Friction Surfaced Alloy 718 Deposits: Effect of Process Parameters on Coating Performance

The repair of alloy 718 parts used in aerospace and gas turbine industry is expensive, as well as, takes a long time. While many fusion-based repair technologies are available, their applicability is rather limited as they present various metallurgical problems, such as cracking, segregation, residual stresses. This work proposes using a solid-state deposition technique, friction deposition, to conduct these repairs in alloy 718. Deposits with a wide range of process parameter combinations are produced. To establish the optimal process parameters for friction deposition of alloy 718, the Taguchi design of experiments technique is applied. Further, the influence of axial force, spindle speed, and traverse speed on shear strength is investigated using Analysis of Variance. It was found that the axial force is the most dominant factor influencing the shear strength of coating, followed by traverse speed and spindle speed. Rotational speed significantly influenced the grain size of the deposits. The average grain size of the deposits increased with increasing the rotational speed (1000 to 1400 rpm). The post-deposition direct aged alloy 718 samples showed tensile strength higher than the minimum requirement of Aerospace Material Specification for the bulk materials in the solution treated and aged condition.