ICMCTF2000 Session D4/E5-1: Properties and Applications of Diamond, Diamondlike and C-BN Coatings

Wednesday, April 12, 2000 1:30 PM in Room Royal Palm Salon 4-6

Wednesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	D4/E5-1-1 Implementation of Diamond Like Carbon (DLC) Coating in a Production Aerospace Mechanism with Low f=riction and good wear as key factors L.E. Fisher (Boeing Military Aircraft and Missile Systems Group) What is believed to be the first production implementation of a Diamond Like Carbon (DLC) coating for a friction and wear (non-optical) aerospace application is described. The application is a nominally 5 micron thick single layer, amorphous, hydrogenated, silicon containing, DLC coating, applied to a PH 13-8 Mo Stainless Steel substrate utilizing an RF Plasma Assisted Chemical Vapor Deposition process. Particular performance focus for the mechanism is on low sliding friction, low wear due to sliding action and vibration, and tolerance of foreign object/debris contamination. Design problems with an early configuration led to redesign tradeoff studies, followed by down selection to 3 competing coating technology concepts that were then subjected to limited developmental testing including corrosion, endurance sliding and vibration, and contamination. Superior results obtained with DLC during the developmental tests led to its incorporation in formal qualification testing and ultimately in production for an important component of the B2 Bomber. Descriptions of the component function and performance requirements, competing coatings tested, empirical results with decision rationale, DLC coating and masking issues and production considerations, as well as some "lessons learned" are included.
2:10 PM		D4/E5-1-3 Abrasion of Steel by Boron Carbide S.J. Harris (Ford Scientific Research Lab); G.G. Krauss (Ford Scientific Research Labs); G.L. Doll (Timken Research) We have shown previously that diamondlike carbon is sufficiently abrasive to polish the surface of a steel pin sliding against it. In the present work we measure the abrasiveness of a boron carbide coating. This coating is far more abrasive than any diamondlike carbon coating that we have examined. However, just as is the case with DLC, boron carbide loses its abrasiveness remarkably quickly. We believe our results suggest an important chemical interaction between boron carbide and steel.
2:30 PM		D4/E5-1-4 Application of Diamond-like Carbon Films to Sliding Tools for Electron Guns for Cathode Ray Tube Y. Jun (J&L Tech. Ltd., Korea); K.-R. Lee (Korea Institute of Science and Technology, Korea); B.-K. Jeong, S.-K. Kwon, J.-I. Jang, C.-H. Kim (LG Electronics Inc., Ltd., Korea) The surface morphology of sliding tools, which are sliding between electric plates of electron gun of Cathode Ray Tube (CRT) to control the gap between the plates, are very crucial. The scratches can be made by the friction on the surface of plates when these tools are sliding in and out between the plates. Since the gap and surface scratch of electric plates play major roles in the performance of electron gun and the electron beam coming out from the cathode of CRT, it is very important to keep the surface of tools smooth and clean. Diamond-like Carbon (DLC) film of 1µm thickness was deposited on the sliding tools to improve the tribological property and wear protection. Deposition has been done by Plasma Enhanced CVD (PECVD) using r.f. frequency with benzene. The hardness of the film was 25GPa as measured by nanoindentation. The frictional coefficient with respect to steel ball was observed as low as 0.1. During the field test in the assembly line, the coated tools showed the friction coefficient of about 0.2. Both number and size of the surface scratch in the eletrode plates were significantly reduced when using DLC coated sliding tools. The performance of electron gun was also much improved. The lifetime of tool was changed with the various deposition conditions. In the best result, the lifetime of the tool was prolonged by three times in the assembly line.
2:50 PM		D4/E5-1-5 Mechanical and Tribological Properties of a-C/a-C:Cr Multilayer Coatings K.J. Ma (Professor, Taiwan); C.G. Chao (University, R.O.C.); D.S. Liu (Chung-Cheng Institute of Technology, Taiwan); D.G. Teer (Company Teer Coatings Ltd, United Kingdom) Carbon based coatings, diamond like carbon or amorphous hydrogenated carbon, which demonstrated excellent hardness, chemical inertness, low friction and wear resistance, have been successfully used as low load protective coatings for both magnetic and optical discs. These properties also make carbon based coatings promising candidates for the higher load wear protection of machine parts and tools. Alternated a-C/a-C:Cr (about 2.5?m thickness) coatings were made by DC magnetron sputtering from graphite and Cr target in an argon discharge. Mechanical and tribological properties measured by indentation, scratch and pin-on-disc test. The critical scratch load of a-C/a-C:Cr multilayer coatings for total failure is approach 100 N. The friction coefficient remains within the range of 0.08-0.1 at loads between 10 and 40 N during a pin-on-disc wear test, using 5 mm WC/Co ball as a slider. The wear depth only reaches 0.6 um A after a one hour wear test. The surface of a-C/a-C:Cr multilayer coatings undergoes cyclic deformation, and failure eventually occurs as a result of fatigue. The greater compliance and fracture toughness of the a-C/a-C:Cr multilayer coatings allows greater strains or strain energy to be stored before coating failure, and hence significantly improves wear resistance.
