A Thermoanalytical Study of Mixtures of Polyvinyl Alcohol with Succinic Acid after Plastic Deformation under High Pressure

Mixtures of polyvinyl alcohol and amber acid of different composition were subjected to plastic deformation under the pressure of 1.5 GPa at the equipment of the Bridgman-anvil type and the DSC method was used to study heat processes in nondeformed and deformed samples. It is shown that two processes occur simultaneously in PVA under heating: the endothermal process of decomposition of intermolecular bonds and mass decrease related to loss of adsorbed water. After plastic deformation, a decrease in the enthalpy of melting occurred in both components of the PVC–amber-acid mixtures. A low-temperature phase with T_melt 30–40° C lower than in the initial polymer was formed in the acid and a decrease in the relaxation process enthalpy was observed in the polymer.     

Solid-liquid phase equilibria in the Al-Fe-Si system at 727 °C

Different experimental techniques were combined to acquire better insight into the solid-liquid phase equilibria that tend to be established in the Al-Fe-Si ternary system at 727 °C under a pressure of 1 atm (101,350 Pa). Isothermal diffusion experiments followed by oil quenching were first carried out. The crystal nature, lattice parameters, morphology, and chemical composition of the different solid phases in equilibrium with the liquid were determined by x-ray diffraction, optical microscopy, scanning electron microscopy, and electron probe microanalysis. Points on the liquidus boundary were then positioned both directly by chemical analysis of liquid samples taken from solid-liquid mixtures equilibrated at 727 °C and indirectly by thermal analysis of Al-Si mixtures with controlled iron additions. On the one hand, it has been confirmed in agreement with currently accepted data that the compounds ϑAl₁₃Fe₄, αAl_7.4Fe₂Si (τ₅), and δAl₃FeSi₂ (τ₄) are in equilibrium at 727 °C with Al-Fe-Si liquids, the compositions of which have been refined. On the other hand, the authors have shown that the ternary compound γAl₃FeSi is in equilibrium at 727 °C with a ternary Al-Fe-Si liquid containing 10.5 to 16.5 at.% Si and 3.2 to 3.5 at. % Fe.     

Effect of temperature on the formation of a microstructure upon equal-channel angular pressing of the Al-Mg-Sc 1570 alloy

Nonequilibrium Ni(C) solid solutions supersaturated with carbon to 10.2 at % were synthesized by mechanochemical method. An analysis of diffraction patterns showed that the formation of Ni(C) solid solutions is accompanied by an increase in the probability of appearance of deformation stacking faults. When the carbon content in the initial Ni-C mixtures is above 20 at %, the fcc Ni(C) solid solution resulting from the mechanical synthesis transforms into the metastable Ni₃C nickel carbide with a hexagonal structure. The thermal stability of nonequilibrium Ni(C) solid solutions was determined. The solid solutions formed from the mixtures with carbon contents from 7 to 15 at % undergo partial decomposition accompanied by the carbide precipitation upon heating to 300°C. The decomposition of the metastable Ni₃C carbide starts at a temperature T _s ~ 464.8°C; the thermal effect is —ΔH=10–13 kJ/mol. The effective radius of carbon atoms in the Ni(C) solid solutions was determined; it is equal to Rc _eff=0.061 nm.     

Plasma-chemical polymerization in CH<Subscript>4</Subscript>-based mixtures containing various amounts of rare gases

For constant-current glow discharge in Ar + Ne + CH₄ mixtures in a pressure range of 13–250 Pa and a discharge current range of 5–100 mA, the following characteristics were determined: gas temperature; longitudinal electric field intensity; radiation line intensities of Ne (3p → 3s) and Ar (4p → 4s) transitions; intensities of H_α, H_β, and H_γ lines of Balmer series; concentrations of Ne, Ar, and H atoms in metastable and resonance states; concentration of atomic hydrogen; and growth rate of polymer films. The composition of the polymer films was analyzed with the use of infrared spectroscopy. Mathematical modeling of discharges under the selected conditions was carried out. The results of calculations were compared to the experimental data. The mechanism of processes that proceed in the glow discharge plasma is shown to depend strongly on the Ne-to-Ar concentration ratio, which results in the qualitative difference between the compositions of films that were grown at the same pressure and discharge current, as well as in the difference between the growth rates of the films.     

