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.     

Electric-spark alloying of steel with tungsten-free hard metals

Conclusions A study was made of the ESA of steel with tungsten and tungsten-free TN type hard metals in different units and under different conditions, with and without anode dressing. It has been established that in alloying under finishing conditions the erosion of a dressed TN-20 alloy anode is greater than that of an undressed one; this is due to the formation of stable oxide films on the electrode surfaces. In contrast to this, in treatment under rough conditions the erosion of an undressed anode is greater because the oxide films cannot withstand the higher thermal stress generated during alloying. In ESA with tungsten alloys maximum erosion under both finishing and rough conditions is observed with undressed specimens. This is attributable to the formation of a defective zone promoting periodic brittle disintegration in the course of treatment. Removing the defective zone decreases the erosion of the material. The most favorable conditions for the formation of a reinforced layer are created in the alloying of a dressed cathode surface, and consequently it is best to perform ESA with a specific time of not more than 1 min/cm². Use of treatment conditions with large thermal loads increases the thickness and hardness of the reinforced layer. Reinforcement with TK type alloys sets up a stress which is greater on the specimen surface and extends to a greater depth than the stress generated in alloying with TN type hard metals. Electrodes made of the tungsten-free TN-20 hard metal can be used instead of tungsten alloy electrodes for the ESA of processes V and VI. The resultant reinforced layer is sufficiently thick and continuous.Translated from Poroshkovaya Metallurgiya, No. 11(239), pp. 64–69, November, 1982.     

Effect of niobium carbide on the properties of tungsten-free hard alloys

Conclusions A study was made of the effects of alloying with niobium carbide of the carbide phase of a TiC-Ni-Mo hard alloy (in amounts equal to 2,5,10, and 25 mole% relative to the TiC content) upon the physicomechanical properties of the alloy. It is shown that raising the amount of NbC in the alloy increases its transverse rupture strength (to 132 kg/mm²) and impact strength, leaving its hardness virtually unchanged (91 HRA); the improvement in properties is attributable to a slight increase in the ductility of the grains of the hard phase — a complex TiC-NbC carbide.Translated from Poroshkovaya Metallurgiya, No. 9 (129), pp. 83–86, September, 1973.     

Production of VT20 AND VT9 titanium alloy powders

Conclusions The hydrogenation-dehydrogenation method offers an effective means of producing industrial titanium alloys in powder form. It has been established that hydride-grade titanium alloy powders meet, without charge enrichment, the chemical composition requirements laid down by technical standards for VT20 and VT9 industrial alloys. The H-D process brings about changes in the phase composition and structure of alloys: The amount of the -phase diminishes, and the alloy structure becomes more fine-grained. Consequently, by varying H-D process parameters it is possible to exercise control over the properties of powders.Translated from Poroshkovaya Metallurgiya, No. 11(227), pp. 1–6, November, 1981.     

Properties of titanium alloy VT6 fibers obtained by rapid solidification of the melt

We have studied the chemical, physicochemical, and technological properties of titanium alloy VT6 fibers in the initial state and after vacuum annealing for one hour at 500–1300°C. We have carried out fractographic, microstructural, and qualitative x-ray spectral microanalysis of the fibers. We have established that in the initial state, the fibers possess high values of the physicomechanical characteristics; the decrease in the properties of the fibers with a rise in temperature was determined by observing changes in the microscopic and macroscopic structure and the chemical composition. Vacuum annealing of VT6 fibers allows us to improve their compressibility with different combinations of hardness, strength, and conductivity characteristics.Institute of Problems in Materials Science, National Academy of Sciences of Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4, pp. 85–90, March–April, 1994.     

Effect of a microstructure and surface hydrogen alloying of a VT6 alloy on diffusion welding

The effect of a structural type (lamellar, fine, gradient) and additional surface alloying with hydrogen on the diffusion bonding of titanium alloy VT6 samples is studied. It is shown that the surface alloying of VT6 alloy parts with hydrogen allows one to decrease the diffusion welding temperature by 50–100°C, to obtain high-quality pore-free bonding, and to remove the “structural” boundary between materials to be welded that usually forms during welding of titanium alloys with a lamellar structure.     

Structural and hydraulic characteristics of porous materials made of VT6 titanium alloy fibers

The structural and hydraulic characteristics (maximum, average, and hydraulic pore diameters, permeability, and sinuosity of the pore channels) have been studied in materials made of discrete VT6 alloy fibers obtained by rapid solidification of a melt. The materials have structural parameters that are similar to those in materials made from smooth cylindrical fibers or powders and are superior in regard to permeability.Institute of Material Sciences, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5/6, pp. 85–89, May–June, 1995.     

Laws of capillary transport in porous materials prepared from titanium alloy VT6 fibers

A study was made of the kinetics of capillary absorption of ethanol in highly porous (70–75%) materials prepared from discrete fibers of titanium alloy VT6 (specimen dimensions 330×20×(0.4–1.3) mm). The fibers, 3 mm in length and 20–140 μm in diameter, were obtained by rapid solidification from the melt. Capillary transport against the force of gravity up to the equilibrium height of capillary rise was investigated in an atmosphere of saturated ethanol vapor. Experimental data on the rate of absorption were analyzed with reference to the properties of the pore space structure—effective pore size, tortuosity of the pore channels, and free surface area. The laws of capillary transport of ethanol in porous materials composed of titanium alloy VT6 fibers, discrete copper fibers, and grade VTEM-2 titanium powder were compared. It was shown that, with regard to the speed of absorption, the advantage of fiber materials over those made from powder is attributable to the less convoluted pore channels in the former. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 67–74, January–February. 1997.     

Hardening VT6 alloy by electroplastic rolling

Electroplastic rolling may be used to produce VT6 titanium-alloy sheet with ultrafine-grain structure and improved performance. The influence of the true strain on the structure and mechanical properties of the alloy is studied.     

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.     

Impact toughness of layered VT6 alloy semiproducts

Layered semiproducts produced by pressure welding of sheet workpieces of a VT6 titanium alloy are studied. Possible methods of achieving isotropic mechanical properties of the semiproducts are discussed. The pores that are present in solid-phase joint zones are found not to influence the impact toughness of the samples in which layers lie perpendicular to a notch. The fracture surface has a ductile character with certain fracture zones.