材料期刊网

为进一步提高铌合金的高温性能,在HЦУ铌合金上分别制备了3种涂层:料浆法Si-Fe-Cr-Ti涂层,料浆法Si-B-Ti涂层以及以等离子喷涂MoSi2为内层、硼和硅扩散层为外层的复合涂层,测定了他们在空气介质中的1 400℃等温蠕变和1 400～250℃热循环蠕变特征和持久寿命.试验表明:等离子喷涂/扩散复合涂层的持久寿命、断裂塑性和蠕变速率显著优于其他2种涂层,复合涂层表面出现蠕变裂纹后,当下阶段的蠕变速率几乎没有改变,大于70％的持久寿命服役在涂层表面有裂纹的情况下;应力较高下,等温蠕变速率高于热循环蠕变者;应力较低下,等温蠕变速率低于热循环蠕变者;持久寿命与蠕变速率对应,但规律相反;复合涂层中,涂层呈多层和多孔隙形式,阻止了裂纹扩展;复合涂层含有能够愈合缺陷的易熔化合物,不仅能填充裂纹,而且使得涂层中生成的裂纹顶端圆滑.

Three kinds of protective coatings were prepared on НЦУ Nb-based alloy respectively,including Si-Fe-Cr-Ti and Si-B-Ti coating by slurry method,and compound coating (inner MoSi2 layer by plasma spraying and diffusion outer layer based on B and Si element).The tensile creep characters and stress rupture life of coatings were measured by isothermal test at 1 400 ℃ and thermo-cyclic test under 1 400 ～ 250 ℃,respectively.Results showed that endurance life,broken plastic and creep rate of the plasma spray / diffusion composite coating were much better than those of the other 2 kinds of coatings.Mter creeping crack emerged on the surface of composite coating,the creeping rate in this stage changed little,and higher than that of 70％ stress rupture life existed in the cracked situation on the surface.When the stress was higher,the isothermal creeping rate was higher than that of thermo-cyclic test.When the stress was relatively lower,the isothermal creeping rate was lower than that of thermo-cyclic test.Moreover,the stress rupture life was just corresponding to the creeping rate,but the changed rules were opposite.The composite coating exhibited multilayer and porous formation,which could prevent the cracks spreading.Besides,the composite coating contained the low-grade melting compound that not only fulfillled crack,but also formed circle shape in a crack tip.