Materials Science Forum Vol. 724

Abstract: Sintered ZTA(zirconia toughened alumina) which has good mechanical properties at a low temperature was produced by milling and mixing with Al₂O₃ and ZrO₂(3Y-TZP). In order to examine the effect of sintering aids on the mechanical properties of ZTA, fracture toughness and hardness of the produced ZTA were observed in accordance with change of the added quantity of ZrO₂ Scanning electron microscopy and X-ray diffraction technique were applied to observe microstructural change and phase transformation during the process. Experimental results showed that the addition of sintering aids in ZTA at a low temperature induced densification and adding SiO₂ and talc lowered sintering temperature and promoted crystallization process of the compound. The mechanical strength of ZTA added ZrO₂ showed higher mechanical strength and SEM analysis revealed that Al₂O₃ and ZrO₂ during the sintering process restrained the grain growth each other. Especially, the 92% Al₂O₃ added sintering aids showed more than 98% of the theoretical density and more than 1500 Hv of hardness value at a low temperature of 1400. It was also showed that the fracture toughness is gradually increasing first and decreasing later in accordance with the quantity of ZrO₂.

Abstract: The assembled monolithic compound spiral reinforced concrete column in this paper is consisted of two concrete columns reinforced by high-strength compound spiral hoop and jointed by encased steel and bolts. Experiments of four specimens under low cyclic loading and different axial compressive loads are carried out, and the result testifies that the anti-seismic property of this measure is not worse than the integral compound spiral hoop columns under the same load.

Abstract: A self-made sectional die made of high-performance graphite, SiC ceramic and Ni-based superalloy was firstly designed and developed. The TiO₂ ceramic, with original TiO₂ powders of average particle size ~25 nm and 80 wt.% anatase + 20 wt.% rutile, was fabricated by plasma activated sintering (PAS) at 500600 °C for 3 min under applied uniaxial pressure of 2001000 MPa using the sectional die. The influences of sintering temperature and applied pressure on the density, phase transformation and grain growth of the TiO₂ ceramic were investigated. The results showed that the sintering temperature and applied pressure played key roles in determining the relative density, phase composition and grain size of the TiO₂ ceramic. The relative density and grain size increased and the anatase phase transformed into the rutile phase slowly or quickly as the sintering temperature or the applied pressure increased. In particular, the increase of sintering temperature was very advantageous to the phase transformation, and the increase of applied pressure was quite effective to inhabit the grain growth. All the averaged grain sizes of TiO₂ ceramics were less than 100 nm in the present experimental conditions. Moreover, the relative density of the sintered ceramic were over 95% when the optimized sintering parameters were 600 °C × 500MPa or 500 °C × 1000MPa. The TiO₂ ceramics were composed of only the rutile phase when the applied pressure and the sintering temperature were not less than 300 MPa and 550 °C, respectively.

Abstract: Waste cotton linters from textile industry were used as templates to be transformed as cotton fiber/SiO complex after sol impregnation, carbonization, carbon thermal reduction reaction, to prepare nanoSiC fibers and nanoparticles. The phase of final products were identified by XRD as β-SiC, and the diameter size of nanoSiC fiber was ranged as 20~100mm analyzed by SEM and TEM. Based on the thermodynamic analysis of each step in the thermal reduction on carbon / SiO composite to generate nanoSiC fibers, the nanoSiC fibers were generated by the vapor reaction between SiO and CO, and its growth mechanism was deduced as vapor-solid. For the reuse of cotton linter, thus the research provides a new solution.

Abstract: The commercial pure Mo sheet was shot peened to increase high-temperature mechanical and thermal resistance. Shot peenining was conducted on the surface of cold-rolled Mo sheet with 0.4MPa of shot pressure. The hardness of bcc Mo sheet was increased with increase of shot peening time. Surface hardenss is gradually increased to 120s at the 0.4MPa pressure, but the profiles become almost flat at the prolonged time. The grains were deformed and work hardened in the surface layer. The surface roughness was also increased with peening time. The grain size of shot-peened Mo sheet was smaller than that of cold-rolled Mo sheet in the all recrystallization temperature range. The reason for this could be a larger density of nucleation sites caused by the higher surface deformation of shot-peened Mo sheet. Mo₂C carbide phase was analyzed on the surface of recrystallized Mo sheet at the secondary recrystallization temperature range. It was considered that molybdenum carbide was formed due to the evaporation of graphite heating element in the hot-zone furnace. From this study, shot peening of Mo sheet could be a good cold work hardening method to improve high-temperature mechanical and thermal resistance properties.

