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%.