Microstructural Characterization and Mechanical Properties of Metastable Beta and α+β Titanium Alloy Electron Beam Weldments

Abstract

In the present study, the microstructural and mechanical properties of Ti-15V-3Cr-3Al-3Sn (Ti-1533) and Ti-6Al-4V (Ti-64) electron beam welds have been studied. Optical microscopy investigations revealed the presence of three different zones, namely, the fusion zone (FZ), the heat-affected zone (HAZ), and the base metal (BM). In Ti-1533 weld, the BM comprises equiaxed β grains while the FZ consists of large columnar β grains. Further, the HAZ constitutes coarse equiaxed β grains near the FZ. However, in the case of Ti-64 weld, the BM comprises a slightly elongated α phase and transformed β phase while the FZ consists of an acicular martensitic phase. Welds prepared with Ti-1533 exhibit a lower ultimate tensile strength (UTS) of 726 ± 5 MPa, yield strength (YS) of 702 ± 5 MPa, and % elongation (%El) of 12 compared to its BM (YS: 738 ± 5 MPa; UTS: 778 ± 5 MPa; %El: 15). The lower strength in Ti-1533 weld is due to the presence of coarse columnar β grains in the FZ while Ti-64 weld exhibits superior tensile properties (UTS: 993 ± 5 MPa; YS: 959 ± 4 MPa; %El: 9) compared to its BM (UTS: 910 ± 5 MPa; YS: 856 ± 5 MPa; %El: 14). The higher strength for Ti-64 weld could be attributed to the formation of acicular martensitic α′ in the FZ. However, Ti-64 welds subjected to postweld heat treatment (PWHT) showed a decrease in strength (UTS: 922 ± 4 MPa; YS: 858 ± 4; %El: 12) compared to as-welded Ti-64 welds. This is attributed to the formation of the diffusional product α+β phase in the FZ. In contrast, Ti-1533 welds subjected to PWHT showed a rapid increase in tensile property (UTS: 1224 ± 6MPa; YS: 1205 ± 8; %El: 9) values and hardness (380 HV) values compared to as-welded Ti-1533 welds. This increase in strength after PWHT is due to uniform precipitation of alpha particles in the β matrix, which was evidenced by transmission electron microscope results.

Keywords:

• Electron beam welding
• Ti-15V-3Al-3Cr-3Sn
• Ti-6Al-4V
• microstructure
• hardness
• tensile strength

Acknowledgments

The authors are grateful for the grants or other forms of assistance for the creation of this manuscript. The authors thank the help of Imran Khan, IIT Gandhinagar, for carrying out some TEM investigations.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Aeronautics Research Development Board (ARDB) vide Government of India, Ministry of Defence [Project No. 1979].