MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
Effect of Cooling Rate on Microstructure and Fracture Characteristics of β-Rich α + β Type Ti-4.5Al-3V-2Mo-2Fe Alloy
GunawarmanMitsuo NiinomiKei-ichi FukunagaDaniel EylonShiro FujishiroChiaki Ouchi
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2001 Volume 42 Issue 7 Pages 1339-1348

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Abstract

This study investigated the effect of cooling rate on microstructure and fracture characteristics of β-rich α+β type Ti–4.5Al–3V–2Mo–2Fe alloy rolled plate. Particular attention was paid to the roles of the local and continuous secondary phases within prior β grain in the static fracture toughness. A variety of microstructures containing different types, morphologies, sizes and volume fractions of secondary phases were obtained in matrix β (within prior β grain) with varying cooling rates; namely, water-quenching (WQ), air-cooling (AC), furnace-cooling (FC) and slow furnace-cooling (SFC) from various solutionizing temperatures in the α+β field. The types of secondary phases are martensite α (orthorhombic α′′), acicular α and plate-like α observed in WQ, AC and FC specimens, respectively. While, there is no or lack secondary phase observed in matrix β for SFC specimen. Deformation-induced martensite (α′′), DIM, was observed in WQ specimens after testing. The results showed that the fracture toughness, JIC, and calculated flow stress, σf, of the microstructures containing a secondary phase depend mainly on the type and width of the secondary phase. The JIC of microstructures containing a secondary phase, in general, is superior to that of the microstructures lacking secondary phases. Both the martensite α and DIM appear to increase JIC. In a particular condition, JIC decreases slightly with increasing width of acicular α for microstructure containing predominantly local acicular α, but increases monotonously with further increases in the width of acicular α. JIC increases considerably with increasing width of plate-like α. The increase of JIC is mainly due to increasing the effect of extrinsic toughening mechanism.

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© 2001 The Japan Institute of Metals and Materials
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