Room-temperature deformation behavior of directionally solidified multiphase Ni−Fe−Al alloys

Directionally solidified (DS) β+(γ+γ′) Ni−Fe−Al alloys have been used to investigate the effect of a ductile second phase on the room-temperature mechanical behavior of a brittle 〈001〉-oriented β (B2) phase. The ductile phase in the composite consisted of a fine distribution of ordered γ′ precipitates in a γ (fcc) matrix. Three microstructures were studied: 100 pct lamellar/rod, lamellar+proeutectic β, and discontinuous γ. The β matrix in the latter two microstructures contained fine-scale bcc precipitates formed due to spinodal decomposition. Room-temperature tensile ductilities as high as 12 pct and fracture toughness (K _Q) of 30.4 MPa were observed in the 100 pct lamellar/rod microstructure. Observations of slip traces and dislocation substructures indicated that a substantial portion of the ductility was a result of slip transfer from the ductile phase to the brittle matrix. This slip transfer was facilitated by the Kurdjumov-Sachs (KS) orientation relationship between the two phases and the strong interphase interface which showed no decohesion during deformation. In microstructures which show higher values of tensile ductility and fracture toughness, 〈100〉 slip was seen in the β phase, whereas 〈111〉 slip was seen in the β phase in the microstructure which showed limited ductility. The high ductility and toughness are explained in terms of increased mobile dislocation density afforded by interface constraint. The effect of extrinsic toughening mechanisms on enhancing the ductility or toughness is secondary to that of slip transfer. A. MISRA, formerly Graduate Student, Department of Materials Science and Engineering, University of Michigan is Research Associate     

Effect of TiO2 on equilibrium phase sinter at oxygen partial pressure of 5×10−3 atm

Abstract

The effect of TiO₂ content on the phase compositions of sinter was conducted under reaction equilibrium at oxygen partial pressure of 5×10^?3 atm. The results showed that TiO₂ mainly existed in the phase of perovskite. With the increase in TiO₂ content, the content of secondary hematite phase increased and the ratio of hematite and magnetite in the sinter phase decreased. Meanwhile, the ratio of perovskite and Ca₂SiO₄ increased and the increased level of perovskite was larger than that of the Ca₂SiO₄ phase. The volume fraction of the phase silico-ferrite of calcia and alumina decreased from 44·9 to 41·5%, and the chemical formula of silico-ferrite of calcia and alumina changed from 4·7CaO.9·2Fe₂O₃.Al₂O₃.2·3SiO₂ to 1·6CaO.4·9Fe₂O₃.Al₂O₃.1·8SiO₂ when the percentage of TiO₂ was from 0 to 12 mass-% in the sinter.     

Structure and properties of 10Γ2ΦБ steel after hot plastic deformation

Recrystallization in 10Γ2ΦgB steel (strength class K60) is investigated. The influence of key parameters of two-stage thermomechanical treatment on the ferrite grain size and the work of impact is shown. Thermomechanical treatment of 10Γ2ΦgB steel intended to improve the strength and viscoplastic properties is tested industrially.     

Stability of hume-rothery phases in Cu−Zn alloys at pressures up to 50 GPa

The crystal structure of the γ-brass phase Cu₅Zn₈ is confirmed with single-crystal X-ray diffraction and a charge-coupled device (CCD) detector to be cubic with 52 atoms in the unit cell, space group , and the refined atomic positions are in good agreement with previously reported data. The structural behavior of α-(fcc), β-brass (cI52) phases of the Cu−Zn alloy system has been studied under pressure using diamond anvil cells and powder X-ray diffraction with synchrotron radiation. The appearance of additional peaks in the diffraction patterns of α- and β-phases indicates the beginning of transitions to new phases at 17 and 37 GPa, respectively. The complex cubic γ-brass phase (52 atoms in the unit cell, space group is observed to be stable up to at least 50 GPa. The bulk modulus K ₀ was determined as 140(4) GPa for α-, 139(5) for β-, and 121(2) for γ-phase assuming K ₀ ^′ =4. The structural stability of brass phases of the Cu−Zn system under pressure is discussed in terms of the Hume-Rothery mechanism. O. DEGTYAREVA, Post-doctoral Research Associate, formerly with the Geophysical Laboratory, Carnegie Institution of Washington This article is based on a presentation made in the symposium entitled “Fourth International Alloy Conference,” which occurred in Kos, Greece, from June 26 to July 1, 2005, and was sponsored by Engineering Conferences International (ECI) and co-sponsored by Lawrence Livermore National Laboratory and Naval Research Laboratory, United Kingdom.     

