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Wear 262-164, 1993, pp. 40-46.
Abstract Wear mechanisms have been analysed for a hard alloy prepared from cobalt and tungsten carbide when rubbed against polymers and their composites. The influence of the polymer chemical structure on hard alloy wear by the oxidation-fatigue mechanism was considered, as well as the effect of the hard alloy surface roughness and composite formulation on the running-in process. The relative area of layers transferred by friction onto the hard alloy surface during contact interaction was found to affect the mechanism by which the surface wears. The abrasive wear mechanism changes for the oxidation mechanism in the case of steady friction transfer layer formation owing to weaker friction hardening of the hard alloy surface layer, and to fatigue tear-out of carbide grains.
E-Book Content
40
Wear, 262-164
(1993)
40-46
Mechanisms of hard alloy wear in frictional processes with polymers and composite materials A. L. Zaitsev Metal-Polymer Research Institute, Academy of Sciences, Gomel 244652 (Belartu)
Abstract Wear mechanisms have been analysed for a hard alloy prepared from cobalt and tungsten carbide when rubbed against polymers and their composites. The influence of the polymer chemical structure on hard alloy wear by the oxidation-fatigue mechanism was considered, as well as the effect of the hard alloy surface roughness and composite formulation on the running-in process. The relative area of layers transferred by friction onto the hard alloy surface during contact interaction was found to affect the mechanism by which the surface wears. The abrasive wear mechanism changes for the oxidation mechanism in the case of steady friction transfer layer formation owing to weaker friction hardening of the hard alloy surface layer, and to fatigue tear-out of carbide grains.
1. Introduction Sintered hard alloys possessing unique mechanical, thermophysical and chemical properties whose wear resistance is an order of magnitude higher than that of steels have found numerous applications in machine building for making wear-resistant friction unit elements and components of processing equipment [l]. They operate successfully in the unlubricated friction assemblies found in diamond processing machine tools and can be used in abrasive environments, corrosive liquids, at high temperatures, in vacuum and under other severe friction conditions. Broad areas of application and the search for new applications where cobalt and tungsten hard alloys are used require detailed understanding of the friction properties under concrete conditions of operation. Despite numerous publications [2] devoted to the cutting and rubbing processes, there is no agreed opinion on the main causes that make hard alloys wear out. In fact, the wear mechanism for tungsten carbide and cobalt-based hard alloys rubbing against polymers and polymer-based composites is not understood. This work is an attempt to fill the gap in this field of knowledge.
2. Experimental details Tests were carried out with thermoplastic and thermosetting polymers of different chemical structures that are mostly used for making friction machine compo-
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nents: high density polyethylene (HDPE) (GOST 1633878), polycaproamide (PCA) (PA-6, OST 6-06-09-76), polytetrafluoroethylene (PTFE) (F-4, GOST 10007-78), phenolformaldehyde polymer (PF) (LBS3, GOST 90378) and epoxy compound (EDC) (ED-20, GOST 1058778) hardened with maleic anhydride. Counterfaces were prepared from hard alloy WC6-M (GOST 3882-80) containing dispersed tungsten (94 mass%) of average size 1.3-1.6 pm and cobalt carbide (6 mass%). Also, composites based on phenol resin and graphite filler differing in the amount of functional additives (up to 5 mass%) were tested. The chemical structures,