Powder Metallurgy and Metal Ceramics (v.56, #5-6)

Aluminum alloy 1050 strips are roll-bonded with interlayer Al2O3 particles. The effect of rolling parameters on the bond strength, such as the content of Al2O3 particles, plastic deformation, and rolling temperature are investigated by peel test. It is established that higher bond strength can be obtained by increasing the rolling temperature, reducing the thickness, and decreasing the alumina content. The peeling surface of samples versus alumina content is characterized by scanning electron microscopy.
Keywords: roll bonding; bond strength; fracture surface; aluminum; alumina

Mechanical Properties and Fracture Mechanisms of Commercially Pure Multilayer Iron Produced by Strip Joint Rolling by Yu. F. Lugovskoi; Yu. N. Podrezov; V. A. Nazarenko; D. G. Verbylo; O. Yu. Koval (245-252).
Multilayer materials (1.2–0.25 mm thick) are produced by sintering in a container at 850°C and cold rolling of ten-layer briquettes of commercially pure iron. It is shown that the tensile strength of the materials studied is proportional to the total true strain value by rolling and reaches 1400 MPa at percentage extension 1%. Endurance limit increases up to 670 MPa. With increasing strain degree by rolling, the structural elements inside layers reduce in size, when high interlayer strength between macro layers. The best correlation of endurance limit of materials with micro yield strength is observed, when 0.01% of residual strain.
Keywords: strength; ductility; fatigue; rolling; layers; iron

The paper describes the evolution of a nanoscale powder in the cyclic heat treatment process that induces first-order phase transition. Transformation α-Fe ↔ γ-Fe in the temperature cycling range 800 ↔ 1450 K is used as an example to obtain a thermal hysteresis (temperature difference between the forward and inverse transformations). The existence of a thermodynamic hysteresis is justified in conditions when the ergodic hypothesis is not valid for nanosystems, resulting in the difference between forward and inverse transformations α-Fe ↔ γ-Fe because of the difference in their energy barriers. The thermal hysteresis is determined by the superposition of size-dependent kinetic hysteresis and size-dependent thermodynamic hysteresis. Three different cases of size dependence of the hysteresis loop width for the volume content of the new phase are identified. A potential weak size effect or zero size effect in a wide nanosize range resulting from the compensation of kinetic and thermodynamic hystereses is justified for the first time. The correlations between the size of nanopowder particles, cycling rate, and hysteresis loop width for the volume content of the new phase exhibit logarithmic dependence.
Keywords: thermal cycling; nanoscale powder; iron polymorphic transition; size effect; thermodynamic hysteresis; kinetic hysteresis; loop width

Effect of Graphite Content on Mechanical Properties and Friction Coefficient of Reinforced Aluminum Composites by P. Sharma; S. Sharma; R. Kumar Garg; K. Paliwal; D. Khanduja; V. Dabra (264-272).
Aluminum matrix composites (AMCs) reinforced with different content (wt.%) of graphite (Gr) reinforcing particles are synthesized by stir casting technique. The fraction of reinforcing particles ranges from 5 to 15 wt.% at 5 wt.% intervals. Microstructures, density, porosity, hardness, tensile strength, and friction coefficient of fabricated particulate reinforced AMCs are studied. The scanning electron microscopy reveals a non-uniform distribution of reinforcing particles in the aluminum metal matrix. A non-uniform distribution of reinforcing particles is also confirmed by the elemental maps of C (Gr) present in particulate reinforced AMCs. The density of particulate reinforced AMCs decreases from 2.69 to 2.55 g/cm3, while the porosity increases from 0.37 to 2.45% with an increase in the fraction of reinforcing particles in the aluminum matrix from 0 to 15 wt.%, respectively. Both the hardness and ultimate tensile strength are reduced from 49.5 to 42 HV and 161.5 to 150 MPa, respectively, with a reduction in elongation from 8.6 to 6.5% with an increase in the volume fraction of reinforcing particles in the aluminum matrix from 0 to 15 wt.%, respectively. The average coefficient of friction reduced from 0.45 to 0.22 with an increase in the volume fraction of reinforcing particles in the aluminum matrix from 0 to 15 wt.%, respectively.
Keywords: aluminum matrix composites; stir casting; scanning electron microscope; graphite; tensile strength

