An Investigation Of Phase Transformation Superplastic Diffusion Bonding Of Near α-phase Titanium Alloy To Austenite Stainless Steel

Bonding of titanium alloy and stainless steel is very often in the fields like aviation, chemical plants, etc. Several welding techniques such as fusion welding, brazing, explosive welding and diffusion bonding have been employed to bond titanium alloy and stainless steel, but unable to achieve adequate joints for application and need high temperature. Phase transformation superplastic diffusion bonding (PTSD) is a new bonding method. When material in superplastic state, the interdiffusion rate of relative elements can be speeded up, and it is possible to bond the materials at relative lower temperature and shorter time.The solid-state direct diffusion bonding of TA17 near (-phase titanium alloy to 0Cr18Ni9Ti austenite stainless steel under phase transformation superplastic diffusion bonding has been carried out on Gleeble-1500D. Tensile testing of bonding joints has been carried out, and bonding joints have been investigated by metallograph observation, fracture morphology, concentration profiles of various elements in the bonded region, microhardness measurement, phases appeared in the joints and microimage analysis.The relationship between the ultimate tensile strength of the joints and technical parameters of bonding has been experimentally investigated. Optimized bonding parameters have been obtained. Under the conditions of Tmax=890℃, Tmin=800℃, thermal cycle number N=10cycles, bonding pressure P=5MPa, heating rate Vh=30℃/s and cooling rate Vc=10℃/s, the ultimate tensile strength of the joint reached its maximum value (307MPa), which is 60 MPa more than the maximum strength ever achieved by traditional bonding techniques. Under the optimized conditions, the bonding time is much shorter and bonding temperature is much lower. TiFe,TiFe2,TiNi,σ-phase and solid solution based on β-Ti are detected in the bonded area, and a series of transition areas are evident in the metallograph. The width of transition areas and the amount of intermetallics increase due to the interdiffusion between titanium alloy and stainless steel reinforced by the increment of maximum thermal cycle temperature and thermal cycle number. Both the brittle intermetallic compound (TiFe) and the solid solution based on (-Ti were formed on the fracture surface of bonding joints, and the more in quantity the solid solution is, the higher the ultimate tensile strength is. At the same time, the mechanism of phase transformation superplastic diffusion bonding has been theotetically analyzed and the result has been approved experimentally.