Abstract: nanoTiO₂/PBO composite fiber was prepared with a chemical method by depositing nanoTiO₂ on the surface of PBO fiber which was treated by silane coupling agent. The process parameters on the preparation of nanoTiO₂/PBO composite fiber were optimized according to the interfacial adhesion between the composite fiber and epoxy resin, and the coating mechanism of nanoTiO₂/PBO composite fiber was also discussed. The results show that the uniform nanoTiO₂/PBO composite fiber with high interfacial adhesion can be prepared on the PBO fiber which was pretreated by silane coupling agent with a concentration of 1.5 % for 35 min at room temperature, in which the nanoTiO₂ aqueous solution with a concentration of 1.0wt% was ultrasonic dispersed for 1h in alkaline environment (pH 11), and then the PBO fiber was immersed in the dispersed solution at 60 °C for 6 h to prepare nanoTiO₂/PBO composite fiber. The single fiber pull-out strength of the prepared composite fiber was increased by 85.28 % compared with that of the untreated PBO fiber. Silane coupling agent was a bridge of PBO and nanoTiO₂, hydrogen bond association and like dissolves like were attributed to the improvement of interfacial adhesion between nanoTiO₂ and PBO fiber.

Abstract: The Ti₃AlC₂/Al₂O₃ in situ composites were successfully synthesized from the system of Ti-TiC-Al-TiO₂ by reactive hot pressing at 1350 °C. The effect of TiC content on the phase composition, microstructure and mechanical properties were investigated in detail. The results indicate that the fabricated products possess the highest purity as the TiC contents reduce to 90 % of its theoretical content. This deviation is mainly attributed to the decomposition of Ti₃AlC₂ and vaporization of Al at high temperatures. The effect of TiC content on the fracture toughness, flexural strength, Vickers hardness of Ti₃AlC₂/Al₂O₃ composites was also discussed in detail.

Abstract: Translucent β-Si₃N₄ sintered ceramics have been fabricated by using AlN-MgO sintering additives. In the present study, the authors employed AlN-MgO as a standard sintering aid, and investigated the effects of sintering conditions on the translucency of Si₃N₄. Furthermore, various oxides such as HfO₂, Sm₂O₃, Y₂O₃, Sc₂O₃, La₂O₃, Nd₂O₃, CeO₂, CaO, ZrO₂ etc. were used as the sintering aids of Si₃N₄, and the sintered β-Si₃N₄ ceramics exhibited different transmittances in the visible region. It was found that the transmittance of sintered ceramics was mainly affected by the sintering additives.

Abstract: As the dynamic recrystallization (DRX) behavior of hot-deformed austenite is the basis of determining controlled rolling schedule for steel, in the present work, the dynamic recrystallization behavior of austenite of a 0.22%C-1.30%Mn-0.04%Nb micro-alloyed steel was investigated by means of high temperature compression tests on the Thermecmastor-Z simulator. By the analysis of true stress-strain curves at different deformation stages, the hot deformation equation of austenite was established for the steel. As a result, the energy to induce recrystallization of austenite for the steel is 419.1 kJmol^-1, as it was influenced by the drag effect of micro-alloyed element Nb in solid solution. The ratio (σ_c/σ_p) of critical stress σ_c (where DRX occurs) to peak stress σ_p is 0.93 while the ratio (ε_c/ε_p) of critical strain ε_c to peak stress ε_p is 0.52 for the steel. The austenite grain size of dynamic recrystallization of the micro-alloyed steel is refined by decreasing the deformation temperature and improving the stain rate.

Abstract: In order to improve the microstructure and mechanical properties of High Speed Steel (HSS), electromagnetic stirring method is adopted to enhance the solidification of target materials in this paper. The results show that optimization of the microstructure, refinement of the grain, reducing in segregation of the alloy elements, and improvement of the comprehensive properties of HSS can be obtained by the electromagnetic stirring through changing the morphology and distribution of the carbide.