Multicriteria Optimization, Sensitivity Analysis, and Prediction of Bond Characteristics of Vacuum Diffusion Bonded Aero Engine Ti6Al4V Alloy Joints

Joining titanium (Ti) alloys with conventional processes is difficult due to their complex structural properties and ability of phase transformation. Concerning all the difficulties, diffusion bonding is considered as an appropriate process for joining Ti alloys. Ti6Al4V, which is an α+β alloy widely used for aero engine component manufacturing, is diffusion bonded in this investigation. The diffusion bonding process parameters such as bonding temperature, bonding pressure, and holding time were optimized to achieve desired bonding characteristics such as shear strength, bonding strength, bonding ratio, and thickness ratio using response surface methodology (RSM). Empirical relationships were developed for the prediction of the bond characteristics, and sensitivity analysis was performed to determine the increment and decrement tendency of the shear strength with respect to the bonding parameters. Various criteria were applied to achieve the desired bond characteristics and their effects; optimum values and limits were evaluated through graphical and numerical optimization. The predicted and experimented results are validated and found that they are in good agreement with each other. The microstructural examination and X-ray diffraction (XRD) analysis were performed to analyze the effect of process parameters and interface metallurgical changes, respectively. Analysis of Variance (ANOVA) test results show that the most dominant bonding parameter is bonding temperature, which is followed by bonding pressure and holding time for most of the bond characteristics. From the sensitivity analysis, shear strength of the bonds was highly sensitive to bonding temperature.