Laser Deposition of Stainless Steel – Titanium Carbide Composites for Repair of Critical Aerospace Components

Open Access
Author:
Lia, Frederick
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 16, 2014
Committee Members:
  • Richard Martukanitz, Thesis Advisor
  • Gary Lynn Messing, Thesis Advisor
Keywords:
  • Additive Manufacturing
  • Directed Energy Deposition
  • laser deposition
  • Metal Matrix Composite
  • carburized surface
  • SS 431
  • and TiC
Abstract:
This research project entailed the use of an experimental composite material for developing a laser deposition process that simulates carburized and chromium electroplated surfaces for bearing applications. Two gear component materials were chosen as substrates, carburized AISI 8620 steel (8620 steel) and Inconel 718® with a chromium electroplated surface. The experimental material included AISI stainless steel 431 (SS 431) as the matrix and titanium carbide (TiC) particle as the reinforcement material. The directed laser deposition process was used to deposit the composite material onto the substrate. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and a particle size analyzer were used to characterize selected powders used during the laser deposition experiment. Deposited materials were evaluated by microstructural analysis, Vickers micro hardness testing, and EDS-mapping for examining the dissolution reaction of the reinforcement particles within the SS 431 matrix. Performance testing of the laser deposited composite material was also conducted and included rolling contact fatigue testing and tribological analysis. Vickers hardness testing indicated that the hardness of the SS 431/20 wt% TiC deposited on the 8620 steel matched the hardness of the carburized 8620 steel. Micro hardness of the deposited materials was found to be 750 in the Vickers scale. SEM images showed that some of the TiC particles dissolved and the Ti and C were reprecipitated in the SS 431 matrix. The higher carbon within the matrix material enhanced the overall hardness of the laser deposit. Chemical analysis by EDS further supported this finding. The TiC particles were dissolved into small unstable dendrite around the surface of the TiC particle. The dissolved TiC phase that surrounded the original TiC particle formed a secondary phase in the matrix alloy by reprecipitation during cooling. Rolling contact fatigue tests indicated that the composite deposit exhibited slightly greater wear, due to hard particle expulsion, that resulted in lower rolling contact fatigue life when compared to the 8620 steel that had been carburized. The SS 431 – TiC composites were also attempted to replace the chromium electroplated surface on Inconel 718® substrate. However, the deposited composite materials were diluted by Inconel 718® substrate and significantly reduced the hardness of deposited materials which did not meet the requirement.