Effect of porosity on microplastic deformation of iron base powder materials

Conclusions By the method of subjecting beams of uniform strength to bending tests we measured the modulus of elasticity of sintered iron base materials in a broad interval of porosity (0–40%).With porosity from 10 to 25% the curves of microyield are reduced to a single curve of strain-hardening of compact material by normalization to the coefficients K = E_o/E_gq.Deviations from similarity are found in the region of small (<10%) and high (>25%) porosity. The authors bring these effects into connection with the change of the structural state of the material.In the region of microplasticity (_pl = 10^–6-10^–3) a characteristic feature of iron base sintered materials with porosity of less than 25% is parabolic strengthening: ^1/2. An analysis of the curves of microyield in coordinates -^1/2 revealed that strengthening proceeds in stages.For materials with porosity of more than 25% the yield stress and strain are correlated by a dependence of the type ln .Translated from Poroshkovaya Metallurgiya, No. 7(319), pp. 79–84, July, 1989.     

Sintering of constructional powder materials by high-frequency currents

Conclusions The results are presented of a study into the possibility of sintering powder materials of complex composition by means of high-frequency currents. Relationships have been found between the critical temperature of specimens and the graphite and chromium contents of the starting charge. The microstructure has been investigated, and the mechanical properties determined for specimens of various compositions sintered at the critical temperatures.Presented to the Fifth Republican Scientific-Technical Conference on Powder Metallurgy, Kiev, March 29–31, 1966.Translated from Poroshkovaya Metallurgiya, No. 12, pp. 15–20, December, 1966.     

Structure and properties of composite sintered material of the type iron-cast iron

New antifriction alloys, synthesized from mixtures of iron and cast iron powders, have been developed. A special cast iron, with interdendritic point graphite inclusions, whose initial forms and sizes remain the same after sintering while being distributed among the grains, is used to create the composite materials. Starting at sintering temperatures of 800°C a pearlitic ferrite or pearlite structure forms with initial graphite inclusions that prevent formation of structure-free cementite. A composite antifriction material with a low friction coefficient can be obtained by optimizing the process parameters and charge composition as well as the microstructure of the alloys.Scientific and Industrial Association Bakkonditsioner. Translated from Poroshkovaya Metallurgiya, No. 1 (361), pp. 60–63, January, 1993.     

Mechanical treatment of powders of refractory carbides

Conclusions The model of mechanical treatment constructed in this work makes it possible to reduce all the parameters of this treatment to three generalized parameters: the mean energies of movement of the spheres_s, particles _p, and the fraction of absorbed energy . The main input parameters of the conditions are the vibrational speed V_a = A and the flow of the powder qv.On the basis of calculations of the energy characteristics of mechanical treatment of the powders of the tantalum carbides and semicarbides we can estimate the contribution of mechanical energy of this treatment to the activation of the processes of synthesis of the semiand subcarbides of these metals. Specifically, the effect of synthesis of the refractory tantalum semicarbide directly in the chamber of the vibratory mill during mechanical treatment can be explained.Translated from Poroshkovaya Metallurgiya, No. 4(280), pp. 91–96, April, 1986.     

Manufacture of antifriction parts for a power saw by the powder metallurgy method

Conclusions The part, bush, of the Druzhba power saw manufactured out of cermet alloys has better service properties than the bush made of LS 59-1. When producing the bushes of the hinged frame of the Druzhba power saw it is best to use iron-graphite material ZhGr1.5, which permits producing parts with high service properties and effects an economy when manufacturing by the powder metallurgical method of about 10,000 rubles annually.Translated from Poroshkovaya Metallurgiya, No. 7 (67), pp. 95–98, July, 1968.     

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.     

Properties of Highly-Dense Iron‐Base Powder Metallurgy Materials Pressed without Zinc Stearate

The possibility of obtaining highlydense compacts by single pressing and sintering and the use of heatresistant solid lubricants (graphite, talc) instead of conventional lubricant was studied. It was shown that the addition of graphite is most effective to obtain highly-dense powder metallurgy materials since it substantially facilitates ejection of the part from the die and improves the mechanical properties.     

