Directed energy deposition of Ni-Al-Cr-C composites: Microstructural evolution during solidification and wear

Laser engineered net shaping (LENS (TM)) allows for the deposition of novel hybrid materials with microstructures composed of solid solution and precipitation strengthened metallic matrices, along with a distribution of reinforcing in situ formed hard ceramic and solid lubricant phases. In this study, four different composites in the Ni-Al-Cr-C system were fabricated via LENS (TM) as potential candidate materials for high temperature wear resistant components. Microstructural evolution during solidification and sliding wear were studied at room and elevated temperatures. Experimental and solution thermodynamic simulations were used to evaluate the evolution of various compositions of hard chromium carbides and solid lubricant graphite dispersed into a continuous gamma/gamma' (L1(2)) matrix. By tailoring the microstructures along the build direction, desired hardness and wear properties were achieved for the different Ni-Al-Cr-C composites. Specifically, compositional modification of chromium and carbon were determined to drastically affect the corresponding phase morphology and properties. The two lowest wear rates measured were for the Ni-14Al-9Cr-29 C (at%) composite at 500 degrees C and Ni-12Al-3Cr-45 C (at %) composite at room temperature. Mechanistic studies using surface and subsurface scanning and transmission electron microscopies in the wear surfaces revealed this was a result of a combination of increased hardness/load-bearing and formation of tribochemical protective oxide glaze layers.