The study covers the effect of alloying elements on the kinetics and mechanism of oxidation at 1150 °С for 30 hours of heat-resistant nickel alloys obtained using such technologies as centrifugal SHS metallurgy (SHS(M)), vacuum induction melting (VIM), elemental synthesis (ES), hot isostatic pressing (HIP). A comparative analysis was carried out for alloys based on nickel monoaluminide and standard AZhK and EP741NP alloys. It was found that kinetic dependences are described mainly by parabolic approximation. The logarithmic law of oxidation with the rapid (within 3–4 hours) formation of the primary protective layer is typical for alloys doped with molybdenum and hafnium. In the case of AZhK and EP741NP, oxidation proceeds according to a parabolic law at the initial stage (2–3 hours), and then according to a linear mechanism with the voloxidation and complete destruction of samples. Oxygen and nitrogen diffusion proceeds predominantly along the nickel aluminide grain boundaries and it is limited by the Al2O3 + Cr2O3 + XnOm protective film formation. SHS(M) alloys feature by a positive effect of zirconium and tantalum added as dopants on heat resistance. The Ta2O5 phase is formed in the intergranular space, which reduces the rate and depth of oxidation. The zirconium-containing top layer Al2O3 + Zr5Al3O0.5 blocks the external diffusion of oxygen and nitrogen, thereby improving heat resistance. Doping with hafnium also has a positive effect on oxidation resistance and leads to the formation of submicron and nanosized HfO2 inclusions that suppress the grain boundary diffusion of oxygen. MoO3, Mo3O4, CoMoO4 volatile oxides are formed in alloys with a high content of molybdenum and compromise the protective layer integrity. A comparative analysis of the oxidation kinetics and mechanism for samples consisting of the base β-alloy with Cr + Co + Hf additives showed a significant effect on the heat resistance of the sample preparation method. As the proportion of impurity nitrogen decreases and the Cr2O3 sublayer is formed, the oxidation mechanism also changes.

The article discusses the features of combining the self-propagating high-temperature synthesis (SHS) of the Ti3AlC2 MAX phase porous skeleton with infiltration by aluminum melt in a spontaneous mode in order to obtain enlarged samples of Ti3AlC2–Al ceramic-metal composite (MAX cermet) in an air atmosphere. A new scheme was developed for obtaining long-length SHS cermet samples from a bulk density charge with spontaneous infiltration by melt in the same direction with the combustion wave movement, which makes it possible to regulate the time gap between the end of the Ti3AlC2 synthesis and the beginning of the spontaneous pore filling with aluminum melt. This technology was used to obtain a Ti3AlC2 SHS skeleton with a total length of 250 mm and a diameter of 22–24 mm where the depth of infiltration with pure aluminum was about 110 mm, and impregnation with the Al–12%Si alloy was 130 mm. The paper provides comparative data on density, microstructure, and phase composition at different areas along the length of MAX cermet samples obtained. It was found that infiltration with pure aluminum destroys the Ti3AlC2 MAX phase to transform it into a mixture of TiC + TiAl3 phases in the SHS cermet, and 12 % Si added to the Al melt promote Ti3AlC2 preservation in the cermet to a some extent. Instead of MAX cermet samples with the target composition of Ti3AlC2–Al and Ti3AlC2–(Al–12%Si), long-length samples of SHS cermets with a different actual phase composition were obtained: TiC–TiAl3–Al and TiC–Ti3AlC2–TiAl3–(Al–12%Si), respectively, where the Ti3AlC2 MAX phase either practically absent or present in small quantities. The average hardness values of TiC–TiAl3–Al and TiC–Ti3AlC2–TiAl3–(Al–12%Si) SHS cermets were HB = 640 and 740 MPa, density ρ = 2.88÷3.16 g/cm3 and 3.03÷3.13 g/cm3, and residual porosity П = 17.0÷24.6 % and 17.6÷20.3 %, respectively.

Research into WC–Co submicron hardmetals involving measurement of hardness, coercivity and microstructural characterization, as well as analysis and comparison of results from recent literature led to the development of a unified constitutive expression for Vickers hardness in a form that separates the effects of the tungsten carbide grain size from those of the cobalt binder volume fraction. With the proposed expression for HV one may recalculate and compare hardness values for hardmetals featuring the same average grain size but differing in the binder matrix content. The paper shows that, in contrast to the Lee-Gurland model, the proposed constitutive expression framework treats the hardmetal hardness as a function of the carbide skeleton hardness (HWC) and contiguity (C) described as HV = CHWC. The carbide skeleton hardness depends on the WC grain size only, and it is described by the Hall-Petch equation. The results of parallel hardness and coercivity measurements led to an empirical equation relating Hc to the WC grain size and the Co volume fraction. Based on the complete experimental data, the relationship between the coercivity and Vickers hardness was explored, and a simplified relationship between these physical values was proposed to carry out the primary HV evaluation based on the measured coercivity values. As noted in the paper, the above equations are valid for relatively narrow WC grain size distributions with a maximum coefficient of variation of 0.5.

