Error in the determination of the particle-size distribution of a powder with a laser analyzer

Conclusions Simple expressions have been obtained from known parameters of a flow-type chamber for estimating errors in laser analyzer measurements of the main numerical particle size distribution characteristics of powders obeying the logarithmic normal law. It is shown that, in spite of marked errors (Fig. 1) in size measurements on single particles whose trajectories are deflected from the laser beam center, it is possible to attain high accuracy in the measurement of numerical particle distribution characteristics by suitable choice of aero or hydrodynamic particle stream focusing [5] (Table 1: maximum error in the determination of the amount of the main fraction in a powder of particle size 3/2 _f = 1.9% at 2_j = 15 and _f = 4.3% at 2_j = 72 m). Without good particle stream focusing, measurements may be very inaccurate (Table 1: _f = 24% at 2_j = 120 m and _f = 55.5% at 2_j = 170 m). The accuracy of laser analyzer measurements grows with increasing curvature (coefficient n) of analyzer calibration characteristics and vice versa. The q/qt relationships obtained may find application in the assessment of errors in particle size analyses of powders with particle distributions differing from the logarithmic normal law.Translated from Poroshkovaya Metallurgiya, No. 12(288), pp. 15–20, December, 1986.     

Special features of the ductile-brittle transition in iron-based powder materials. II. Physicomechanical model of the ductile-brittle transition in cracking resistance tests

Conclusions The presence of pores in the material leads to the redistribution of stresses in the material and to localization of strains in small volumes between the pores. The susceptibility to ductile failure increases with increasing porosity.At –196°C, the failure mechanism of the porous materials based on iron changes from ductile to brittle (cleavage) with decreasing porosity. The dependence of cracking resistance on the porosity of these materials is nonmonotonic and the maximum cracking resistance is recorded at porosity values at which the failure mechanism changes. The nonmonotonic nature of cracking resistance reflects the high sensitivity of this characteristic to the change of the stress state in the material. The change of the stress state in the ductile-brittle transition temperature range can be described by the condition _f = _T. In the porous materials examined this condition is valid because of the specific form of the _f- and _T- dependences. The model of the ductile-brittle transition proposed in this work can be used to determine the analogy between the cold brittleness temperature T_br and the critical value of porosity _c corresponding to the point of intersection of the _f- and _T- curves for the porous materials.Translated from Poroshkovaya Metallurgiya, No. 3(303), pp. 39–42, March, 1988.     

Influence of working media on the cyclic strength of an AD33-B composite (report 2)

Conclusions With low volumes of accumulated damages (8%) to a test base of 2 · 10⁵ cycle in not more than 150 h the influence of corrosive media on the residual strength of AD33-B composite is not significant.At levels of cyclic stresses of _a>0.6_b, the use of AD33-B composite in 3% NaCl solution and water is undesirable without anticorrosion measures.Translated from Poroshkovaya Metallurgiya, No. 8(260), pp. 77–80, August, 1984.     

Strength characteristics of the materials obtained by hot forging of porous powder preforms. II. Effect of heat treatment on the tensile and shear strength and the compressive yield stress

Conclusions Annealing of the powder metallurgy steels leads to a reduction in the values of the parameters _t, , and ^c _0.2. During this process, they become lower than those of the hot rolled (worked) products. However, after annealing, the stability of all the three characteristics increases. Quenching followed by a low-temperature tempering improves the parameters _t, , and ^c _0.2, but in this case, brittleness of the material increases. With increasing tempering temperature, all the three parameters decrease and at 600°C, they are virtually at the same level as that obtained after annealing at this temperature.The change in the yield stress after quenching and tempering or after annealing determines to a significant extent the nature (whether brittle or ductile) of shear fracture.Translated from Poroshkovaya Metallurgiya, No. 4(280), pp. 73–75, April, 1986.     

A theoretical and experimental investigation of the plastic deformation process of sintered composite materials. III. An investigation of the spatial redistribution of the phases of a composite material in plastic deformation of it

Conclusions As in porous bodies, in dense composite materials plastic deformations may cause an increase in the local concentration (density) of elements of the hard phase in zones of active flow of the material. The intensity of structural rearrangement (regrouping) of the phases in a composite material is determined by the character of the relationship of the function of plasticity of the medium to the amount of the average (hydrostatic) stresses in the body being deformed and is related to the degree of deformation obtained by this body through the derivative (_ij)/_ii. The mutual disposition of the elements of the hard phase in a material may be fixed in any stage of the process of working by pressure if the conditions are created for combined flow of the different phases in the body being deformed.Translated from Poroshkovaya Metallurgiya, No. 10(298), pp. 53–57, October, 1987.     

