The effect of Ta substitution for Nb on the microstructure and wear resistance of an Fe-Cr-C hardfacing alloy

Abstract

The effect of Ta substitution for Nb on the microstructure and wear resistance of an Fe-Cr-C hardfacing alloy deposited with gas tungsten arc welding (GTAW) process was investigated. Results showed that the microstructure of the base composition was a hypoeutectic one consisting of primary austenite dendrites and eutectic constituents of γ+M7C3. Addition of Nb did not change the hypoeutectic nature of the microstructure. However, coarse semi-cuboidal NbC was formed in the microstructure. Moreover, compared with the base composition, higher eutectic content and finer austenite dendrites were observed as a result of Nb addition. Ta substitution for Nb has changed the microstructure from hypoeutectic to hypereutectic containing primary hexagonal M7C3 carbides in an eutectic matrix along with coarse semi-cuboidal TaC particles. Hardness test results revealed that the hardness value increased by the addition of Nb or Ta. Maximum hardness value was obtained from Ta-containing coating. Reciprocating wear test results were directly related to the hardness of the hardfacing alloys. Hence, Ta-containing coating exhibited a superior wear resistance mainly due to the formation of primary hexagonal M7C3 carbides and coarse TaC precipitates. As well, Scanning Electron Microscopy (SEM) of the worn surfaces revealed evidences of abrasive and delamination wear mechanisms.