Specific features of formation of nanostructured electrospark protective coatings on the OT4-1 titanium alloy with the use of electrode materials of the TiC-Ti<Subscript>3</Subscript>AlC<Subscript>2</Subscript> system disperse-strengthened by nanoparticles

The effect of nanodispersed additives of ZrO₂, Al₂O₃, NbC, W, WC, and WC-Co into the composition of the TiC-Ti₃AlC₂ electrode on the kinetics of formation of coatings by electrospark doping (ESD) on the titanium alloy of the OT4-1 grade on varying the duration of pulsed discharges in a wide range is investigated. The structure, phase composition, properties (continuity, thickness, microhardness, friction coefficient, wear resistance, and heat resistance) are investigated. The optimum energy mode of the ESD treatment of the OT4-1 titanium alloys by new electrode materials is determined. It is found that the introduction of a nanodispersed component is favorable to an increase in continuity and the microhardness of electrospark coatings and a substantial increase in wear resistance and heat resistance of titanium alloys.     

Structure and Wear Resistance of Coatings on Titanium Alloy and Steels Obtained by Electrospark Alloying with AlN ― ZrB2 Material

We have studied the process of electrospark alloying of titanium alloy VT6 and steels with a composite material based on AlN ZrB₂ with ZrSi₂ additive. We have established that Al₂SiO₅ and ZrSiO₄ forming in the coating directly during its formation play the role of a solid lubricant. Under optimal conditions for electrospark alloying of the titanium alloy, the coefficient of friction is 0.13, the wear is 6 m/km for a sliding velocity of 14 m/sec and a load of 2.56 MPa. Ceramics based on AlN ZrB₂ can be recommended for use as wear-resistant and corrosion-resistant coatings.     

Formation of electrospark coatings of the VK8 hard alloy with the Al2O3 additive

The results of studying the formation of coatings by electrospark alloying with the use of an electrode material based on the VK8 tungsten-containing alloy with the addition of an aluminum oxide nanopowder are presented. It is shown that introducing Al₂O₃ into the hard alloy promotes an increase in the mass transfer coefficient, microhardness, and wear resistance of the formed coatings. The duration of electric discharges exerts a significant effect on the phase composition of the alloyed layer.     

Plasma coatings of (TiCrC)-(FeCr) composite powder alloys: Structure and properties

The coatings of the (TiCrC)-(FeCr) composite are deposited on steel and titanium alloy by plasma method. The composition, structure, and tribotechnical properties of these coatings are studied in comparison with traditional materials based on the Ni-Cr alloy. The effect of preliminary surface treatment methods, i.e., sandblasting treatment and electrospark alloying, on coating properties is examined. The fretting corrosion of coatings is investigated. It is established that coatings based on double titanium-chromium carbide have considerably greater wear resistance than that of Ni-Cr alloys at almost equal friction coefficients. It is established that electrospark alloying is competitive with traditional sandblasting treatment in environmental effect and coating-to-based adhesion. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 37–45, 2007.     

Laws of Formation of Electrospark Coatings from Alloys of the Ni – Cr – Al – Y System

The main parameters of electrospark alloying of steel 45 with anodes made from Ni – Cr – Al – Y alloys have been investigated. The anodes were fabricated by casting and hot pressing. The highest values of the mass transfer coefficient were observed in the case of electrospark alloying with hot-pressed alloys. Microstructure and x-ray phase analyses of electrospark coatings revealed the presence of solid solutions based on nickel, iron, chromium as well as intermetallic compounds. Coatings obtained by electrospark alloying with hot-pressed alloy are more wear-resistant than are coatings obtained by alloying with cast alloys.     

Effect of electrospark alloying on the wear resistance of cutting inserts made of VK8 alloy

The paper presents the results from x-ray phase analysis and wear-resistance tests (discontinuous cutting) of cutting inserts made of VK8 (WC-8% Co) hard alloy. The inserts have an electrosparkdeposited coating based on the AlN-Ti/ZrB₂ system with Ti/ZrSi₂ additions and the TiN-AlN system. These results allow one to infer the possible causes of different wear resistance of cutting inserts with electrospark-deposited coatings. Among such causes are intensive oxidation of titanium (unlike zirconium) during electrospark alloying followed by the formation of brittle oxide phases and the shielding effect of ZrO₂ (it prevents globules from destruction during both alloying and service).     

