Nb-Ti-Si基超高温合金表面Ge-Y改性硅化物渗层的组织形成

FORMATION OF Ge-Y MODIFIED SILICIDE COATINGS ON Nb-Ti-Si BASE ULTRAHIGH TEMPERATURE ALLOY

为提高Nb-Ti-Si基超高温合金的高温抗氧化性能,采用Si-Ge-Y共渗工艺在其表面制备了Ge-Y改性的硅化物渗层.利用XRD,SEM和EDS分析了渗层的结构和相组成,并对其组织形成机理进行了讨论.结果表明:所制备的渗层具有明显的分层结构,由外至内依次为(Nb,X)(Si,Ge)_2(X代表Ti,Cr和Hf)外层和(Ti,Nb)_5(Si,Ge)_4内层;Ge在渗层中的含量由外向内逐渐增加.与Y改性硅化物渗层相比,Ge-Y改性硅化物渗层的组织并未发生显著改变,但Ge的添加会在一定程度上减少Si在共渗层表面的吸附和沉积,对渗层的生长有明显的抑制作用.保温不同时间(0—8 h)所制备的渗层具有相似的结构,渗层的生长动力学曲线符合抛物线规律.

Nb-Si base ultrahigh temperature alloy is a promising candidate for high temperature applications due to its high melting point, high strength and relatively low density at elevated temperatures. However, the poor oxidation resistance of this alloy has still be a major barrier to its high temperature applications. Ge and Y modified silicide coatings on an Nb-Ti-Si based ultrahigh temperature alloy have been prepared successfully by co-depositing Si, Ge and Y in order to improve its high temperature oxidation resistance. The structure, constituent phases and formation process of the coatings have been revealed using XRD, SEM and EDS. The results showed that the coatings had obvious layered structure which was composed of a （Nb, X）（Si, Ge）2 （X represents Ti, Cr and Hf elements） outer layer and a （Ti, Nb）5（Si, Ge）4 inner layer. The concentration of Ge in the coating increased with increase in the distance away from the coating surface. Compared with the single Y modified silicide coating, the addition of Ge did not change the coating structrue, but reduced the absorption and deposition of Si and retarded the coating growth. The coatings prepared at 1250℃ for different time （0-8 h） had similar structures and the coating growth kinetics followed a parabolic law.