Papers by Author: Hu Zhang

Abstract: The microstructure evolution of Ni-45Ti-5Al(atomic fraction, %) alloys prepared by directional solidification with liquid-metal-cooling at different temperatures of 1450°C, 1550°C and 1650°C was investigated. The results showed that the macrostructure in directional solidification growth region was obvious columnar grains. The microstructure was cellular growth structure, and composed of primary NiTi matrix and Ti2Ni precipitates. The preferred orientation of NiTi and Ti2Ni were respectively [100] and [111] direction. It was found that aluminum was dissolved in both NiTi and Ti2Ni phase. The Al content in the matrix was higher than it in the precipitates. As heating temperature increasing, the microstructure evolution was inconspicuous and the average cellular spacing was 30~50μm. The Ti2Ni volume percent was most when the heating temperature was 1550°C.

Abstract: Multi-component Nb-(11,15)Si-5Hf-30Ti-4Al-4W-2B-(8,16)Cr alloys have been proposed, attempting to obtain the Nb-Si based alloys with a comprehensive property. The results show that three phases of NbSS, Nb5Si3 and Laves Cr2Nb exist in the alloys with a Cr content of 16 at%. With increasing Si and Cr contents the fracture toughness KQ decreases, while the oxidation resistance at 1250°C and strength at 1250°C and 1350°C exhibit an increasing tendency. The 15Si-16Cr alloy shows the highest strength and oxidation resistance, and the lowest toughness; they are 385MPa at 1350°C, 215mg/cm2 at 1250°C for 100 h, and 5.45 MPa•m1/2 at room temperature, respectively. The 11Si-8Cr alloy with an NbSS/Nb5Si3 microstructure only has the highest toughness of 11.87 MPa•m1/2, its strength and oxidation resistance are the lowest.