The effect of carbon content on the mechanical properties of tungsten carbide-cobalt hard alloys

Summary A study was made of the effect of graphite and-phase contents on the properties of VK8 alloy. It was found that, in the presence of the-phase in the alloy in the form of lakes or dendrites (lace), indicating carbon deficiency, the strength of the alloy is greatly reduced. Slight decarburization, taking the form of-phase formation along the interphase boundaries, has practically no effect on the strength of VK8 alloy. The presence of graphite in an amount of less than 0.5 vol. % has little effect on the wear resistance of VK8 alloy, and slightly raises its strength. A high graphite content substantially lowers both strength and wear resistance.     

Development of tungsten-carbide-base corrosion-resistant composite materials with a binder of PKh8N15 stainless steel

Conclusions The bend strength of VNS20 and VNS32 composites is determined by the quantity of ₁phase and depends little upon the content of binder (PKhl8N15 steel). The hardness, on the other hand, depends substantially upon both the ₁-phase content and upon the quantity of binder.The VNS20 and VNS32 composites sintered at the temperatures of the start of formation of the liquid phase in the tungsten carbide—PKhl8N15 steel system, when compaction is completed and the rate of formation of ₁-phase is still insignificant, have the optimum properties.With a satisfactory level of physicomechanical properties, the VNS20 and VNS32 composites show high corrosion resistance in a medium of nitrine with additions of nitric acid.An increase in the strength of VNS type composites may be obtained by reducing the diffusion reaction of tungsten carbide with stainless steel.Translated from Poroshkovaya Metallurgiya, No. 5(281), pp. 69–75, May, 1986.     

Extrusion of a viscoplastic powder mixture

Summary It has been established that, in the extrusion of a viscoplastic mixture through a cylinder-confuser-cylinder space, the relationship between the rate of flow Q and the pressure dropp is described by the expression: {ie691-01} where the coefficients depend on geometrical parameters and the rheological properties of the mixture, a being proportional to {ie691-02} and {ie691-03} is the yield strength and the plastic viscosity).Translated from Poroshkovaya Metallurgiya, No. 9 (57), pp. 6–9, September, 1967.     

Magnetic investigation of microstress in hard alloys

Conclusions The variation of microstress in Co-(Ti, W)C solid solutions and two-phase titanium-tungsten hard alloys of various compositions is essentially similar in character to that in the corresponding systems Co-WC and WC-Co. The level of microstress in the cobalt and carbide phases of two- and three-phase titanium hard alloys changes sharply as a function of alloy composition (cobalt and titanium carbide contents). The microstresses in the Co phase (tensile) and in the WC phase (compressive) do not change sign, while the microstress (Ti, W)C in the titanium phase does change sign, when the cobalt or titanium carbide content of the alloys is varied.The character of microstress variation in titanium-tungsten hard alloys depends also to a large extent on their structure — the presence of continuous carbide skeletons in low-cobalt alloys and of (Ti, W)C grain conglomerates in alloys of comparatively high cobalt content. The composition of the cementing phase and the presence of additional phases (graphite, ₁ phase, pores) can also be expected to constitute contributory fators.In the case of three-phase titanium-tungsten alloys, the most widely used hard-alloy tool materials, there is a correlation between the microstress in their cobalt phase and their transverse rupture strength, which could be utilized for the formulation of new grades of alloys of this type.Translated from Poroshkovaya Metallurgiya, No. 10(166), pp. 64–71, October, 1976.     

Reactions of TiNi with Oxygen

X-ray diffraction and metallography have been applied to study the formation conditions for the phase in Ti₄Ni₂O in the reaction of TiNi with oxygen. The phase diagram for the Ti Ni O system indicates that the phase (Fe₃W₃C structure type) is a solid solution of oxygen in Ti₂Ni. For TiNi made in an oxygen-bearing medium or from initial materials contaminated with oxygen, one gets the phase and Ni₃Ti. Those phases are formed also in surface oxidation as products from the initial interaction of the alloy with oxygen. They occur when there is a low oxygen partial pressure, as on annealing TiNi powder in a vacuum given by a rotary pump or in a layer under scale formed on a cast TiNi specimen on oxidation in air. The layer under the scale is formed because of the preferential loss of titanium from the TiNi and consists of Ti₄Ni₂O, Ni₃Ti, and an Ni(Ti) solid solution, which in turn occurs because of preferential loss of titanium from Ni₃Ti. In the subsequent oxidation stages, there is selective oxidation of Ti₄Ni₂O to lower titanium oxides. The decomposition of TiNi alloy containing oxygen when the composition is varied near the equiatomic one can be used for practical purposes. For example, the segregation of the hydride-forming phase may improve the hydrogen uptake by the alloy, while the dispersed segregation of Ni₃Ti and the lower oxides may favor hardening.     

