ICMCTF1998 Session A2: Coatings to Resist Wear at High Temperatures

Monday, April 27, 1998 1:30 PM in Room Council/Chamber/Cabinet

Monday Afternoon

Start	Invited?	Item
1:30 PM		A2-1 Sulfate Based Coatings for Use as High Temperature Solid Lubricants P.J. John (University of Dayton); J.S. Zabinski (Air Force Research Laboratory) Solid lubricant coatings are being sought for high temperature applications in advanced jet engine technologies. In the past, oxides and fluorides have been used as lubricants in >500°C applications. Sulfates have recently been identified as a class of high temperature solid lubricants. Pulsed laser deposition has been used to grow thin films of CaSO₄, SrSO₄, and BaSO₄. These coatings have exhibited coefficients of friction below 0.2 for pin-on-disk tests conducted at 500°C. The pin and disk materials have an effect on the friction properties, with Inconel, sapphire, and TiN coated steel specimens and pins performing better than steel. The utility of incorporating these sulfate coatings into layered and composite structures with nickel and chromium will be discussed.
1:50 PM		A2-2 Particle Size Effects on the Elevated Temperature Erosion Behaviour of Ni-Cr/WC_p MMC Based Coatings D.Y. Pena, M.M. Stack (UMIST, United Kingdom) A significant recent development in the study of solid particle erosion of materials at elevated temperatures has been the construction of materials performance maps. Such maps provide a means of minimizing the degradation of materials for a given set of conditions. For composite materials, such as MMCs, they also enable optimization of materials parameters such as volume fraction, size and spacing of the reinforcement. The object of this work was to investigate the effect of increasing erodent size on the wastage of Ni-Cr/WC_p MMC based coatings at elevated temperatures. The performance was investiaged at a range of temperatures and WC volume fractions using alumina particles as an erodent. The apparatus used was a laboratory simulated fluidized bed, the environment was oxidizing and the velocity ranged between 1 and 5 ms^-1. The results showed that eordent size had a significant effect on the transitions between the wastage regimes for such materials. Materials performance and selection maps were constructed, for kinetic energy versus temperature, showing the regions in which the various volume fractions exhibited "low" wastage. The potential of such maps to assist in the production of "tailored" coatings, for specific applications at elevated temperatures, is addressed in this paper.
2:10 PM		A2-3 Engineering Properties of Alternative Hard Chrome Coatings for Aerospace Applications D.L. Dull, V.S. Sundaram, M.S. Pollack (The Boeing Company) Several dry processed coatings are being evaluated as alternatives to hard chromium plating to protect the wear surfaces of fatigue and non-fatigue sensitive aircraft parts such as landing gears, flap tracks, etc. We are specifically looking at High Velocity Oxy-Fuel (HVOF), D-Gun^®, and Super D-Gun^® processes for line-of-sight coatings and plasma processes such as the plasma source ion implantation (PSII) for non-line-of-sight coatings. Boeing recently joined the Advanced Technology Program sponsored by the National Institute for Standards & Technology (NIST) to develop diamond-like carbon coating deposition using PSII. In addition, Boeing is working with several other vendors and research laboratories to find alternative coatings that might meet our engineering requirements. In evaluating a selected coating, the engineering design criteria considered include microstructure, corrosion resistance, wear characteristics, and fatigue performance. Alloys under consideration include high strength steels, corrosion resistance steels, titanium, and nickel based alloys. Preliminary results from several different types of coatings are very promising. Limited implementation of these coatings into production has been accomplished.
2:30 PM		A2-4 The Effect of Coating Residual Stress on the Fatigue Life of Thermal Spray Coated Steel and Aluminum R.T.R. McGrann, D.J. Greving, J.R. Shadley, E.F. Rybicki (The University of Tulsa); T.L. Kruecke, B.E. Bodger (Southwest Aeroservice, Inc.) The acceptance of thermal spray coatings in many applications depends on the fatigue performance of the coated part. One of the factors that influences the fatigue life of thermal spray coated components is the residual stress in the coating. This study investigates the fatigue performance of tungsten carbide (WC) thermal spray coating systems. Bending fatigue tests of specimens with WC-Co coatings on both 4130 steel substrates and 6061 aluminum substrates were conducted. Fatigue life (S-N) curves were created. The through-thickness residual stress level in the thermal spray coatings was determined using the modified layer removal method. The effect of the residual stresses on the performance of the coated specimens was analyzed. It was found that there is a direct relation between the residual stress in the coating and the fatigue life of the coated material. Fatigue life can be increased by a factor of ten due to the level of compressive residual stress in the coating.
