Modification of Refractory Metals by CVD and Its High Temperatutre Oxidation Resistance

难熔金属的CVD改性及其高温抗氧化性能

基本信息

批准号：
01470062
负责人：
MARUYAMA Toshio
金额：
$ 4.1万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

Demands for high strength materials for high temperature use is growing in energy related industries. The high temperature oxidation resistance of metallic materials is a key for the usage in oxidative environment. Refractory metals with high melting points such as molybdenum and tungsten are candidates for the base metals of metallic materials for high temperature use. However, these metals forms volatile oxides and suffer from severe oxidation. The oxidation resistance of metallic materials is provided by the formation of protected oxide scales of alumina, chromia or silica. In this study, aluminizing and siliconizing of the surface of molybdenum were carried out by pack cementation to form the protective alumina or silica scales in the oxidative environment.Aluminizing provided the Mo_3 Al_8 coating layer in which cracks were easily introduced by the difference of thermal expansion between the coating and the Mo substrate and by the stress arising from the formation of alumina in the crack tips. The propagation of cracks during oxidation degraded the oxidation resistance. Silico-aluminized coating on molybdenum was per-formed by pack cementation at 1323 K. The coating was composed of Mo_3Al_8 containing about 1 at. % Si in which Mo (Si, Al)_2 and Mo_5 (Si, Al)_3 precipitated beneath the surface and at the coating/Mo interface, respectively. The oxidation of the coated molybdenum at 1520 K in air gave the thin alumina scale, exhibiting good oxidation resistance. The crack formation in the coating layer was seldom.The microstructure of the coating layer was predicted by the phase diagram of Mo-Si-Al system at 1323K which was made by X-ray diffraction.

能源相关行业对高温用高强度材料的需求不断增长。金属材料的高温抗氧化性能是在氧化环境下使用的关键。钼、钨等高熔点难熔金属是高温用金属材料的基础金属的候选材料。然而，这些金属会形成挥发性氧化物并遭受严重氧化。金属材料的抗氧化性是通过形成氧化铝、氧化铬或二氧化硅的受保护氧化皮来提供的。本研究采用包渗法对钼表面进行渗铝和渗硅处理,在氧化环境中形成氧化铝或氧化硅保护层。渗铝提供了Mo_3 Al_8镀层,该镀层因热膨胀差异而容易产生裂纹。涂层和钼基体之间以及裂纹尖端形成氧化铝所产生的应力。氧化过程中裂纹的扩展降低了抗氧化性。在1323 K下通过包渗法在钼上形成硅铝化涂层。该涂层由含有约1at的Mo_3Al_8组成。％Si，其中Mo（Si，Al）_2和Mo_5（Si，Al）_3分别沉淀在表面下方和涂层/Mo界面处。涂层钼在1520 K空气中氧化生成薄薄的氧化铝氧化皮，表现出良好的抗氧化性。镀层很少产生裂纹。通过X射线衍射绘制的Mo-Si-Al系1323K相图预测了镀层的显微组织。