分类: 材料科学 >> 材料科学(综合) 提交时间: 2023-03-19 合作期刊: 《金属学报》
摘要: 采用先磁控溅射Zr 膜, 再Si-Y扩散共渗的方法, 在新型Nb-Ti-Si-Cr 基超高温合金表面制备了ZrSi2-NbSi2复合渗层, 分析了渗层的显微组织及形成机制, 并研究了其在1250 ℃的恒温氧化行为. 结果表明, 1150, 1250 和1350 ℃下Si-Y共渗4 h 所制备的渗层具有相似的显微组织, 均主要由ZrSi2外层, (Nb, X)Si2 (X=Ti, Cr, Zr 和Hf)中间层和(Ti, Nb)5Si4内层组成.恒温氧化实验结果表明, 所制备的渗层具有优异的抗高温氧化性能. 氧化时渗层表面形成了由SiO2, TiO2, ZrSiO4和Cr2O3混合组成的致密氧化膜, 能够在1250 ℃空气中保护基体合金至少100 h 不被氧化.
分类: 材料科学 >> 材料科学(综合) 提交时间: 2023-03-18 合作期刊: 《材料研究学报》
摘要: 用扩散渗法在Nb/NbCr2合金表面制备硅化物涂层, 研究了基体合金和涂层在1250℃的氧化行为。结果表明:在Nb/NbCr2合金表面渗Si 所得硅化物涂层由(Nb, Cr)Si2和(Cr, Nb)Si2两相组成, 过渡层为(Nb, Cr)5Si3, 涂层的生长动力学服从抛物线规律。基体合金在1250℃氧化形成的氧化膜为Nb2O5和CrNbO4交替分布的疏松组织, 与基体有剥离现象。渗Si 涂层在1250℃氧化形成的氧化膜较为致密完整, 与残留涂层结合良好, 为SiO2和CrNbO4混合氧化膜, 改善了合金的高温抗氧化性能。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2023-03-19 合作期刊: 《金属学报》
摘要: Nb- Ti- Si base in situ composites which consist of Nb solid solution (Nbss) and silicides (a-Nb5Si3, b-Nb5Si3, g-Nb5Si3 and/or Nb3Si) phases, have shown great potential as alternative materials to Ni-based superalloys due to their high melting points (beyond 1700 ℃ ), good formability, low density (6.6~7.2 g/cm3) and high strength. However, a major hindrance to the applications of these alloys at elevated temperatures is their poor oxidation resistance. Alloying is an effective method to improve the integrated properties of the alloys, especially for the oxidation resistance. Up to now, many beneficial elements such as Ti, Al, Cr and Sn have been employed to ameliorate their oxidation resistance. Nevertheless, there is no systematic and comprehensive investigation on the effect of Zr contents on the microstructure and oxidation behavior of the alloys based on Nb-Ti-Si system. The aim of this work is to clarify the effects of Zr contents on phase selection, microstructure and high temperature oxidation resistance of Nb-Ti-Si based alloys in detail. The constituent phases, microstructure and composition of the alloys under as- cast state and after oxidation were investigated by OM, XRD, SEM and EDS. Thus, six Nb-Ti- Si base ultrahigh-temperature alloys with compositions of Nb-22Ti-15Si-5Cr-3Hf-3Al-xZr (x=0, 0.5, 1, 2, 4, 8, atomic fraction, %) were prepared by vacuum non-consumable arc-melting. The results show that the alloys with different Zr contents are mainly composed of Nbss and g-(Nb, X)5Si3 (X represents Ti, Hf, Cr and Zr). However, the addition of Zr has an obvious affect on the microstructure of Nb-Ti-Si base alloys. Both the sizes and amounts of primary g- (Nb, X)5Si3 increase with increase in Zr contents. Alloys with different Zr contents were oxidized at 1250 ℃ for 1~50 h, respectively. It is found that both adhesion and compactness of the scales are improved effectively by increase in Zr contents. The scales of alloys with higher Zr contents (x=4 and 8) after oxidation for 50 h show an obvious layered structure: the outmost layer is only composed of TiO2, the middle layer mainly consists of ZrO2, TiNb2O7 and TiO2, and the inner layer is mainly comprised of Si-rich oxides. The mass gain per unit area and the thickness of the scale after oxidation decrease with increase in Zr contents in the alloys, indicating that the addition of Zr can improve the oxidation resistance of the alloys significantly.