合金元素对Nb-Ti-Al-C合金氧化行为的影响

Effect of alloying elements on oxidation behavior of Nb-Ti-Al-C alloys at high temperature

利用真空非自耗电弧炉制备不同Al含量的Nb-25Ti-8C合金,研究Nb-Ti-Al-C合金的组织结构及其高温氧化行为。研究表明,Nb-25Ti-8C-(0,5,10)Al合金由Nbss和(Nb,Ti)C两相构成;Nb-25Ti-8C-15Al合金由Nbss、(Nb,Ti)C和Nb3Al三相构成。800~1000℃氧化过程中,合金氧化膜为由Nb2O5,Ti O2,Al2O3,Nb O2及Ti Nb2O7多种氧化物构成的混合氧化膜。Ti、Al活性元素可优先与氧发生选择性氧化,抑制氧化物Nb2O5生成,提高氧化膜致密度和合金抗氧化性,并且氧化温度越高,Al元素改善铌合金抗氧化性能效果越明显。Nb-25Ti-8C合金800℃氧化时表现出良好的抗氧化性能,1000℃氧化时Nb-25Ti-8C-x Al合金的抗氧化性能明显优于C-103。随氧化温度升高,氧化膜中Nb2O5含量增加,导致氧化膜与合金基体的内应力增大,引起外层氧化膜脱落。碳化物中C元素以CO2形式挥发导致氧化层表面形成氧化空洞。

Nb-25Ti-8C alloys with different Al contents were fabricated by a vacuum non-consumable arc-melting method. Microstructure and oxidation behavior of the Nb-25Ti-8C-( 0,5,10,15) Al alloys were investigated. The results show that the Nb-25Ti-8C-( 0,5,10)Al alloys consist of niobium solid solution( Nbss) and carbide of( Nb,Ti) C,and the Nb-25Ti-8C-15 Al alloy consists of Nbss,( Nb,Ti)C,and Nb3 Al phases. In the range of 800 and 1000 ℃,the oxide layers of the alloys consist of Nb2O5,Ti O2,Al2O3,Nb O2 and Ti Nb2O7 phases. The oxidation resistance of the alloys improves with doping of Ti and Al due to the elements reaction with oxygen primarily,this causes the decrease of solubility and diffusion rate of oxygen into the Nbss matrix. Furthermore,the oxidation reaction of Al and oxygen becomes more obvious with increasing oxidation temperature. Nb-25Ti-8C alloy exhibits excellent oxidation resistance when oxidized at 800℃. In addition,the oxidation rate of Nb-25Ti-8C-x Al alloy is less than that of industrial niobium alloy C-103 at 1000 ℃. The fraction of Nb2O5 in the oxide scale increases with increasing oxidation temperature,which leads to the enhancement of the internal stress between the oxide film and alloy matrix,and the exfoliation of the outer oxide film. C element in the carbides volatilizes as CO2 lead to formation of oxidation of empty on the surface of oxide film.