Powder Metallurgy and Metal Ceramics (v.50, #7-8)

12 August 2011 marked the 100th anniversary of Valentin Eremenko’s birth, an academician of the Academy of sciences of the Ukrainian Soviet Republic, an outstanding physical chemist, a founder of the Institute for Problems of Materials Science, National Academy of Sciences of Ukraine. Eremenko’s papers on the physical chemistry of fine particulate systems and surface phenomena, chemical thermodynamics of alloys and metal compounds, and physicochemical analysis of metal and metallic systems have highly been praised by national and international scientific community. Eremenko’s chemical concept of phenomena that occur at interfaces in heterogeneous systems has been brilliantly proven by experiment and widely used in studies focusing on surface phenomena, powder metallurgy processes, compatibility of materials, soldering, etc. The physicochemical constants for simple and complex substances derived from analysis of the phase diagrams and thermodynamic properties of metal, metallic, and semiconductor systems have been included into handbooks and are an important, fundamental component of modern materials science. Eremenko’s scientific ideas and scientific areas are further elaborated by his school of physical chemists.
Keywords: physical chemistry of inorganic materials; scientific school of physical chemists; phase diagram; thermodynamics of metal systems

Phase equilibria in the Ti-Si-B-C quaternary system as a basis for developing new ceramic materials by T. Ya. Velikanova; M. A. Turchanin; K. Ye. Korniyenko; A. A. Bondar; P. G. Agraval; V. V. Kartuzov (385-396).
Using the CALPHAD method, a thermodynamic model of the Ti-Si-B-C quaternary system is developed for the first time. Based on calculations of phase equilibria, a way for tetrahedration of this system is proposed. Fragments of the phase diagrams that have not been studied previously are calculated for the boundary ternary systems, with calculations for Si-B-C being performed for the first time. It is concluded that there is no quasiternary eutectic with participation of ZrB2, B4C, and SiC compounds in the Ti-Si-B-C system. It is shown that additions of titanium carbide to the ZrB2 + B4C + SiC mixture should lead to reactions resulting in solid-state formation of graphite (for example, during sintering or hot pressing) or its crystallization as a primary phase during separation from the melt, in a wide range of compositions. It should be taken into account in development of materials from these refractory compounds.
Keywords: phase diagram; thermodynamic model; tetrahedration; CALPHAD; quasiternary eutectic

Structure and properties of titanium-aluminum alloys doped with niobium and tantalum by A. A. Bondar; V. T. Witusiewicz; U. Hecht; M. V. Remez; V. M. Voblikov; N. I. Tsyganenko; Ya. I. Yevich; Yu. M. Podrezov; T. Ya. Velikanova (397-415).
Ternary as-cast Ti55−x Nb x Al45, Ti53−x Nb x Al47, Ti55−x Ta x Al45, and Ti53−x Ta x Al47 alloys, where x = 0, 4, 8, and 12, and Ti45Nb8−x Ta x Al47 and Ti47Nb8−x Ta x Al45 quaternary alloys, where x = 2, 4, and 6, melted in a laboratory arc furnace from pure components (~99.9 wt.%) are studied by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), differential thermal analysis (DTA), and compression testing. The alloys are found to consist mainly of a superfine lamellar structure of decomposition β → α → α + γ → α2 + γ and contain tiny islands of the γ phase and also the β phase at 12 at.% Nb or Ta. The CALPHAD approach is used to obtain a thermodynamic description of the Al − Nb − Ta − Ti system, which adequately reproduces the experimental data. The compression tests performed at room temperature show that the ternary alloys with 45 at.% Al are characterized by higher strength but lower plasticity than the alloys with 47 at.% Al. For the Ti46Nb8Al46 and Ti46Ta8Al46 alloys, high strength in the temperature range 20 – 800°C and a drop in plasticity to 2 – 4% at 200 – 600°C are revealed. Among the quaternary alloys examined, the best combination of strength and plasticity (σ02 = 1043 MPa, σult = 1612 MPa, εpl = 12.4%) is exhibited by the Ti47Nb4Ta4Al45 alloy.
Keywords: TiAl; lamellar structure; strength; plasticity; Al-Nb-Ta-Ti; CALPHAD; phase equilibria

