To investigate the oxidation behavior of TiC-base alloys containing molybdenum, TiC-10% Ni and TiC-10% Ni-(2.5∼18.57)% Mo alloys were prepared by sintering. These alloys were exposed in still air at 600°∼1300°C. The oxidation process and the effect of molybdenum on oxidation were studied by the weight gain, surface recession, X-ray diffraction and microstructure observations of scales. The following results were obtained.
(1) Addition of molybdenum to TiC-10% Ni alloy increased the weight gain due to oxidation below 1100°C, which was most effective at 700°∼800°C. This effect was, however, decreased at higher temperatures and at 1300°C molybdenum increased the oxidation resistance reversely.
(2) From the X-ray diffraction data, it appeared that at higher temperatures the oxidation of molybdenum was suppressed to cause the appearance of metallic molybdenum in the scales and NiO·TiO
2 was also increased, while at lower temperatures NiO was combined preferentially with NiO·MoO
3 and decreased the NiO·TiO
2 content in the surface layer of scales.
(3) From measurements of the surface recession, it was found that the progress of oxidation of all the alloys at 1000°C was parabolic and the parabolic rate constant increased in proportion to the molybdenum content. But at 1300°C, the surface layer of scales became porous and no parabolic relation was found in all the alloys.
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