Preparation And Performance Study Of Nano-tungsten Carbide Powder

Ultra-fine cemented carbides, well known as "the teeth of industry", have been widely applied in many fields of industry such as machining, electron, medical treatment, war industry due to their high -strength and high-rigidity. Nanometer WC powders are the important raw materials of ultra-fine cemented carbides and nanometer W powders are the important raw materials of nanometer WC powders and nanometer / ultra-fine cemented carbides. In this thesis we used tungsten concentrate as the raw materials to produce ultra-fine ammonium paratungstate (APT), ultra-fine tungsten oxide(WO₃) and nanometer W powders. Further more we trial-produced nanometer WC powders and ultra-fine cemented carbides.The phase and grain size were exanmined by XRD, and the uniformity and microstructure of WC powders were investigated by SEM, TEM and BET. The total carbon (C_t) and free carbon (C_f) of ultra-fine / nanocys- talline powders were analysized by composition analysis instrument. Mechanaical properties were tested by material testing machine and hardness machine. The following results are obtained:1. Added special medicament (1#) in the high peak solution produced by tungsten metallurgy ion exchange to control the nucleation periods and growth periods of APT. By changing the mode of temperature control, the rotate speed of whisk and the end-point of solidification, we can obtain ultra-fine APT. By adding special medicament (2#) we can achieve solid-liquid separation to obtain ultra-fine APT, which has a Fess particle size about 1～10um.2. During the preparation of nanometer W powders, the orthogonal experiment results showed: the best process is reducing tempeture 650℃, materieal thickness 4 mm, time 1 hour. The factors affecting grain size in order is: reducing tempetureâ†'material thicknessâ†'time.3. During the preparation of nanometer W powders, tungsten oxide powders reduced by hydrogen in a special boat. The influence of tempeture, material weight and hydrogen flux on preparation process was studied. BET of the obtained nanometer W powders is above 10m²/g (BET grain size is 30nm).4. The micro-structre of nanopowder was characterized by TEM, SEM, BET and XRD technologies. It has been found that the size of the powder is about 30nm in average. The grain morphology mainly is sheet-polygon or short-flake. And some grains can almost spherical.5. Using the nanometer W powders, we can obtain nanometer WC powders in the condition of 1050℃carbonized 2 hours in hydrogen atmosphere. BET of the obtained nanometer WC powders is about 3.53m²/g, grain size is around 100 nm.6. Using the nanometer WC powders prepared ultra-fine cementedcarbide in 1360℃.The diameter size of the obtained cementedcarbide is about 0.34um.The hardness and fracture toughness areabout 1600 kg/mm² and 10.32 MPa·m^1/2.