Crack propagation during Charpy impact toughness testing of Ti−Al−V−Mo−Zr alloy tubes containing equiaxed and lamellar microstructures

• Published in: Journal of alloys and compounds 2021-01, Vol.852, p.156581, Article 156581
• Main Authors: Chi, Guangfang, Yi, Danqing, Jiang, Bo, Yang, Lingyun, Liu, Huiqun
• Format: Article
• Language: English
• Subjects: Charpy impact test; Crack propagation; Damage tolerance; Electron backscatter diffraction; Electron microscopy; Extrusion; Fracture surfaces; Fracture toughness; Globularization; Heat treating; Heat treatment; Impact damage; Impact strength; Impact toughness; Lamellar structure; Microscopy; Molybdenum; Propagation; Solid solutions; Ti-Al-V-Mo-Zr alloy; Titanium alloys; Titanium base alloys; Tubes; Vanadium; Zirconium base alloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2020.156581

Numerous reports have elucidated the importance of impact toughness measurements for investigating the damage tolerance of a material. However, the effect of heat treatment parameters on impact toughness and the crack propagation mechanism in titanium alloys has rarely been addressed. Herein, the impact toughness of extruded Ti−Al−V−Mo−Zr alloy that comprises equiaxed and lamellar α microstructures has been investigated by conducting Charpy impact tests. The resulting fracture surface and alloy microstructure were examined by scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. The obtained results revealed that the colony size decreased after a solid solution and aging treatment, whereas subcritical annealing and slow cooling led to the globularization of lamellar α grains. After globularization, the impact toughness of the alloy increased by 69.2% and 50.0%, respectively; however, the impact toughness of the sample after the solid solution and aging treatment decreased by 61%. During impact testing, the direction of crack propagation was oriented toward the low-angle boundary region. Furthermore, a dissolved secondary phase was formed in the vicinity of the fracture surface, which increased the resistance of the alloy to crack propagation. The present study provides significant guidance for the preparation of titanium alloys with superior impact toughness properties. •Developed a new heat treatment process to improve the impact toughness of Ti−Al−V−Mo−Zr alloy.•Effect of microstructure on crack initiation and propagation was investigated.•The impact toughness of the alloy after globularization improved 69.2% and 50.0%, respectively.