The present invention concerns articles having an outer surface that bears at least two layers of metal particles, wherein the at least two layers comprise an outermost layer and an intermediate layer; the outermost layer consisting essentially of aspherical metallic particles having a mean particle size of 50 to 500 microns; and the intermediate layer consisting essentially of substantially spherical metallic particles having a mean particle size of from 50 to 500 microns. In some embodiments, the outer surface has a volume porosity of between about 20% to about 80%.