Some features of the electric-spark alloying of high-speed steel with hard metals by the local coating deposition method

Conclusions An investigation has been carried out into the processes of erosion and AL formation during the ESA of R9K5 steel with a standard and a tungsten-free hard metal by the LCD method. It is shown that the tungsten-free NTsKhN45 alloy is superior to the standard VK6M hard metal in ESA efficiency and comparable to it in AL surface finish. It has been established that AL formation is controlled by two opposed processes, viz., transfer of anode material to the cathode and its disintegration as a result of cathode erosion in the liquid-vapor and solid phases under the action of repeated spark discharges. The general features of the process — nonadditivity, a cyclic character of variation of specific values of anode erosion and cathode weight gain, and AL thickness limitation — remain the same as in nonmechanized vibration ESA. A secondary electrode heating effect has been observed, which can be utilized for increasing the efficiency of ESA. On the basis of considerations of maximum process efficiency and alloyed layer thickness and surface finish, optimum alloying conditions are proposed (a large I_sc and a low capacitance at an electrode pass number n=4–5).Translated from Poroshkovaya Metallurgiya, No. 3(291), pp. 30–36, March, 1987.     

Increasing the wear resistance of surface layers of high-speed steel by electric-spark alloying and laser treatment

How the combined action of high-energy spark alloying and laser treatment affect the wear resistance of high-speed steel cutting tools has been studied. That action has been found to form a strengthened layer of composite refractory compounds on the tool surface, thus making it hard and wear-resistant, and create a protective barrier that reduces the adhesive interaction of the cutting tool with a chip. The tribological properties and the durability of the cutting tool can be enhanced by alloying the surface layer with elements and compounds that form stable oxides tightly bonded to the substrate. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(408), pp. 44–51, July–August, 1999.     

Effect of grain size of WC-Co-B alloying electrodes on the formation of a reinforced layer during electric-spark alloying

Conclusions A study was made of the effect of grain. size of electrodes made of a low-cobalt hard metal microalloyed with amorphous boron, on the cathode weight gain, and quality of resultant coatings. With decreasing alloying electrode grain size, the cathode weight gain grows and the coating structure becomes more continuous.Translated from Poroshkovaya Metallurgiya, No. 11(215), pp. 80–83, November, 1980.     

Effect of alloying additions on the liquid-phase state of refractory metals and their crystallization processes

Summary An analysis is made, by considering the electronic structure of atoms of the principal and alloying elements, of the structural characteristics of refractory metals in the liquid state and of their crystallization process. An attempt is made to explain, in terms of the stable electronic configurations of the valency electrons of interacting atoms, the processes of liquid-phase reaction of the transition d metals with various elements. It is shown that alloying additions producing an increase in the statistical weight of stable d⁵ configurations of the interacting atoms will help to strengthen and stabilize the short-range-ordered groups in the melt, thereby promoting the appearance of a large number of stable crystallization nuclei.Translated from Poroshkovaya Metallurgiya, No. 4 (64), pp. 47–52, April, 1968.     

Effect of electrode (tool) material density on the electric-spark alloying process

Conclusions Determinations were made of the effect of sintering temperature on density, hardness, and transverse rupture strength for VK6 and T30K4 hard metals. The relationship was found between the increase in volume of the layer forming on the cathode base plate and the starting porosity of a hard-metal alloying electrode. It is shown that a residual porosity of hard metals of 7–9% ensures optimum conditions of coating formation in the ESA of steel.Translated from Poroshkovaya Metallurgiya, No. 7(223), pp. 53–55, July, 1981.     

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.