Processing, mechanical behavior, and microstructural characterization of liquid phase sintered intermetallic-bonded ceramic composites

Intermetallic-bonded ceramic (IBC) composites with various amounts of a WC or TiC carbide phase mixed with a Ni₃Al or FeAl binder phase were successfully fabricated by liquid phase sintering and hot isostatic compaction methods. The influence of carbide type, binder type, and binder content on the flexural strength, hardness, fracture toughness, and corrosion resistance of IBC composites was investigated. Experimental techniques used to characterize the mechanical behavior included Vickers hardness, four-point flexure at 25 and 800°C, indentation fracture, indentation strength, and mass loss corrosion testing. In addition, the microstructure was characterized using optical and scanning electron microscopy to examine the polished and etched microstructures, the cracks located at the corners of the hardness indents, and the fracture surfaces produced by the flexure testing. Correlations were made between the mechanical properties of flexural strength and hardness and the microstructural parameter of contiguity. Experimental results indicate that the strength at 800°C of IBC composites with Ni₃Al compares favorably to the room-temperature strength. At 25°C, plastic deformation of the Ni₃Al and FeAl binders occurs, but the strength of the composite with FeAl is higher due to strong bonding along the carbide-binder interfaces. WC-based composites yielded higher flexural strength and fracture toughness values, while TiC-based composites produced higher hardness values. Increased binder amounts produced higher values of flexural strength and fracture toughness due to a reduction in the number of carbide-carbide interfaces and an increase in plastic deformation in the crack-tip region, respectively. The Ni₃Al composites corroded in 10% nitric acid but resisted corrosion in 10% hydrochloric and 10% sulfuric acids. The FeAl composite exhibited opposite behavior in the three adds. The contiguity was observed to be proportional to the hardness but inversely proportional to the flexural strength.