Journal
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA
Volume 21, Issue 6, Pages 1283-1290Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S1003-6326(11)60854-6
Keywords
Nb-Ti-Si based ultrahigh temperature alloy; homogenizing treatment; aging treatment; microstructural evolution; microhardness
Categories
Funding
- National Natural Science Foundation of China [51071124]
- Doctorate Foundation of Northwestern Polytechnical University, China [CX200605]
- Ministry of Education, China [20096102110012]
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Directionally solidified (DS) specimens of Nb-Ti-Si based ultrahigh temperature alloy were heat-treated at (1 500 C, 50 h) and (1 500 degrees C, 50 h) + (1 100 degrees C, 50 h), respectively. The results show that the microstructures become uniform, the long and big primary (Nb, X)(5)Si-3 (X represents Ti and Hf elements) plates in the DS specimens are broken into small ones, and the eutectic cells lose their lamellar morphology and their interfaces become blurry after heat-treatment. Meanwhile, the (Nb, X) 5Si3 slices in the eutectic cells of the DS specimens coarsen obviously after heat-treatment. Homogenizing and aging treatments could effectively eliminate elemental microsegregation, and the segregation ratios of all elements in niobium solid solution (Nbss) in different regions tend to 1. After heat-treatment, the microhardness of retained eutectic cells increases evidently, and the maximum value reaches HV1 404.57 for the specimen directionally solidified with a withdrawing rate of 100 mu m/s and then heat-treated at (1 500 degrees C, 50 h) + (1 100 degrees C, 50 h), which is 72.8 % higher than that under DS condition.
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