Settling Behavior of Welding Carbides

A common problem faced during PTA deposition or laser cladding of metal matrix composite powders containing tungsten carbide particles is the carbide settling in the weld pool. This creates a carbide free zone at the top of an overlay and such layer does not have the required wear characteristics expected from the overlay. Another problem is too high carbide concentration at the substrate - overlay interface which can lead to brittleness and delamination. The root cause of this problem is a difference in densities of tungsten carbide and metal matrix. The density of cast tungsten carbide (W₂C/WC) is 16.45 g/cm³ while densities of most Ni alloys are around 8 g/cm³. The difference in particle densities does not create problems during welding only in a weld pool but also causes particle segregation in a powder container during handling and/or in a powder hopper while feeding a powder blend into a welding torch. It is possible to tailor a density of new carbides to decrease or eliminate the density difference between metal matrix and carbide. As example, a new type of welding carbide (TiW)C_1-X is benchmarked against tungsten carbide in its settling behavior as a function of carbide density, size and morphology.