Solidus surface of the Al–Ti–Pd system in the Al–AlPd–TiPd–Ti region by O. V. Zaikina; V. G. Khoruzha; K. Ye. Korniyenko; T. Ya. Velikanova (416-428).
The Al–Ti–Pd system has been studied by microstructural analysis, electron microprobe analysis, x-ray diffraction, and differential temperature analysis in the composition range 0–50 at.% Pd (Al–AlPd–TiPd–Ti partial system) at subsolidus temperatures. The solidus surface of the system is constructed for the first time. At subsolidus temperatures, there are two ternary compounds, τ1 (Al61Ti26Pd13, AuCu3 type) and τ3 (Al44Ti35Pd21, MgZn2 type), a continuous solid solution (β0 phase) between isostructural (CsCl type) high-temperature modifications of AlPd and TiPd equiatomic phases, and terminal solid solutions based on β-Ti and α-Ti and TiAl, Ti2Al5, TiAl3, and Al3Pd2 binary compounds and ε phase. The above-mentioned phases participate in 11 four-phase invariant equilibria involving the liquid phase and are represented by isothermal tie-line triangles in the temperature range between 630 and 1205°C.
Keywords: solidus surface; partial system; compound; isothermal plane

Projections of the liquidus and solidus surfaces of the Al2O3-HfO2-Gd2O3 phase diagram by S. M. Lakiza; Ya. S. Tishchenko; L. M. Lopato (429-441).
The phase equilibria during crystallization of alloys in the Al2O3-HfO2-Gd2O3 system are studied for the first time by physicochemical methods. The liquidus and solidus surfaces on the composition triangle as well as the melting diagram and crystallization scheme are constructed. No new ternary compounds or appreciable ternary solid solution regions are found in the system. The maximum temperature in the system is 2820°C and corresponds to the AL + F + GA (E3) three-phase eutectic. Since crystallization in the system finishes with eutectic reactions, it allows materials of the quasiternary system to combine the unique properties of HfO2-based T and F solid solutions and the properties of other phases in composite materials.
Keywords: ceramics; hafnia; alumina; gadolinia; phase diagram; eutectic materials

Projection of the solidus surface of the Fe–Mo–C system in the composition range 0–40 at.% C by T. A. Velikanova; M. V. Karpets; S. U. Artyukh; S. O. Balanetskii; V. M. Petyukh; P. G. Agraval; M. A. Turchanin (442-451).
The solidus projection of the Fe–Mo–C system in the composition range 0–40 at.% C is constructed for the first time using EDX, SEM, HT-DTA, HT-XRD, Pirani–Alterthum method, Vickers microhardness measurement, and CALPHAD modeling technique. It is established that there are M6C + (Mo2C) + (Mo), M6C + (Mo) + σ, M6C + σ + R, M6C + R + (α-Fe), M6C + (α-Fe) + (γ-Fe), M6C + (γ-Fe) + (Mo2C), and (γ-Fe) + (Mo2C) + Fe2MoC three-phase equilibria on the solidus surface, whose temperatures are decreasing from 1484 to 1100°C. It is shown that M6C carbon intermetallide is a linear phase in terms of carbon on the solidus surface with the homogeneity range Fe38.2–45.3Mo47.5–40.4C14.3 for metal components, within which the lattice parameters change from 1.1152(3) to 1.1072(8) nm. CALPHAD modeling shows that, besides the above-mentioned equilibria on the solidus surface, there are three-phase equilibria with participation of orthorhombic stabilized (Fe3C) cementite and monoclinic Fe2MoC molybdenum cementite: (γ-Fe) + (Fe3C) + C, (γ-Fe) + (Fe3C) + Fe2MoC, (Fe3C) + Fe2MoC + C, and Fe2MoC + (Mo2C) + C.
Keywords: Fe–Mo–C system; solidus surface projection.