Features of formation and the structure,composition, and properties of electrospark coatings on the ZhS6U nickel alloy with the use of the KhTN-61 SHS-Ts alloy

Features of the mass transfer of a KhTN-61 SHS-Ts electrode material onto a substrate of a ZhS6U nickel alloy with a variation in frequency (1000–1400 Hz) and time (25–70 μs) of pulsed discharges was studied. A complex of studies of the structure, composition, and properties of the formed coatings was carried out. The optimum frequency-energetic mode of the treatment (E = 0.30 J, f = 1000 Hz, and τ = 50 μs), which was characterized by a high rate of coating at a satisfactory degree of the roughness of the surface layer, is found. As a result of electrospark alloying (ESA) at the optimum energetic parameters, 40-μm-thick coatings with a uniformity of 95% and a microhardness of 5.2 GPa form on the surface of the nickel alloy. The ESA treatment of a ZhS6U nickel alloy with the use of KhTN-61 SHS-Ts electrode material allows us to enhance its wear resistance (by more than a factor of 10), hardness (by a factor of 2), and heat resistance, as well as to decrease (by a factor of 5) the friction coefficient.     

Structure and Properties of Composite Electrospark,Laser, and Magnetron Deposited AlN ― TiB2 Coatings

A comparative investigation of the coatings produced by electrospark alloying, laser gas-powder deposition, and magnetron sputtering using composite AlN ― TiB₂ material was carried out. It is shown that the presence of oxygen in the working atmosphere is responsible for the oxidation of aluminum nitride, and also the appearance of refractory compounds of the Ti ― Al ― O system in the coatings. During electrospark and laser alloying globular regions form on the surface by a mechanism of liquid-phase sintering, due to the mass transport of a metallic component from the substrate. The composite layer of a magnetron coating sinters by a mechanism of solid-phase interaction. The dispersion-strengthened structure of electrospark coatings is highly wear resistant, while the continuity, high dispersion, and heterogeneity of the structure of magnetron coatings permits their recommendation for corrosion protection.     

Electric-spark hardening of VT3-1 titanium alloy with tungsten-free composite ceramics

The mass transfer and wear resistance of both monolayer and multilayer coatings on VT3-1 alloy are examined. The coatings are deposited by electrospark alloying (ESA) with composite titanium and zirconium refractory ceramics. It is shown that the wear resistance of these electrospark-deposited coatings is 1.6 to 3 times higher in fretting corrosion in unlubricated friction as compared with the conventional WC + 3% Co coating. In addition, the multilayer structure permits four-to fivefold increase in the coating thickness as opposed to the monolayer WC + 3% Co ESA coating.     

Electroerosion resistance and structural phase transformations in electrospark and laser deposition of titanium alloys using composite ceramics based on ZrB2-ZrSi2 and TiN-Cr3C2 systems

The paper examines the mass transfer kinetics, structure, phase and chemical compositions, and micromechanical properties of electrospark and laser coatings on titanium alloys (including their combination) deposited using composite materials based on the ZrB₂-ZrSi₂ and TiN-Cr₃C₂ systems. The electrospark deposition of both materials is characterized by a relatively high mass-transfer coefficient (∼40–60%) over a wide range of treatment time t ≥ 1 min/cm². It is determined that after prolonged electrospark deposition (t = 7 min/cm²), ZrB₂-ZrSi₂ coatings have structurally heterogeneous surface with smoothed Ti-alloy localities caused by the melt crystallization and modified with alloying components. It is shown that ZrB₂-based coatings are promising along with conventional wear-resistant coatings based on refractory titanium compounds. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 151–161, 2008.     

Globular structure of electrospark-deposited coatings on VK8 alloy

The paper examines the composition and structure of electrospark coatings based on AlN-TiB₂ (TBSAN) and AlN-ZrB₂ (TsBSAN) electrode materials deposited on VK8 alloy. Kinetic dependences of mass transfer are studied. In spite of the close structures and mechanical properties of TBSAN and TsBSAN electrode materials, the coatings substantially differ in structure and properties. The kinetic dependences of mass transfer, which differ for TsBSAN and TBSAN electrodes, generally confirm that the mass transfer in electrospark alloying of a hard-alloy substrate occurs in three stages and show distinctions in the electroerosion mechanism for these electrode materials.     

