Hot gas erosion resistance of a vapor-deposited Cu-Cr coating

The effectiveness of a vapor-deposited Cu-Cr coating in protecting a NARloy -Z (Cu-3 wt.%Ag-0.5 wt.%Zr) substrate was investigated in a hydrogen/oxygen rocket engine test facility. The rocket facility generated high-temperatur e, high-pressure flows of combustion gas. The Cu-Cr-coated NARloy-Z article was actively cooled by cryogenic gaseous hydrogen so that the coating surf ace temperature was maintained below 650 degrees C. The coating provided go od protection for the NARloy-Z substrate under both hydrogen- and oxygen-ri ch hot gas environments. In erosion tests (hydrogen rich), the coating rema ined as a metallic mixture of Cu and Cr phases. In the erosion/oxidation te sts (oxygen rich), the coating surface formed a protective Cr2O3 scale unde r a thin layer of Cu-oxides. The ability of the coating to withstand repeti tive thermal shocks from the hot gas impingement without cracking was attri buted to the close match of thermal expansion properties between the Cu-Cr coating and the NARloy-Z substrate. (C) 1999 The Boeing Company. Published by Elsevier Science S.A.