Duan Xinglong

A New Technology of Microcrystallizing Leucite to Reinforce Dental Glass Ceramics

The key technology and the main mechanism of microcrystallizing leucite to reinforce dental glass ceramics were investigated. The feedstock powders were selected, mixed according to the ratios of the theoretical composition of leucite, ball—milled, melted at 1600°C and then cooled to room temperature quickly. The cooled clinkers were ball—milled again to 4 μm. After cold—isostatic pressure molded and air sintered at 1500°C for 1 h, the dental glass ceramics were fabricated. They have following characteristics: excellent mechanical properties (mean compressive strength is 206. 6 MPa), low sintering temperature and good reoccurrence to keep steady quality.

Research on ultrafine WC-10Co cemented carbide with high properties

WC-10Co nanocomposite powder produced by spray pyrolysis-continuous reduction and carbonization technology was used, and the vacuum sintering plus sinterhip process was adopted to prepare ultrafine WC-Co cemented carbide. The microstructure, grain size, porosity, density, Rockwell A hardness (HRA), transverse rupture strength (TRS), saturated magnetization and coercivity force were studied. The experimental results show that average grain size of the sample prepared by vacuum sintering plus sinterhip technology was about 420 nm, transverse rupture strength was more than 3460 MPa, and Rockwell A hardness of sintered specimen was more than 92.5. Ultrafine WC-10Co cemented carbide with high strength and high hardness is obtained.

The preparation of CoWO4/WO3 nanocomposite powder

Ammonium metatungstate and cobalt nitrate were mixed at the molecular level in distilled water and then spray-decomposed to CoWO4/WO3 nanocomposite powder. The particle morphology, crystalline size, forming course, chemical composition and phase structure of the powder were studied by SEM, TEM, DTA-TG, IR and XRD, respectively. Results show that the powder is homogeneous, spherical and nano-aggregated.Ammonium metatungstate and cobalt nitrate were mixed at the molecular level in distilled water and then spray-decomposed to CoWO4/WO3 nanocomposite powder. The particle morphology, crystalline size, forming course, chemical composition and phase structure of the powder were studied by SEM, TEM, DTA-TG, IR and XRD, respectively. Results show that the powder is homogeneous, spherical and nano-aggregated.

Powder Extrusion Molding of Nanocrystalline WC-10Co Composite Cemented Carbide

The rods that were shaped from nanocrystalline WC-10.21 Co-0.42 VCI Cr3 C2(wt%) composite powders by using powder extrusion molding (PEM) were investigated. The nanocrystalline WC-10.21 Co-0.42 VC/Cr3 C2 (wt%) composite powders were prepared by the spray thermal decomposition-continuous reduction and carburization technology. In order to improve the properties of rods shaped by using powder extrusion molding, the cold isostatic pressing (CIP) technology was used before or after debinding. Specimens were sintered by vacuum sintering and hot isostatic pressing (HIP). The density, Rockwell A hardness, magnetic coercivity, and magnetic saturation induction of sintered specimen were measured. The microstructure of the green bodies and the sintered specimens was studied by scanning electron microscopy (SEM). Results show that the rod formed by using powder extrusion molding after debinding and followed by cold isostatic pressing can be sintered to 99.5% density of composite cemented carbide rods with an average grain size of about 200–300 nm, magnetic coercivity of 30.4 KA/m, Rockwell A hardness of 92.6 and magnetic saturation induction of 85%. Superfine WC-10Co cemented carbide rods with excellent properties were obtained.

Influences of Carbon Content on the Properties and Microstructure of Ultrafine WC-10Co Cemented Carbide

WC-10Co nanocrystalline composite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing (HIP). Influences of carbon content on properties and microstructure of ultrafine WC-10Co cemented carbide were investigated. The results show that the relative density of the ultrafine WC-10Co cemented carbides can reach 99.72%, and the transverse rupture strength (TRS) was higher than 3 890 MPa, Rockwell A hardness (HRA) was higher than 92.5, the average grain size was less than 460 nm, when carbon content in nanocrystalline composite powder was 5.54wt% and the ball-milled time was 48 hours, ultrafine WC-10Co cemented carbide with excellent properties and homogeneous microstructure was obtained.