Diffusion Bonding Characteristics of SP-700 Titanium Alloy

摘要

In recent years, there is a growing interest in superplastic forming and diffusion bonding of the titanium alloy SP-700 (Ti-4.5Al-3V-2Fe-2Mo), because of its low processing temperatures. In this study, the diffusion bonding characteristics of SP-700 were examined at temperatures of 775 - 825℃ and at pressures of 1.4 - 2.3MPa. The effects of the diffusion bonding conditions on bonding strength were evaluated by shear tests. The highest shear strength of 550MPa was obtained by diffusion bonding at 825℃ for 2 hours or more hours with 2.3MPa when starting with the samples of the "maximum surface roughness", Rmax, being 6.5μm. It was demonstrated that the strength of diffusion bonding was greatly improved with the smoother surfaces. For example, the shear strength attained at 825℃ with the samples of 6.5μm of surface roughness was equally achievable at 775℃ with a surface roughness of 3.3μm. This is an advantage of this alloy in diffusion bonding because the bonding temperature is lowered to temperatures below 800℃, which is not possible with conventional titanium alloys. Test results will be discussed from the viewpoints of the diffusion bonding parameters such as temperature, pressure, time and surface condition. Diffusion bonding of SP-700 to other titanium materials such as Ti-6Al-4V and CP-Ti will be also presented.