| dc.description.abstract | Tungsten is a rare element and the supply is limited. It has some unique properties, such as very high density, very high melting point, high electrical conductivity, high tensile strength and hardness, and it is a part of the tungsten carbide/cobalt composite, which is widely used for mining and drilling equipment.
In this study several different samples were prepared in attempt to achieve a tungsten carbide coating on alpha silicon carbide support. The Pechini method with a 50wt% loading of W, with ammonium metatungstate as W precursor, was used to coat the α-SiC support, and subsequent drying, calcination and carburization were performed. Various carburization schedules in CH4/H2 gas mixtures were used to form tungsten carbides. Some of the samples were impregnated with nickel or copper at the different stages of the synthesis process.
Analysis of XRD spectra after carburization showed formation of different tungsten carbides and metallic tungsten, depending on carburization schedule. Nickel and copper were found in the samples impregnated with either of those. SEM images after carburization showed that only partial tungsten carbide coating on the α-SiC was achieved. Instead, small tungsten carbide clusters that eventually broke off from the surface of α-SiC were formed, creating small tungsten carbide particles.
A wetting experiment was conducted on the some of the synthesized powder samples. The powders were placed in a small glass sample holder along with a metal alloy and then placed in a high temperature furnace for 8 hours at 950 °C. The addition of copper or nickel seemed to enhance the wettability of tungsten carbide powder by metal alloy, and coimpregnation seemed much more successful than impregnation at a later stage. The wetting of samples without nickel or copper was very poor.
Some of the synthesized powder samples along with a nickel base alloy powder were used in a thermal spraying test to make a coating on steel plates. The coating of the synthesized samples had a lot more voids compared to the coating of a commercial WC powder. | |
