Functionally Gradient Coatings by Laser Direct Deposition

Laser deposition is a technique that enables selective surface modification of a part.  A metallic or ceramic layer can be added locally to the surface of a part to improve the hardness or corrosion resistance without changing the properties of the bulk material.  In this talk, case studies on functionally gradient coatings by laser cladding are presented.  First, Co-Cr-Mo material was deposited on a Ti-6Al-4V substrate transitioning from 0 to 100%.  The microstructures and composition of the functionally gradient material (FGM) were characterized using an optical microscope, SEM, EDS and XRD.  EDS results showed a gradual transition to 50% Co-Cr-Mo and ~100% Co-Cr-Mo on the top layer.  XRD analysis showed the absence of a brittle intermetallic phase that forms between Titanium and Cobalt.  As the amount of Co-Cr-Mo increased, the microhardness of the FGM samples significantly increased.  The bonding strength of the coatings on substrates was tested.   Second, functionally gradient coating (FGC) is demonstrated by varying the ratios of TiC to Inconel 690 from 0 to 40% volume.  There was a near absence of internal voids in the uncoated TiC particles.  A drastic evolution in the microstructure was observed with increasing TiC percentages and the presence of carbide particles coincided with a refinement of the matrix microstructure and introduction of a finely dispersed crystalline phase.  The results also showed a significant correlation between TiC content and wear resistance.