Nb coating), layer Ⅱ(Ti-Nb miscible layer containing small amount of AlNb;), layer Ⅲ(Ti-riched TiNi layer), layer Ⅳ(near equiatomic TiNi layer). The shear strength of the joint increases first and then decreases with the increase of Nb depositing temperature and welding temperature. The joint prepared at Nb depositing temperature of 850 ℃ and diffusion welding temperature of 900 ℃ achieves the highest shear strength, up to 82.0 MPa.