This research was conducted to obtain non-stoichiometric tantalum-hafnium carbonitride powder of the Fm3m (225) structural type using a combination of mechanical activation (MA) and self-propagating high-temperature synthesis (SHS) methods. Mechanical activation for 60 min in a low-energy mode (347 rpm) forms Ta/Hf/C composite particles 1 to 20 μm in size with a layered structure and contributes to a uniform distribution of elements. SHS of a mechanically activated Ta + Hf + C mixture in a nitrogen atmosphere (0.8 MPa) leads to the formation of a single-phase tantalum-hafnium carbonitride powder with the Ta0.25Hf0.75C0.5N0.3 composition where particles feature by a ≪spongy≫ morphology with pores and caverns and consist of submicron grains. Spark plasma sintering (SPS) was used to obtain a bulk sample of tantalum-hafnium carbonitride with a grain size of 3 to 5 μm, relative density of 98.2 Ѓ} 0.3 %, hardness of 19.8 Ѓ} 0.2 GPa, and crack resistance of 5.4 Ѓ} 0.4 MPa・m1/2. The kinetics of (Ta,Hf)CN oxidation at 1200 °C in air is described by a parabolic law suggesting the formation of an Hf6Ta2O17 + mHfO2 oxide layer with a low oxygen diffusion rate where the oxidation rate is 0.006 mg/(cm2・s). A (Ta,Hf)CN oxidation mechanism is proposed, which states that Ta2O5 and HfO2 are formed on the surface of grains at the first stage that react with each other at the second stage to form a Hf6Ta2O17 homologous superstructure and monoclinic HfO2. CO, CO2, NO and NO2 gaseous oxidation products are released with the formation of pores and cracks.

The LaB6–VB2 alloy with the eutectic structure was obtained by cold crucible induction melting followed by crystallization. The mole ratio of components in the initial powder mixture was 35 : 65. The structure and composition of the LaB6–VB2 material were studied by X-ray diffraction, scanning electron microscopy, and X-ray microanalysis. The composition of the alloy is represented by two boride phases — cubic LaB6 and hexagonal VB2. Two-phase eutectic regions up to 500 μm in size represent a LaB6 matrix filled with 0.8–2.0 μm thick VB2 fibers (filamentary, rod crystals). VB2 fibers are predominantly oriented along the direction of the temperature gradient that appeared when cooling the melt, i.e. from the outer surface of the sample to its center. The integrated phase area analysis was used to determine the eutectic composition: 42 Ѓ} 1 mol% LaB6 and 58 Ѓ} 1 mol% VB2.

Protective coatings were applied by electrospark deposition (ESD) using zirconium electrodes to improve the performance of the Ni-containing alloy obtained using the selective laser melting (SLM) technology. The kinetics of mass transfer was studied in 5 different frequency-energy processing modes. An analog-to-digital converter was used to determine the average number of pulse discharges, single-pulse energy, and the total energy of pulse discharges for 1 min of processing (ΣЕ) for all the modes used. In low-energy processing modes (ΣЕ = 1459÷2915 J), a weak mass transfer was observed, and the cathode weight gain was recorded only in the first minutes. As the processing time increased, a decrease in the substrate weight was observed. The roughness of coatings (Ra) varied in the range of 3.9–7.2 μm. In high-energy modes (ΣЕ = 5197÷17212 J), due to intense electrode heating, a steady cathode weight gain was observed, but the formed coatings featured by increased roughness: Ra = 7.4÷8.6 μm. The Ra parameter for the original SLM samples was 10.7 μm. The formed coatings featured by a thickness of 15–30 μm, high continuity (up to 100 %), hardness of 9.0–12.5 GPa, elastic modulus of 122–145 GPa, and friction coefficient of 0.36–0.49. The ESD processing promoted an increase in wear resistance of the SLM alloy by 7.5–20 times, and oxidation resistance by 10–20 % (t = 1150 °C, τ = 30 h). It was found that the coating obtained in the low-energy ESD mode with energy ΣЕ = 2915 J featured the best performance (hardness, modulus of elasticity, roughness, wear resistance and oxidation resistance).

Since 2017, Volgaburmash JSC (Samara, Russia) tested purchased 90%WC–10%Co carbide powder mixtures and finished carbide drill bits from various manufacturers. The work was carried out in order to check the possibility of using purchased products as raw materials at the plant to reduce the production cycle for the manufacture of carbide inserts for roller cone bits. This intercommodity substitution (outsourcing) is carried out with the aim of potential cone bit cost reduction and production process acceleration so that the plant can operate in the heavily competitive environment of foreign and domestic markets. The article focuses on the analysis and detailed comparison of the micro- and macrostructure, physical, mechanical, chemical and processing properties of purchased hard-alloy mixtures and sintered inserts of various manufacturers including Volgaburmash JSC. All properties of materials under study were determined in accordance with the VBM JSC company standard STP 582-17. Much attention is paid to comparing crack resistance or Palmqvist fracture toughness values of the alloy and analysis of microstructure images and fracture propagation pattern after using scanning electron microscopy tests. In addition, consideration is given to such important hard alloy properties as hardness and transverse bending strength. Based on the results of the conducted research, conclusions are presented on the expediency of using purchased hard-alloy materials at the Volgaburmash JSC metallurgical shop in comparison with internally manufactured materials.