| Title |
Correlation between Microstructural Evolution and Impact Toughness of Ti-6Al-4V
Alloy under Different Annealing Conditions Using Instrumented Charpy Impact Tests |
| Authors |
황정우(Jung Woo Hwang) ; 양준하(Junha Yang) ; 김재호(Jae Ho Kim) ; 정영웅(Yeongwoong Jung) ; 염종택(Jong-Taek Yeom) |
| DOI |
https://doi.org/10.3365/KJMM.2026.64.4.267 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
Ti-6Al-4V alloy; Microstructure; Impact toughness; Instrumented Charpy impact test; Crack propagation |
| Abstract |
Ti?6Al?4V alloys for aerospace structures require damage-tolerant design, so their impact
resistance should be quantitatively interpreted by separating crack initiation and crack propagation
contributions. In this study, microstructures were tailored by fixing the annealing time and air cooling while
varying the annealing temperature from 820 to 1040 °C, resulting in equiaxed (EM, 820?860 °C), bimodal
(BM, 920?960 °C), and lamellar (LM, 1000?1040 °C) microstructures. Microstructural characterization was
performed using SEM and EBSD analyses, followed by tensile testing. Instrumented Charpy impact tests
were conducted to partition the total absorbed energy (ET) into crack initiation energy (EI) and crack
propagation energy (EP), enabling correlations among microstructural features, tensile properties, and
toughness. Tensile test results indicated that EM maintained nearly constant ultimate tensile strength (UTS,
995?997 MPa) with a slight increase in elongation (24.9?25.8%). In contrast, BM exhibited gradual decreases
in UTS (966?979 MPa) and yield strength (YS, 848?875 MPa), with elongation decreasing from 25.5 to 22.8%.
LM exhibited a pronounced loss of ductility, with elongation decreasing from 12.2% to 7.8%. Impact test
results indicated that ET ranked as BM > EM > LM, with values of 15.8?18.9 J, 13.0?14.8 J, and 10.1?11.6
J, respectively. In the EM condition, ET degradation was dominated by reduced EP, while EI remained nearly
unchanged. In contrast, EI and EP in the BM condition were maximized at lower annealing temperatures and
decreased concurrently with increasing temperature. Crack-path analysis demonstrated that enhanced EP in
BM arose from frequent crack deflection at primary α (αp)?transformed β (βt) interfaces and packet/lamellar
boundaries, whereas crack propagation remained relatively straight in EM and LM. These results provide
quantitative annealing?microstructure guidelines for optimizing impact toughness in Ti?6Al?4V alloys by
identifying key microstructural factors controlling EP. |