Copper-gallium alloys containing 18–70 WT.% Ga

Conclusions A study of specimens produced by the powder metallurgy technique has demonstrated that six stable phases occur in the system gallium-copper at room temperature, namely, (31.5–33.8 wt.% Cu), ₃ (55.5–58.5 wt.% Cu), ₂ (61–62 wt.% Cu), ₁ (63–70 wt.% Cu), ₁ (77 wt.% Cu), and an solid solution of gallium in copper (80.5–100 wt.% Cu).Translated from Poroshkovaya Metallurgiya, No. 4 (124), pp. 70–74, April, 1973.     

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.     

Strength characteristics of matrials produced by hot forming of porous powder compacts. I. The influence of porosity,carbon content,and the method of compacting on the tensile,shear, and compressive yield strengths

Conclusions The mechanical characteristics (_t, ) of powder metallurgy steels depend upon the porosity as a weakening factor and work hardening as a strengthening one. The tensile strength is more sensitive to porosity and less susceptible to work hardening than the shear strength. The compressive yield strength depends practically only upon work hardening and the size of the metal cross section.In comparison with hot rolled of the same composition, powder metallurgy low-porosity steels possess higher characteristics _t, , and _0.2 ^comp , which may be explained by the strengthening action of work hardening.Powder metallurgy steels produced by extrusion have higher values of _t than hot formed as the result of improvement in the quality of the intergranular contacts and orientation of the nonmetallic inclusions while there is practically no difference in the characteristics and _0.2 ^comp of these materials.Translated from Poroshkovaya Metallurgiya, No. 3(279), pp. 88–91, March, 1986.     

Buckingham-potential parameters and relations between them for solids

Parameters m and n in the Buckingham potential in the form =[U₀mn/(m – n)]{(1/m)Y^–m – (1/n)exp[n(1–Y)]} have been calculated for 79 elements and 35 compounds, which have been compared with data on =c_v/(U₀) and =KV₀/c_v, in which U₀ is the cohesion energy, Y=(V/V₀)_1/3, V a volume with equilibrium value V₀, ... c_v the specific heat, the thermal-expansion coefficient, and K is the bulk elastic modulus. It is found that m is dependent essentially on and n on . These relationships have been approximated, and conclusions are drawn from them about the most reliable input data, particularly K because of the large spread in published values. A study is made on the relation of m and n to the positions of the elements in the periodic system and the electron structures.Institute of Problems of Materials Sciences, National Academy of Sciences of the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, No. 5–6, pp. 118–126, May–June, 1994.     

Metal pressure in cold rolling in the elastic aftereffect zone of porous strip

Conclusions The metal pressure at the end of the forward slip zone and the beginning of the elastic aftereffect zone of a porous strip being rolled is given by the expression p=_t. This pressure differs from that normally employed in theoretical calculations by the coefficient , which is greater than unity and grows appreciably with increasing strip density and Poisson's ratio of the corresponding nonporous material.Translated from Poroshkovaya Metallurgiya, No. 3(195), pp. 7–10, March, 1979.     

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.     

Reaction of Composite Ceramic Materials with Corrosionally Active Media

The oxidation of composite powders and monolithic AlN SiC, AlN SiC TiB₂, and AlN SiC ZrB₂ ceramics in air up to 1600°C was studied by the methods of thermogravimetric, differential thermal, x-ray diffraction, and electron-probe microanalysis. The exceptionally high corrosion resistance of these materials was established. The corrosion resistance and possibility of using structural ceramics of the systems TiB₂ AlN, TiB₂ TiN, and TiC_0.5N_0.5 in sea water was demonstrated. The toxicity of Si₃N₄, AlN, BN, and TiN powders was analyzed on the basis of their reactions with biochemical media. It was proven that TiN based materials are highly stable in the oral cavity.     

Cold shortness and nature of failure of iron-manganese powder alloys

Conclusions The level and nature of variation of impact toughness in the iron-manganese powder alloys are similar to the vacuum-melted cast alloys. The lowest cold brittleness threshold was recorded for the alloys with 20–23% Mn (determined at –253°C) containing the maximum amount of -martensite and positioned at the boundary of the + + and + regions. Brittle fracture in these alloys takes place by the intercrystalline mechanism, and the inclusions, depending on their composition, size, and distribution, can both support crack propagation and delay this process. The possible mechanisms of failure of the powder materials are proposed on the basis of the literature data and own experimental investigations.Translated from Poroshkovaya Metallurgiya, No. 12(300), pp. 77–83, December, 1987.     