Phase equilibria and multiphase reaction diffusion in the Cr-C and Cr-N systems

The phase formation in the Cr-C and Cr-N systems was investigated using reaction diffusion couples. The carbides were prepared by reaction of chromium metal with graphite powder in the range 1143 to 1413 °C in argon atmosphere; the nitride samples by reaction of the metal with N₂ (≤31 bar) in the range 1155 to 1420 °C. While the carbide samples showed the three chromium carbide phases in form of dense diffusion layers between 1100 and 1400 °C, porosity occurred at temperatures above 1400 °C. The composition of the phase bands was measured by the means of electron probe microanalysis. For the Cr₂₃C₆ phase, a slightly higher C composition was found than given in the literature. In Cr-N diffusion couples both the δCrN_1−x and βCr₂N formed phase bands at T≥1150 °C. Because decomposition processes occurred upon cooling, quenching experiments were carried out in the range 1370 to 1420 °C at 31 bar N₂ to stabilize the phases. The EPMA investigations of the homogeneity ranges yielded a large increase of the homogeneity range for δCrN_1−x with increasing temperature. The nonmetal diffusion coefficients in all phases of both systems were calculated from layer growth and/or from concentration profiles. In δCrN_1−x the N diffusivity was found to be strongly dependent on the composition. The Vickers microhardnesses of the various phases were obtained by measuring the diffusion layers.     

Phase equilibria and multiphase reaction diffusion in the Cr-C and Cr-N systems

The phase formation in the Cr-C and Cr-N systems was investigated using reaction diffusion couples. The carbides were prepared by reaction of chromium metal with graphite powder in the range 1143 to 1413 °C in argon atmosphere; the nitride samples by reaction of the metal with N₂ (≤31 bar) in the range 1155 to 1420 °C. While the carbide samples showed the three chromium carbide phases in form of dense diffusion layers between 1100 and 1400 °C, porosity occurred at temperatures above 1400 °C. The composition of the phase bands was measured by the means of electron probe microanalysis. For the Cr₂₃C₆ phase, a slightly higher C composition was found than given in the literature. In Cr-N diffusion couples both the δCrN_1−x and βCr₂N formed phase bands at T≥1150 °C. Because decomposition processes occurred upon cooling, quenching experiments were carried out in the range 1370 to 1420 °C at 31 bar N₂ to stabilize the phases. The EPMA investigations of the homogeneity ranges yielded a large increase of the homogeneity range for δCrN_1−x with increasing temperature. The nonmetal diffusion coefficients in all phases of both systems were calculated from layer growth and/or from concentration profiles. In δCrN_1−x the N diffusivity was found to be strongly dependent on the composition. The Vickers microhardnesses of the various phases were obtained by measuring the diffusion layers.     

A calorimetric study of the process of formation of a supramolecular high-density polyethylene structure in mixtures with different oxides after plastic deformation under high pressure

Mixtures of ultrahigh-molecular-weight polyethylene with 95 wt % oxides of different elements were subjected to plastic deformation under the pressure of 1 GPa at a high pressure device of the Bridgman anvil type and thermal effects were studied using the DSC technique. Thermograms contained exothermic peaks with a maximum at 50–90°C related to cold crystallization of the polymer. The process of polymer fusion was described by two peaks with the maximums at T ₁ = 125–128°C and T ₂ = 136–139°C. The low-temperature peak was related to fusion of a structure with high amounts of defects formed on the oxide surface.     

Effect of the austenite stability on the fracture mode and mechanical properties of aging nonmagnetic alloys after different strengthening treatments

Aging austenitic alloys with a stable (N26Kh5T3; M _s < −196°C) and metastable (N25Kh2T3; M _s = −130°C) austenite have been investigated after employing different methods of heat and thermomechanical treatments, namely, (1) aging at a temperature T _a = 600°C (A); (2) strengthening using phase-transformation-induced hardening (“phase naklep” (PN)) and subsequent aging at T _a = 600°C (PN + A); (3) deformation to 30% (D) at T _d = 600°C after preliminary aging at the same temperature (A + D); and (4) PN + A + D. In this case, the alloy with stable austenite has not been strengthened by phase naklep. Structure, fracture mode, ultimate strength, yield strength, relative reduction of area, and relative elongation have been studied depending on the duration of aging τ_a upon these strengthening treatments. It has been established that the physicomechanical properties of the alloys depend not only on τ_a, but also on the testing temperature. It is shown that all above physicomechanical characteristics of the alloys under consideration are affected substantially by the austenite stability.     

