Microstructure evolution of in-situ (Ti,W)C-Al2O3 particle-reinforced alloy fabricated by gas tungsten arc cladding

This paper reports the fabrication of TiC-Al2O3 or (Ti,W)C-Al2O3 ceramic reinforced metal matrix composites (MMC) using gas tungsten arc cladding. For fabrication of the MMC, an in-situ reaction was used to reduce oxides by employing C and Al as reducing materials during the cladding process, and the strengthened particles formed on the surface by solid state reaction were then grown through interaction in the metal matrix. The reactions forming phases in this system were subsequently examined through thermodynamic calculations. Results showed that TiC and Al2O3 peaks were observed in XRD for the reduction of TiO2 and WO3 by Al and C. The cladded hardfacings were covered by a composite slag zone, which consisted of Al2O3 particles embedded in Al and Ti based ceramic matrix, and that carbide particles such as TiC and (Ti,W)C were distributed intensively inside the MMC zone. Most of the TiC particles in the MMC zone had a slow growth rate because the interface controlled the growth; however, some particles that highly interacted with metals exhibited a dendrite structure. (Ti,W)C particles without dendrite growth formed a spherical shape, and the size of the particles was controlled by diffusion of the solute. Following the dissolution and precipitation process, (Ti,W)C-strengthened particles were found to have a sintering-like core/rim structure. Furthermore, the microhardness of the clad obtained was 600-900 HV0.2, which is significantly better than that obtained with commercial TiC powder.