Abstract
The present paper treats the cementation of Mo on Ni and Ni-alloys. It is known that the vapour pressure of Mo is lower than that of Ni on which Mo vapour precipitates. When a nickel rod covered with Mo powder is heated ordinarily in hydrogen atmosphere, the complete cementation is not attainable, even when conditions (heating temperature, time, diffusing agents, etc.) are changed. X-ray analysis indicated that the amount of Mo cemented on the Ni surface is proportional to the cementation temperature, but if this temperature exceeds a critical point of cementation, Ni alone cements conversely on Mo surfaces, and the Mo cementation ceases. After heating for about nine hours at a temperature lower than the critical point, the cementation ceases with incomplete saturation.
The complete cementation was done by the “two-stage heating” According to this method, thb cementation is performed, on the first stage heating, at the temperature (e. g. 1100°) lower than the critical point, and then the final cementation is done at still higher temperatures.
The X-ray analysis showed that the amount of Mo cemented on the surface of the sample prepared by this method is 100%, and Mo sinters in Ni down to 0.22mm in thickness (See Fig. 10).
From the present experiment, it is seen that by this “two-stage heating”, any metal of the lower vapour pressure can be cemented on another metal of the higher vapour pressure.
The critical cementation point of pure Ni is 1150° and it is raised by the addition of Fe, Cr, or Cu.