Wear- and Scaling-Resistant Coatings Based on TiCN

The composition, structure, and properties of coatings obtained by the high-velocity gas-flame spraying of composite powders based on TiCN with additions of SiC, AlN, SiC AlN/Al₂O₃ and a binder of NiCr based alloy were investigated. The working surfaces of coatings were studied by metallographic, petrographic, x-ray diffraction, electron-probe analyses, and scanning electron microscopy. It was determined that coatings 200 m in thickness had a typical finely dispersed lamellar structure with layers enriched in titanium alternating with layers of NiCr alloy. The tribological properties of developed coatings were superior to those of the standard WC + 8% Co alloy: under dry friction at a load of 2 MPa and sliding velocities in the range 5-15 m/sec the coefficient of friction was 0.17-0.11, and wear rate 3.4-8.5 m/km. The high oxidation resistance of the coatings is due to the presence, in the outer scale layer, of refractory compounds Al₂SiO₅, (Cr, Al)₂O₃, and Al₂TiO₅, which prevent the diffusion of oxygen into the substrate. The mass gain of the coating based on TiCN SiC AlN was 1.42 mg/cm₂ at 1450°C.     

Phase equilibria in W-Fe-Co-Ni system alloys. I. Alloys containing 10% (Fe + Co + Ni) at 1400–1200°C

Conclusions The isostructural intermediate -phases of Fe₇W₆ and Co₇W₆ in the W-Fe-Co system form a continuous series of solid solutions and transformation of the L + peritectic equilibrium into, the similar L + (Co₇W₆), occurring in a narrow temperature range (1640–1630°C) is observed. In the W-Fe-Co-Ni system in the 1470–1460°C range transition of the L + (Fe₇W₆)+ peritectic equilibrium into the similar. L + (Co₇W₆+ is also observed.Upon completion of crystallization and at temperatures of 1400–1200°C alloys of the primary section with 10% (Fe + Co + Ni) have a two-( + or +) or three-phase (+ +) structure. In alloys rich in iron at temperatures below 1215°C FeW may form instead of (Fe₇W₆) phase.Translated from Poroshkovaya Metallurgiya, No. 4(280), pp. 60–64, April, 1986.     

Reaction of Tungsten with Liquid Co ― Sn Alloys

The solubility of tungsten in Co Sn melts and the growth kinetics of a W₆Co₇ phase layer at the tungsten melt interface were studied at 1200°C. The liquid alloys composition in the three-phase equilibrium W W₆Co₇ melt was established as (at. fraction) 0.51 Co, 0.49 Sn, 2.3·10^–3 W. The solubility of tungsten in the investigated range of melt compositions is well represented by the equation lgx _W = –0.964-3.420x _Sn, where x _W and x _Sn are atomic fractions of the elements in the melt. The calculated thermodynamic properties can be used for the analysis of other systems which include cobalt and tungsten.     

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.     

The phase equilibria in W-Fe-Co-Ni system alloys. II. Isotherms of the solidus and the phase composition of alloys containing 10 and 20% (Fe + Co + Ni) at temperatures above 1200°C

Conclusions The isostructural intermediate -phases Fe₇W₅ and Co₇W₆ in the W—Fe—Co system form a continuous series of -solid solutions. In the 1640–1630°C range the L + (Fe₇W₆) peritectic equilibrium in this system changes to a similar L + (Co₇W₆) equilibrium, where is the tungsten-base boundary solution.In the W-Fe-Co-Ni polythermal tetrahedron in the 1470–1460°C range conversion of the L +(Fe₇W₆)+, peritectic equilibrium into the similar L + (Co₇W₆) + , where is the nickel-, -ironcobalt-base boundary solution, occurs.Upon completion of crystallization at 1400°C, the W-Fe-Co system alloys with 10–20% (Fe + Co) have a + phase composition, while the W-Fe-Co-Ni system alloys with 10–20% (Fe + Co + Ni) accordingly have + , + + or + . At temperatures below 1215°C in alloys rich in iron, FeW may be formed instead of -phase and therefore the alloys may have an + FeW, + + FeW, + + + FeW and + + FeW phase composition.Translated from Poroshkovaya Metallurgiya, No. 5(281), pp. 86–89, May, 1986.     

