Formation of MoSi2 and Si/MoSi2 coatings on TZM (Mo–0.5Ti–0.1Zr–0.02C) alloy by hot dip silicon-plating method

Abstract

MoSi2 and Si–MoSi2 coatings were deposited on TZM alloy by using a hot dip silicon-plating method. The composite coatings mainly consist of MoSi2 and Si with a small amount of C/SiO2/ZrSi2. The composite coatings have fine MoSi2 grain size and higher surface silicon concentration. The diffusion layer mainly consists of MoSi2 layer and Mo5Si3C layer under the deposition time is 10 min. The diffusion layer is divided into three layers when the deposition time ranges from 15 to 25 min, which consists of Si–MoSi2 layer, MoSi2 layer and Mo5Si3 interface layer. The gradient structure can reduce the stress mutation between coating and the substrate, and further reduce the possibility of crack propagation. SEM and CLSM results show that a large amount of MoSi2 grains are covered by a silicon layer when the deposition time is longer than 10 min, which results in a very low coating surface roughness. And the lowest values of Sa and Sq are 0.292 and 0.391 μm, respectively. Meanwhile, about 65.375%–79.898% of the coating surfaces are covered by silicon when the deposition time is 20–25 min.