3:30 PM		D4/E5-1-7 In Pursuit of c-BN Thin Film Heteroepitaxy H. Feldermann, C. Ronning, H. Hofsäss, Y.L. Huang, M. Seibt (Universität Göttingen, Germany) Cubic boron nitride (c-BN) thin films are most commonly deposited on silicon substrates. Regardless of the deposition technique used, a cross-section of the samples reveals a layered structure with a textured hexagonal BN (h-BN) interface between the Si substrate and the c-BN film, which is also textured. The h-BN interface has its (0002) planes oriented parallel to the (111) c-BN planes with a 2:3 lattice match. As this h-BN layer always forms before the cubic phase, it seems to provide the boundary conditions necessary for c-BN nucleation. In this paper we investigate the possibility of nucleating c-BN films directly on suitable substrates. Using mass selected ion beam deposition, c-BN films were grown on various crystalline substrates that have an oriented lattice structure matching the one of c-BN. The selected substrate materials additionally exhibit a high binding ionicity, so that their structure is preserved during the ion bombardment. Cross-sectional transmission electron microscopy (TEM) and energy dispersive x-ray analysis (EDX) were used to characterize the interface between the substrate and the films obtained. The results can help to clarify the role of substrate temperature and of compressive stress in c-BN film formation.
3:50 PM		D4/E5-1-8 Diamond for Tooling Applications: Success Through Simultaneous Optimisation of Substrate and Deposition Technology J. Karner, D. Franz (Balzers Limited, Liechtenstein); St. Feistritzer (Böhlerit GmbH, Germany) CVD and PVD coatings are today widely accepted in the tooling industry as wear protective coatings. The acceptance of diamond coated tools has increased in recent years in certain market segments, in the large market segments however a major breakthrough has not been achieved until now. Two major problems in diamond deposition have been the reason for slower market growth than predicted. Large scale economic production and the adhesion problem. The first problem has been overcome today by some diamond deposition technologies, especially by the Balzers HCDCA (High Current DC-Arc)-technique. This deposition technology is today used successfully in production in different locations for the deposition of Balinit Diamond on carbide inserts and round tools. Yet still a major drawback for succesful diamond tooling was the adhesion problem. While in the conventional PVD coating technology a broad range of substrate materials is suited for deposition, the requirements for diamond deposition on the substrate quality are much more restricted. Depending on the application different substrates and pretreatment technologies have to be applied. This requires a close relationship between the carbide-, tool manufacturer and the job coater. The paper will report on the progress in combined optimisation of tool - and deposition technology to offer a solution for successful high end machining. About 10 years after the start of diamond deposition on cemented carbides Boehlerit offers now a new solution: In connection with the BAL (Boehlerit Aluminium) geometry and a special hard metal grade, developed for diamond deposition, these diamond coated indexable inserts are the long expected solution for cost effective machining of synthetic materials like glass fibre and carbon fibre composites: the lifetime can exceed by far that of PCD-tools.
4:10 PM		D4/E5-1-9 Comparison Between the Erosive Impact Performance of Diamond Films Deposited Using the Microwave Surfajet and the Hot Flame Techniques D.P. Dowling, K Donnelly, R.V. Flood, M. McConnell, G. Morgan (Enterprise, Ireland); S. Hogmark (The Ångström Laboratory, Sweden); P. Hollman (Uppsala University, Sweden) Diamond coatings are currently used for a range of tooling applications due to their extreme hardness, chemical inertness and wear resistance. In this investigation an assessment is made of the erosive impact resistance of diamond coated cemented carbide. The diamond films were deposited using two techniques a microwave Surfajet and hot flame. The Surfajet is a type of surfatron in which the microwave power is coupled directly into the deposition chamber using a cylindrical discharge tube or antenna. The H₂, CH₄ and O₂ reactant gases are supplied coaxially with the microwaves (2.45 GHz) and enter the vacuum chamber as a plasma jet, from which the diamond film is deposited. Diamond film growth rates are approximately 0.5 µm / hour. In the hot flame technique the coatings are deposited from a C₂H₂ and O₂ gas mixture, film growth rates of up to 60 µm / hour are obtained. In addition to the two deposition techniques, two different pre-treatment methods were used in order to enhance the adhesion of the diamond coatings on the cemented carbide surfaces. The first method involved the removal of the cobalt binder using acid leaching. The second pre-treatment involves neutralising the cobalt by reacting it with silicon at 1100^oC prior to diamond deposition. The resultant cobalt silicide layer that is formed on the surface of the cemented carbide does not cause graphitisation of the growing diamond film. Erosive wear tests were carried out using a centripetal erosion tester in which SiC particles were impacted at a 90^o angle to the coated substrates. The impact momentum of the particles was increased until the diamond coating failed either due to film removal or spalling (hole formation). Once spalling was initiated coating delamination generally occurred over the entire area of exposure to the erosive particles. The erosive impact resistance of diamond was found to increase with film thickness in the range 1 to 16 µm. Surfajet deposited coatings survived higher impulse energies than the diamond films deposited by the hot flame technique. For example a 6.4 µm Surfajet film failed at an impulse to penetration of 5.0 µmNs, compared to 1.5 µmNs for a hot flame coating with similar thickness. Other factors found to affect erosive impact performance include diamond film quality, adhesion, roughness, porosity and crystallite size.
