Bing Liang

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.

Hydrochloric Acid Corrosion Behavior of Nb2O5-Al2O3 Ceramics Prepared by Microwave Sintering

The influences of Nb2O5 on the phase, microstructure and hydrochloric acid corrosion behaviors of Nb2O5-Al2O3 ceramics sintered with 2.45 GHz microwave energy were investigated. The results showed that Nb2O5 reacted completely with Al2O3 to form AlNbO4 and densified the pure Al2O3 at a lower sintering temperature and in a short sintering time. Nb2O5-Al2O3 ceramic samples were corroded in diverse concentration hydrochloric acid for different time. Weight loss rate of Nb2O5-Al2O3 ceramic rose dramatically when the corrosion time was not longer than 4 h, and it increased slowly beyond 24 h. After Nb2O5-Al2O3 ceramic samples were corroded for 1 h, pitting corrosion was observed by scanning electric microscope, which was consistent with the analysis results of the scanning Kelvin Probe.

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 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 Cold Isostatic Pressing 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 effects of cold isostatic pressing (CIP) on microstructure and mechanical properties were investigated. The results show that only WC and Co3W3C (γ-phase) were detected by XRD without any else phases, even though Co. Dense WC-8Co cemented carbide samples were obtained and relative density reached over 98%. The pressing method, instead of pressure, took an important role in the mechanical properties of WC-8Co cemented carbide. KIC and TRS of WC-8Co cemented carbide were improved at least 27% and 24%, respectively, by the use of CIP. WC-8Co cemented carbide with excellent mechanical properties (HRA>93.5, KIC>11MPa·m1/2, TRS>870MPa) was obtained by using CIP.

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 Nb2O5/La2O3 Additions on Mechanical Properties of Al2O3 Ceramics Prepared by Microwave Sintering

The influence of Nb2O5 and La2O3 on the phase and microstructure evaluation and mechanical properties of composite 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. La2O3 reacted with Al2O3 to form LaAl11O18 completely, 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 composite ceramics.

Mechanical Properties of WC-Co Cemented Carbide Prepared via Vacuum Sintering

WC-Co cemented carbide specimens were prepared via vacuum sintering. The influences of composition and sintering temperature on phase composition, microstructure and mechanical properties of WC-Co cemented carbide were investigated. The results show that dense specimens were obtained in the sintering temperature range of 1280~1400°C and the relative density reached over 95%. Only WC and Co3W3C (-phase) were detected by XRD without any else phases, even though Co. With the ascended sintering temperature, hardness increased and the transverse rupture strength (TRS) ascended to peak value and then descended. WC-Co cemented carbide with excellent mechanical properties (HRA>90, TRS~700MPa and KIC>10MPa•m1/2) were obtained.

Effect of SiC and ZrO2 on Low Temperature Oxidation Resistance of MoSi2 Nanocomposites

The single and synergism effect of SiC and ZrO2 nanoparticles on low temperature oxidation resistance of MoSi2 were investigated by thermo-gravimetric analysis (TGA), phase and micrograph analysis of surface film. The results show that at the oxidation temperature of 600°C, the addition of 10%ZrO2 results in obvious oxidation mass gain of MoSi2, and discontinuous protective film forming on the surfaces, which makes “pesting” phenomenon still occur. The addition of 10%SiC accelerates the oxidation of MoSi2, but compact SiO2 protective film formed on the surface after some time of oxidation, avoiding the occurrence of large scope of “pesting” phenomenon. The synergism of 10%ZrO2 and 10%SiC promotes the formation of compact, even silicate glass film on the surface of MoSi2, as a result, significantly improves the low temperature oxidation resistance of MoSi2.

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.