Ning ZHANG
,
Hongqiang RU
,
Xudong SUN
,
Qingkui CAI
材料科学技术（英）
The α-SiC in 0.5μm size powders were coated with Al2O3 and Y2O3 by a coprecipitation coating (CPC) method for fabrication of SiC/YAG composites. The same powder preparation was carried out by conventional mechanical mixing (MM) method for comparison. Two kinds of SiC/YAG composites were manufactured by pressureless sintering using the different powders, named CPC composite and MM composite thereafter respectively. It is shown that the CPC composite has the advantages of homogeneous distribution of YAG phase and of being sintered to high density at a low temperature, 100℃ lower than that of MM composite. The strength (573 MPa) and hardness (23.3 GPa) of the CPC composite are significantly higher than those (323 MPa and 13.5 GPa) of the MM composite, respectively.
关键词:
Coprecipitation
,
null
,
null
M.M.El-Sayed Seleman
,
Xudong SUN
,
Liang ZUO
,
K.A.Khalil
材料科学技术（英）
Alumina-(0 similar to 20 vol. pct) iron composites were fabricated by hot-pressing of well-mixed-alumina and iron powders at 1400 degreesC and 30 MPa for 30 min. Hot-pressed bodies with nearly theoretical density were obtained for addition up to 10 vol. pct Fe, but relative density decreased gradually with further increase in Fe addition. The materials exhibit a homogeneous dispersion of Fe. Fracture strength of the composites exhibits a maximum value of 604 MPa at 15 vol. pct Fe, which is 1.5 times that of alumina alone. Fracture toughness increases with the increase in Fe content, reaching 7.5 MPa.m(1/2) at 20 vol. pct Fe. The theoretical values of fracture toughness was calculated and compared with the experimental one. Toughening mechanisms of the composites are also discussed.
关键词:
M.M.El-Sayed Seleman
,
Xudong SUN
,
Liang ZUO
材料科学技术（英）
Thermal shock behaviour was investigated for two morphologically different composites comprising an alumina matrix and 20 vol. pct Fe particles for a wide range of quenching temperature differences (∆T=100~800°C) and compared to a monolithic alumina. The retained strength and critical quenching temperature difference, ∆Tc, of the two composites were a significant improvement over the values for the respective monolithic alumina. Crack lengths and densities were shown to be greater for the alumina than for the two composites at all quenching temperature differences. The thermal shock resistance parameters for monolithic alumina and the two composites were calculated according to their mechanical and physical properties. The calculated results agree well with the experimental one and indicate possible explanations for the differences in thermal shock behaviour.
关键词:
Alumina-iron composite
,
null
,
null
M.M.El-Sayed Seleman
,
Xudong SUN
,
Liang ZUO
材料科学技术（英）
Two morphologically different composites comprising an alumina matrix and 20 vol. pct Fe particles have been fabricated by hot pressing technique. Two kinds of microstructures, i.e. a dispersive distribution of Fe particles and a network distribution of Fe particles in alumina matrix, have been produced. Both composites are tougher than the virgin alumina matrix. The fracture toughness of the composite with a network microstructure is much higher than the composite with a microstructure of dispersed particles. For the particulate dispersion microstructure, the main limitation to the toughening is the lack of plastic deformation of the ductile Fe due to the pull out of Fe particles, indicating weak bonding at the Al2O3/Fe interface. For the network microstructure composite, the gauge length of the ductile phase is much larger, allowing the ductile Fe to be stretched to failure between the crack faces. The weak bonding at Al2O3/Fe interface can promote partial debonding and contribute further to toughening in the network microstructure composite.
关键词:
