Microhardness variation in relation to carbide development in heat treated Cr3C2-NiCr thermal spray coatings

Cr3C2-NiCr thermal spray coatings have been extensively used to mitigate high temperature wear. During deposition compositional degradation occurs through dissolution of the carbide phase into the matrix. High temperature exposure leads to transformations in the microstructure, which influences the coating microhardness. While such developments have been investigated in short-term trials, no systematic long-term investigations of the microhardness variation as a function of microstructural development have been presented. In this work, high velocity sprayed Cr3C2-NiCr coatings were heat treated at 900 degreesC for up to 60 days in air and argon. With treatment, matrix phase supersaturation was reduced, while widespread carbide nucleation and growth generated an expansive carbide skeletal network. An initial softening of the coatings occurred through matrix phase refinement, the subsequent hardness recovery was a function of carbide development. Treatment in air generated further hardness increases as a result of internal oxidation. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.