THE EFFECT OF THE OXIDE FILM ON THE SOLID-STATE WELDABILITY OF THE TITANIUM VT6 SHEET

The influence of the oxide film on the formation of a solid-state joint under pressure welding is steel remaining poorly researched. In this regard, the solid-state weldability of sheet samples of commercial titanium alloy VT6 with different thickness of the surface oxide layer has been investigated in vacuum at temperatures ranging from 600 to 750 °C. The thickness of the oxide layer on the previously polished surface of the flat samples was regulated by a maturing time in the desiccator at room temperature for 1, 10, 30 and 180 days. The pressure welding of sheet samples of the VT6 alloy at a constant pressure for 2 hours was carried out in vacuum at a residual air pressure below P = 2.0×10-3 Pa. Scanning electron microscopic studies and mechanical tests were carried out to estimate the quality of solid-state joints (SSJ) in the welded samples of alloy VT6. Hold time under pressure at 700 °C leads to the disappearance of the oxide film in the area of SSJ. Shear strength tests have revealed that the SSJ strength increased with increasing the welding temperature in the temperature range of 600-750 °C. It is apparently associated with the dissolution of the oxide layer, and the solid solution hardening of the alloy with oxygen in the area of SSJ. Fractographic analysis of samples with SSJ after shear strength tests indicated that predominantly viscous fracture took place after welding at temperature of 750 °C