No 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.

The results of studies of wear resistance and tribological properties of experimental single carbide hard alloys grades with modified Co-Mo-Ti binders upon conditions of friction without lubricant on stainless steel are presented. All the data obtained were compared with similar parameters for the basic alloy VK8 (Co-Mo), on the basis of which the experimental grades were developed. Tribological tests were performed on tribometer which implemented a scheme of friction "pin on disk" at constant sliding speed and normal load values with artificially heated tribo contact zone. Studies have found that partial substitution of cobalt in a binder by Mo and Ti has led to a decrease in average friction rates. It was established that the greatest wear resistance and the best tribological characteristics were obtained for specimens of experimental grade 2.22 (5,65%Co+1,8%Mo+0,6%Ti). The process of friction for this pin material was characterized by the formation of secondary structures with high shielding properties, reducing of the adhesive interaction of materials, low volume wear intensity, minimal friction coefficient, as well as the least roughness of friction tracks on the counter body (disk). An increase in the proportion of molybdenum in the binder of more than 5% reduced the wear resistance of the experimental grades in comparison with the basic alloy VK8.

The study objective: modeling of the temperature distribution along the front surface of the lathe cutter for a given moment of the cutting system evolution. The problem to which the paper is devoted. To evaluate the influence of the geometric parameters of the secondary plastic zone of on the characteristics of the temperature distribution for the front surface of the lathe cutter. Research methods. Geometric parameters of the plastically deformed layer are defined by digital modeling of contact processes by the finite element method. Some initial data for computer modeling and subsequent verification of its results are carried out on the basis of a full-scale experiment with longitudinal turning of a work piece made of stainless steel 12X18H9T with a T15K6 solid-alloy plate. The novelty of the work. Prediction of the temperature on the cutter front surface for a given moment of the cutting system evolution based on a scientific approach of using hydrodynamic analogies to the evaluation of deformation processes in the machined material and combined data of a full-scale and digital experiment. The study results. By means of a digital experiment, the boundaries of the secondary plastic zone in the chip are determined, then a temperature distribution curve is made on the cutter front surface in two variants: for variable and for a constant average thickness of the deformed layer. It is found that the average value of the contact temperature in both cases differs slightly and agrees well with the results of the full-scale experiment. The difference between the maximum temperature values is significant: with a variable layer thickness, the calculated temperature is 11% lower than for the variant with a constant value of this parameter. Conclusions: to calculate the average temperature in the secondary plastic zone, the average value of the deformed layer thickness can be used. In the case of solving problems related to determining the maximum temperature in the cutting zone, it is advisable to take into account the change in the thickness of the plastically deformed layer in the chip along the cutter front surface.