Formation of high-density TiN/Ti<Subscript>5</Subscript>Si<Subscript>3</Subscript> ceramic composites using preceramic polymer

The formation, microstructure and properties of high-density TiN/Ti₅Si₃ ceramic composites created by the pyrolysis of preceramic polymer with filler were investigated. Methylpolysiloxane was mixed with TiH₂ as filler and ceramic composites prepared by pyrolysis at 1200°C to 1600°C under N₂, Ar and vacuum were studied. When a specimen with 70 vol.% TiH₂ was pyrolyzed up to 1600°C in a vacuum after a preheat treatment at 850°C in a N₂ atmosphere and subsequently heat-treated at 1600°C for 1 h under Ar at a pressure of 2 MPa, a ceramic composite with full density was obtained. The microstructure of the ceramic composite was composed of TiN and Ti₅Si₃ phases. Under specific pyrolysis conditions, a ceramic composite with a density of 99.2 TD%, a Vickers hardness of 18 GPa, a fracture toughness of 3.5 MPam^1/2, a flexural strength of 270 MPa and a electrical conductivity of 6200 ohm⁻¹·cm⁻¹ was obtained.     

Annealing-induced softening of copper and molybdenum for high strain rate deformation

The effect of annealing on the high strain rate deformation properties of copper and molybdenum was studied. Samples were extracted using spark erosion and were annealed under various conditions. High strain rate stress-strain curves at ∼700 s⁻¹ and 1500 s⁻¹ were measured using a split Hopkinson pressure bar. Recrystallization occurred for the copper and molybdenum at annealing temperatures of 300 °C and 1200 °C, respectively, and resulted in a significant softening of the samples compared to their unannealed state. Generally, copper and molybdenum are annealed at much higher temperatures and it is suggested that lower temperature annealing may provide cost savings during the manufacturing processes.     

Activation of thermal processes in mixtures of some vanadium compounds with LiOH as a result of plastic deformation under high pressure

V₂O₅, V₂O₃, HVO₃, and mixtures of these compounds with 15% LiOH were subjected to plastic deformation at a pressure of 2 GPa and room temperature on high-pressure testing machines of the type of Bridgman anvils. The investigation of the samples was performed using differential scanning calorimetry, thermogravimetry, and X-ray diffraction analysis. The presence of LiOH in the mixtures decreased the thermal stability of vanadium compounds. During plastic deformation the LiV₃O₈ phase was formed in mixtures, the amount of which increased with heating the samples to 200°C. It is assumed that the ions that form by treatment under pressure can affect the structure formation processes in mix samples.     

Effect of the austenite stability on the physicomechanical properties of invars strengthened by combined treatments

This work is devoted to the investigation of an N30K10T3 invar alloy with metastable austenite (martensite point M _s ≈ −80°C) and an N40K10T3 invar with stable austenite (M _s < −196°C). The Curie points of the alloys are θ_C ≈ 200 and 310°C, respectively. Effects of aging of preliminarily deformed invars on the hardness, thermal-expansion coefficient, stress-corrosion resistance, and coercive force have been studied. It has been demonstrated that these properties of quenched alloys can be affected by both deformation and decomposition of the supersaturated solid solution. In the metastable alloy, the coefficient of linear expansion depends on temperature and aging time; no such dependence is observed in the stable alloy.     

Tin-modified gold-based bulk metallic glasses

Tin was selected as a modifying element in low-gold-content (50 at.%) bulk metallic glasses (BMGs) aiming at developing alloys with cost-effective performance. New gold-based Au–Sn–Cu–Si alloys were fabricated by injection-casting into a copper mold. The as-cast BMG Au₅₀Sn₆Cu₂₆Si₁₈ with 18.6-karat gold and a diameter of 1 mm possessed a lower glass transition temperature (T _g) of 82°C (355 K), a lower liquid temperature of 330°C (603 K), and a super-cooled liquid region of 31°C. The viscosity range of this BMG Au₅₀Sn₆Cu₂₆Si₁₈ was from 10⁸ to 10⁹ Pa s measured at a low applied stress of 13 kPa. To compare the viscosity with different applied stresses, its viscosity clearly increased with applied stress below T _g but not so obvious above T _g. The low viscosity of this BMG Au₅₀Sn₆Cu₂₆Si₁₈ at around 102°C, which is very close to the boiling temperature of water (100°C), rendered easy thermal–mechanical deformation in a boiling water-bath by hand-pressing and tweezers-bending. Such a deformation capability in boiling water is beneficial to the further applications in various fields.     