The gas saturation of semi-finished titanium alloys produced from metal powder using the technique comprising cold pressing, vacuum sintering, and subsequent severe plastic deformation by twist extrusion is analyzed. The main sources are considered and the quantitative analysis of pollution of sintered alloys with nitrogen and oxygen impurities contained in the powder particles on their surface and in the pore spaces of the billet is conducted. It is established that the quality of the starting titanium powder has the biggest impact on the pollution of alloys. It is shown that the use of titanium powders with low content of impurities allows keeping the oxygen and nitrogen content of synthesized semi-finished products at the level meeting the requirements of the reference documentation for VT1-0 titanium and heat-resistant titanium alloys. It is shown that the share of impurities entering the synthesized alloy from (i) the oxides on the powder particle surface and (ii) the air filling the closed pore space of the billet is insignificant.
Keywords: powder metallurgy; titanium powder; severe plastic deformation; twist extrusion; impurity; oxygen; hydrogen; nitrogen; titanium oxide

The volume fraction of reinforcement and milling time are two important factors in fabricating aluminum metal matrix composites via powder metallurgy (P/M) techniques. In the present work, the effects of volume fraction of reinforcement and milling time on the microstructure, relative density, hardness, and compressive strength were studied. The Al7075 and SiC powders were mixed by a planetary ball mill for about 4 and 8 h, and Al7075–x vol.% SiC specimens (x = 4, 6, 8) were fabricated by a uniaxial cold press and sintered at 873 K (600°C) for 1 h. The crystallite size and morphology of the powder particles were analyzed with X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results showed that with increasing milling time and volume fraction of the reinforcement phase, the hardness and compressive strength increased. The SEM illustrates that the number of voids increases as SiC content increases, but their size decreases.
Keywords: Al7075; SiC particles; powder metallurgy; mechanical milling; compressive strength

Effect of Porosity on Strength and Electrical Conductivity of NiO–3.5YSZ Composite and Its Ni–3.5YSZ Cermet by I. O. Polishko; Y. M. Brodnikovskyi; D. M. Brodnikovskyi; B. D. Vasyliv; V. Y. Podhurska; S. M. Shevchenko; V. I. Chedryk; M. Andrzejczuk; O. D. Vasylyev (293-304).
The change in porosity of the Ni–3.5YSZ (ZrO2 stabilized with 3.5 mol.% Y2O3) composite, when produced, and the effect of porosity on the strength and electrical conductivity is studied. The porosity was provided by adding granular starch to the mixture of NiO and 3.5YSZ powders. The content of 18 vol.% pore-forming agent in the Ni–3.5YSZ cermet provides open porosity 47.1%, while its strength and electrical conductivity are 74.3 MPa and 0.93 · 106 S/m, respectively.
Keywords: ceramic fuel cell; substrate anode; NiO–YSZ composite; Ni–YSZ cermet; strength; electrical conductivity; pore-forming agent; granulation

High-Velocity Air Plasma Spraying of (Ti, Cr)C–32 wt.% Ni Clad Powder by Yu. S. Borisov; A. L. Borisova; M. V. Kolomytsev; O. P. Masyuchok; I. I. Timofeeva; M. A. Vasilkovskaya (305-315).
The influence of air plasma spraying (parameters such as plasma gun power, spraying distance, plasma gas flow, anode diameter) of (Ti, Cr)C–32 wt.% Ni clad powder on the characteristics of resultant coatings (structure, microhardness, porosity, phase composition) is studied. The experimental procedure is designed using the mathematical planning method. The experimental data are processed to derive regression equations, determining the quantitative dependence of average microhardness and stability of microhardness characteristics on spraying process parameters. It is found that plasma gun power and plasma gas flow have the greatest impact on microhardness of the coatings and ΔX/HVav parameter, which characterizes the reproducibility of coating properties. The spraying distance has hardly any influence on the properties studied within the test range (160–220 mm). The hardness of coatings produced from the (Ti, Cr)C–32 wt.% Ni clad powder (12.15–14.58 GPa) is higher than that of the coatings obtained by air plasma spraying of a mechanical mixture of 75 wt.% (Ti, Cr)C + 25 wt.% NiCr (5.3–12.6 GPa).
Keywords: cermets; double titanium–chromium carbide; clad powder; high-velocity air plasma spraying; properties of coatings; microhardness; experimental design