Alloys of the Ti-Si-Sn system (titanium corner): phase equilibria, structure, and mechanical properties by I. D. Gorna; M. V. Bulanova; K. O. Valuiska; M. D. Bega; O. Yu. Koval’; A. V. Kotko; Ya. I. Evich; S. O. Firstov (452-461).
The joint effect of Si (5, 7, and 10 at.%) and Sn (3–15 at.%) on the structure and mechanical properties of Ti-rich as-cast Ti-Si-Sn alloys is studied. Hypoeutectic alloys with 10 at.% Si are shown to possess the highest level of properties due to a greater volume fraction of the (β*) + Ti5Si3. eutectic. It is shown that the dependence of strength and hardness of Ti-Si-Sn alloys on Sn content is nonmonotonic. The properties improve with increasing tin content to 7–10 at.% due to the solid-solution hardening mechanism. The elastic modulus and plasticity of all the alloys decrease with increasing Sn content. The elastic modulus for the alloys with 7–15 at.% Sn almost halves, decreasing to 65–60 GPa. The level of long-term hot hardness of the alloys at different temperatures depends on Si and Sn content. In general, tin additions increase heat resistance of all the alloys studied. The deviation from the dependence for individual alloys results from variation in their phase composition. The mechanical behavior of Ti-rich Ti-Si-Sn alloys depending on Sn content is determined by the formation of the intermetallic Ti3Sn phase.
Keywords: titanium alloys; doping; silicon; tin; eutectic; Ti5Si3 ; Ti3Sn; structure; mechanical properties

A study of the Al-Ni-Pt alloy system. Phase equilibria at 1100 and 1300°C by B. Grushko; D. Kapush; V. Konoval; V. Shemet (462-470).
The Al-Ni-Pt phase diagram studied in the whole compositional region at 1300 and 1100°C. The Al2Pt phase found to extend up to at least Al53Ni23Pt24 composition, separating the Al3Pt2 and Al3Ni2 phase fields. The Al-Ni β phase dissolves up to 38 at.% Pt at 1100°C, while at 1300°C the β region probably extends between the isostructural CsCl-type phases forming at the Al-Pt and Al-Ni terminals. The AlNi3 phase (γ′) extends up to 35 at.% Pt at practically constant Al concentration, while the high-temperature AlPt3 extends up to 15 at.% Ni. A ternary phase is formed in a wide compositional region between the regions of γ, γ′, β, and AlPt3. Apart from the AuCu-type structure of this ternary phase earlier reported, also its C-centered orthorhombic superstructure with a fourtimes larger unit cell revealed in the high-Al part of the compositional region.
Keywords: transition metal alloys and compounds; phase diagrams

Shape memory effect in ZrIr and Zr-Ir-Co alloys by Yu. V. Kudryavtsev; O. L. Semenova (471-478).
The paper examines the capability of ZrIr alloys, which undergo martensitic transformation at temperatures higher than 700°C, to develop thermomechanical properties accompanying the transformation. The ZrIr sample is found to recover its shape, after being deformed, during heating at a rate of 100°C/sec to temperatures higher than the martensitic transformation temperature. The Zr-Ir-Co ternary alloy shows the same property when heated at a rate of about 1–2°C/sec. The temperature dependence of resistivity of these alloys is considered.
Keywords: shape memory effect; martensitic transformation; zirconium; iridium; cobalt

High-temperature x-ray diffraction (HT-XRD) is used to study the evolution of phase states of arc-melted and spinning 51.9Fe11.1Mo26.3Cr10.7C (at.%) alloys in the temperature range 293-1573 K. It is established that α- and β-Mn-like phases (χ and π, respectively) and solid solutions based on α- and γ-Fe identified by HT-XRD in the temperature range 293–978 K are metastable. A diffusion-free method for mutual transformations of Mn-like phases in the temperature range 873–978 K is proposed. It is shown that increase in temperature in HT-XRD conditions stabilizes metastable Mn-like phases. It is experimentally established, for the first time, that a stable β-Mn-like phase exists near the solidus in the Fe–Mo–Cr–C system. It is concluded that congruent crystallization is a way of forming a stable π-phase of composition Fe5MoCr2.5C. It is found out that a stable χ-phase and equilibria with its participation, α + η + M23C6 + χ and χ + α + π + L, exist in the temperature range 1473–1523 K in the Fe–Mo–Cr–C system. It is determined that decomposition and/or mutual transformations of metastable Mn-like phases in 51.9Fe11.1Mo26.3Cr10.7C alloys occur at T ≈ 978 K, which is close to the temperature of α-Mn ⇔ β-Mn polymorphic transformation in pure manganese.
Keywords: Fe–Mo–Cr–C system; stable and metastable Mn-like phases; high-temperature x-ray diffraction; rapidly quenched alloys; Rietveld analysis