The phase evolution and microstructural stability of an orthorhombic Ti-23Al-27Nb alloy

The phase evolution and microstructural stability were studied for an orthorhombic Ti-23Al-27Nb alloy. Monolithic sheet materials were produced through conventional thermomechanical processing techniques comprising nonisothermal forging and pack rolling. Phase evolution studies showed that, depending on the heat treatment schedule, this alloy may contain several constituent phases including: α₂ (ordered close-packed hexagonal D0₁₉ structure), B2 (ordered body-centered cubic, bcc), β (disordered bcc), and O (ordered orthorhombic based on Ti₂AlNb). Differential thermal analysis studies indicated that the B2 transus temperature was 1070 °C. Heat treatment and transmission electron microscopy studies showed that the α₂+B2 phase field extended between 1010 and 1070 °C. From 875 to 975 °C, a two-phase O+B2 field existed. Sandwiched between these two-phase regimes was a narrow three-phase α₂+B2+O field. Below 875°C, an O+β field existed. All heat treatments at or above 875°C, followed by quenching, resulted in equiaxed microstructures. However, below 875 °C, the B2 phase transformed into a mixture of O and bcc phases with lenticular morphologies. Cellular precipitation of O+β platelets at O/B2 and α₂/B2 grain boundaries occurred depending on solutionizing and aging temperatures, which is explained by the compositional gradient between the bcc phases.     

The phase evolution and microstructural stability of an orthorhombic Ti-23Al-27Nb alloy

The phase evolution and microstructural stability were studied for an orthorhombic Ti-23Al-27Nb alloy. Monolithic sheet materials were produced through conventional thermomechanical processing techniques comprising nonisothermal forging and pack rolling. Phase evolution studies showed that, depending on the heat treatment schedule, this alloy may contain several constituent phases including: α₂ (ordered close-packed hexagonal D0₁₉ structure), B2 (ordered body-centered cubic, bcc), β (disordered bcc), and O (ordered orthorhombic based on Ti₂AlNb). Differential thermal analysis studies indicated that the B2 transus temperature was 1070 °C. Heat treatment and transmission electron microscopy studies showed that the α₂+B2 phase field extended between 1010 and 1070 °C. From 875 to 975 °C, a two-phase O+B2 field existed. Sandwiched between these two-phase regimes was a narrow three-phase α₂+B2+O field. Below 875°C, an O+β field existed. All heat treatments at or above 875°C, followed by quenching, resulted in equiaxed microstructures. However, below 875 °C, the B2 phase transformed into a mixture of O and bcc phases with lenticular morphologies. Cellular precipitation of O+β platelets at O/B2 and α₂/B2 grain boundaries occurred depending on solutionizing and aging temperatures, which is explained by the compositional gradient between the bcc phases.     

Evaluation of the invariant reactions in the Ta-rich region of the Ta-B system

Invariant reactions in the Ta-rich side of the Ta-B system were evaluated. The alloys were arc melted from pure materials. Pellets prepared from powder mixtures of Ta and TaB were heat treated under vacuum at 1900 and 1950 °C. The microstructures of the alloys were characterized through scanning electron microscopy images and x-ray diffraction (XRD). The microstructural analyses confirmed the type of reactions occurring in Ta-rich region; however, the composition of the liquid phase should be altered: (a) L ↔ Ta_SS+Ta₂B from 23 to 18 at.% B and (b) L+TaB↔Ta₂B from 27 to 22.5 at.% B. The formation of Ta₃B₂ was confirmed as the understoichiometry of Ta₂B. The decomposition of Ta₂B occurs between 1900 and 1950 °C. The XRD data for alloys with composition between 34 and 50 at.% B indicate the existence of a new high-temperature phase.     

