Dissolution of CR3C2 in a nickel matrix during sintering. I. Reaction of chromium carbide with nickel during solid-phase sintering

The Effect of Heat Treatment on the Oxidation Mechanism of Blended Powder Cr3C2-NiCr Coatings

“…Solid-state sintering in Cr 3 C 2 -Ni composites has been reported at temperatures of 700 to 800°C by Vlasyuk et al (Ref 8,9). Cr atoms were thought to diffuse into the Ni binder, generating a physical bond between the two phases as well as forming a band of low Cr content NiCr alloy around the carbide periphery, which is consistent with the results of this study.…”

“…2). Vlasyuk et al (Ref 8,9) reported a similar stable carbide composition while treating Cr 3 C 2 -NiCr composites up to 900°C. Taylor (Ref 10) observed variable results during heat treatment of Cr 3 C 2 -based blended powder plasma and D-Gun coatings.…”

“…It is possible that the excess C was dissolved within the NiCr alloy or incorporated as a fine phase that was not distinguished from the carbide particles. Similarly, the evident alloying of Ni by Cr in the work of Vlasyuk et al (Ref 8,9) suggests that it is unlikely that only C diffuses in the work of Taylor (Ref 10). In addition, the complex structures of Cr 3 C 2 and Cr 7 C 3 highlighted by Guilemany et al (Ref 15) suggests that it is unlikely that the structure simply reorients itself from that of Cr 3 C 2 to Cr 7 C 3 , as would be required for a C-only diffusion mechanism.…”

“…Each of the above studies highlighted either Cr or C diffusion without detailing specifically the response of the alternate element. While not detected until very high temperatures in the work of Vlasyuk et al (Ref 8,9), C must diffuse away from the carbide phase at lower temperatures since Cr 3 C 2 is the most C rich of the chromium carbides and hence could not accommodate excess C within the carbide structure as would be required by Cr dissolution alone into the NiCr alloy. It is possible that the excess C was dissolved within the NiCr alloy or incorporated as a fine phase that was not distinguished from the carbide particles.…”

“…Cr atoms were thought to diffuse into the Ni binder, generating a physical bond between the two phases as well as forming a band of low Cr content NiCr alloy around the carbide periphery, which is consistent with the results of this study. Diffusion appeared unidirectional up to 900°C (Ref 8,9) with no Ni diffusion into the carbide phase in spite of the increasing degree of Cr alloying in the Ni phase with increasing temperature. In contrast to the work of Vlasyuk et al (Ref 8,9), Taylor (Ref 10) hypothesized that it was the C, not Cr, that was the principal diffusion species based on the formation of Cr 7 C 3 and Cr 23 C 6 at the grain boundaries within the NiCr splats of Cr 3 C 2 -NiCr coatings.…”