Narrow Results

Continuous silicon carbide fiber-reinforced silicon carbide (SiC_f/SiC) composites are promising structure candidates for future fusion power systems such as gas coolant fast channels, extreme high temperature reactor and fusion reactors, because of their intrinsic properties such as excellent mechanical properties, high thermal conductivity, good thermal-shock resistance as well as excellent physical and chemical stability in various environments under elevated temperature conditions. In this study, bonding of tungsten and SiC_f/SiC was produced by hot-press method. Microstructure analyses were performed using SEM and TEM.

A mechanism for rapid, single-step synthesis and fabrication of intermetallic compounds having brittle–ductile ingredients at low temperature is suggested. Employing this mechanism, highly pure, dense Mg₂Si pellets were obtained using silicon nanoparticles and micron-sized magnesium particles as starting materials. Silicon nanoparticles chop magnesium particles and produce highly-activated mixture through a planetary ball-milling. Magnesium/silicon interface increases by increasing dispersity of silicon nano-particles in magnesium. Consequently, final product was prepared only by consolidation at 300^∘C for 5min without any post-treatment. The pure phase of Mg₂Si with grain sizes about 200nm and with no evidence of presence of MgO was achieved. The Seebeck coefficient, electrical and thermal conductivity were measured to be $-$220 $\mu$VK${}^{-1}$, 72 ${\mathrm{\Omega }}^{-1}$cm${}^{-1}$ and 3.48Wm${}^{-1}$K${}^{-1}$ at 823K for nondoped Mg₂Si, indicating that this method does not degrade the properties of the product, despite the fact that fabrication is performed rapidly and at low temperature.

A shape memory alloy (SMA) as part of some products and system has been used to keep their shape at any specified temperature. By using this characteristic of the shape memory alloy it can be solved the problem of the residual stress by difference of coefficients of thermal expansion between reinforcement and matrix within composite. In this study, TiNi/Al6061 shape memory alloy composite was fabricated through hot press method, and the optimal fabrication condition was created. The bonding effect of the matrix and the reinforcement within the SMA composite was strengthened by cold rolling. The SMA composite can be applied as the part of airplane and vessel, and used under tough condition of repetitive thermal shock cycles of high and low temperatures. Therefore, the thermal shock test was performed for the SMA composite, and mechanical properties were evaluated. The tensile strength of the SMA composite showed a slight decline with the thermal shock cycles. In addition, acoustic emission (AE) technique was used to quantify the microscopic damage behavior of cold rolled TiNi/Al6061 shape memory alloy composite that underwent thermal shock cycles. The damage degree on the specimen that underwent thermal shock cycles was discussed. Actually AE parameters such as AE event, count and energy was analyzed, and these parameters was useful to evaluate the damage behavior and degree of the SMA composite. The waveform of the signal caused by debonding was pulse type, and showed the frequency range of 160 kHz, however, the signal by the fiber fracture showed the pulse type of high magnitude and frequency range of 220 kH.

This investigation shows that by a drastic increase in the pressure at hot pressing sintering there are possibilities to increase the fracture stress value and the mechanical strength of the carbonated apatite samples. It is also possible to obtain carbonate hydroxyapatite, containing the same carbonate content as from the start. However, the temperature should be kept below 1073 K. In this case, the final product will have a mechanical strength lower than that of bone. The carbonate hydroxyapatite is biocompatible.