Effect of process parameters of Plain Water Jet on the cleaning quality, surface and material integrity of Inconel 718 milled by Abrasive Water Jet

Abrasive Water Jet (AWJ) is considered as a promising milling method for difficult-to-machine aeronautical materials as Inconel alloy 718 (IN718). However, grit embedment during AWJ is known as a detrimental effect on certain applications as aircraft repair, where surface condition may play an important role on additive material technologies. To overcome this problem, Plain Water Jet (PWJ) has been used in the present study as cleaning process and demonstrated to be an effective method to remove grit particles from the surface with marginal alterations of surface state. In this paper, firstly the influence of AWJ process parameters on abrasive embedment and surface texture on IN718 specimens milled by AWJ were addressed. Then these surfaces were subjected to PWJ cleaning process and were extensively characterized in terms of grit embedment, surface texture and roughness, erosion depth, microhardness and residual stresses. Before cleaning, the milled surfaces presented a grit embedment level varying between 7 % and 14 %. One setting condition was selected for performing PWJ cleaning which reduced the grit level up to a quarter of the initial total surface area (less than 4 % in all cleaned surfaces) without relatively modifying neither the surface texture nor the erosion depth. Comparable microhardness gradients were observed before and after PWJ cleaning which corresponded to similar to 30 % higher than the bulk values at surface and then decreased beneath the surface up to 200 mu m before to reach bulk value (similar to 245 HV). Compressive residual stress state at surface initially induced by AWJ milling in some surfaces remained unchanged after PWJ process but in other ones was slightly relieved (similar to 50 MPa). Residual stresses after PWJ process resulted from - 630 MPa to - 315 MPa depending on the milling process parameters.