原位合成NbC及Nb/C比对Ni-Si体系组织的影响

Effect of in-situ synthesised NbC and ratio Nb/C on microstructures of Ni-Si system

利用激光熔覆技术,以Ni、Si、Nb和C元素粉末为原料,改变[Nb+C]加入量及Nb和C之间的相对量,在高温合金表面原位合成NbC/Ni3Si基复合材料涂层.借助金相显微镜,X射线衍射仪对涂层组织进行分析.结果表明,熔覆层由-γNi固溶体、Ni3(Si,Nb)和NbC组成.衍射图中NbC峰的出现证明在激光熔覆过程中NbC强化相可以由Nb和C直接原位反应形成.当NbC的质量分数增加时,熔覆层的枝晶组织明显变细,主要以树枝状、等轴晶的形态存在.当NbC的质量分数一定,Nb相对量较多时,枝晶间形成弥散分布的富Nb增强相Nb3Ni2Si,增强了熔覆层的强度,另一方面还阻止晶粒长大使熔覆层组织细化;当C元素相对过量时,会以游离态的形式析出,从光学显微组织观察发现对晶粒有细化效果.

Laser cladding technology was used for in-situ synthesis of NbC/Ni3Si composite coating on the nickel-matrix superalloy substrate, where the powders of Si, Ni, Nb and C were taken as raw materials and the content of [Nb＋C] and ratio of Nb to C were adjusted. The coating was investigated by means of optical microscopy and X-ray diffraction （XRD）. The result showed that the coating was composed of 7-Ni, Ni3 （Si,Nb） and NbC. The peak of NbC was found, confirming that NbC phase was formed by in-situ reaction. The coating exhibited a typical dendritic and equiaxed microstructure, and the grain size decreased with NbC content increasing. Nb3Ni2Si were found when increasing Nb content, which baffled the grain coarsening. When excessive of C was added, it was separated out in the form of free state and resulted in grain refining according to the observation of optical microscopy.