The present invention concerns processes for etching a porous titanium foam or porous titanium alloy foam where a clean, dry foam product is immersed into an aqueous acid solution comprising about 0.5 to about 5 volume percent HF and about 5 to about 20 volume percent HNO.sub.3 for a time sufficient to achieve a desired surface roughness and heating the etched foam to remove residual titanates. The etching process increases the porosity at the surface of the foam but the etchant does not penetrate fully into the interior of the foam so that adequate mechanical properties are maintained. The etching process also increases the coefficient of friction at the foam surface. The foam may comprise an open-celled orthopaedic or dental implant, or may comprise a coating on the surface of a substrate.