Electric-spark Alloying Of Steel Research Articles

BUILDING OF ALLOYED SURFACE LAYER DURING ELECTRIC SPARK TREATMENT OF STEEL 35 BY THE RHENIUM

The results of the study of the effect of the composition and structure of the alloyed layer on the surface of steel 35 during electric spark alloying using rhenium anode material were shown. (Research purpose) The research purpose is investigating the effect of the electric spark alloying of steel with rhenium on the composition and structure of the alloyed layer. (Materials and methods). Rhenium Re (99.99 percent) was used as the anode material, steel 35 was used as the cathode. As equipment - BIG-1, Elitron-22-AM with AG-2 unit, IMEIL installation; SEM EVO-50 XVP "S.ZEISS", RigakuMiniFlex-II diffractometer (Japan), Cu-Ka radiation, ICDD database; VLO-200, VLR-220 scales; PMT-3M microhardometer. The samples were cleaned in an ultrasonic bath. (Results and discussion) The composition and structure of the alloyed layer were investigated. The change in the elemental content of the alloyed layer in depth showed a high Re content near the outer surface of the alloyed layer and at a depth of up to 10-15 micrometers, which rapidly decreased with an increase in depth to 27-30 micrometers in the opposite phase to Fe. It was determined that the formation of the obtained phases in the melt microvanna was accompanied by high temperatures during electric mass transfer. (Conclusions) The results of the study of the effect of the modes of electric spark alloying of 35 rhenium steel on the phase composition and efficiency were shown. They proposed an energy indicator, gave its assessment in comparison with others. It is of interest to continue the study of electrospray doping with rhenium, to clarify the modes that increase efficiency.

Modification of anode material VK8 by silicon for electric spark alloying of steel 35

Metal-ceramic coatings on steel 35 were obtained by the method of electric spark processing with different duration of control pulses, using a new electrode material WC—7.5 % Co—7.5 % Si for applying electric spark coatings on steel 35. It is shown that WC particles were deposited into the coating as a result of solid-phase transfer, which intensified with increasing discharge duration. The addition of silicon to WC—Co electrode materials can significantly reduce the coefficient of friction of the formed coatings. In general, the use of WC—Co—Si coatings can increase the heat resistance of steel up to 5 times, reduce the coefficient of friction of steel 35 to 47 %, and increase the wear resistance of its surface from 3 to 10 times.

Effect of Chromium Addition and Regimes during Electrospark Alloying with Aluminum Matrix Anode Material of Steel 45

Introduction. Electrospark alloying is used to produce hardening coatings. Anodic materials with unique properties include metal matrix composites based on aluminum. The aim of the work is to develop new aluminum matrix anode composite materials with high efficiency indicators during electrospark alloying of carbon steel 45. Materials and Methods. Structural carbon steel 45 was used as the substrate (cathode). Aluminum matrix materials are chosen as the anode materials. The value of the cathode weight increment and the anode erosion were determined by the gravimetric method on the Shinko Denshi HTR-220 CE electronic scale with an accuracy of ±∙10–4 g. To study the microstructure and metallography of the surface of the anode materials, the microscopes EVO-50 XVP and Altami MET 3 APO from S. ZEISS were used. The device CALOTEST CSM Instruments was used to study coatings for microabrasive wear. Results. There is developed a methodological scheme for achieving the efficiency of the electric spark alloying parameters and the properties of the doped layer depending on the composition of the anodic metal matrix composite material based on aluminum with the addition of chromium and processing modes. The mode of Institute of Materials Science electrospark installation with pulse energy of 14.4 J was set for anode material application during electrospark alloying. It is established that after electric spark alloying of steel 45, the hardness and wear resistance of the surface increase by 2-3 times, and the heat resistance ‒ by 5–18 times. Discussion and Conclusion. The series of increasing the cathode mass, the erosion resistance of the electrode materials, mass transfer coefficient, heat resistance, hardness and wear resistance of the alloyed layer are obtained. The obtained series are a convenient tool for achieving various efficiency parameters in electric spark alloying depending on the selected anode material and processing modes.

Electric-Spark Alloying of Steels by Materials Based on WK Alloy with Admixtures of Chromium Carbide

The electric-spark alloying of 45 steel with electrodes made of WC + Co + (2–4)% Cr3C2 hard alloys obtained by sintering on the “coating-substrate” boundary leads to the formation of an intermediate zone. This zone is formed as a result of cavitation mixing of the materials of the electrodes in the course of spark discharge and its composition corresponds to the composition of high-alloy high-speed steel. The intermediate zone increases the cohesion strength between the coating and the substrate, the depth of the obtained layer, and its wear resistance.

Electric-spark alloying of steels with chromium carbide base alloys

It is shown that, of the Cr3C2-Fe cermets investigated, KKhZh-50 alloy is the best alloying electrode material. Alloying should be performed under “soft” conditions (Epulse ≤−2 J). The quality of the reinforced layer depends on the pulse energy and the base and electrode materials. The continuity of the layer increases and its surface roughness and thickness decrease with increasing pulse energy. Anode erosion and alloyed layer formation are affected by the secondary structure on the electron surface. For KKhZh-50 alloy its formation decreases anode erosion and the cathode weight gain, while for KKhNF-15 alloy, by contrast, it increases them. It is proposed that, to increase the corrosion resistance of such coatings (by about two orders), 65G steel should be alloyed in two stages, first with KKhZh-50 cermet and then with nickel.