Effect of reduction temperature on some properties of ultrafine iron powders and hot-forged specimens

Conclusions A study was made of the processing properties of a reduced ultrafine electrolytic iron powder. The key parameter determining these properties is powder reduction temperature, which controls also the density of finished parts. An investigation into the process of structure formation during the heating of compacts for hot forging demonstrated the feasibility of producing -Fe of grain size 1 m or less. The principal parameters determining the conditions of production of an ultrafine -Fe grain are compact heating temperature and rate and duration of holding at the heating temperature. It is shown that ultrafine iron powders can be employed for manufacturing high-strength ultrafine-grained materials.Translated from Poroshkovaya Metallurgiya, No. 4(280), pp. 1–7, April, 1986.     

“Activity” of powders in the sintering of single-component compacts

Summary A study has been made of the shrinkage characteristics of compacts obtained by pressing: 1) active powders of electrolytic origin, 2) powders thoroughly deactivated by high-temperature annealing, and 3) a mixture of equal amounts of the above two powders. It is shown that the observed shrinkage characteristics can be qualitatively explained by assuming that, in addition to the usual mechanism of deactivation operating during annealing, there is also a mechanism of activity loss resulting from defect migration from active to deactivated particles.Translated from Poroshkovaya Metallurgiya, No. 4 (64), pp. 18–21, April, 1968.     

Determining equations for compressible plastic porous solids

Conclusions The scalar properties of a compressible porous solid can be characterized by a pair of equations expressing the dependence of hydrostatic pressure p and tangential stress intensity t on the ratio between the rates of volume change e and shape change , porosity, and parameters characterizing the state of the material of the powder and the porous solid. The p and functions must satisfy Eq. (14), with p being a monotonically increasing limited function of S=e/ and t increasing at S 0, attaining a maximum at S = 0, and decreasing at S 0; at ¦S¦ 0. During the plastic deformation of compressible materials, hydrostatic pressure can affect shear strains, while tangential stresses can lead to volume changes. Together with this form there exists a form of determining equations expressed by the loading surface equation (16) and the relationship (18). In the case of a rigorously convex surface these two forms are equivalent.Translated from Poroshkovaya Metallurgiya, No. 4(220), pp. 17–23, April, 1981.     

Comparison of diffusion calculations for two models of powder mixtures

Summary The advantages and drawbacks are discussed of two models of powder mixtures: The model based on single-particle approximation and the concentric sphere model. Calculated values obtained by using both models are compared with experimental data.Translated from Poroshkovaya Metallurgiya, No. 1, pp. 23–24, January, 1968.     

Effect of sintering conditions on the structure and mechanical properties of P/M aluminum base alloys

Conclusions A magnesium addition promotes densification of Al-Cu alloy specimens sintered for short periods of time in the range 595–635C. Longer sintering at 615 and 635C results in higher specimen porosity. At a temperature above 595C Al-Cu alloys experience severe coarsening. Alloying with magnesium does not significantly affect the structure of the alloys. A magnesium addition improves the mechanical properties of an Al-Cu alloy. The extent to which magnesium alters the mechanical characteristics of heat-treated Al-Cu alloys depends on sintering conditions. The highest strength — 340 MPa and =6% — is exhibited by specimens sintered for 45 min at 595C.Deceased.Translated from Poroshkovaya Metallurgiya, No. 9(297), pp. 29–34, September, 1987.     

Formation of detonation coatings applied on an iron base

Conclusions The results of x-ray diffraction analysis indicate a complex multiphase composition of the areas adjoining the zone of contact of the coating with the base related to occurrence of the and -structural transformations. Mutual mixing of the materials of the coating and base in the liquid phase leads to alloying and stabilization of the high temperature modification of iron (-Fe) and cobalt (-Co).The structural transformation ( -Fe) has a significant influence on the processes of formation of detonation coatings of powders of pure metals (Co-Ni) applied on iron and leads to a reduction in the level of mechanical properties of the joint.In the coating itself significant mixing of the sprayed metals occurs including different mechanisms of mass transfer such as mass transfer in the liquid and solid phases [1] with a depth of penetration of more than 10 m.On the boundary of the joint of the coating with the iron base relatively weak diffusion interaction of the contacting metals is observed. The width of this zone (5–10 m) is significantly less than that in spraying of a Co-Ni coating on an aluminum base [1].Translated from Poroshkovaya Metallurgiya, No. 10(298), pp. 60–65, October, 1987.     

