As a refractory metal, niobium has been used in space field. Niobium tungsten alloy has high strength at high temperature and good plasticity at room temperature. It can be made into various processing materials and parts by conventional forming processing technology, which can be used for space shuttle skin, nuclear reactor engineering, jet engine parts, space power generation system thermal radiation screen and catheter, etc. China's chang 'e-3 related facilities part of the use of niobium tungsten alloy.
Niobium tungsten alloy destructive oxidation happens in high temperature aerobic environment, need through the alloying coating modification and coating protection, high temperature but alloying modification will seriously affect the mechanical properties, so the alloy coating on the surface of the coating protection become a research focus, surface coating of high temperature oxidation resistance directly determines the shuttle engines with niobium tungsten alloy working temperature. Dongfang tantalum industry co., LTD. Prepared the silicon chemical coating for niobium tungsten alloy by slurry melting. They developed the niobium tungsten alloy nb521-1, the main ingredient is 5w-2mo-1zr, the rest is Nb. The coating preparation process is as follows: Si, Ti, Cr powder is mixed in a certain proportion, a certain amount of organic solvent is added and put into corundum jar. The material is mixed with ball mill, and the roller is used. The rotating speed is 200~300r/min.
They found that the alloy coating in the process of preparation and use of coating accumulation, accumulation area coating surface is significantly different from other normal areas, a little accumulation and line accumulation of two surface defects. The coating slurry is mixed with coating debris, which will accumulate on the prepared coating surface after melting. However, in the process of melting and burning, when the shedding area of the coating exceeds the self-leveling ability of the residual slurry, it will cause line accumulation and accompany surface defects such as leakage coating. The comparison of the energy spectrum of the coating of normal area and stacking area shows that the composition of the coating area at point stacking or line stacking is not significantly different from that of normal coating. Stacking coating is consistent with normal coating structure, mainly composed of outer layer, main layer and diffusion layer. The normal coating thickness is about 120 microns, and the point stacking coating thickness is about 120 microns, while the thickness of the line stacking area fluctuates greatly, and the thicker coating area has a thickness difference of about 50 microns compared with other areas. Point stacking refers to the embedding of coating particles into the coating surface, which has little influence on the cross-section, while line stacking refers to the superposition of slurry in the process of coating preparation. Although it does not affect the structure of the coating, it has great influence on the thickness of part of the coating.
