日本金属学会誌

J. Japan Inst. Metals, Vol. 55, No. 11 (1991),
pp. 1222-1231

Aluminized Molybdenum by Pack Cementation and its Resistance to High-Temperature Oxidation

Toshio Maruyama1, Bi Xiao Fang2 and Kazuhiro Nagata1

1Department of Metallurgical Engineering, Faculty of Engineering, Tokyo Institute of Technology, Tokyo
2Graduate Student, Tokyo Institute of Technology, Tokyo. Present address: NKK Corporation, Kawasaki

Abstract:

High-temperature oxidation of various intermetallic powders in the molybdenum-aluminum system was examined at a constant rate of heating in air. Powders of Mo3Al8 and MoAl4 exhibited good oxidation resistance. Molybdenum aluminide was coated on Mo by pack cementation at 1323 K using the pack of Al, NH4Cl and Al2O3. The aluminide coating consisted mainly of Mo3Al8. A thin layer of Mo3Al was also formed between Mo3Al8 and Mo. The coating layer grew by inward diffusion of Al. Several cracks were observed in the coating layer. The formation of cracks resulted probably from stress during cooling, which arose from the difference not only in molar volumes but also in thermal expansion coefficients. Oxidation behavior of the coated molybdenum indicated that the coated Mo3Al8 itself possessed the oxidation resistance with the formation of a thin film of alumina. However, the cracks degraded the resistance. The elimination of cracks in the layer is indispensable for the improvement of oxidation resistance.


(Received 1991/7/8)

Keywords:

molybdenum aluminide, pack cementation, Mo3Al_8, high temperature oxidation, alumina


PDF(Free)PDF (Free)     Table of ContentsTable of Contents

Please do not copy without permission.