Effect of the electrospark alloying regime on the durability of high-speed steel R6M5K5 cutters

The effect of electrospark alloying with refractory compounds based on WC, TiC, TiN, and TiB₂ on the mechanical and service properties of high-speed steel R6M5K5 cutters was investigated. Increasing the electrospark discharge energy by increasing the current strength to 3 A, and the specific alloying time to 1.2–1.8 Msec/m², increased the alloyed layer depth, but decreased the microhardness. Further increase of alloying time did not produce further increase in layer depth. The optimal regimes of electrospark alloying were determined from durability tests of the hardened cutting tool. The greatest increase in durability (by 1.3–1.4 times) was obtained at I=1.5–2 A, τ=0.9–1.5 Msec/m², at which values the optimal combination of hardness and coating depth was attained.     

Surface Hardening of Hard Tungsten-Carbide Alloys: A Review

Russian and non-Russian research on the surface hardening of hard tungsten-carbide alloys to improve the wear resistance is reviewed. There is great scope for improving the wear resistance and durability of hard-alloy components by surface strengthening on the basis of various coatings, including coatings with 100-nm structural components. On hard tungsten-carbide alloys, the most common coatings consist of titanium carbide TiC and nitride TiN, characterized by high lattice binding energy and high melting point. If such coatings are applied to hard-alloy tools, the frictional coefficient is reduced by a factor of 1.5–2.0 when cutting steel. The use of a TiN + ZrN ion-plasma coating reduces the frictional coefficient by a factor of 5.9. At present, multilayer coatings are widely employed. The most widespread are TiN + TiC and Al₂O₃ + TiC coatings. Their wear is proportional to the coating thickness. These multilayer coatings still leave room for improvement in the wear resistance of hard alloys. In Russia, the potential of hard alloys with a strength gradient from a ductile and high-strength core to a wear-resistant surface is being explored. At the Research Institute of Refractory Metals and Hard Alloys, a method has been developed for producing alloys with variable cobalt content over the thickness of the cutting insert. That permits change in alloy composition from VK20 to VK2 over the sample thickness. Correspondingly, the wear resistance of the insert’s working section is equivalent to that of VK2 alloy, while the base is able to withstand considerable flexural stress. Recently, cutting tools with a diamond coating on hard alloys have been adopted in practice. To increase the durability of hard-alloy VK inserts, strengthening based on concentrated energy fluxes may be employed. Examples include treatment of hard-alloy surfaces by γ quanta, ion beams, and laser beams, electroexplosive alloying, and electrospark strengthening.     

Wear resistance of a plasma-electrospark zirconium diboride-based coating on aluminum alloy D16T

The paper examines the structure, phase composition, and mechanical properties of ZrB₂-based plasma coatings formed on D16T aluminum alloy under different conditions. It is established that coatings with an electrospark sublayer are characterized by stronger adhesion with the substrate as compared with that deposited on the base after conventional sandblasting. The wear resistance of this coating in dry friction is comparable with the monolithic VK15 hard alloy. Laser treatment of the coating in open air decreases the wear by 25% at low sliding rates and simultaneously decreases the hardness by 50%. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 53–59, 2007.     

Influence of alloying elements and grain refiner on microstructure,mechanical and wear properties of Mg-Al-Zn alloys

In the present investigation, the effects of alloying elements (Sn, Pb) and grain refiner (Ag, Zr) on microstructure, mechanical and wear properties of as-cast Mg-Al-Zn alloys were studied. The alloys were prepared through melting-casting route under a protective atmosphere and cast into a permanent mould. The microstructure of the base alloy consisted of α-Mg, Mg₁₇Al₁₂ continuous eutectic phase at the grain boundary and Mg-Zn phase was distributed within the grains. Addition of Sn and Pb suppressed the formation of continuous Mg₁₇Al₁₂ eutectic phase and formed Pb enriched Mg₂Sn precipitates at the grain boundary as well as inside the grain. The Ag and Zr addition to Mg-Al-Zn-Sn-Pb alloy suppressed the Mg₁₇Al₁₂ phase formation and refined the grains leading to improve mechanical properties. Addition of Sn, Pb and grain refiner (Ag, Zr) significantly enhanced the tensile strength and elongation but reduced hardness. The Ag addition imparted best tensile properties, where ultimate tensile strength (UTS) and elongation are 205?MPa and 8.0%, respectively. The fracture surfaces were examined under SEM which revealed cleavage facets and dimple formation. Therefore, the cleavage fracture and dimple rupture were considered as the dominant fracture mechanisms for developed Mg alloys. The cumulative volume loss of Mg alloys increased with sliding distance and applied load. The coefficient of friction decreased with sliding distance. The microscopic observation, analysis of the wear surface and coefficient of friction revealed that the wear mechanism of developed Mg alloys changes from abrasion oxidation to delamination wear.     

