Comparison of the microstructures and abrasive wear properties of stellite hardfacing alloys deposited by arc welding and laser cladding

The microstructure of cobalt-based hardfacing alloys deposited by manual metal arc (MMA) welding, tungsten inert gas (TIG) welding, and laser cladding has been investigated as part of a study attempting to establish the relationship between microstructure and abrasive wear properties. For typical deposition conditions, the differences in freezing rates associated with the three processes are found to give rise to large differences in microstructure. The MMA process is found to lead to the largest degree of dilution of the hardfacing deposit; the TIG and laser deposits exhibited much lower levels of mixing with the base plate. For the deposition conditions used in this study and for the alloys examined, the scale of the microstructure decreases in the order MMA, TIG, and laser cladding, leading to an increase in the deposit hardness in the same order. It is found that with alumina as an abrasive, the wear rate persistently is higher with the MMA deposits (which have the coarsest microstructure with the lowest starting hardness), the weight loss being approximately linear with time. The laser and TIG deposits, which have more refined microstructures and slightly higher carbon concentrations, both are found to exhibit significantly lower wear rates. Initially, the TIG samples are the most resistant to abrasion, even though their microstructure compares with that of the laser samples; this is a consequence of their higher ductility associated with a lower rate of strain hardening. The laser samples, which contain a lower matrix iron concentration, strain harden more rapidly; consequently, they exhibit an initial decrease in wear rate. With the much harder silicon carbide abrasive, all samples show similar wear rates which do not decrease with time. The wear data are found to correlate with scanning and transmission electron microscopy observations, and it is possible to rationalize the interaction among microstructure, abrasive, and alloy deposition processes.