Wei Hua Chen

Microstructure and Properties of Al2O3-ZrO2 Ceramics Prepared by Microwave Sintering

ZrO2 doped with 7.5% (volume percent) nanoalumina ceramics were prepared by microwave sintering processes. The effects of nanoalumina additions and various sintering temperature on densification, phase composition, microstructure and mechanical properties of Al2O3-ZrO2 ceramics were investigated. The results show that the m-ZrO2 phase transformed into t-ZrO2 during the process of microwave sintering. Relative densities between 95% and 99% were attained in the different conditions. In any cases the grain size was maintained at a submicron scale at a processing microwave sintering. The presence of Al2O3 grains had an effect of hindering grain growth of ZrO2 grains. When the microwave sintering temperature was 1500°C, 7.5Al2O3-ZrO2 composite ceramics presented excellent mechanical properties: HV=12.0 GPa, σf=715.7 Mpa, KIC=11.9 MPa·m1/2. Compared with that of pure ZrO2 ceramic, the bending strength and the fracture toughness were improved 45% and 23% at least, respectively. The fracture mode was associated with sintering temperature: when the sintering temperature was 1350°C~1450°C, the intergranular fracture and transgranular fracture coexisted; when the sintering temperature was 1500°C, intergranular fracture was the main fracture mode.

Mechanical Properties of Nb2O5-Al2O3 Ceramics Prepared by Microwave Sintering

The influence of Nb2O5 on the phase and microstructure evaluation and mechanical properties of Nb2O5-Al2O3 ceramics sintered with 2.45 GHz microwave energy was investigated. The results showed that Nb2O5 could densify the pure alumina with a lower sintering temperature and a short sintering time. Nb2O5 reacted with Al2O3 to form AlNbO4 completely and the amount of AlNbO4 increased with the increasing content of Nb2O5, distributing at the Al2O3 grain boundaries. The specimen doped with 10 vol.% Nb2O5 sintered at 1500 °C exhibited plenty of columnar grains with draw ratio about 1:3. The existence of columnar grains enhanced the microhardness and fracture toughness of Nb2O5-Al2O3 ceramics.

Effects of Dispersant on Microstructure and Properties of GPLs/Al2O3 Composite Ceramics via Microwave Sintering

Three dispersants cetyl trimethyl ammonium bromide (CTMAB), N-N dimethyl formamide (DMF) and N-methyl pyrrolidone (NMP) were added to disperse graphene (GPLs) and a type of graphene/alumina composite ceramics was fabricated by microwave sintering. The GPLs dispersion was characterized by Zeta potential, XRD and SEM. The experimental results show that anionic dispersant NMP has the best dispersion effect with no impurities when pH value is 5. Using dispersant NMP, 0.4vol.%GPLs/Al2O3 composites with high dispersion obtains a relative density of 98.76% at 1500°C for 30 min by microwave sintering. The microhardness, fracture toughness and flexural strength of this composites are 19.58GPa, 6.19MPa·m1/2 and 365.10MPa, respectively. Its fracture toughness respectively increases by 47% and 15% than that of composites using dispersants DMF and CTMAB.

Effects of Nb2O5/La2O3 Synergistic Modification on Phase Composition, Microstructure and Mechanical Properties of Al2O3 Ceramics Prepared by Microwave Sintering

Nb2O5-7.5La2O3-Al2O3 composite ceramics were prepared by microwave sintering. The influence of Nb2O5 and La2O3 proportion on the microstructure and mechanical properties of Al2O3 ceramics was investigated. The results show that when the Nb2O5 content was lower than La2O3, the columnar LaAl11O18 grains were generated by the reaction of La2O3 with Al2O3. When the Nb2O5 content was higher than La2O3, the surplus Nb2O5 induced the formation of columnar Al2O3 grains. The growth of columnar Al2O3 grains were promoted synergistically by LaNbO4 formed in-situ and Nb2O5. The 5Nb2O5-7.5La2O3-Al2O3 composite ceramic exhibited excellent comprehensive properties: ρr=99.3% (relative density), HV=11.2GPa (microhardness), KIC= 6.4MPa·m1/2 (fracture toughness), σ=304.3MPa (bending strength).

Effect of Nano-Al2O3 on the Microstructure and Properties of ZrO2 Dental Materials Prepared by Microwave Sintering

Al2O3(x)/ZrO2 composite ceramics were successfully prepared by microwave sintering. The influence of variety content of nanoAl2O3 on mechanical properties and microstructure of ZrO2 dental materials were studied, and analysied the mutual relations of chemical composition, mechanical properties and microstructure to investigate the reason of strengthening and toughening. Results indicated that The relative density of the Al2O3(x)/ZrO2 composite ceramics reached more than 96.8%.The HV hardness ,bending strength and fracture toughness presented excellent mechanical properties as 12.5GPa, 753.8MPa and 11.8MPa·m1/2 with the content of nanoAl2O3 was 7.5%. Compared with that of pure ZrO2 ceramics, the bending strength and the fracture toughness were improved 19% and 96%, respectively. The main crystal phases in this composite ceramics were t-ZrO2 and α-Al2O3.The nanoAl2O3 have a obvious effect on the strength and toughness of ZrO2 based ceramics. The reason of strengthening and toughening mainly the additions reduced the ZrO2 grains growth and promoted grains size uniformity, and changed the fracture mode from transgranular fracture to intergranular fracture characteristics.

Effect of Sintering Time on the Mechanical Properties of WC-8Co Cemented Carbide for Friction Stir Welding Tool

WC-8Co cemented carbide specimens were prepared via vacuum sintering. The influences of sintering time on phase composition, microstructure and mechanical properties of WC-8Co cemented carbide were investigated. The results show that dense specimens were obtained in the sintering time range of 15min~60min and the relative density reached over 95%. Only WC and Co3W3C (γ-phase) were detected by XRD without any else phases, even though Co. With the ascended sintering time, the transverse rupture strength (TRS) increased and hardness ascended to peak value and then descended. WC-Co cemented carbide with excellent mechanical properties (HRA>90, TRS~630MPa and KIC>7MPa·m1/2) were obtained. It would be a good candidate for applications of friction stir welding tool.

Effect of Rare Earths and Vanadium on Microstructure and Mechanical Properties of High Chromium Cast Iron

Effect of RE and V on microstructure and mechanical properties of high chromium cast iron were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, impact test and wear test. The results show that proper modification using RE combined with V makes the alloy present a more refined and homogenous austenite matrix, and makes the morphology of carbide changing from thick lath to thin lath, and rosette-like. Modification can also increase hardness, wear resistance and impact toughness of high chromium cast iron.

Mechanical Properties of La2O3-Al2O3 Ceramics Prepared by Microwave Sintering

The influence of La2O3 on the phase and microstructure evaluation and mechanical properties of La2O3-Al2O3 ceramics sintered with 2.45 GHz microwave energy was investigated. The results showed that La2O3 could densify the pure alumina with a lower sintering temperature and a short sintering time. La2O3 reacted with Al2O3 to form LaAl11O18 completely and the amount of LaAl11O18 increased with the increasing content of La2O3, distributing at the Al2O3 grain boundaries. The specimen doped with 10 vol.% and 15 vol.% La2O3 sintered at 1500 °C exhibited plenty of columnar grains with draw ratio about 1:4. The existence of columnar grains enhanced the microhardness and fracture toughness of La2O3-Al2O3 ceramics.