Effect of carbon on the surface properties of liquid iron

Conclusions A study was made of the effects of temperature and composition on of Fe-C melts. It was found that, in the hypoeutectic range of compositions, the polytherms of of the melts investigated are not straight lines and are characterized by a positive temperature coefficient of . Carbon exhibits surface activity in liquid iron. A hypothesis is advanced in explanation of this phenomenon. The wetting of alumina by Fe-C melts was investigated at various carbon concentrations and temperatures. Raising the carbon content improves wetting in the system (Fe-C)_L-A1₂O₃.Translated from Poroshkovaya Metallurgiya, No. 10 (118), pp. 57–61, October, 1972.     

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.     

Mechanical properties of materials obtained from an ultrafine aluminum nitride powder

Conclusions A study was made of the mechanical properties of materials produced from an ultrafine aluminum nitride powder. It is shown that use of such a fine powder enables virtually nonporous specimens to be produced having high strength characteristics: _c=1600 MPa, _tr= 320 MPa, microhardness of 16,800 MPa, microstrength of 3100 MPa, and microbrittleness of 1.9. On the basis of the results obtained it is possible to recommend aluminum nitride sintered from an ultrafine powder as a good-quality constructional ceramic material.Translated from Poroshkovaya Metallurgiya, No. 12(240), pp. 65–69, December, 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.     

The phases in the lanthanum-germanium system

Conclusions The lanthanum-germanium system was investigated. The existence of four, previously established compounds was confirmed. The width of the homogeneity region of the lanthanum-rich compounds is narrow. The width of the homogeneity region of lanthanum digermanide extends over the composition range LaGe-LaGe_2.0, which corresponds to germanium contents of 42–51%. Lanthanum digermanide exhibits two modifications with crystalline structures of the -ThSi₂ and -GdSi₂ types, which are capable of independent existence at room temperature. The phase with an -GdSi₂ type structure forms at germanium contents corresponding to the compositions LaGe_1.8-LaGe_2.0, while the -ThSi₂ type structure forms at germanium contents lower than theoretical (42–45 wt.%). At the composition LaGe_1.7, the phases with the -GdSi₂ and -ThSi₂ type structures coexist.Translated from Poroshkovaya Metallurgiya, No. 12 (72), pp. 42–44, December, 1968.     

Mechanical properties of multilayer steel-copper composites

Conclusions The tensile strength _t and fatigue limit _–1 of powder metallurgical and cast MLCs grow with decreasing mean layer thickness h starting from 5000 Å. In cast Type 45 steel/copper composites high tensile strength _t (222 kgf/mm²) combines with high impact strengtha _n (8 kgf-m/cm²) and hardness (42–45 HRC). With powder metallurgical and cast MLCs, at any given life NG the cycle stress necessary for fatigue fracture grows with decreasing mean layer thickness (within the h = 5000-500 Å range investigated).Translated from Poroshkovaya Metallurgiya, No. 11(203), pp. 33–37, November, 1979.     

Structural Features and Properties of Alloy 84% WC ― 16% Co,Obtained by Hot Pressing in the Solid and Liquid Phases. Part 2. Influence of the Temperature at which the Specimens are Made on Their Physicomechanical Properties

We have studied the changes that occur in the resistivity, the transverse bending strength, and the fracture toughness (cracking resistance) of a hard alloy obtained by hot pressing at about 500 MPa and sintering over a wide range of temperatures (950-1450°C) as well as the how those parameters are affected by solid-phase and liquid-phase annealing. The porosity dependence of the resistivity is shown not to be single-valued. Other factors affect the resistivity, e.g., the degree of particle interaction and the state of the structural components, which vary with the porosity. The resistivity curve for hot-pressed specimens has an inflection in the region of 1200°C. The resistivity increases at a faster rate at lower temperatures. In the temperature range studied the porosity dependence of the transverse bending strength and the fracture toughness is linear: _b = ⁰ _b(1 – 3.53) and K _1c = K ⁰ _1c (1 – 3.44). Prolonged solid-phase annealing of hot-pressed specimens improves their mechanical properties owing to a decrease in porosity.