Mechanical behavior of Al−Li−SiC composites: Part I. Microstructure and tensile deformation

The microstructure and tensile properties of an 8090 Al−Li alloy reinforced with 15 vol pet SiC particles were investigated, together with those of the unreinforced alloy processed following the same route. Two different heat treatments (naturally aged at ambient temperature and artificially aged at elevated temperature to the peak strength) were chosen because they lead to very different behaviors. Special emphasis was given to the analysis of the differences and similarities in the microstructure and in the deformation and failure mechanisms between the composite and the unreinforced alloy. It was found that the dispersion of the SiC particles restrained the formation of elongated grains during extrusion and inhibited the precipitation of Al₃Li at ambient temperature. The deformation processes in the peak-aged materials were controlled by the S′ precipitates, which acted as barriers for dislocation motion and homogenized the slip. Homogeneous slip was also observed in the naturally aged composite, but not in the unreinforced alloy, where plastic deformation was concentrated in slip bands. The most notorious differences between the alloy and the composite were found in the fracture mechanisms. The naturally aged unreinforced alloy failed by transgranular shear, while the failure of the peak-aged alloy was induced by grain-boundary fracture. The fracture of the composite in both tempers was, however, precipitated by the progressive fracture of the SiC reinforcements during deformation, which led to the early failure at the onset of plastic instability.     

Thermodynamic properties of Na2O-SiO2-CaO melts at 1000 to 1100 °C

The thermodynamic properties of Na₂O-SiO₂ and Na₂O-SiO₂-CaO melts have been measured using the galvanic cell Activities of Na₂O were calculated from the reversible emf of the cell. This is possible because the activity of Na₂O in the Na₂O-WO₃ liquid is known from previous work. Data for the binary Na₂O-SiO₂ system were obtained between 1000 and 1100 °C and for compositions ranging from 25 wt pct to 40 wt pct Na₂O. At 1050 °C, Log varied from approximately 10.2 at 25 wt pct Na₂O to approximately −8.3 at 40 wt pct Na₂O, the dependence with respect to composition being nearly linear. The Gibbs-Duhem equation was used to calculate the activities of SiO₂(s), and the integral mixing properties,G ^M, H^M, andS ^M, were derived. At the di-silicate composition,G ^M = −83 kJ/mol,H ^M = −41 kJ mol andS ^M = 33 J/mol K at 1000 °C. (Standard states are pure, liquid Na₂O and pure, solid tridymite.) The activity data are interpreted in terms of the polymeric nature of silicate melts. Activities of Na₂O in the Na₂O-CaO-SiO₂ system were measured for the 25, 30 and 35 wt pct Na₂O binary compositions with up to 10 wt pct CaO added. The addition of CaO caused an increase in the activity of Na₂O at constant . The experimental data agree well with the behavior predicted by Richardson’s ternary mixing model.     