Effect of phase composition and microstructure of sintered TiN-Cr electrode material on the main characteristics of the process of electric-spark alloying of steels

Solid solutions and the eutectic in the alloying electrode decrease its erosion during ESA, while the intermetallic compound and other brittle phases increase it. The erosion resistance of the anode grows with decrease in its porosity, and shows a correlation with the variation of its strength. A sufficiently strong bond between the phases in the heterophase material increases the latter's erosion resistance and leads to the formation of erosion products of mainly fine fractions. The presence in the anode of phases which can form iron-base solid solutions or intermetallic compounds with the basis material has a beneficial effect on the cathode weight gain. Phases which do not have this ability are retained on the cathode only when they have a strong bond with a phase (e.g., the metallic binder) which itself can form both solid solutions and intermetallic compounds with the basis.

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

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

Electric-spark alloying of steels with TiN-Cr materials

A single spark discharge produces on the anode a conical crater whose depth, shape, and mean diameter depend on the phase composition of the anode material. The total anode erosion is sharply reduced by the addition of 10% Cr to titanium nitride, and becomes stabilized at a chromium concentration in the anode of 40%, which is due to a decrease in the extent of brittle disintegration of the anode. The process of formation of the reinforced layer is affected by the phase composition of the anode material and by the particle size and phase composition of the erosion products. The presence of intermetallic compounds and solid solutions in the anode material improves the conditions of formation of the layer, while a eutectic component in the anode material and oxides in the erosion products have a deleterious effect on them. The highest coefficient of transfer (K = 0.25) is attained in ESA with electrodes containing more than 40% Cr. The microhardness of the reinforced layer falls (from 17,000 to 8230 MPa) and its thickness and continuity grow (from 5 to 50 μm and from 30 to 100%, respectively) with increasing volume fraction of chromium in the anode material. A TiN + (40–60%) Cr composite may be recommended as an electrode material for the electric-spark alloying of steels, to which, however, additions must be made capable of raising the coefficient of transfer without adversely affecting the key characteristics of the alloyed layer.

Effect of structure of titanium diboride on the conditions of formation of coatings in the electric-spark alloying of steel

Effect of structure of titanium diboride on the conditions of formation of coatings in the electric-spark alloying of steel

Electric-spark alloying of steel with heterophase materials based on TiN and Al2O3

Electric-spark alloying of steel with heterophase materials based on TiN and Al2O3

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

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.

Electric-spark alloying (ESA) of steel with titanium carbide in its homogeneity range

A correlation exists between changes in the parameters of the process of ESA of steel with titanium carbide in its homogeneity range and changes in the electronic structure of TiCx. The erosion of titanium carbide, weight gain of the steel cathode, and proportion of fine-fraction particles in the erosion products of TiC grow with increasing degree of completeness of the carbon sublattice. This promotes growth of the alloyed layer, and is a result of a strengthening of the covalent component of the Ti-C bond, which predominates in the electronic energy spectrum of TiCx. It has been found that the number of pearlitic colonies in the spark-heat-affected zone falls with decreasing distance from the alloyed surface, which is due to carbon impoverishment of this zone resulting from the carbon combining chemically with the titanium.

Effect of boron and chromium boride microadditions to VK6M alloy on cathode weight gain in the electric-spark alloying of steel

An investigation was carried out into the effect of boron and chromium boride micro-additions on the phase composition of electrode materials based on VK6M hard metal. Optimum alloying electrode composite compositions were established for the ESA of type 45 steel. The most favorable conditions were determined for ESA with alloying electrodes made of WC-Co-B and WC-Co-CrB2 composites.

Electric-spark alloying of steels with WC-Co hard metals

A study was made of the electroerosion and cathode weight increase accompanying the ESA of steels with WC-Co hard metals and of some properties of resultant alloyed layers. In ESA the best results are obtained with VK20 alloy under “soft” conditions and with VK15 alloy under “hard” condition. The optimum alloying time is 5–10 min/cm2 in process No. 2 and 3–5 min/cm2 in process No. 5. Under these conditions ESA by the “soft” process (with VK20 alloy) ensures the formation of a hard (2200 kgf/mm2) “white” layer of the same thickness (40 μm).

Electric-spark alloying of steel with heterogeneous molybdenum-containing zirconium nitride materials

A study was made of the possibility of employing ZrN-Mo composites as materials for ESA electrodes. It is shown that the erosion of such a composite cathode decreases with rise in the Mo content of the material. The process of strengthened layer formation is affected not only the by particle size distribution of the erosion products but also by their phase composition. The formation of volatile oxides has a deleterious effect on the surface strengthening process. The best characteristics — a high degree of continuity, large thickness, close contact with the basis material, and strong adhesion to it — are exhibited by the layer forming during ESA with a 40 vol.% ZrN + 60 vol.% Mo composite electrode. During electric-spark processing a redistribution of carbon takes place in the surface layers of the cathode, the highest carbon concentration being reached in the “white” layer, and the ferrite grain decreases in size and changes in shape.

Electric-spark alloying of steel with hetrophase materials based on ZrN and Al2O3

A study was made of the ESA of steel with electrodes made of ZrN-AlaO3 composites with and without MO and W additions. Al2O3 contents in excess of 10 vol. % adversely affect the conditions of formation of a strengthened layer and increase the amount of brittle rupture erosion products by decreasing the thermal fatigue resistance of the electrode material. In ESA with composites sintered in argon the coefficient of transfer is 1.5–2 times higher and the total weight gain three times greater than in alloying with composites sintered in nitrogen. The ESA of steel with a Mo-containing ZrN-Al2O3 composite results in the formation of a strengthened layer which is more continuous and adheres more closely and more strongly to the basis material than a strengthened layer produced by ESA with a composite containing the same amount of W. ESA is accompanied by a redistribution of carbon in the surface layers of the cathode, resulting in the attainment of a maximum carbon concentration in the white layer, as well as by a comminution of the ferrite grain and a change in its shape.

Electric-spark alloying of steel with alloys of the Nb-Zr-B system

Electric-spark alloying of steel with alloys of the Nb-Zr-B system