Effect of doping with p-elements (Al, Si, Ge, Sn) and zirconium on the structure and properties of titanium-boride eutectic alloys by N. I. Tsyganenko; A. A. Bondar; O. O. Bilous; L. V. Artyukh; S. Yu. Artyukh; V. M. Voblikov; D. G. Verbilo; T. Ya. Velikanova; S. O. Firstov (491-511).
The effect of silicon, germanium, tin (X), and aluminum on the structure, physicochemical and mechanical properties of Ti-B-X and Ti-Al-B (5 and 7.5 at.% B) ternary and Ti-Al-B-X and Ti-Zr-Al-B (9 at.% Al and 5 at.% B; 8.5 at.% Al and 7.5 at.% B) quaternary alloys is studied by metallography, scanning electron microscopy (SEM), X-ray diffraction, differential thermal analysis (DTA), microhardness measurements, Vickers hardness measurements (from room temperature to 900°C), bending tests (room temperature), and compression tests (from room temperature to 700°C). The alloys are melted in an arc furnace from pure materials. Doping with p-elements (Al, Si, Ge, and Sn) does not change the specific titanium-boride eutectic structure in the two-phase (Ti) + TiB field. The doping additions hardly change the chemical composition of the eutectic and only decrease the boron content by 1–2 at.%. The Al, Si, Ge, and Sn (p-elements) are not soluble in TiB titanium borides and completely concentrate in the metal matrix in two-phase (Ti) + TiB alloys. The temperature of incipient sharp softening is shown to be exclusively connected with the matrix composition. It is determined that p-elements increase the hardness and strength of titanium-boride eutectic alloys in the entire temperature range of interest and increase the temperature of incipient sharp softening from 500 to 600-650°C.
Keywords: titanium-matrix composites; eutectic alloys; boride reinforcement; solid-solution hardening; hot hardness; high-temperature strength

The composition and temperature dependences of thermodynamic functions of mixing in liquid alloys of copper with rare-earth metals and their variation in the series are considered. It is shown for majority of systems in the series that the most intensive interaction between components is observed in the composition range enriched with copper. The negative deviations of thermodynamic properties of mixing increase with decreasing temperature. The main features of the temperature–composition dependence are explained under the assumption that chemical short-range ordering like a chemical compound forms in the Cu–REM liquid alloys. The temperature–composition dependence of thermodynamic functions of mixing is described in the framework of the ideal associated solution model.
Keywords: copper; rare-earth metals; liquid binary alloys; thermodynamic activity; mixing enthalpy; excess heat capacity of mixing; associated solution model

Thermodynamic and thermochemical characteristics of holmium silicides by L. V. Goncharuk; V. R. Sidorko; N. P. Gorbachuk; M. V. Bulanova (528-537).
The Gibbs free energy, enthalpy, and entropy of formation of holmium silicides HoSi2–a (HoSi1.82), HoSi2–b (HoSi1.67), Ho3Si4, HoSi, HoSi1–x (HoSi0.98), Ho5Si4, and Ho5Si3 are determined by the electromotive force method. The heat capacity and enthalpy of HoSi1.67 in the temperature range 55–2007 K are measured with adiabatic and mixing calorimetry. The enthalpy and entropy of α → β polymorphic transformation and melting of HoSi1.67 are established. Temperature dependences of the heat capacity, enthalpy, and entropy of HoSi and Ho5Si3 are evaluated based on the behavior of heat capacity of mono- and lower silicides of rare-earth metals and their melting enthalpies in the series from La to Lu.
Keywords: Gibbs energy of formation; enthalpy of formation; entropy of formation; enthalpy; heat capacity; entropy; reduced Gibbs energy; holmium silicides

