Room and elevated temperature sliding wear behavior and mechanisms of additively manufactured novel precipitation strengthened metallic composites

Laser Engineered Net Shaping (LENS T) is an additive manufacturing technique used to fabricate complex 3-D components directly from a CAD model. LENS (TM) permits the processing of novel, tailored hybrid materials with unique microstructures spanning across multiple length scales that are not possible to achieve via conventional melt or solid-state powder processing techniques. Such novel microstructures include solid solution/precipitation strengthened metallic matrices with a refined uniform distribution of reinforcing in situ formed hard ceramic and solid lubricant phases. In this work, two such novel composites composed of Ni-18Al-11Cr-9C and Ni-14Al-8Cr-29C (at%) were processed via LENS T. The tribological properties of the composites were assessed at room temperature (RT) and 500 degrees C to determine the chemical and microstructural evolution during wear. Due to the variation in graphite (C) content in the composites, different microstructures of nickel aluminide and chromium carbide phases were formed during solidification that affect the dry sliding wear behavior. It was determined with SEM/EDS and Raman spectroscopy that NiO and Cr2O3 are the predominate phases on the room temperature wear surfaces, while at 500 degrees C, NiCr2O4 (spinel structure) becomes the main tribochemical phase, forming an oxide glaze layer at the sliding interface that further mitigates friction and wear. Overall, the increase from 9 at% to 29 at% C in the composite did not lower the dry sliding friction coefficient; however, there was a reduction in the 500 degrees C sliding wear rate to 7.1x10(-6) mm(3)/N.m and increase in the micro- and macro-hardness of the composite to HV0.3 = 539 and HRC = 48, respectively.