Activity of carbon in nickel-rich Ni-Mo and Ni-W alloys.

Effects of molybdenum and tungsten on carbon activity in nickel have been experimentally determined at 1000, 1100, and 1200 °C. Seventeen nickel-molybdenum and thirteen nickel-tungsten binary alloys were carburized in a flow of purified methane and hydrogen mixed gas. A sealed capsule technique was also employed for carburization of a few series of nickel-molybdenum alloys. The carbon concentration was determined either by hot extraction techniques (LECO and Coulomatic) or by weight gains of these specimens. The carbon concentration at a constant carbon activity decreases with increasing either molybdenum or tungsten concentration in nickel. The effect of tungsten on the carbon solubility in nickel is slightly larger than that of molybdenum. The experimental data were analyzed in terms of the regular solution model with two sublattices due to Hillert and Staffansson. Temperature dependence of the interaction coefficients between carbon and molybdenum or tungsten was expressed as DG/RT = −4.45 + 11650/ T and DG /R = 1.21 + 9010/. [ABSTRACT FROM AUTHOR]