Friction welding of electron beam melted γ-TiAI alloy Ti-48AI-2Cr-2Nb

Electron beam melting (EBML a commercial powder-bed additive manufacturing process, is emerging as a cost effective technique for producing complex-shaped end-use parts in gamma titanium aluminides (γ-TiAI). In near future, γ-TiAI parts manufactured by EBM can be expected to find wide-spread use, especially in aeroengines. ln most applications, these EBM parts may have to be welded to other parts that are conventionally produced. Similarly, a need may often arise for welding two or more of these EBM parts together. In the current work, rotary friction welding of electron beam melted γ-TiAI alloy Ti-48AI-2Cr-2Nb (at. %) was investigated using cylindrical bars of ∼ 12 mm diameter and 70 mm height (the build direction was along the bar axis). The effects of pre-weld and post-weld heat treatments (1275°C/2 hours/furnace cooling) were also examined. Detailed microstructural studies, microhardness tests, and room temperature tensile tests were conducted on the friction welded joints in various conditions. Studies show that EBM parts in alloy Ti-48AI-2Cr-2Nb can be friction welded in both as-fabricated and heat treated conditions without any serious cracking problems. However, in as-welded condition, the joints were found to fail at the weld interface at very low strength levels. The pre-weld heat treatment seemed to offer no particular benefit. After post-weld heat treatment at 1275 °C, however, the joints were found to fail in the base material away from the weld interface at impressive strength levels. The post-weld heat treated joints, all along, showed a very homogeneous microstructure consisting of equiaxed γ and lamellar colonies of γ+α₂. Based on the current findings, it is appropriate to carry out friction welding of EBM parts in alloy Ti-48AI-2Cr-2Nb in as-fabricated condition. After welding, it is necessary to heat treat the joints at slightly below the α-transus temperature. Since a similar heat treatment is anyway needed for EBM parts in alloy Ti-48AI-2Cr-2Nb, the post-weld heat treatment is not any particularly taxing. (author)