Mechanical behavior of Al−Li/SiC composites: Part II. Cyclic deformation

The deformation and failure mechanisms under cyclic deformation in an 8090 Al−Li alloy reinforced with 15 vol pct SiC particles were studied and compared to those of the unreinforced alloy. The materials were tested under fully reversed cyclic deformation in the peak-aged and naturally aged conditions to obtain the cyclic response and the cyclic stress-strain curve. The peak-aged materials remained stable or showed slight cyclic softening, and the deformation mechanisms were not modified by the presence of the ceramic reinforcements: dislocations were trapped by the S′ precipitates and the stable response was produced by the mobile dislocations shuttling between the precipitates to accommodate the plastic strain without further hardening. The naturally aged materials exhibited cyclic hardening until failure, which was attributed to the interactions among dislocations. Strain localization and slip-band formation were observed in the naturally aged alloy at high cyclic strain amplitudes, whereas the corresponding composite presented homogeneous deformation. Fracture was initiated by grain-boundary delamination in the unreinforced materials, while progressive reinforcement fracture under cyclic deformation was the main damage mechanism in the composites. The influence of these deformation and damage processes in low-cycle fatigue life is discussed.     

Lattice correspondence and fivefold twins of the orthorhombic (2/1, 1/1) and (1/0, 2/1) approximants in a Ga−Fe−Cu−Si alloy

In the rapidly solidified and annealed Ga₄₆Fe₂₃Cu₂₃Si₈ alloy, the base-centered orthorhombic (2/1, 1/1) and (1/0, 2/1) approximants of the decagonal quasicrystal, with lattice parameters of a=2.00 nm, b=1.25 nm, and c=1.40 nm and a=0.76 nm, b=1.25 nm, and c=2.40 nm, respectively, were found to coexist with a definite lattice correspondence relationship. At the interphase boundary, their {101} planes and the 〈101〉 directions in these planes coincide. There are four possible types of lattice correspondences which have been confirmed by electron diffraction patterns as well as by high-resolution electron microscopy (HREM) images. Moreover, such lattice correspondence relationships can be accounted for by the structural subunits with angles of n×72 deg in these two orthorhombic approximants: flattened hexagons in the (1/0, 2/1) approximant, and octagons called “crown” subunits in the (2/1, 1/1) approximant. Various tilings of the crown subunits are discussed. In addition, fivefold rotational twins occur abundantly in both of these approximants and intergrowth between them is common. This can also be explained by their respective characteristic structural subunits. S.P. GE, formerly Graduate Student, and K.H. KUO, Professor, Department of Materials Physics, University of Science and Technology Beijing, 100083 Beijing, China     

A mass-spectrometric study of the thermodynamics of the Fe−Cu and Fe−Cu−C(sat) systems at 1600°C

The Knudsen cell-mass spectrometer combination has been used to study the Fe?Cu and Fe?Cu?C_(sat) alloys at 1600°C. Activity coefficients in the Fe?Cu system are closely represented by the equations $$\begin{gathered} \ln \gamma _{Fe} = 1.86N_{Cu}^2 + 0.03, (0< N_{Fe}< 0.7) \hfill \\ \ln \gamma _{Cu} = 2.25N_{Fe}^2 - 0.19, (0.7< N_{Fe}< 1.0) \hfill \\ \end{gathered} $$ with an uncertainty in the quadratic terms of about 5 pct. For the iron-rich carbon-saturated alloys, the activity coefficient of copper is given by the equation $$\ln \gamma _{Cu} = 2.45(N'_{Fe} )^2 + 0.3N'_{Fe} + 0.03, (0< N'$$ to within an uncertainty of about 10 pct. N _Fe ^′ represents the fraction N_Fe/(N_Fe+N_Cu), etc. The activity coefficient of iron in this region is found to be essentially constant at 0.69±0.05.     

Effect of microstructural degradation on acoustic emission during tensile deformation of 2·25Cr–1Mo steel

Abstract

In this paper a systematic study has been undertaken to correlate the microstructural variation with acoustic emission parameters during tensile deformation of 2·25Cr–1Mo steel. Tensile testing of normalised and thermally aged samples has been carried out at a strain rate of 6·66×10^?4 s^?1 with simultaneous monitoring of acoustic emission (AE) parameters. Results have shown that acoustic emission activities are higher for normalised condition and the same decreased with the severity of thermal aging. Higher acoustic emission activities in normalised condition have been attributed to the presence of fine coherent M₃C and Mo₂C precipitates, which strengthen the matrix as a result of precipitation hardening. The reduction in acoustic emission activities in thermally aged condition has been found to be due to spheroidisation and coarsening of carbide precipitates which result in an increase in inter particle spacing.

