Oxidation of double glow plasma discharge coatings of iridium on molybdenum for liquid fuelled rocket motor casings

Abstract

Dense and uniform coatings of iridium (Ir), 5-7 mm in thickness, were deposited onto molybdenum (Mo) substrates by double glow plasma discharge in the temperature range of 800-850uC at 35 Pa. During deposition, the Mo substrate was biased at a voltage of 2300 V while the 99?9% Ir target was at a bias voltage of 2800 V. After deposition, the Ir coating was ablated using an oxyacetylene torch with a flame temperature of y2000uC to determine the high temperature stability of the coated substrate. The morphology and microstructure of the Ir coating were observed using scanning electron microscopy while the composition and structure were measured using X-ray diffraction and energy dispersive spectroscopy. The thickness of the as deposited Ir coating was uniform and the interface between the coating and the substrate exhibited excellent adhesion with no evidence of delamination and cracks. After exposure to the flame, the surface of the as ablated coating presented imperfections including pores, bulges and cracks; however, the Ir coating retained sufficient adhesion to limit the weight loss of the Ir coated Mo substrate to 10 mg cm 22 s 21 .

Oxidation Resistance of Ir/HfO2 Composite Coating Prepared by Chemical Vapor Deposition: Microstructure and Elemental Migration

“…This substantially impacts the service life of a material when used in high-temperature oxidizing environments. Additionally, under high-temperature oxidizing environment conditions, Ir is susceptible to micropore diffusion and agglomeration along grain boundaries, forming rapid diffusion channels along these grain boundaries [35][36][37]. As oxidation proceeds, the density of the micropores in Ir increases, and they agglomerate along the grain boundaries, facilitating outward movement.…”