NbC纤维增强共晶镍基合金的超高梯度定向凝固组织研究OA

NbC fiber reinforced high-temperature eutectic nickel-based alloys were prepared using liquid metal cooling(LMC)directional solidification process.By using methods such as SEM,XRD,EDS,and EPMA,the microstructures and formation mechanisms of eutectic nickel-based alloys in different regions were analysed.The effects of various process parameters,including the pulling rates(v=2、7 and 12 μm/s)and melt temperatures(T=1 550、1 580 and 1 600℃),on the microstructures were studied.According to the differences in microstructural types and morphologies,directionally solidified eutectic nickel-based alloys can be divided into two regions,i.e.the start zone and the composite zone.The start zone is mainly composed of Nb-rich and W-rich block carbides,while the composite zone above the start zone is mainly composed of distributed NbC fibers arranged in a directional manner.The growth of NbC fibers during directional solidification can be divided into three stagess,namely,the initial stage,competitive stage,and stabilizing stage,based on the changes in morphology and special distribution of the NbC phase.As the pulling rate increases,the volume fraction of the NbC fiber increases,and the mass fractions of C,Nb,and W in the NbC fibers decreases,with a more significant decrease in the Nb content.As the melt temperature increases,the volume fraction,cross-sectional area,and spacing of the NbC fibers all increase,and the mass fractions of C,Nb,and W in the NbC fibers also increase,with a more significant increase in the W content.