Contribution of electrospark alloying to the oxidation resistance of hard tungsten alloys

The paper examines the contribution of electrospark alloying to the oxidation resistance of hard tungsten alloys. It is established that the oxidation of carbides results from their electronic structure. When WC and hard tungsten alloys are heated to 1000°C, a brittle scale consisting of WO₃ and CoWO₄ rapidly forms. The oxidation resistance reduces as follows: TiC → Co → W → HTA (if TiC is more than 10%) → WC-Co → WC. The oxidation rate of hard tungsten alloys may be a criterion of their serviceability. It is shown that the oxidation resistance of hard tungsten alloys becomes much higher after their electrospark alloying with aluminum, titanium, and chromium and with wear-resistant composite TsLAB-2 ceramics based on the ZrB₂-ZrSi₂-LaB₆ system with Ni-Cr-Al (30 mole%) binder. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 145–150, 2008.     

Corrosion behavior of zirconium diboride-based ceramics and electrospark coatings in 3% NaCl solution

The paper examines the corrosion behavior of AlN-ZrB₂, AlN-TiN, and ZrB₂-LaB₆ composite materials and associated electrospark coatings based on aluminum alloy AL9 in 3% NaCl solution. It is shown that the electrochemical corrosion resistance of composites is close to that of titanium nitride. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 54–57, 2007.     

High-temperature oxidation of composite AlN-ZrB2-ZrSi2 ceramics

The high-temperature (to 1450°C) oxidation of AlN-ZrB₂-ZrSi₂ powders and compact ceramic materials with different contents of ZrB₂-ZrSi₂ solid solution in air is examined using scanning electron microscopy and differential thermal, thermogravimetric, x-ray phase, and x-ray spectrum microanalyses. It is established that the hot-pressed (practically porousless) ceramic materials have high corrosion resistance up to 1350–1400°C when scale components (individual oxides) interact with each other to form solid solutions based on aluminum oxide, zirconium oxide, and aluminum borate. These phases become sintered in the presence of the liquid B₂O₃ phase, self-reinforced scale being formed. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 196–203, 2008.     

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.     

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.     

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.     

Changes in Structure and Physicochemical Properties of Spark Coatings Based on TiN and TiB2 after Treatment with Concentrated Solar Radiation

Studies have been made on the structure and properties of spark coatings made of TiN and TiB₂ on steel U8 after treatment with concentrated solar radiation. It is found that the absorption capacity of the steel raised by a factor 2–3. The concentrated radiation reduces the coefficient of friction of the spark coatings made of TiN and TiB₂ by a factor 1.4, while the wear rate is reduced by a factor 1.6–2 by comparison with the untreated material. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 64–69, July–August, 2005.     

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.     

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).     

Application of coatings of some transition metal borides by plasma-deposition

Conclusions During plasma-deposition chromium, zirconium, titanium, and tungsten borides experience thermal dissociation and react with nitrogen in the working gas and with oxygen in the ambient atmosphere. This leads to the formation in coatings of nitrides and oxides of the metals and of boron. The amount of such inclusions depends on the coating deposition conditions. Optimum conditions for the plasma-deposition of CrB₂ and ZrB₂ have been chosen. CrB₂ and ZrB₂ coatings adhere to Kh18N10T steel with strengths of 0.153±0.01 and 0.144±0.04 kgf/mm², respectively. A nickel aluminide undercoat more than trebles the adhesional strength of boride coatings on Kh18N10T steel. The processes developed for the manufacture of transition metal borides and its optimum conditions and methods for their deposition on Kh18N10T steel by the plasma process may be recommended for adoption in industry.Translated from Poroshkovaya Metallurgiya, No. 5(209), pp. 73–76, May, 1980.     

Wear-Resistant Layered Electrospark Coatings Based on ZrB2

We have studied the composition and tribological parameters (coefficient of friction and wear rate) of coatings obtained in electrospark alloying (ESA) of steel 45 with the composite ceramic ZrB₂ – SiC – B₄C based on zirconium diboride. We have shown that layer-by-layer electrospark alloying using Ti – Al – N composites to form an undercoat reduces the coefficient of friction of the coating down to 0.12-0.20 while maintaining a rather low wear level (7-11 μm/km). We have analyzed the effect of the composition of the secondary structures which are formed during tribo-oxidation under dry friction conditions.     

Erosion-resistant coatings for gas turbine compressor blades

The effect of ion-plasma coatings made from high-hardness metal compounds on the erosion and corrosion resistance and the mechanical properties of alloy (substrate) + coating compositions is comprehensively studied. The effects of the thickness, composition, deposition conditions, and design of coatings based on metal nitrides and carbides on the relative gas-abrasive wear of alloy + coating compositions in a gas-abrasive flux are analyzed. The flux contains quartz sand with an average fraction of 300–350 μm; the abrasive feed rate is 200 g/min; and the angles of flux incidence are 20° (tangential flow) and 70° (near-head-on attack flow). Alloy + coating compositions based on VN, VC, Cr₃C₂, ZrN, and TiN coatings 15–30 μ m thick or more are shown to have high erosion resistance. A detailed examination of the coatings with high erosion resistance demonstrates that a zirconium nitride coating is most appropriate for protecting gas turbine compressor blades made of titanium alloys; this coating does not decrease the fatigue strength of these alloys. A chromium carbide coating is the best coating for protecting compressor steel blades.     