Thermodynamic properties of Al–Eu liquid alloys by M. I. Ivanov; M. O. Shevchenko; V. V. Berezutskii; V. G. Kudin; V. S. Sudavtsova (538-543).
The mixing enthalpies of Al–Eu liquid alloys are measured by the calorimetric method at 1300 to 1473 K. The thermodynamic properties of Al–Eu melts are calculated in the entire composition range using the ideal associated solution model. The thermodynamic activities of melt components show negative deviations from ideal behavior and the mixing enthalpies show significant exothermic effects. The minimum mixing enthalpy of Al–Eu melts is –23.0 ± 2.2 kJ/mole at xEu = 0.39.
Keywords: aluminum; europium; melt; calorimetry; enthalpy; activity

Physicochemical phenomena at interfaces by V. P. Krasovskii; V. I. Nizhenko; Yu. V. Naidich (544-551).
The thermodynamic theories for surface tension of solutions, Gibbs adsorption equation, surface stability condition, experimental data (composition dependences of surface tension and molar volumes of alloys), and thermodynamic activities of components by volume are used to determine the composition, integral and excess Gibbs energies of formation, and activities of components in the surface layer of Ti–Cu and Zr–Cu melts. The solutions formed in the surface layer and volume show a negative deviation from Raoult’s law. The copper adsorption curve for alloys has a slanting maximum. The composition of the surface layer differs little from that of the volume. The Gibbs energies of formation of the solution and their excess values are negative at all compositions of the surface layer. They are lower than thermodynamic values in the volume.
Keywords: Ti–Cu and Zr–Cu melts; capillary phenomena; surface energy; Gibbs energy of formation of the solution in the surface layer; composition of the surface layer

Wetting of hafnium dioxide by pure metals by A. V. Durov (552-556).
The wetting of hafnium dioxide ceramics by pure metals, such as copper, silver, gold, germanium, silicon, tin, iron, cobalt, nickel, palladium, platinum, aluminum, titanium, and zirconium, is studied. Evidence of HfO2–iron interaction is found: relatively good wetting and darkening of ceramics near the drop. It is also revealed that HfO2 keeps its stoichiometry when interacts with noble metals, platinum and palladium.
Keywords: wetting; contact interaction

The decrease in geological surveys in Ukraine complicates field tests of experimental batches of diamond bits produced using advanced scientific developments. The strength of samples that model an impregnated layer of diamond bits both in terms of their composition and production method has been tested in laboratory. The process for producing the samples is similar to the vacuum impregnation technology developed previously for crown bits. The performance of these crown bits during granite boring is also modeled. The experimental results are used to evaluate the strength and performances of the impregnated diamond layer and to draw a conclusion that the improvement of diamond crown bits is a promising area.
Keywords: adhesion; diamond; strength; wear resistance; diamond layer; crown bit

Interaction of 25% chromium steel with boron powder by V. I. Dybkov; V. R. Sidorko; V. G. Khoruzha; A. V. Samelyuk; L. V. Goncharuk (564-571).
Thermochemical treatment of industrial chromium steel (15Kh25T–25% Cr) in amorphous boron powder in the temperature range 850–950°C and reaction times up to 43200 sec (12 h) results in the formation of two boride layers at the steel–boron interface. The microstructure of the outer layer bordering the boron phase consists of elongated crystals of the (Fe,Cr)B and (Cr,Fe)B compounds, while that of the inner layer adjacent to the steel base consists of elongated crystals of the (Fe,Cr)2B and (Cr,Fe)2B compounds. Both layers reveal a pronounced texture. Their diffusional growth kinetics is close to parabolic x 2 = 2k 1 t, where x is the total thickness of both layers (m), k 1 is the layer growth-rate constant (m2 ∙ sec–1), and t is time (sec). The temperature dependence of the growth-rate constant of boride layers on the steel surface is described by a relation of the Arrhenius type k 1 = 1.72 ∙ 10–8 exp (–137.1 kJ · mole–1/RT). Microhardness values are 17.8 GPa for the outer layer, 15.9 GPa for the inner layer, and 1.70 GPa for the steel base. The dry abrasive wear resistance of borided steel samples is more than 250 times greater than that of non-borided ones.
Keywords: thermochemical treatment; chromium steel (15Kh25T–25% Cr); amorphous boron powder; boride layers; microstructure; growth kinetics; microhardness; abrasive wear resistance