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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.

在能源相关行业中，对用于高温用途的高强度材料的需求正在增长。金属材料的高温抗氧化性能是其能否在氧化环境中使用的关键。具有高熔点的难熔金属如钼和钨是用于高温用途的金属材料的基底金属的候选物。然而，这些金属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的氧化皮来提供的。本研究采用固体渗铝和渗硅的方法对钼表面进行渗铝和渗硅，在氧化环境中形成保护性的氧化铝或氧化硅氧化膜，渗铝形成Mo_3Al_8涂层，由于涂层与钼基体之间的热膨胀差异和裂纹尖端氧化铝形成的应力，涂层中容易产生裂纹。氧化过程中裂纹的扩展降低了抗氧化性。在1323 K下，采用包埋渗法在钼基体上制备了硅铝共渗涂层。涂层由Mo_3Al_8组成，其中Mo_3Al_8含量约为1at. %的Si，其中Mo（Si，Al）_2和Mo_5（Si，Al）_3分别在涂层表面和涂层/Mo界面处析出。在1520 K的空气中氧化的涂层钼得到薄的氧化铝膜，表现出良好的抗氧化性。用X射线衍射法绘制了Mo-Si-Al系1323 K相图，预测了涂层的显微组织。