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铁道科学与工程学报

JOURNAL OF RAILWAY SCIENCE AND ENGINEERING

Vol. 17    Special 1    November 2007

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Effect of microstructure on impact toughness of TC21 alloy
CHEN Jun(陈  军)1, ZHAO Yong-qing(赵永庆)1, ZENG Wei-dong(曾卫东)2

1. Northwest Institute for Nonferrous Metal Research, Xi’an 710016, China;
2. Northwestern Polytechnical University, Xi’an 710072, China

Abstract:The impact toughness of TC21 alloy after different types of forging and heat treatments was studied. The results show that heat treatment at 915 ℃ for 1 h followed by air-cooling can achieve the highest impact toughness. The crack propagation path of bimodal microstructure is different from that of lamellar microstructure. Boundaries of primary α grain are observed to be preferential sites for microcrack nucleation. With the increase of heat treatment temperature, the volume fraction of primary α phase decreases and the nucleation sites of microcrack at the primary α phase boundaries also decrease, the impact toughness value is effectively improved. The microcracks of lamellar microstructure are located on α/β interface, or the boundary of colony, and/or grain boundary α phase. The crack propagates cross the colony, or along the colony boundary, and/or along β grain boundary. The crack propagation path of lamellar microstructure is dependent on the size, direction of colony. The crack path deflects at grain boundaries, colony boundaries, or arrests and deviates at α/β interface because of crisscross α lamellar. Therefore the impact toughness value of basket microstructure is higher than that of Widmanstatten microstructure.

 

Key words: TC21 titanium alloy; bi-modal microstructure; lamellar microstructure; impact toughness

ISSN 1672-7029
CN 43-1423/U

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