Shotaro Morozumi1, Michio Kikuchi1 and Shinzo Sugai2
1The Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendai
Diffusion couples of molybdenum with several nitrides, i.e. AlN, BN, Si3N4, TiN, respectively, were heated in vacuum for up to 36×104 s at various temperatures ranging from 1573 to 2173 K. The couples were then examined for composition, growth rate, structure, and hardness of reaction layers, especially for the Mo-BN couple.
Main results obtained are as follows:
(1) In the Mo-AlN system, AlN was sublimated at 1823 K and did not reacted with Mo.
(2) In the Mo-Si3N4 system, Si3N4 decomposed at 1773 K, and Si diffused into Mo and formed three kinds of molybdenum silicides at the surface. The microstructure near the interface between Mo3Si and Mo was observed by transmission electron microscopy.
(3) In the Mo-TiN system, TiN decomposed at 1770 K and Ti diffused into the surface of Mo forming the Mo-Ti solid solution.
(4) In the Mo-BN system, two sublayers of Mo2B and MoB, identified by X-ray measurement, were formed in the surface of Mo at all the experimental temperatures. The layer thickness of the former compound is larger than that of the latter. Apparent activation energy for the growth of overall layer was estimated to be 377 kJ/mol. The hardness of the layer was measured and the microstructure near the interface between Mo2B and Mo was observed by transmission electron microscopy.
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