Tribotechnical characteristic of a powder metallurgy iron-ceramic rubbing pair

Conclusions Friction of powder metallurgy iron on a ceramic with sliding rates of 11 and 22 m/sec is characterized by an intensity of wear of less than 3.0 m/km, a coefficient of friction of 0.17–0.33, and smoothing of the rubbing surfaces to R= 0.063.-0.25 mThe primary factors determining the tribotechnical characteristics are the dynamic equilibrium between the formation and failure of surface films on the iron and ceramic formed as the result of transfer of iron and oxidation of it.The chemical composition of the ceramic does not have a significant influence on the tribotechnical characteristics in rubbing in a pair with powder metallurgy iron.Translated from Poroshkovaya Metallurgiya, No. 9(321), pp. 36–40, September, 1989.The authors express thanks to N. I. Gorbatov for help in application of the coatings.     

On the strength of cermet alloys

Summary The results of mechanical tests obtained on alloys of TiC-Co, TiC-Ni, TiC-Mo, close by their nature to the alloy WC-Co at temperatures of 20 and 1200C, confirm G. S. Kreimer's view that refractory compoundsmetal alloys are fragile within wide ranges of change in bond and temperature as opposed to V. A. Ivensen's assertion (Powder Metallurgy No. 5, 1961).It is shown that skeletal structure of material of the SiC-C type secures greater strength than the structure of the scattered type.     

Sintering kinetics of tantalum carbide

Conclusions Tantalum carbide sinters at a temperature above 2500C. Decreasing the powder particle size activates the sintering process, but even with a powder of 0.17-m particle size specimens sintered at 2700C have a porosity of 11%. Coarse powders (> 7–8 m) sinter, without densification, at 2000–2200C by a surface self-diffusion mechanism. Fine powders (<7–8 m) undergo densification already at temperatures above 1400C by a diffusion-viscous flow and a volume self-diffusion mechanism during long holding periods and also probably by an activated grain-boundary sliding mechanism in the initial stage of sintering after rapid heating.Translated from Poroshkovaya Metallurgiya, No. 10(238), pp. 16–19, October, 1982.     

Synthesis of Alloy Ti ― 6Al ― 4V with Low Residual Porosity by a Powder Metallurgy Method

The possibility of producing titanium alloy Ti 6Al 4V with minimal residual porosity from mixtures of elemental powders by the method of pressing and sintering without hot deformation during or after sintering was investigated. Various powder mixtures based on titanium and titanium hydride with alloying additions of either elemental powders having different particle sizes, or master alloys, were studied. It was shown that the synthesis of Ti 6Al 4V from mixtures of titanium hydride and master alloys is optimal with respect to the attainment of high relative density. In this case the sintered material has density up to 99%, homogeneous microstructure with relatively small (100-120 m) -phase grains, and a low concentration of impurities, in particular oxygen, which provide a high level of mechanical properties (_ten = 970 MPa, = 6%).     

Creep of highly-porous iron compacts under conditions of cyclic α ↔ γ-transformations

Features of the creep of highly-porous iron compacts with cyclic -transformation are studied. Possible reasons are explored for acceleration of deformation during -transformation and sintering of compacts with -transformation.Kharkov University. Translated from Poroshkovaya Metallurgiya, Nos. 3–4, pp. 19–23, March–April, 1994.     

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.     

Effect of the parameters of dynamic hot pressing on the structure and properties of the powder material ZhGr0.8D2N3G3CaF214. II. Heating temperature and time before dynamic hot pressing,protective atmosphere in sintering and dispersity of solid lubricant

Conclusions With heating temperature before DHP equal to 1000°C and heating time of 1200 sec, the specimens have the best antifriction characteristics. On the other hand, an increase of DHP impairs the physicomechanical properties (except impact toughness), and a change of the temperature has an ambiguous effect on them.Comparatively good physicomechanical properties and the smallest linear wear were found in specimens sintered in dissociated ammonia, in vacuum, and in a container with fusible seal. Specimens sintered in dissociated ammonia and dried hydrogen have a low friction coefficient.The effect of the dispersity of inclusions of solid lubricant on the mechanical properties is imperceptible, but on the friction coefficient and on linear wear it is substantial. Optimal is the use of particles of the fraction +100 m: thanks to their spongy shape they adhere more strongly to particles of the matrix, and that has a favorable effect on the antifriction properties.Translated from Poroshkovaya Metallurgiya, No. 9(333), pp. 53–58, September, 1990.