Ronghua Wei

Aspects of plasma-enhanced magnetron-sputtered deposition of hard coatings on cutting tools

Abstract Plasma-enhanced magnetron-sputtered deposition (PMD) is a physical vapor deposition process that combines plasma–ion bombardment with conventional magnetron sputtering to produce wear-resistant coatings with unique microstructural and tool-wear properties. With respect to microstructural properties, TiN deposited using the PMD process shows a very fine grain size and high internal stress with excellent adhesion and cohesion properties. With respect to tool-wear properties, end mills, shaper cutters, and hobs coated with TiN using the PMD process, show improved life when compared to those using arc-evaporation and unbalanced magnetron sputtering processes. The microstructural and tool-wear characteristics are believed to result from the plasma and ion-bombardment properties of the PMD coating process. In this paper, we present a summary description of the PMD plasma–ion bombardment process as well as gear-cutting wear measurements for PMD-coated cutting tools.

Practical applications of ion beam and plasma processing for improving corrosion and wear protection

Abstract A multi-year project for the US Army has been investigating the use of various ion beam and plasma-based surface treatments to improve the corrosion and wear properties of military hardware. These processes are intended to be complementary to, rather than competing with, other promising macro scale coating processes such high velocity oxy–fuel (HVOF) deposition, particularly in non-line-of-sight and flash chrome replacement applications. It is believed that these processes can improve the tribological and corrosion behavior of parts without significantly altering the dimensions of the part, thereby eliminating the need for further machining operations and reducing overall production costs. The ion beam processes chosen are relatively mature, low-cost processes that can be scaled-up. The key methods that have been considered under this program include nitrogen ion implantation into electroplated hard chrome, ion beam assisted chromium and chromium nitride coatings, and plasma-deposited diamond-like carbon and chromium oxycarbide coatings. Several examples of practical applications including bearing assemblies, hydraulics, and engine components, will be presented along with associated wear and corrosion test results.

Microstructure and tribological performance of nanocomposite Ti–Si–C–N coatings deposited using hexamethyldisilazane precursor

Thick nanocomposite Ti–Si–C–N coatings (20–30 μm) were deposited on Ti–6Al–4V substrate by magnetron sputtering of Ti in a gas mixture of Ar, N2, and hexamethyldisilazane (HMDSN) under various deposition conditions. Microstructure and composition of the coatings were studied using scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy, while the mechanical and tribological properties of these coatings were studied using Rc indentation, and micro- and nanoindentations, solid particle erosion testing, and ball-on-disk wear testing. It has been observed that the Si concentration of these coatings is varied from 0% (TiN) to 15% (Ti–Si–C–N), while the structure of these coatings is similar to the nanocomposite Ti–Si–N coatings and consists of nanocrystalline B1 structured Ti(C,N) in an amorphous matrix of SiCxNy with the grain size of 5−>100 nm, depending on the coating preparation process. These coatings exhibit excellent adhesion when subjected to Rc indentation tests. The ...

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.

Thick sputtered tantalum coatings for high-temperature energy conversion applications

Thick sputtered tantalum (Ta) coatings on polished Inconel were investigated as a potential replacement for bulk refractory metal substrates used for high-temperature emitters and absorbers in thermophotovoltaic energy conversion applications. In these applications, high-temperature stability and high reflectance of the surface in the infrared wavelength range are critical in order to sustain operational temperatures and reduce losses due to waste heat. The reflectance of the coatings (8 and 30 μm) was characterized with a conformal protective hafnia layer as-deposited and after one hour anneals at 700, 900, and 1100 °C. To further understand the high-temperature performance of the coatings, the microstructural evolution was investigated as a function of annealing temperature. X-ray diffraction was used to analyze the texture and residual stress in the coatings at four reflections (220, 310, 222, and 321), as-deposited and after anneal. No significant changes in roughness, reflectance, or stress were observed. No delamination or cracking occurred, even after annealing the coatings at 1100 °C. Overall, the results of this study suggest that the thick Ta coatings are a promising alternative to bulk substrates and pave the way for a relatively low-cost and easily integrated platform for nanostructured devices in high-temperature energy conversion applications.

Effects of Al and V Additions on Mechanical Response in Thick TiSiCN Nanocomposites Deposited Using Plasma-Enhanced Magnetron Sputtering

Thick TiSiCN and TiAlVSiCN nanocomposite coatings were fabricated by plasma-enhanced magnetron sputtering (PEMS). Characterizations by electron probe microanalyzer (EPMA) and XRD revealed the dependence of films with various precursor flow rates on the constituent composition and structure evolution in coatings. HRTEM images clearly confirmed that a nanocomposite structure existed with grain size below 10 nm. It was believed that nanocrystalline TiCxN1-x-based phases with B1 structure were embedded in an amorphous SiCyNz matrix, and such phase segregation ameliorated the hardness and H/E ratios. In the scratch and ball-on-disc wear tests, the evidence from crack initiation resistance, friction coefficient, and worn surfaces verified that thick nanocomposites exhibited remarkable tribological resistance. Hybrid anti-wear mechanisms on the basis of mechanical property variation, composition distribution, and microstructure evolution were proposed to elucidate the favorable durability of these thick films.

Mechanical, Microstructural and Tribological Properties of Low-Surface Energy DLC Coatings

This presentation discusses a study of low surface energy (LSE) diamondlike carbon (DLC) films. Plasma immersion ion deposition (PIID) technique was used to prepare various DLC films on silicon and 316 stainless steel (SS) substrates. To study the film properties and search for optimal coatings with lower surface energy, low friction and high wear resistance, various precursors were used to prepare the DLC film. The coating microstructures were studied using scanning electron microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM); the mechanical properties were characterized using nano-indentation; the tribological properties were studied using a pin-on-disc tribometer; and the surface energy (contact angle) was measured.© 2006 ASME