High temperature resistant multi-component silicide coating on the surface of niobium alloy and its preparation method, the coating's component phase is [(Nb1‑x‑yTixCry)1‑z, Rz]Si2, R is one or more of the metal elements Mo,W,Zr,Hf,Ta, where x,y,z respectively represent the mole number of the corresponding element. And 0.05≤x≤0.2,0.05≤y≤0.3,0.05≤z≤0.4; Firstly, according to the molar ratio of [(Nb1‑x‑yTixCry)1‑z, Rz] : Si = 1:2.01 ~ 2.1, weigh each metal powder and silicon powder, and put them into the mixing machine to fully mix for 12 ~ 24h; The niobium alloy workpiece was embedded with mixed multi-component metal powder and placed in a graphite crucible, and then the graphite crucible was placed in a discharge plasma sintering furnace for sintering. The sintered coating sample can be homogenized and heat treated in a vacuum or protective atmosphere. The invention provides a composite preparation process of discharge plasma sintering + homogenization heat treatment. The process is simple, the coating structure is uniform, the composition is controllable, and the coating has excellent high temperature oxidation resistance at 1200 ~ 1600℃.
By coating slurry containing Si, Mo, Ti, HfO2 and Al on niobium alloy, and then melting and firing under high temperature vacuum to prepare high temperature anti-oxidation silicide coating, the coating can effectively solve the problem of severe oxidation of niobium alloy above 800℃, especially at 1100℃. The Chinese patent CN104561882A discloses a double-layer coating with bottom coating Mo1-xWx(Si1-y-zAlyBz)2+ top coating Mo1-xWx(Si1-y-zAlyBz)2-(10-20) w.% HfSi2 on the surface of niobium alloy by high energy plasma spraying process. The coating has excellent resistance to high temperature oxidation at 1500-1800℃. It can be seen that multi-component silicide coating is the future development direction of high temperature protective coating on niobium alloy surface. Although some of these systems have been successfully applied to the high temperature protection of niobium alloy in the aerospace field, simplifying the coating preparation process, improving the uniformity of the coating structure, the controllability of the composition structure and preparing higher performance protective coatings have been the focus of the research on the anti-oxidation silicide coatings on the surface of niobium alloy.
The discharge plasma sintering process is a new powder metallurgy sintering technology which has been paid much attention in recent years. It has the characteristics of sintering under pressure. The plasma generated by pulse current and the pressure during sintering are conducive to reducing the sintering temperature of the powder. At the same time, the characteristics of low voltage and high current can make the powder sintering densification quickly. Its technological advantages are very obvious: uniform heating, fast heating rate, low sintering temperature, short sintering time, high production efficiency, fine and uniform product organization, can maintain the natural state of raw materials, and can obtain high density materials. At present, researchers have tried to use discharge plasma sintering process to prepare anti-oxidation coating on the surface of niobium alloy, but the microstructure of the coating is lack of density, and there is a large internal stress in the coating, which is easy to produce large cracks in the process of high temperature oxidation, and even the coating will collapse, thus losing the protective effect.
