Melissa Klingenberg

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.

The effect of transport ratio and ion energy on the mechanical properties of IBAD niobium nitride coatings

Abstract Niobium nitride films were produced by ion beam assisted deposition (IBAD) using low (90 eV) and moderate (750–800 eV) energy nitrogen ion beams and electron-beam evaporated niobium. The transport ratios (ion to atom arrival ratios) used were approximately 0.062, 0.125, 0.25, 0.33, 0.50, 0.75 and 1.0. The resulting microstructure, crystal phase, and composition of the films were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and Rutherford backscattering spectrometry (RBS). The hardness, coefficient of friction, and wear resistance were assessed. The research detailed herein describes relationships between IBAD process parameters, NbN film structure and phase, and the mechanical properties of the films.

Update on alternatives for cadmium coatings on military electrical connectors

Summary The most promising candidate coating processes to replace cadmium and hexavalent chromium in electrical connector applications are technologies that are already being used on electrical connectors to some extent, or demonstrate both considerable promise for the application and sufficient maturity. These include: • Electroplated aluminum (AlumiPlate®) • Electroplated alkaline zinc-nickel (5–15% nickel in the deposit) • Electroplated tin-zinc (at least 20% zinc in the deposit) Future efforts will focus on these three most promising candidates. In addition, to support efforts being undertaken by electrical connector manufacturers, two EN-based technologies, both incorporating occluded particles, will also be evaluated. Coatings with both CCCs and TCPs will be considered, as available, and cadmium with CCC will be used as the control. The most promising candidate coating processes from emerging alternatives were also identified. These are technologies that show promise for electrical connector applications, but require further development for the electrical connectors employed by TARDEC. These include: • Alloys deposited from ionic liquids • Magnetron sputtered aluminum alloys • Tin-indium alloys Future efforts may consider these candidates as the technology matures and becomes more feasible for electrical connectors.

Alternatives to dichromate sealer in anodizing operations

Abstract Ogden Air Logistics Center (OO-ALC) is the primary facility within the United States Air Force for maintaining and overhauling aircraft landing gear. Aluminum landing gear components are anodized at OO-ALC to provide enhanced corrosion resistance, paint adhesion, and wear resistance; a sodium dichromate sealing operation usually completes the anodizing process. During sealing, the pores of the anodized (oxide) layer are hydrated, which fills the pores and provides improved corrosion resistance. However, this sealer contains hexavalent chromium, which is listed on the Environmental Protection Agencys list of industrial toxic chemicals that are targeted for voluntary reduction or elimination. The specification that outlines the sodium dichromate sealing process delineates three alternative processes that are approved for use: 1) boiling de-ionized water, 2) cobalt acetate, and 3) nickel acetate. While some research to support the use of these and other sealing processes has been gathered under past efforts, additional work must be conducted to fully integrate non-chromate sealers into OO-ALCs anodizing operations. To meet this need, the Air Force Research Laboratory tasked Concurrent Technologies Corporation to identify viable alternatives to the sodium dichromate sealer, conduct testing on these alternatives, and recommend the most promising sealer(s) for implementation based on the test results. This paper will describe the requirements for anodizing and sealing operations within OO-ALC, as well as the sealing technologies that are available and a path forward to demonstrate/validate the most promising alternatives for the specific needs and applications of OO-ALC.

Hard Chromium Replacement Candidates for Non-Line-of-Sight Landing Gear Applications

Introduction. Electroplated hard chromium (EHC) is a proven coating process, but many environmental, health, and safety (EHS) issues and regulations are associated with its use. As a result, the Department of Defense (DoD) has investigated and implemented thermal spray coatings to replace EHC in its maintenance facilities. High velocity oxygen-fuel (HVOF), a type of thermal spray process, deposition of tungsten carbide-17 percent (%) cobalt (WC-17Co) has largely replaced EHC in line-of-sight (LOS) applications; however, it has been incapable of repeatedly depositing uniform coating thicknesses on complex (i.e., non-LOS [NLOS]) geometries[1]. Therefore, the United States Air Force Research Laboratory – Advanced Power Technology Office (AFRL – APTO), in conjunction with Concurrent Technologies Corporation (CTC), sought both electroless and electrochemically deposited chromium(Cr-) free coatings that could treat NLOS parts. Most suitable candidates contained nickel (Ni), which has other health concerns, denoted in Table 1. It also is listed on the Environmental Protection Agency’s list of hazardous substances and is on the watch list as an emerging contaminant by the Office of the Deputy Under Secretary of Defense for Installations and Environment Chemical and Material Risk Management Directorate (CMRMD). As a result, Ni-based products are expected to become more heavily regulated and, thus, not suitable for midto long-term solutions. To address this problem, the team investigated non-Cr and nonNi technologies (i.e., largely cobaltbased coatings), with fewer health concerns and potentially reduced restrictions as compared to EHC (see Table 1).

Ion Energy/Momentum Effects During Ion Assisted Growth of Nb X N Y Films

In a previous paper, it was shown that the tribological properties of Nb x N y thin films produced by ion beam assisted deposition (IBAD) depend strongly on the beam energy and the ion-to-atom (R) ratio. This study was designed to separate ion energy vs. ion momentum effects on film stress, crystalline phase, grain size, morphology, and composition, all of which influence the tribological properties of the films. Inert ion beams (Kr, Ar, and Ne) were used in conjunction with a nitrogen gas backfill to independently control ion energy and ion momentum transfer to Nb x N y films. The ion species, energies, and R ratios were chosen to create a matrix of coatings that exhibited the same total energy deposition with different momentum transfer or the same momentum transfer but different total energy deposition. The resultant films were characterized using Rutherford Backscattering Spectroscopy (RBS), x-ray diffraction (XRD), atomic force microscopy (AFM), and residual stress analysis. Crystalline phases and texture, as well as residual stress, were more closely correlated with ion momentum transfer to the coating atoms than with overall ion energy input.