EFFECTS OF PRECOATING SURFACE TREATMENTS ON FATIGUE OF TI-6A1-4V

Grit blasting is a common procedure of roughening surfaces to promote physical attachment of porous coatings, but it has been shown to reduc e fatigue strength. Shot peening is known to increase fatigue strength by inducing compressive surface stresses; however, it is not known ho w subsequent grit blasting affects these benefits. This study examines the endurance limits, S-e, of ELI grade Ti-6A1-4V specimens under rot ating cyclic bending, including polished (control); belted and beaded; belted, beaded, and grit blasted; and belted, beaded, shot peened, an d grit blasted, Belting and beading resulted in a slight increase in S -e; grit blasting caused a 15% reduction in S-e from polished. Fifty p ercent of this reduction was recovered when shot peening preceded grit blasting, suggesting that residual compressive surface stresses, indu ced by peening, were not eliminated by the blast process, Roughness av erages and RMS values did not correlate with S-e trends. SEM results s howed classical fatigue fractures, consistent with surface crack initi ation. (C) 1995 John Wiley and Sons, Inc.