Preparation Of α—Al₂O₃/W Nanocomposite By Explosive Sintering

Alumina ceramic, one of the ceramic materials produced most largely and used most widely, can be used in the inclement circumstance, where metal and macromolecule materials can't work, because of its excellent properties, such as high temperature resistance, electric insulation, good abrasive resistance, high hardness, good corrosion and oxidation resistance, steady chemistry and low price, etc. But low toughness of ceramic limits its use in many fields; so improving its toughness has become the core of the ceramic study by adding nanometer particles as second phase. Inthis paper, the α-Al2O3/W (Ni) nanometer powder was made by the heterogeneous precipitation, and then sintered by the explosive sintering.This dissertation discussed the preparation of a-Al2O3/W (Ni) nanometer powder by the heterogeneous precipitation and effects on the phase transformation temperature to alpha alumina with additive of nanometer tungsten or nickel.Al2O3/W and Al2O3/Ni nanocomposite powders, with mean particle size less than 50nm, were prepared by using A1(NO3)3-9H2O and (NH4)2CO3 solutions as raw materials and tungsten and nickel nanometer powders as additives in different ratios respectively. Alpha Al2O3/W(Ni) nanocomposite was attained by calcining Al(OH)3/W(Ni) dried gel at 1000℃(1100,1150℃) in vacuum for an hour. Adding tungsten or nickel nanometer powder can reduce the phase transformation temperature to alpha alumina. Al(OH)3 dried gel transforms to ct-Al2O3 with tungsten additive at 1000℃, while with 10vol% nickel additive at 1150℃.The composite powder is simply mechanically mixed together, aluminacoating on the surfaces of nanometer tungsten or nickel powder. No new phases, which are different from Al2O3 and Ni, were observed.The shock wave of blast compacts the powder. Meanwhile the heat is generated from powder collision and friction, which makes powder under the high temperature and pressure and be sintered to a high-density block. The nanometer grains won't grow up instantly by the explosive sintering, which is superior to the traditional sintering at this aspect.The α-Al2O3/5vol%W composite block has a diameter of 6mm and a height of 15mm, in which the grains are kept in nanometer sizes. Seen from the SEM image of the fracture surface of α-Al2O3/W composite, the fracture is of toughness.