By Kevin C. Schoeffel and Yung C. Shin, Center for Laser-based Manufacturing, School of Mechanical Engineering, Purdue University, West Lafayette, Indiana
Ceramic particulate reinforcement enhances the already superior mechanical properties of nickel-based super alloys. Reinforcement particles alter the matrix microstructure of the metal matrix composites (MMC) to improve wear resistance, hardness, etc. Laser direct deposition allows localized addition of MMC with properties tailored to the application. This research focuses on the effects of particle concentration on microstructural changes and mechanical property improvement.
In the present work, laser direct deposition was used to build multi-layer structures of nickel-based alloy Inconel 690 reinforced with titanium carbide particles at 18.4%, 27.2%, and 40.0% by volume. Optical and electron microscopy of sectioned specimens revealed a uniform distribution of titanium carbide particles throughout the multi-layer depositions and a near absence of internal voids or incomplete melting. The ratios of Inconel 690 to TiC in the depositions matched the levels in the initial powder mixtures. The presence of carbide particles coincided with refinement of matrix microstructure and introduction of a finely dispersed crystalline phase when the titanium carbide percentage was increased to 40%. High-temperature dissolution of titanium carbide was not detected. The hardness test revealed that the hardness increased with increasing percentage of TiC particulates from 20 in the base metal to 40 HRC in 40% TiC reinforced metal matrix composite. Wear tests results using pin on a disk apparatus also showed that wear scars were generally elliptical, nearly rectangular, and higher carbide content caused more wear of the steel ball used, thus indicating higher hardness of the surface.
Predictive numerical modeling results were also shown. The multiphysics numerical model assisted in designing a suitable operating condition of the laser direct deposition and also predicted the even dispersion of the particulates during the laser direct deposition of metal matrix composites.
Figure: SEM micrograph of the deposited Inconel690/TiC40% metal matrix composite, exhibiting a uniform distribution of the particulates.