Effect of friction stir welding speed on mechanical properties and microstructure of nickel based super alloy Inconel 718

Abstract

In this study, 4 mm thick nickel based super alloy Inconel 718 has been friction stir welded using different traverse speeds of 30, 50 and 80 mm min⁻¹ at a rotation rate of 400 rev min⁻¹. Since the Inconel 718 alloy was friction stir welded in the annealed condition, a significant increase in mechanical properties has occurred. Microstructural evolution in the nugget (NG) zone has been investigated using electron back scattering diffraction (EBSD) at the top surface and near the base of the NG as well as across the transverse cross-section. Low resolution EBSD scan across the NG to the base material showed great reduction in grain size from the base material to the NG region. High resolution EBSD scans showed that the NG region is dominated by dynamically recrystallised grain structure with very fine grains that was varied in size from the top to the base of the NG.

Keywords:

• Friction stir welding
• Nickel based super alloy
• Inconel 718
• Electron back scattering diffraction
• Grain size
• Crystallographic texture

The authors would like to thank Dr W. Kyffin, TWI Ltd, for providing the welds. In addition, the authors would like to thank Wenyongpeng (IMMPETUS) for hardness measurement.