Constitution diagram of the system titanium-silver

Summary The titanium-silver phase diagram was investigated over the concentration range from 20 to 100 at. % Ag by means of metallographic, thermal, and x-ray diffraction analyses. It was confirmed that the system contains two intermediate phases, and. The phases are based on the compounds TiAg andTi₂Ag, which are isostructural with the compounds TiCu and Ti₂Cu. The temperatures of nonvariant transformations were determined, and the character of the transformation taking place in the silver-rich alloys was established.Translated from Poroshkovaya Metallurgiya, No. 7 (79), pp. 55–59, July, 1969.     

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.     

Kinetics of external dissolution of metals in metallic melts. (Review)

Conclusions Dissolution rate under diffusion conditions is usually controlled by three parameters, D, , and c_m. Since the dependence of D and values on the individual properties of metals (D 10^–5 cm²/sec, 10^–3 cm) is slight,dissolution rate under diffusion conditions is determined chiefly by cm, which thus constitutes the principal criterion governing the choice of a metal compatible with any given melt. Dissolution under kinetic conditions does not appear to be typical of metals, since even tungsten, which has the highest crystal lattice energy of all metals [62], dissolves under diffusion conditions [19, 20, 63–66].It thus follows that detailed researches into the dissolution kinetics of metals in metallic melts are hardly likely to reveal any new corrosion-resistant metallic materials. The existing liquid-metal corrosion inhibitors are refractory compounds such as nitrides or carbides [67]. This does not mean, of course, that investigations into the dissolution kinetics of solid metals in metallic melts serve no useful purpose, since they are concerned not only with corrosion, but also with a number of other processes referred to in the introduction to this survey.Translated from Poroshkovaya Metallurgiya, No. 8 (92), pp. 39–54, August, 1970.     

Phase Composition of Electrospark Tungsten Carbide-Based Coatings after Heating and Isothermal Soaking

A study of phase formation on electrospark coatings with WC Co Cu electrodes on R6M5 high-speed steel during isothermal heat treatment at the operating temperature of the coating. Copper tungstate CuWO ₄has been found to form, with its crystal lattice coherently bound to the basic carbide phase of the coating, tungsten monocarbide, through tungsten semicarbide as intermediary. The results complement the data on phase formation during the application of WC-based coatings and during their subsequent use with sliding friction.     

Phase equilibria in the solidification range of alloys of the Ti-Ru-Ir system

Conclusions The processes taking place during solidification of the alloys of the Ti-Ru-Ir ternary system have been examined for the first time. The results show that the system contains three nonvariant quaternary equilibria with the liquid of the incongruent type: L + + at 2220°C, L + + at 1920°C, and L + + at 1465°C.In the region with the composition 0–50% Ti, the processes take place in the direction to the Ti-Ru side of the concentration triangle where they are also completed at the temperature of the binary eutectic L '+ equal to 1855°C. In the region with the composition 50–100% Ti the processes are completed at 1460°C at the nonvariant point corresponding to the eutectic reaction L + of the Ti-Ir binary system.Translated from Poroshkovaya Metallurgiya, No. 11(299), pp. 72–77, November, 1987.     

Cyclic strength of hard metals

Conclusions The fatigue limit of the titanium carbide and tungsten carbide alloys investigated on a basis of 5·10⁸ cycles lies in the range (20–30)·10⁷ Pa, and is thus comparable with the endurance of type ShKh high-carbon (1% C-Mn-Si-Cr) ball-bearing steels. The strength and character of fracture of the hard metals are determined by the properties and structural state of their phase constituents. The highest strength is exhibited by tungsten carbide and titanium carbide alloys with evenly distributed equal-sized carbide grains. The character of fracture of the hard metals varies depending on their method of loading, from brittle in static loading to tough-and-brittle in cyclic loading. On time bases not exceeding 10⁶ cycles titanium carbidehard metals are comparable in fatigue resistance to the standard tungsten-containing hard metals.Translated from Poroshkovaya Metallurgiya, No. 9(273), pp. 67–71, September, 1985.     

