Papers by Author: Xuan Hui Qu

Abstract: The precipitation behavior of γ' phase after continuous solution cooling tests was examined in superalloy FGH96. The results indicate that, with the increase of cooling rate, the mean diameter of secondary γ' precipitates decreases as well as the shape changes from cuboid to spherical. Either under water cooling or cooling at 10 °C/min and 25 °C/min, the highest strength can not be obtained.

Abstract: Abstract. Aluminum nitride(AlN) powders were synthesized by carbonthermal reduction of Ammonium aluminum carbonate hydroxide(AACH). The AACH were prepared from ammonium alum and ammonium hydrogen carbonate by precipitation method and AACH adhere to carbon black during precipitation. The precursor has a high reaction activity (near 100% of nitridation ratio after heated in flow nitrogen at 1400°C, 2h). After carbon remove in muffle furnace at 700 °C, white color Aluminum nitride (AlN) powder attained and mean size is 100 nm. The specific surface area of the powders decreased with increasing of concentration of ammonium alum and ammonium hydrogen carbonate, which range from 22 m2/g to 7 m2/g, particle size vary from 58 to 120 nm. Phase presents in the products during heating in flowed nitrogen were observed by X-ray diffraction. The -Al2O3 formed when the precursor heated to 1200°C, AlN was founded at 1300°C and the reaction ended at 1400°C, the reaction temperature and annealing time were much lower than nitridate the mixture of Al2O3 and carbon black. Particle size was increased when reaction temperature increased from 1400°C to 1550°C.

Abstract: Diamond/Si/C porous preform was prepared with phenolic resin, Si, Diamond and graphite. Subsequent reactive vapor infiltration (RVI) of gaseous silicon at 1600 °C for 2 h in vacuum atmosphere resulted in the formation of a compact Diamond/SiC composite. The influence factors of perform porosity were investigated, including process pressure and raw materials. Density and microstructure of Diamond/SiC composites were also discussed. The results showed that the open porosity of preform was mainly influenced by the pressing pressure. It can also be affected by the content, morphology and the particle size of diamond. The preform with open porosity higher than 20% after RVI treatment can obtain Diamond/SiC composites with high density. However, over-high porosity of the perform will cause a mass of unreacted Si exists in the composite which is unfavorable for its application. In order to reduce the content of residual Si, open porosity of preform should be no higher than 40%.