2:50 PM		A2-5 Elevated and Room Temperature Friction, Wear, and Fatigue Strength Comparisons of Hard Chrome and Several Alternative Coatings J.D. Schell (General Electric) Pending changes in OSHA regulations for permitted exposure limits to hexavalent chrome ions during hard chrome plating operations are driving interests in alternative coatings. The variety of applications for hard chrome suggests that a number of engineering perfomrance factors need to be considered in replacing hard chrome. The author will address several factors of particular interest to many users of hard chrome; friction, wear, and fatigue strength effects. Selected elevated and room temperature data for hard chrome plate and several alternative coatings will be presented and discussed. Amongst the alternative coatings, the author will cover two HVOF coatings, WC-17%Co and Triballoy 400, and two PVD coatings, chrome nitride and titanium-aluminum nitride.
3:10 PM		A2-6 Break
3:30 PM		A2-7 Phase, Residual Stress and Texture in Triode-Sputtered Tantalum Coatings on Steel S. Lee, W. Windover (US Army Armament Research) This work reports the study of a prototype large diameter steel cylinder triode-sputtered with thick tantalum coatings on top of a very thin niobium under-layer, which was performed at Battelle, Northwest for the protection of the bore against wear and erosion. X-ray diffraction phase, texture and residual stress studies were made, and anisotropy, isotropic and directional elastic modulus were calculated from single crystal elastic constants. Tantalum has two phases - a harder tetragonal beta phase and a softer, more ductile body-center-cubic alpha phase. Our phase determination was based on X-ray diffraction and X-ray fluorescence analyses, hardness, electric resistance measurements and SEM microstructure. Two approaches were taken to determine internal stresses in the coatings- a phase-sensitive X-ray diffraction method, and a radius of curvature method. Because of the low anisotropy factor in tantalum, and the low level of preferred orientation in the single-phased alpha tantalum, X-ray residual stress determination yielded excellent results. Locally developed software was used to obtain high-resolution pole figures to determine crystalline texture. In the Battelle cylinder, triode sputtered with thick tantalum coating on top of a niobium under-layer, alpha-phase tantalum, preferred (110) orientation, and high tensile residual stresses were observed. The (110), (100), (211) and (321) pole figures showed respectively 1, 2, 4 and 8 poles. However, in other sputter-deposited tantalum specimens on steel, without using the niobium under-layer, the coatings generally consist of mixed alpha and beta phases. Phase composition and distribution of the phases in the specimens during nucleation and growth must be considered in texture and residual stress characterization. Phase and texture affect materials properties, and residual stress can cause cracking, buckling, de-bond and adhesion failure in coatings and thin films. Phase, stress and texture should be determined and optimized as a function of sputtering deposition parameters in future development of refractory coatings for wear and erosion applications.
3:50 PM		A2-8 Tribological Properties of Diamond-like Nanocomposite Coatings at High Temperatures C. Venkatraman, C. Brodbeck (Advanced Refractory Technologies, Inc.) Diamond-like Nanocomposites (DLN) films are amorphous in nature and consist of C, H, Si, O. In addition, metal atoms can be incorporated into the coatings. The DLN coatings exhibit low coefficient of friction, low wear rate, low stress, high hardness and good adhesion on a variety of substrates. The wear resistance of DLN films deposited on silicon substrates was investigated after the samples were thermally annealed in air up to 500 C. The samples were also characterized by micro-Raman spectroscopy and nano-indentation. The investigation revealed that the wear rate of DLN films is very low ( ~ 1.0e-8 mm³/Nm) and film hardness can be correlated with the wear rate of DLN. The wear rate of DLN remained unchanged at higher temperatures except for a large increase at 500 C. The study also investigated the effect of annealing on the thickness of the DLN films.
4:10 PM		A2-9 Wear Resistance of Magnetron Sputtered Cr_xN_y-Coatings Under Conditions of Injection Moulding Machines M. Heinze (Deutsches Kunststoff-Institute, Germany) The degree of machine wear decisively determines the economic feasibility of the plastic process. High temperature of plasticized material, high abrasion by fillers and corrosion attach will remain a problem. In addition, quality loss caused by wear products frequently becomes unacceptably and make it necessary to shorten maintenance periods for replacing the worn components. In the present study the potential of Cr_xN_y-hardcoatings for wear protection in plastic processing units were investigated. Therefore model wear tests were carried out to demonstrate the tribological situation inside the screw/barrel system of injection moulding machines. The test methods covered the solid and the molten state of various moulding compounds. Chrom nitride was found to have high hardness like TiN, corrosion resistance behaviour similar to electroplated chrome under conditions of fast flowing melt. The coatings were deposited on steel, described in characteristics and tested in a model wear test with plasticized moulding material. High temperature of the melt, high abrasion by glass fibres and corrosion attack could only change the coatings properties slightly. Furthermore the results depict a dependent on the plasticized moulding compounds.