US Patent 9080098 Functionally gradient composite article

A composite downhole article is disclosed. The article is selectively corrodible in a wellbore fluid. The article includes at least one corrodible core member comprising a first material that is corrodible in a wellbore fluid at a first corrosion rate. The article also includes at least one outer member disposed on the core member and comprising a second material that is corrodible in the wellbore fluid at a second corrosion rate, wherein the corrodible core member has a composition gradient or a density gradient, or a combination thereof, and wherein the first corrosion rate is substantially greater than the second corrosion rate.