Effect of electrolysis conditions on the formation,structure, and magnetic properties of a finely divided iron-cobalt alloy

Conclusions Changing the Fe²⁺Co²⁺ ratio in the electrolyte strongly affects the composition of the alloy but not its current efficiency; the current efficiency falls only at iron-to-cobalt ratios in excess of 11. At a high cobalt ion concentration in the electrolyte both the current efficiency and the cobalt content of the alloy cease to vary proportionally to the ion concentration. An x-ray diffraction investigation has established that increasing the cobalt ion concentration in the electrolyte decreases the size of iron-cobalt alloy blocks, which manifests itself in the ratio range Fe²⁺Co²⁺=0.6. When this ratio is exceeded, the -phase of the iron-cobalt alloy becomes amorphous, but on the whole the particles of the deposit retain a crystalline structure owing to the presence of an independent crystalline cobalt phase. At high cobalt ion concentrations in the electrolyte the particles forming by electrolysis constitute a pseudoalloy consisting of the -phase of the cobalt alloy and the and -modifications of metallic cobalt. Lowering the Fe²⁺ Co²⁺ ratio brings about a steady decrease in the crystal lattice constant. Magnetic measurements have revealed the existence of maximum values of coercive force and magnetic induction in a range of Fe²⁺ Co²⁺ ratios close to unity.Translated from Poroshkovaya Metallurgiya, No. 9 (225), pp. 1–5, September, 1981.     

Phase equilibria in the ternary systems Zirconium-Vanadium-Boron,Zirconium-Niobium-Boron and Zirconium-Manganese-Boron

Summary The systems Zr-V-B, Zr-Nb-B, and Zr-Mn-B were investigated by the x-ray diffraction technique, and their phase equilibria at 900° C (Zr-V-B and Zr-Mn-B) and 1500° C (Zr-Nb-B) were established. Ternary compounds having an -phase structure were found in the systems Zr-V and Zr-Mn containing a small quantity of oxygen or nitrogen (a=12.153 A and 11.999 A, respectively). Solid solutions of zirconium in NbB and Nb₃B₂ were observed. The compound NbB dissolves 30 at. % Zr, and its lattice constants increase: a from 3.298 to 3.325 A, b from 8.722 to 8.813 A, and c from 3.164 to 3.175 A. The compound Nb₃B₂ dissolves 6 at. % Zr, and its lattice constants increase: a from 6.185 to 6.202 A and c from 3.281 to 3.295 A.Translated from Poroshkovaya Metallurgiya, No. 6(54), pp.49–52, June, 1967.     

Phase equilibria in ternary systems of transition metals of groups IV and V and carbon

Summary On the basis of literature data and the author's own experimental study, phase equilibria in the ternary systems of the transition metals of groups IV and V with carbon are examined. The phase diagrams shown in the figure have been experimentally verified for the systems Ti-Nb-C, Zr-Hf-C, Zr-V-C, Zr-Nb-C, Zr-Ta-C, Hf-Nb-C, Hf-Ta-C, and Nb-Ta-C. Ternary compounds are missing in the majority of the systems investigated; exceptions are provided by the systems Zr-V-C and, probably, Hf-V-C, which are characterized by -carbide formation.     

Sintering behavior of materials based on alumina and titanium and zirconium nitrides

Conclusions A study was made of the sintering kinetics of TiN-Al₂O₃ and ZrN-Al₂O₃ materials in various protective atmospheres, ft was established that during sintering in nitrogen ZrN-Al₂O₃ composites act as reactive substances. ZrO₂ and AlN are formed, the ZrN lattice constant increases, the microhardness of the materials decreases, and the hexagonal- Al₂O₃ phase becomes transformed into the cubic- Al₂O₃ modification witha =7.92 Å. The densification kinetics of specimens of the composite materials and the variation of their electrical resistance were investigated. It is shown that the sintering process occurs in several stages as a result of changes in the mechanism controlling mass transport.Translated from Poroshkovaya Metallurgiya, No. 2(182), pp. 45–47, February, 1978.