Frontier Materials & Technologies

In the practice of drilling oil and gas wells with diamond bits equipped with PDC cutters, cutter quality non-compliance with the declared class occurs. At the same time, the currently used methods of full-scale testing, when granite stone is used as a counterbody, are time-consuming and expensive, which complicates their use for prompt incoming inspection of new batches of PDC cutters arriving for assembly of diamond bits. This necessitated the development of a laboratory tribotechnical facility for quantitative assessment of the ability of PDC cutters to resist abrasion against abrasive materials. The study covers the development of a specialized tribotechnical facility that allows testing PDC cutters of various sizes for wear during friction against a diamond-containing metal work face, for which it is proposed to use diamond cutting wheels. The developed laboratory tribotechnical facility includes: an electromechanical rotary drive (a drilling-and-milling machine); a measuring unit with sensors for normal loads, friction force and temperature of cutter self-heating during testing; a lever loading mechanism; a set of mandrels for the possibility of installing PDC cutters of various sizes; a data collection system and licensed software. The results of practical evaluation of the developed laboratory tribotechnical facility on PDC cutters of various batches showed that testing on the new equipment allows for quick collection of data on the wear rate of the working edges of PDC cutters. The developed methods, equipment and criteria can be used to certify the wear resistance of PDC cutters.

This study shows the possibility of using cutting ceramics as a turning tool. Replaceable standard cutting plates made of VOK-60 and VOK-71 cutting ceramics are used. In the work, based on simulation modelling in the DEFORM software environment, the possibility of high-speed processing with the specified cutting ceramics is substantiated and then experimentally confirmed. Additionally, the authors propose to apply hardening coatings by condensation with ion bombardment, which ensures an increase in the cutting speed to 100 m/min and more with an increase in the service life of the cutting ceramics from 3 to 3.8 times. The maximum stresses in the tool material and the deformation rate of the process material are studied. To select rational solutions in simulation modelling, the authors used the “temperature in the cutting zone”, “stresses in the tool material”, and “tool wear” parameters, which characterise the combined tension of the tool material. The transition from these parameters to the predictive design of cutting ceramics was performed by measuring the cutting force during natural cutting. The measured values of the cutting force components were used to calculate the stresses in the tool material. The study confirmed the hypothesis that the cutting ceramics is capable of operating under the conditions of processing viscous hard-to-machine corrosion-resistant specialised stainless steels such as 09H17N7Yu (C-0.09; Cr-17; Ni-7; Al-1) grade (EU 1.4568, X7CrNiAl17-7), which have a high content of chromium (16–17.5 %) and nickel (7–8 %). The authors propose original technological methods to improve the performance of the cutting ceramics through special heat treatment and coating deposition. In particular, heat treatment in a vacuum at a temperature of 1100–1400 °C for 20–40 min increased the bulk strength of the ceramics, and additional thermochemical treatment by ion nitriding performed at the final stage of heat treatment made it possible to alloy the bond.

Magnesium alloys of the Mg–Al and Mg–Zn systems have a wide effective solidification range (ESR), and as a result, have the tendency to hot brittleness during casting. There are several methods for analyzing and calculating the hot brittleness of magnesium alloys, but they are very labor-intensive. In this regard, the objective of the study is to develop a model for calculating the hot brittleness index (HBI) based on the value of the calculated effective solidification range, identifying and analyzing their relationship in binary and multicomponent alloys based on the Mg–Al and Mg–Zn systems. The ESR was calculated using the Thermo-Calc program (TTMG3 database). The ESR was calculated as the difference between the temperature of formation of a given amount of solid phases and the nonequilibrium solidus temperature. The study showed a good correlation between the calculated values of ESR and hot brittleness index in both binary and multicomponent magnesium alloys. In the Mg–Al system alloys, the calculated dependences of the ESR at 90 % of solid phases (ESR₉₀) show the best correlation with the experimental values of HBI. In the binary alloys of the Mg–Zn system, a qualitatively similar dependence is observed. However, no clear correlation was noted between the ESR and HBI. The ESR₆₅ and ESR₈₀ dependences demonstrate the closest nature. According to the relationship between HBI and ESR, the considered multicomponent alloys are divided into two groups as a first approximation: the first one is the Mg–Al–Zn system alloys; the second one is the Mg–Zn–Zr and Mg–Nd–Zr alloys. Within these groups, the dependence of hot brittleness index and ESR has a nature close to a linear one. To describe the dependence of all alloys, a single equation can be applied if ESR₆₅ is used in the calculations for Mg–Al–Zn alloys and ESR₉₀ – for Mg–Zn–Zr and Mg–Nd–Zr alloys. The proposed model will allow for easy and quick calculation of the HBI, which is very important in the development of new high-tech magnesium alloys.

The paper covers the study of the influence of equal-channel angular pressing (ECAP) on the structure, crystallographic texture, mechanical properties and electrical conductivity of Cu-ETP copper (Russian analogue – M1), as well as the dependence of these characteristics on the orientation of the measurement direction relative to the cross-section (from −45 to 90°). The specific electrical conductivity and strength characteristics of the material in the as-delivered condition (hot-rolled) and the effect of annealing at a temperature of 450 °C of the original sample are investigated. Mechanical tests for uniaxial tension, a study of microhardness using the Vickers method and a study of specific electrical conductivity based on measuring the parameters of the vortex field excited in the surface layers of the body are carried out. It is found that ECAP processing leads to a significant increase in the ultimate tensile strength to 425 MPa compared to the initial state of 300 MPa. The maximum tensile strength of 425 MPa is achieved at orientation angles relative to the ECAP cross-section of −45°. A significant increase in microhardness to 1364–1405 MPa, tensile strength to 350–425 MPa and electrical conductivity to 101.4–102.4 % IACS is a consequence of the selected directions of cutting the samples relative to the ECAP axis. This indicates the dependence of both mechanical and electrical properties of ultrafine-grained samples on the crystallographic texture orientation. A Cu-ETP copper sample subjected to ECAP with a cutting angle deviating from the ECAP cross-section of the sample by 7.5° has the most optimal crystallographic orientation. In this case, the values of microhardness and electrical conductivity reached 1405 MPa and 102.4 % IACS, respectively.