The results of tribological studies on Fe–Mn–C–B eutectic coatings alloyed with Si, Ni, and Cr are presented. The coatings are produced by gas metal arc welding with use of powder wires (2.4 mm in diameter). Multicriterion assessment is used to analyze the tribological properties of the coatings and determine the most wear-resistant one. This assessment involves first a search of Pareto optimum solutions and then compromise solutions with use of the Chebyshev norm. This approach allows choosing the coating that shows the highest abrasive wear resistance among the six eutectic materials under study at a specific load varying from 3 to 15 MPa.
Keywords: wear resistance; eutectic coatings; multicriterion analysis

The formalism of the associated solution model for ternary melts with both strongly interacting components and components exhibiting repulsion is described. A set of model parameters that adequately describe the thermodynamic properties of melts of three-component Cu–Fe–(Ti, Zr, Hf) systems and boundary two-component systems is established. The thermodynamic mixing functions of ternary melts are calculated in the entire range of compositions and over a wide range of temperatures. In most of the concentration triangle, the thermodynamic properties of melts are characterized by negative deviations from ideal behavior. The thermodynamic properties of melts adjacent to the copper–iron side of the concentration triangle are characterized by positive deviations from the Raoult law. The range of values and topology of the excess thermodynamic mixing functions of Cu–Fe–(Ti, Zr, Hf) melts are determined by pair interactions of the components.
Keywords: thermodynamic properties; liquid alloys; alloys of copper and iron with titanium; zirconium; and hafnium; associated solution model; amorphous alloys

Thermodynamic Properties of Binary Al–Nd Alloys by M. O. Shevchenko; V. S. Sudavtsova; V. G. Kudin; L. O. Romanova; M. I. Ivanov (333-354).
The mixing enthalpies of liquid alloys in the binary Al–Nd system are determined in the ranges 0 < xNd < 0.25 at 1500–1740 K, 0.4 < xNd < 0.64 at 1670–1740 K, and 0.64 < xNd < 1 at 1450–1500 K by isoperibol calorimetry. The melts of the binary Al–Nd system are characterized by significant negative mixing enthalpies: Δ H Al − Nd min = − 44.6 kJ / mol $$ varDelta {H}_{Al- Nd}^{min}=-44.6 kJ/ mol $$ at xNd = 0.34 and 1500 K (extrapolation to the overcooled melt region). Activities of components, entropies, Gibbs energies, and liquidus curve of the binary Al–Nd phase diagram are associated using the model of ideal associated solutions.
Keywords: binary Al–Nd system; mixing enthalpy; entropy; activities of components; Gibbs energy; liquidus; model of ideal associated solutions; isoperibol calorimetry

Simulating the Solidification of Boride–Boride Eutectics by V. V. Kartuzov; O. V. Bystrenko (355-361).
Computer simulations of structurization in boride–boride ceramics are performed using the standard version of phase-field theory. The simulations reproduce the main properties of eutectic structures observed in experiments, i.e., spatial segregation of components, structure formation from an overcooled melt, and complete decomposition of the system when relaxes toward thermodynamic equilibrium. The eutectic colonies formed in the process of directional solidification and the dependence of spatial parameter of the emerging structures on the solidification rate are reproduced as well. The simulations demonstrate that the ordered fibrous structures are formed only in a certain range of solidification rates.
Keywords: eutectic; boride ceramics; directional solidification; structure formation; phase-field theory