Journal
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
Volume 716, Issue -, Pages 157-164Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.msea.2018.01.046
Keywords
Three-stage heat treatment; Ternary microstructure; alpha phase; Mechanical properties
Categories
Funding
- National Natural Science foundation of China [51501020, 51421001]
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This study reported the development of a three-stage heat treatment for TA19 titanium alloy to obtain a ternary microstructure consisting of equiaxed, lamellar and acicular alpha, which were successively acquired in the first stage (I-stage), second stage (II-stage) and third stage (III-stage) treatments. The content ratio among the equiaxed, lamellar and acicular alpha was tailored by controlling the I-stage and II-stage temperatures. Tensile test revealed that an increase of I-stage temperature improved both ultimate strength (UTS) and elongation (EL) due to the increased content of lamellar alpha. However, an excessively high I-stage temperature led to a very low content of equiaxed alpha, coarsening of beta grain and precipitation of grain boundary alpha, which reduced the EL. An increase of II-stage temperature resulted in an increase of UTS and a decrease of EL, because the increased content of acicular alpha produced a number of alpha/beta interfaces, which strengthened the alloy but was detrimental to plasticity. The fractography analysis indicated that majority of heat treated specimens exhibited a completely ductile fracture mode, while a mixed mode of brittle and ductile fracture was observed in specimens, which was subjected to an excessively I-stage temperature.
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