摘要
对A l,Ta含量分别是6wt%A l,0wt%Ta;5wt%A l,4wt%Ta和6wt%A l,4wt%Ta三炉低Cr高W铸造镍基高温合金进行了静态空气下1100℃/2m in^100h等温氧化试验,并对剥落氧化皮和合金试片表面氧化层进行X射线衍射分析,对氧化后的试片表面及横切面进行光学金相、定量金相、扫描电镜及能谱分析。结果表明:低Cr高W镍基高温合金的早期氧化主要表现为富难熔元素相MC,M6C碳化物和α(W,Mo)相的优先选择性氧化。6wt%A l,0wt%Ta合金和6wt%A l,4wt%Ta的合金经1100℃/100h氧化后的最终主要氧化产物均包含N iO,N iA l2O4和N iWO4,此外合金中还分别存在少量的N iNb2O6和N i(Ta,Nb)2O6。合金的氧化动力学曲线遵循分段抛物线规律。A l量相同的情况下,Ta的加入通过增加共晶γ’量和减缓自由态硫对抗氧化的有害作用从而减少合金的氧化增重和延缓氧化皮剥落,提高合金的抗氧化能力。6wt%A l,0wt%Ta的合金与5wt%A l,4wt%Ta的合金具有相当的高温抗氧化能力,仅从高温抗氧化性能考虑,可以考虑以A l代Ta。
The static oxidation tests of three heats of Ta-free （6wt% Al, 0wt% Ta） and Ta-containing （5wt% Al, 4wt% Ta and 6wt% Al, 4wt% Ta） low Cr and high W content cast Ni-base superalloys were carried out in air at 1100℃ for 2min - 100h. The oxides in the surface of the samples and the spalled oxide scales were analyzed by X-ray diffraction （ XRD）. The surface and the cross section of the oxidized samples were investigated by optical metallography, quantitive metallography, scanning-electron microscopy （SEM） and energy-dispersive spectrometry （ EDS）. The results show that the early stage oxidation for low Cr and high W content superalloys is mainly the preferential oxidation of refractory elements rich phases such as MC carbides, MsC carbides and α （W, Mo） phase. The ultimate oxides of both Ta-free and Ta-containing alloys after 1100α/100h isothermal oxidation are NiO, NiAl2O4 and NiWO4. In addition, small amount of NiNb2O6 and Ni（ Ta, Nb）2O6 exist in Ta-free or Ta-bearing superalloys respectively. The oxidation kinetic curves of alloys follow a parabolic rate law in different oxidation stage. The Ta addition at the const content of Al can promote the formation of eutectic γ＇ and decrease the harmful effects of element sulfur, then improve the oxidation resistance by decreasing the weight gain and retarding the spallation of the oxide scales. 6wt% Al, 0wt% Ta alloy possesses a similar oxidation resistance to that of the 5wt% Al, 4wt% Ta alloy. Therefore, it is feasible to replace Ta by Al in case of only considering the high temperature oxidation resistance.
出处
《航空材料学报》
EI
CAS
CSCD
2005年第5期1-7,共7页
Journal of Aeronautical Materials
关键词
NI基高温合金
氧化
钽
碳化物
显微组织
X射线衍射
Ni-base superalloys
oxidation
tantalum
carbides
microstructure
X-ray diffraction
