Proceedings on Engineering Sciences (Jun 2019)
TRIBOLOGICAL CHARACTERISTICS OF EXPERIMENTAL HARD ALLOY GRADES WITH MODIFIED COBALT BINDER UNDER CONDITIONS OF DRY FRICTION ON TITANIUM-ALUMINUM ALLOY VT-3
Abstract
The paper is dedicated to investigations of tribological characteristics of experimental tool hard alloy (HA) grades based on tungsten carbide with modified cobalt binder under conditions of dry friction on disks made of titanium-aluminum alloy VT-3, as well as measures of their surface micro-hardness. All measured parameters were compared with similar characteristics of standard HA grade VK8, on the basis of which these experimental grades were developed. The research found that the surface micro-hardness of all experimental HA grades as pins were higher than that for the basic grade VK8; the highest value was fixed for the HA grade with symbol mark 2.22 (composition of the binder - 5.65% Co +1.8% Mo +0.6% Ti). The highest wear resistance was obtained for 2.23 (5.1%Co+2.7%Mo+0.61%Ti) and 2.21 (5.4%Co+1.43%Fe+0.82% Cu), the lowest – for grade 2.22. The analysis of friction processes peculiarities allows to explain the high wear resistance of grades 2.21 and 2.23 by features of surface structures ("the third body") formation during friction. Friction process for these HA grades include the periods of "the third body" intensive growth to the considerable thickness values, as well as the periods of its abrasion; due to this phenomena resulting wear rates for these two grades proved to be significantly lower than for the base grade VK8. The "third body" generated during friction protects surfaces from wear, at the same time it has its own significant shear resistance and increases actual contact area, due to this phenomena the friction forces for grades 2.21 and 2.23 are somewhat higher than for basic grade VK8. The grade 2.22 is characterized by the highest average friction force and its r.m.s. deviation value, which result in the greatest wear rates for both the HA pins and rotating disks. So according to the results of testing the best results among the investigated experimental HA grades were obtained for grade 2.23: the lowest average friction coefficient and the lowest track surface roughness on rotating disks, as well as the highest wear resistance values.
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