Adherence of Diamond Films Produced by Microwave Plasma Deposition on Sialon Tool Inserts
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ADHERENCE OF DIAMOND FILMS PRODUCED BY MICROWAVE PLASMA DEPOSITION ON SiAION TOOL INSERTS
ROBERT C. McCUNE, D.W. HOFFMAN, T.J. WHALEN AND C.O. McHUGH Ford Motor Company, P.O. Box 2053, Dearborn, MI 48121-2053
ABSTRACT The adherence of diamond films produced by microwave-enhanced chemical vapor deposition (CVD) on SiAION tool inserts was assessed by scratch, indentation and machining tests on aluminum alloys. While the films are nominally adherent during handling and mild cutting operations, the measured adherence values are appreciably lower than values associated with conventional CVD coatings on cobalt-tungsten carbide cutting inserts. An indentation type adhesion test using polished substrates was found to yield reproducible behavior for interfacial crack extension at loads ranging from 15 to 150 kg. The "critical load" in scratch testing was found to be less than 10 N.
INTRODUCTION Recent progress in the ability to form crystalline diamond particles and continuous films from various vapor-phase processes has suggested that cutting tools incorporating such coatings may be consequently developed. Angus and Hayman [I] have reviewed a number of the novel processes for deposition of diamond and diamondlike carbon films from the vapor phase. Because hard coating of metal-cutting tools has achieved widespread acceptance among end users of such products [2], it is reasonable to predict that coated cutting inserts will be among early applications of the new diamond technologies. Two particular areas of interest to manufacturers are: 1.) the prospects of developing low cost, ultra-hard coatings for three-dimensional tool surfaces, and 2.) the possibility of exploiting new engineering materials such as ceramics and fiber-filled composites in applications that had previously been uneconomical due to the high cost of diamond tooling required for machining. As with earlier cutting tool coatings, however, widespread acceptance of diamond-coated tools by the end user will be largely determined by the price/performance characteristics of such tools. Early reports on diamondcoated, cemented-carbide cutting tool inserts [3-5] suggest that growth and adherence of the coating on compatible insert materials will be a significant problem in establishing a family of robust metal-cutting tools. This work reports observations of diamond film adherence on SiAlON cutting tool inserts using techniques which have been previously employed in assessment of film adhesion on cemented carbide inserts. In that regard, the scratch and indentation tests performed, as well as several tests of metal cutting capabilities, are preliminary in nature due to the extremes in physical properties of diamond relative to even the hardest films produced by current physical and chemical vapor deposition technologies. The spirit of the work was, however, to assess the adherence and performance of diamond films made by a repeatable process in terms of currently achievable cuttingtool coating behaviors.
Mat. Ras. Soc. Symp. Proc. Vol. 130. 919S9 Materials Resea
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