Microstructure and Notch Properties of Heat-Treated Ti-4.5Al-3V-2Mo-2Fe Laser Welds

Abstract

The microstructure and transformation behavior of Ti-4.5Al-3V-2Mo-2Fe alloy and its laser welds after various heat treatments were investigated. Notch properties, such as impact toughness and notched tensile strength, were also measured on the welds to choose an appropriate post-weld heat treatment (PWHT) of the alloy. The temperature regimes in which transformed into 0 , 00 or retained as after quenching were identified and discussed. The results indicated that 00 could be obtained primarily by rapid quenching from 880$840 C solution temperatures and was identified as a base-centered orthorhombic (centered on the C face) with the lattice parameters of a ¼ 0:305 nm, b ¼ 0:489 nm, and c ¼ 0:457 nm. The as-welded specimen exhibited fine acicular in the matrix with hardness considerably higher than the mill-annealed base metal. For a PWHT temperature lower than 800 C, the change in microstructure and hardness of the welds depended mainly on the temperature, not on the cooling rate. If the PWHT temperature was higher than 800 C, both the temperature and the cooling rate were important in altering microstructure and hardness of the welds. The welds after a 704 C/4 h treatment could prevent notch brittleness, reduce hardness variation in different regions of the weld, and obtain notch properties similar to the mill-annealed base metal.

Shape Memory Behavior of Superplastic Ti‐4.5Al‐3V‐2Fe‐2Mo Alloy

“…At Institute of Aerospace and Astronautical Science (ISAS/JAXA), spherical fuel and gas tanks have been fabricated by superplastic blow forming of titanium alloy sheets and have been used for several man-made satellites [3]. It has been reported that SP-700 exhibits martensitic transformation upon quenching from high temperature [1,2,4]. Chung et al [4] conducted transmission electron microscope (TEM) observation and claimed that two kinds of martensite phases exist in SP-700, namely with the hexagonal-closepacked (hcp) crystal structure and with an orthorhombic structure.…”

Relationship between Microstructure and Notch Tensile Strength in Ti–15V–3Cr–3Sn–3Al Alloy at Elevated Temperatures

“…1, 17) were used to determine the NTS values of the aged specimens. The use of such configuration could completely reflect notch brittleness of the tested specimens under tensile loading.…”

The Influence of Microstructures on the Notched Tensile Fracture of Ti–6Al–6V–2Sn Welds at Elevated Temperatures

“…The use of such configuration could completely reflect notch brittleness of the tested specimens under tensile loading. [16][17][18]20) For the welds, the notches were located at the center of the fusion zone (FZ) to ensure the crack growth along the weld centerline during tensile loading. Notched tensile tests were carried out in air at a constant displacement rate of 1.0 mm/ min.…”