Dans cet article, on a entrepris une étude systématique afin de corréler la variation de microstructure aux paramètres d’émission acoustique lors de la déformation en traction de l’acier 2·25Cr–1Mo. On a effectué des essais de traction d’échantillons normalisés ou vieillis thermiquement, à une vitesse de déformation de 6·66×10^?4 s^?1, avec surveillance simultanée des paramètres d’émission acoustique (AE). Les résultats ont montré que l’activité d’émission acoustique était plus élevée pour la condition normalisée et que celle-ci diminuait avec la sévérité du vieillissement thermique. On a attribué l’activité d’émission acoustique plus élevée dans la condition normalisée à la présence de précipités fins cohérents M₃C et Mo₂C, qui renforcent la matrice, comme résultat du durcissement par précipitation. On a trouvé que la réduction de l’activité d’émission acoustique dans la condition de vieillissement thermique était due à la sphéroïdisation et au grossissement des précipités de carbure, ce qui a pour résultat une augmentation de l’espacement entre les particules.     

Density of Na2O-Li2O-SiO2-B2O3 Molten Slag at 1 803——1 873 K

The density of three kinds of molten slags was measured by modified sessile dropmethod at 1 803 1 873 K. The density of molten slag is found to decrease with increasing tem-perature. The temperature coefficients of Na2 O-Li2--SiO2 and Li2O-SiO2-B2O3 slag are smallerthan that of Na20-B2O3 slag. The molar volume of slags increases with increasing temperature.     

Effect of Heat Treatment in the Temperature Range 400−1300°C on the Properties of Nanocrystalline ZrO2−Y2O3−CeO2 Powders

Powder Metallurgy and Metal Ceramics - The properties of nanocrystalline powders of compositions (mol.%) 97 ZrO2–Y2O3, 95 ZrO2–3 Y2O3–2 CeO2, 92.5 ZrO2–2.5 Y2O3–5...     

Effect of the composition of sn1−xsbxo2 solid solutions on the sensitivity of semiconductor gas sensors

We have studied the effect of the composition of semiconductor material based on Sn_1–xSb_xO₂ solutions on the sensitivity of semiconductor gas sensors (the ratio of the conductivity of the sensitive element in the presence of gas to its conductivity in air). We have shown that the sensitivity of the sensors increases when the Sb concentration in the semiconductor decreases. We have established that sensors containing solid solutions with 0.001 × 0.01 have optimal sensitivity.Institute of Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 96–99, May-June, 1996. Original article submitted May 25, 1994.     

Thermodynamics of the Na2O−P2O5 system

The activity of Na₂O in the melts of the Na₂O?P₂O₅ system has been determined using a high temperature electrochemical cell with a Na₂O?WO₃ melt at the reference electrode and fused silica as the solid electrolyte as shown below. $$_{Na_2 O - WO_3 melt}^{Pt(s),O_2 (g)} \left| {_{fused silica}^{ Na^ + } } \right|_{Na_2 O - P_2 O_5 melt}^{O_2 (g), Pt(s)} $$ The thermodynamics of the Na₂O?P₂O₅ binary system in the composition range of 50 to 75 mole pet Na₂O has been studied. The activities of Na₂O and P₂O₅ in the melt have been carefully analyzed. The free energy of four sodium phosphates has been evaluated with the help of the phase diagram of this system. Based on this study, a solid-state phase transformation for the 3Na₂O·P₂O₅ compound has been suggested at a temperature below 1217 K. The entropy of the transformation is near zero. The enthalpy of transformation is estimated to be 101.51 kJ/mole 3Na₂O·P₂O₅.