Direct Metal Deposition (DMD) with coaxial powder injection (TRUMPF DMD505 and LASMA 1054 with home made coaxial nozzle installations) is applied for fabrication of 3D coatings and objects from metallic and cermets powder. Injection of various powder compositions by application of an n-channel powder feeder, coaxially with the laser beam allows producing functional coatings locally, in critical areas in accordance with their operational conditions. Attempt to mix various materials in a blend to achieve a composite coating combining desired selected properties of components often leads to creation of various phases and compounds having new properties and thus should be carefully evaluated in advance. A number of coatings had been created from the following powders and their combinations: Mo, MoCo alloy, stainless steel, CuSn, nanostructured WC/Co, Stellite®.
It is shown that additional relatively quick laser processing of working surface yields in significant improvement of tribological properties of functional coating. The processing creates an array of artificial holes serving as reservoirs for debris and/or solid lubricant, gradually releasing during wear into the contact zone. The coatings were tested tribologically for slow speed high pressure dry friction conditions (valve parts, pumps, etc.). Dry friction coefficients are ranging from 0.12 to 0.6 for different coating compositions and surface processing at room temperature and from 0.35 to 0.5 at 450 °C. For phase determination selected samples were analysed with X-Ray diffraction and AFM analysis. It is shown that operational parameters of laser radiation can have a significant influence on coating’s microstructure, regarding the way to take advantage of nanostructured powder, thus defining tribological performance of given coating.