TiAl-Nb鈦鋁介金屬合金的高溫機械性質研究

• Main Authors: Yi-Jou lu, 盧怡州
• Other Authors: Chun-Hao Koo
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/10543309670045952162

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 87 === This research is to investigate the high temperature properties of titanium aluminide (TiAl-Nb) alloys. Three alloys, including Ti-40Al-10Nb﹑Ti-35Al-10Nb and Ti-40Al-15Nb, have been studied to determine their phases and properties at elevated temperature. In the aspect of phase identification, the phases, microstructure and precipitating temperatures of Ti-40Al-10Nb alloy are obtained from previous literature. The experimental results indicate that the main constituents of Ti-35Al-10Nb alloy at room temperature contain a2﹑B2 and w. Single phase b exists above 1200℃, a phase（or a2 phase）precipitates below 1200℃, and then w phase precipitates between 750 and 800℃. The identified phase of Ti-40Al-15Nb alloy is different from literature, which showed the phases at 1200℃ were g and b. In this study it indicates that the phases of Ti-40Al-15Nb alloy at 1200℃are a and b. Above 1290℃ b is the only phase in microstructure, and below 1290℃ a phase precipitates; g phase appears between 1150 and 1140℃, and w phase is observed below 950℃. In the study of mechanical properties at elevated temperature, it is found that g is a very brittle phase which always leads titanium aluminide alloy to fracture. The tensile strength (640Mpa) of Ti-40Al-15Nb alloy at 800℃ is extremely high. There is also an anomalous flow stress effect in the alloy. The yield strength is about 550 Mpa, and the superior effect is due to the exist of rich g phase in microstructure. In the high temperature oxidation test, the temperature limit of oxidation resistance of three alloys are all at 800℃.The oxidation resistance of Ti-40Al-10Nb at high temperature is the best among the three alloys, and Ti-40Al-15Nb alloy is the second.