Directionally solidified eutectic of the B4C - ZrB2 system

An investigation was made of reactions in the Zr - B - C system. The existence of a eutectic in the quasibinary section B₄C - ZrB₂ was confirmed. A directionally solidified eutectic alloy was obtained by zone melting. Its composition was precisely determined as (mol. %) 71.5 B₄C, 28.5 ZrB₂. The effect of melting parameters on the eutectic structure was studied. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 71–75, January–February, 2000.     

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.     

Mechanical and tribological properties of TiN and SiCN nanocomposite coatings deposited using methyltrichlorosilane

The paper examines nanocomposite coatings based on TiN and SiCN obtained by plasma-enhanced chemical vapor deposition (PECVD) using methyltrichlorosilane (MTCS) as one of the precursors. The nanocomposite coatings demonstrate four types of structures depending on deposition modes: nc-TiN, nc-TiN/a-SiCN, nc-TiNC/nc-TiSi₂/a-SiCN, and nc-TiNC/nc-TiCl₂/a-SiCN. The nanohardness and elastic modulus of the coatings reach 31 and 350 GPa, respectively. The coatings on substrates of hard alloys, high-speed steel, and silicon increase the nanohardness of the base from 10 to 100%. The correlation between the H/E ratio and wear resistance is not observed. The coatings deposited at low radiofrequency powers demonstrate good adhesion to silicon substrates. It is shown that the use of MTCS as the main precursor allows one to obtain hard and wear-resistant nanocomposite coatings. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 125–133, 2008.     

Ion-plasma Ti-Al-N coatings on a cutting hard-alloy tool operating under conditions of constant and alternating-sign loads

Structure and phase formation during the deposition of coatings of the Ti-Al-Ni system (Al ≈ 3.5 at %) by the ion-plasma method are investigated. The controlled process parameter was the bias potential (U _b) applied to the substrate made of the VK6 hard alloy. At U _b = 120 V (samples of group 1), titanium nitride close to the stoichiometric composition and solid solution of Al in α-Ti are formed, while at U _b = 120 V (group 2), nonstoichiometric titanium nitride and complex nitride (Ti, Al)N are formed. The hardness and elasticity modulus for coatings of group 1 were equal to 23.8 GPa and 462 GPa, and for group 2 they were 30.8 GPa and 565 GPa, respectively. The latter are characterized by a level of adhesion strength of 53–55 N as opposed to 39–40 N for coatings of group 1. Qualification tests for the durability of the cutting tool with developed coatings are performed. For example, upon turning steel 45, it increases by a factor of 6.3 and for gray cast iron it increases by a factor of 5; during end milling cut of the EI 698-VD alloy it increases by a factor of 2.5.     

Effect of Pulsed Plasma Treatment on Structure and Corrosion Behavior of Sm-Co and Nd-Fe-B Magnets

The combination of conventional ion-plasma deposition and pulsed plasma technologies (PPT) has been applied for rare-earth Sm-Co and Nd-Fe-B based magnets, to provide them with enhanced corrosion resistance. The influence of pulsed plasma treatment on Sm-Co magnets with deposited titanium coatings has been investigated. It was revealed that the thickness of modified layer significantly depends on the thickness of initial titanium film and plasma treatment regimes. As a result of plasma treatment with energy density of 30 J/cm^b for 5 pulses fine-grained layer with me thickness of 70 microns has been formed on the Sm-Co magnet with pure titanium film of 50 μm. According to SEM analyses considerable diffusion of titanium to the bulk of the magnet on the depth of 20 microns took place. Such reaction enhances strong bonding between the coating and the magnet. The effects of plasma processing on corrosion properties of Nd-Fe-B sintered magnets with ferroboron Fe₈₀B₂₀ (wt.%) coatings have been studied. The tests were carried out in naturally aerated sodium sulphate solutions by polarization method. It was shown that polishing of the initial surface before plasma treatment and ferroboron deposition have a strong influence on the corrosion behavior of Nd-Fe-B magnets.     

Effect of Surface Treatment with Concentrated Energy Fluxes on the Properties of Composite Materials Based on Silicon Carbide and Coatings Made from Such Composites

Based on a study of the structure and composition of the composite ceramic SiC - Al₂O₃ - ZrO₂, its tribomechanical properties and behavior in high-temperature corrosion, we recommend the material for use as sealing elements and for deposition of wear-resistant and corrosion-resistant coatings. We have studied the formation of gradient layers when the ceramic surface is modified with refractory titanium compounds TiN - TiB₂ (1:1) with an Fe(Ni) - Cr - Al undercoat using concentrated solar radiation and when the steel surface is modified with laser irradiation of the SiC - Al₂O₃ - ZrO₂ coats. We have shown that laser modification of steel by the silicon carbide-based composite increases its corrosion resistance by a factor of 4–5 at 800–900 °C. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 91–99, July–August, 2005.     

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.     

Influence that nanosecond electromagnetic pulses have on the acquisition of tin and the properties of its alloys

It is established experimentally that the influence that nanosecond electromagnetic pulses (NEMPs) have on the charge melt during the carbothermic reduction of cassiterite in the Na₂CO₃-NaNO₃ medium (1: 0.3) at t = 900–950°C accelerates the formation of the metal phase by a factor of ∼2 and affects its composition. As the duration of irradiation increases to 30 min, the tin content in the crude alloy increases to ∼95%. The influence that the NEMP treatment of the bronze melt has on its physicomechanical properties is revealed. It is shown that the influence of pulses for 10–15-min increases the alloy density to 8.92 g/cm³, hardness by a factor of 1.24, and thermal conductivity by a factor of 2.