James H. Arps

Reduction of wear in critical engine components using ion-beam-assisted deposition and ion implantation

Abstract Ion-beam-induced decomposition of hydrocarbon precursors is an efficient method for the deposition of diamond-like carbon (DLC). A large area, high current beam of 1–10 keV N+ and N2+ ions is used to break up a hydrocarbon precursor, releasing a large fraction of the hydrogen and leaving an amorphous carbon-rich network. This capability has been applied to the improvement of the tribology of combustion engine components. The effect of an intermediate layer of silicon, reacted to form a metal suicide, on the adhesive and wear properties of DLC has been studied by reciprocating pin-on-flat testing under representative loading, lubricating and temperature conditions. A significant reduction in the wear rate is observed when compared with bare and DLC-coated pins without a bond coat. Further experiments were directed at assessing the effect of metal ion implantation on the performance of hard chrome-plated piston rings. Initial results from accelerated wear tests of small treated segments are presented. Samples were implanted with 120 keV yttrium and lanthanum ions at doses of 1 × 1016 and 1 × 1017 ions cm−2. A significant increase in wear was observed at the higher doses. However, a marked improvement was observed in the wear properties of segments co-implanted with nitrogen or oxygen at similar ranges and doses, suggesting the formation of a compound phase which strengthens the material.

Development of Nanostructured Cu-Cr Coatings for Liquid Rocket Engine Applications

[Abstract] Copper-based alloys and composites are candidate materials for high heat flux structural applications in liquid rocket engine propulsion systems because of their high thermal conductivity and high-temperature strength. A major limitation to the use of copper-based materials, however, is their rapid oxidation at high temperatures in an oxidizing environment. In addition, copper-alloy rocket engine combustion chamber linings have been found to deteriorate when exposed to cyclic reducing/oxidizing (redox) environments. This deterioration, known as blanching, can seriously reduce the operational lifetime of the combustion chamber. Protective coatings that shield copper materials from oxidation must be employed to enable their use at temperatures above 650 °C. In this paper, new protective coatings for use in high-temperature oxidation/corrosion environments are presented. Specifically, nanostructured Cu-Cr coatings are produced using ion beam deposition methods. Two vacuum-based surface engineering techniques have been explored: (i) ion beam assisted deposition (IBAD), and (ii) magnetron sputter deposition (MSD). The coating microstructure consists of a fine mixture of Cu and Cr phases in which the sizes of the Cu and Cr particles ranged from 5-30 nm. Isothermal and cyclic oxidation tests indicated a protective chromia scale was formed on the coating surface and the Cu alloy substrate was protected from oxidation degradation. The nanostructured Cu-Cr coating exhibited a combination of properties of superior oxidation resistance, high thermal conductivity, and good match of thermal expansion properties with the substrate. An apparatus and methodology to coat the inside wall of a subscale Cu-alloy combustion chamber liner have been developed. The method uses a rotational cylindrical magnetron sputter deposition system with a composite Cu-Cr target.