4:30 PM		D4/E5-1-10 Deposition and Characterization of Ultra-hard Silicon Carbide Coatings by rf Magnetron Sputtering A.K. Costa, S.S. Camargo (University of Rio de Janeiro, Brazil); C.A. Achete (Universidade Federal do Rio de Janeiro, UFRJ, Brazil); R. Carius (Forschungszentrum Juelich, Germany) Silicon carbide films were deposited onto c-Si substrates from a sintered SiC target on a rf magnetron sputtering system. The influence of substrate temperature (150 to 500°C) and polarization (0 to -100V), Ar pressure (10^-4to 10^-2mbar) and r.f. power (100 to 400W) on the properties of the resulting films was studied. Characterization of the films was done by Vickers microhardness, residual internal stress measurements, gas effusion experiments and Raman spectroscopy. Films with hardness values close to 50GPa and internal stress of about 1.5GPa could be obtained. The increase of substrate temperature results in structural relaxation reducing the internal stress with no impact upon hardness. Substrate polarization produces strong bombardment of the films with Ar implantation. Argon pressure affects the energy of impinging particles so that films with high hardness could be obtained at low pressures. Low power levels results in the highest hardness values but with low deposition rates and high film stresses. Increasing rf power leads to films with somewhat smaller hardness but strongly decreased stress. Upon thermal annealing at temperatures up to 1100°C hardness of the films remained almost unchanged while the Raman spectra showed some broadening only at the highest temperatures, both results suggesting a highly stable material. Additionally, gas effusion results point towards a very compact structure since argon effusion could only be observed at temperatures above 1000°C.
4:50 PM		D4/E5-1-11 Effect of WC Grain Size on the Adhesion of Diamond Films Grown on Chemically Pretreated WC-Co Substrates Y. Chung, W.S. Lee, Y.-J. Baik (Korea Institute of Science and Technology, Korea) The effect of chemical pretreatment method on the adhesion of diamond film on WC-Co substrates with different grain size (K20 and ultrafine grade) was investigated. The average grain sizes of the substrates were 1, 0.7, 0.5 µm, respectively. The substrate was etched by Murakami agent for 10 - 90 min to vary the surface roughness. Surface Co binder phase was etched by H2O2 and H2SO4 solution for 10 - 150 sec. Diamond film was deposited by microwave plasma CVD. Hydrogen and methane were used as precursor gases and methane content was 7%. Substrate temperature and the microwave power were 950oC and 4000W, respectively. The surface roughness was measured by WSI (White-light Scanning Interferometry). The adhesion strength was evaluated by Rockwell C indentation method. The surface morphology was studied by SEM analysis. At a given grain size, the surface roughness increased with etching time of Murakami agent and then saturated. The surface roughness at the saturation point decreased with decreasing WC grain size. Thickness of Co-depleted zone formed near the diamond/WC-Co interface did not depend on the WC grain size. The adhesion strength was strongly dependent on the grain size. The average width of delaminated layer decreased as the grain size increased. More importantly, the scattering of the delaminated width was reduced for the samples having larger WC grains. Those effects were discussed from a viewpoint of WC grain contiguity.
5:10 PM		D4/E5-1-12 A New Design Diamond Disc for Tungsten Chemical Mechanical Polishing Application Y.L. Wang (Taiwan Semiconductor Manufactuirng Companty, Ltd.,, R.O.C.); T.C. Wang, T.E. Hsieh (University, R.O.C.); S.Y. Chiu (National Chiao - Tung University, Taiwan, R.O.C.); Y.L. Wu (University, R.O.C.) Chemical Mechanical Polish (CMP) technology is widely use for global planarization in IC device structure. The metal CMP is a challenge process for metal corrosion. Tungsten is deposited to be a damascene layer and applied to deep-sub-micron process. Tungsten chemical mechanical polish (WCMP) is applied for planarization, corrosive prevention and precipitate residues. However, the WCMP is under the acid environment that made the polish pad conditioner- diamond disc corrosion and diamond drop off to be a scratch source. Therefore, most of WCMP process use "eex-sit"¡¨ pad conditioning to prevent the disc corrosion and diamond drop off. On the other hand, the polish performance such as removal rate, dishing and erosion properties will be influence on pad conditioner. In this study, we design a new gird diamond disc with nano-crystalline diamond shield coated to improve the acid erosion and use "in-sit"¡¨ method to polish tungsten.