Kinetics of Failure Rate Accumulation and TiNi Shape Memory Effect Alloy Fracture Under Mechanical Cycling

Wire specimens, d = 0.1 mm, made of Ti-(50.6-50.8)at.%-Ni alloy were exposed to thermo-mechanical treatment (TMT), thus making the samples straight and providing them with high superelasticity (ε_se). It was established that the most effective method of TMT is annealing with deformation at 500 and 300 °C. The optimum mode of treatment was used in the research of mechanical fatigue of alloys with high superelastic properties. Two stages characterizing the alloy behavior under mechanical cycling were found out: failure accumulation and fracture. It was shown that the duration of the cycles is determined by the value of the preset deformation (σ_set) in relation to the deformation on the plateau-shaped area. The results of low-cycle fatigue of the alloys under investigation were processed by means of the method of least squares. The equations of prognosis of longetivity at the preset level of deformation are presented.     

A study of the functional properties of alloy Ti - 45% Ni - 10% Nb with wide hysteresis of the martensitic transformation

Conclusions 1. Shape-memory alloy Ti - 45% Ni - 10% Nb with a wide hysteresis of the martensitic transformation can be used for thermomechanical coupling of pipelines. Disassembled thermomechanical clutches can be stored at room temperature and assembled with heating to a temperature somewhat exceedingt _room; the joint can be easily disassembled by RSME under deep cooling. 2. Treatment of alloy Ti - 45% Ni - 10% Nb by the recommended method provides the following characteristics of shape recovery: a reversible deformation of high-temperature SME of up to 8%, a degree of shape recovery of up to 60–80%, a temperature range of shape recovery from + 30 to + 90°C, and a reversible deformation of the RSME of 1–2%. 3. The deformation that induces the SME in the considered alloy can be performed from −10 to −70°C at ε=10–12%; the thermomechanical clutches can be stored at a temperature of up to +30°C; the parts can be coupled with the help of a thermomechanical clutch in a temperature range from +30 to +100°C. The coupling is easily detachable after deep cooling due to the realization of the reversible SME. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 19–22, September, 2000.     

High-Temperature-Oxidation Behavior of Iron–Aluminide Diffusion Coatings

Aluminide diffusion coatings were oxidized in air under atmospheric pressure under isothermal and cyclic conditions. The high-temperature efficiency of the pack-aluminized alloys was tested by comparing their oxidation behavior in the temperature range 800–1080°C. The k _p values deduced from the parabolic plots of weight-gain curves showed that α-Al₂O₃ composed the major phase of the oxide scale on samples oxidized at T > 1000°C. For lower temperatures, transient-alumina phases were observed. The aluminide materials also exhibited excellent resistance to cyclic oxidation at 1000°C. The second aim of this study was to dope the aluminide compounds obtained by a pack-cementation process with yttria, which was introduced by metal-organic chemical-vapor deposition (MOCVD). The beneficial effect of the reactive-element-oxide coating is strongly dependent on its mode of introduction, since the oxidation resistance is drastically increased when the Y₂O₃ coating was applied prior to the aluminization process. When applied after the aluminization, the reactive element gave negative effects on the high-temperature oxidation behavior of the iron aluminides. The oxide morphologies, X-ray diffraction patterns and two-stage experiments helped to understand the oxide-scale-growth mechanisms.     

Improving mechanical properties of nextel 610TM- reinforced AI- 224 alloy through θ phase precipitation at the fiber/matrix interface: kinetics of the precipitation process

Earlier studies of Nextel 610 (seeded sol-gel-derived AI₂O₃ multifilament tow developed by 3M) rein-forced Al-224.2 composite panels manufactured by pressure infiltration casting revealed interface delamination as a result of precipitation of the equilibrium θ precipitate and preferential growth at fiber/matrix interface sites. As a result, strengths as high as 91% of rule of mixtures (ROM) were observed. 75 % ROM strengths were observed after extended heating at 350 °C and hencein situ coarsening of the interface θ precipitates. Transverse specimens displaying this still acceptable tensile strength exhibited values of 490 MPa (approaching that of wrought 2_xxx alloys). This combination of high axial and transverse strengths from material in the same condition represents a significant improvement in this class of materials. This process is termed “discontinuously coated interfaces” (DCI^TM). In the present study, the kinetics of the coarsening process were measured at 350 and 400 °C using a new algorithm for the quantitative metallography determinations of the particle distribution at the interface. The interfacial θ coarsening kinetics follows a classical t^1/4 rate law. However, the particle size distribution is contrary to the theoretical predictions. Axial flexure tests on materials subjected to heat treatments at 350 and 400 °C producing close particle sizes result in similar flexure strengths. Thus, it has been demonstrated that the precipitate size and hence distribution at the interface is the most important factor controlling the mechanical properties of the composite.