Abrasive waterjet peening: a new method of surface preparation for metal orthopedic implants.

Abrasive waterjet (AWJ) peening is a new mechanical surface treatment process envisioned for use on metal orthopedic implants. The process utilizes an abrasive waterjet to simultaneously texture and work harden the surface of a metal substrate through controlled hydrodynamic erosion. In this study, a titanium alloy (Ti6Al4V) was subjected to AWJ peening over a range of parametric conditions. The textured surfaces were quantified in terms of the apparent interdigitation volume (V(i)), the effective stress concentration factor (K(t)) posed by the surface topography, and the magnitude of residual stress (sigma(r) ). Topographical features of the prepared surfaces were determined using contact profilometry, and X-ray diffraction was used in evaluating the in-plane residual stress. It was found that a large range in V(i) (9.4-43.8 microm(3)/microm(2)) and K(t) (1.3-2.7) are available through selection of the AWJ peening process parameters. Furthermore, a compressive residual stress (-409 +/- sigma(r) +/- -33) was found to result within the surface of the Ti6Al4V substrates regardless of treatment conditions. When compared to a titanium plasma spray coating used for cementless fixation, the AWJ peened Ti6Al4V exhibited a surface topography with significantly lower effective stress concentration and higher compressive residual stress. Based on results from this study, AWJ peening may serve as a new method of surface treatment for metal orthopedic implants, which supports the development of stable primary fixation and simultaneously enhances the component fatigue strength.