Study On Preparation Of Novel Core/Shell Structured WC-Ni Cemented Carbides And Properties

Micro-nanosized cemented carbides are widely used in some fields, such as,metal processing, precision mold processing and the microelectronics industry, owing to their high strength, high hardness, and excellent wear resistance. Cobalt has been considered as the best bonder of making carbide alloy because of its good wettability and adhesion to the carbide in the fields of carbide alloy. However cobalt is the national strategic metal and the shortage of cobalt resources. So it is imperative to find a more economical material to replace cobalt. In addition, the synthesis of ultrafine and high purity WC-Ni composite powder and its sintering process control are the key to preparation of the excellent performance cemented carbide. Therefore,we studied preparation of novel core/shell structured WC-Ni cemented carbides and their properties. The following main conclusions were made:1. Nanosized nickel powder was prepared by the method of ion hot-liquid phase reduction. The effect of react temperature and holding time on the phase and morphology of nickel powder was systematically investigated. The result show that nickel powder particles were globular-like, which grains size was 26.8nanometer approximately and specific surface area was about 21.4 m2/g when the react temperature was 170°C and holding time was 6h.2. The ultrafine WC powder was prepared by the way of high-energy ball mill. The influence of the voltage and the ball milling time on the particle size, morphology and uniformity of WC powder was studied. According to the results of ball mill,when the voltage was 65V(350r/min) and ball grinding time for 1h, the quality of WC powder was relatively well.3. The core/shell structured WC-Ni composite powder was prepared by the method of ion hot-liquid phase reduction, in which the ultrafine WC powder was regard as artificial crystal nucleus. It showed that the core/shell structured WC-Ni composite powder was in good cladding condition and the dispersion was relatively homogeneous, the cladding layer was about 20 nm.4. The influence of the content of Ni on the organization and properties of core/shell structured WC-Ni cemented carbide and which prepared by ball milling during the process of microwave sintering was studied. The results show that with the increase of Ni content, the relative density, fracture toughness and bending strength of both cemented carbides were increased. However, the hardness decreased. In addtion, It was obvious that the density, fracture toughness and bending strength of core/shell structured WC-Ni cemented carbide were superior to that prepared by ball grinding, but hardness was on the opposite.5. The effect of microwave sintering temperature and holding time on the organization and properties of core/shell structured WC-10 Ni cemented carbide and which prepared by ball milling was investigated. The result show that in the range of temperature from 1375°C to 1475°C, the relative density, fracture toughness and bending strength of both cemented carbides were raised first and then decreased following the increasing of temperature. With the extending of holding time, the relative density, fracture toughness and bending strength were similar to raised first and then decreased. Therefore, When the sintering temperature was 1425°C and holding time was 30 min, the comprehensive properties of WC-10 Ni cemented carbide were relatively better. The hardness was85.3HRA, bending strength was 986.8Mpa, fracture toughness was12.31MPa·m1/2. Compared with the cemented carbide prepared by ball milling,the properties of core/shell structured WC-10 Ni cemented carbide were greatly improved, the fracture toughness and the bending strength were improved13.86% and 12.43%, respectively. However, the hardness slightly decreased 1%.6. The electrochemical corrosion properties of core/shell structured WC-10 Ni cemented carbide and which prepared by ball milling was studied. According to the results, the corrosion resistance of core/shell structured WC-10 Ni cemented carbide were obviously superior to that prepared by ball grinding.