Influence of the Composition and Structure of B4C - Al2O3 Ceramic on the Tribotechnical Characteristics in Friction Against Steel

The morphology and phase composition of friction surfaces and the tribotechnical properties of the (B₄C - Al₂O₃)-steel 45 system are studied under dry friction at various sliding velocities and contact loads. We have found that fine-grained secondary structures are formed on the friction surfaces. The morphology and phase composition of these structures depend on the ceramic composition and on the test conditions. A comprehensive investigation of friction surfaces, using x-ray, electron-diffraction electron-probe, and electron-microscopy analysis, has shown that the structure and morphology of the secondary phases determine the tribotechnical properties of ceramic-steel couples. The maximum wear resistance of B₄C ceramics containing 5-20 mass% Al₂O₃ is determined by the formation of dense secondary-phase thin films on the friction surface. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 49–59, May–June, 2005.     

The WC-Co electrospark alloying coatings modified by laser treatment

The paper analyzes the effect of the laser treatment process on the properties of electrospark alloying coatings. The properties are assessed after laser treatment by analyzing the microstructure and measuring the microhardness and friction force. The tests are carried out on a WC-Co coating (the anode) obtained by electrospark alloying over carbon steel St.45 (the cathode) and molten with a laser beam.     

Surface Modification of AL9 Alloy by Electric-Spark Alloying with Materials of the AlN – Ti(Zr)B2 – Ti(Zr)Si2System

Using x-ray phase, electron-probe microanalysis, and scanning electron microscopy, we have established that heterophase coatings based on an aluminum matrix with a quasi-layered finely dispersed structure reinforced with titanium (zirconium) diboride and borosilicide, and aluminum nitride (alloyed with oxygen) are formed by electric-spark alloying of AL9 alloy with A1N – Ti(Zr)B₂ – Ti(Zr)Si₂ composite ceramics. The wear resistance of the A1N – ZrB2-based coating approached that of the ceramic itself with the sliding speed increased to V ≥ l m/sec. The formation of secondary structures of oxide solid solutions on the coating surface during tribooxidation was investigated.     

Tribological behaviour of silver based self-lubricating composite

Abstract

Silver based composites with varying concentration of graphite and/or MoS₂ were prepared by powder metallurgy method. Impacts of composition on the tribological performance of the composites in ambient air and vacuum were investigated. The lowest friction in air was achieved by Ag–20G (vol.-%) composite, while Ag–20MoS₂ exhibited the best lubricity in vacuum. XPS evaluation revealed the oxidation of MoS₂ in air and a decrease concentration of graphite on the surface of the wear tracks under vacuum. As the proportion of graphite to MoS₂ increased, the friction coefficient and the wear rates ascended gradually in air while decreased sharply under vacuum. As compared with other compositions, Ag–15MoS₂–5G exhibited a comparable stable and good tribological performance as the environmental condition changed for its friction coefficient and wear rate remained around 0·14 and 5×10^?6 mm³ N^?1 m^?1.     

The effect of participate reinforcement on the sliding wear behavior of aluminum matrix composites

The aim of the present investigation is to characterize the friction and wear behavior of aluminum matrix composites reinforced with particulates of SiC, TiC, TiB₂, and B₄C. Sliding wear tests were conducted at two loads (80 and 160 N) using a pin-on-disc apparatus and under dry conditions. The results of the investigation indicate that the coefficient of friction of the composites is about 30 pct lower than that of pure aluminum, while the wear rates of the com- posites are lower by a factor of about 3 and 100 at loads of 80 and 160 N, respectively. The type and size of the reinforcement have a negligible influence on the wear rate and the coefficient of friction of the composites. However, the volume fraction of the reinforcement has a marginal influence on the wear rate. Though the coefficients of friction and the wear rates of the com- posites were broadly similar, the Al-TiC composite alone exhibits a somewhat higher wear rate. The above results of the present investigation have been rationalized on the basis of the inverse rule of mixtures and the existing models for friction and wear.