Austenite phase formation in rapidly solidified Fe–Cr–Mn–C steels

Steels having compositions (wt%) 0.05–0.5C, 12.5–20Cr, 8–25Mn and 0–0.51N have been chill-block melt-spun to ribbons in order to investigate systematically, by X-ray diffractometry and electron microscopy, the effects of rapid solidification and of solute concentrations on the formation of the austenite phase. The austenite is most easily formed at (wt%) 16Cr–8Mn for 0.3C ribbons while ′-martensite or -martensite was observed at lower concentrations of Cr or Mn and -ferrite appeared for Cr >18 wt%. The volume fraction of austenite in the steel ribbons studied was found, by multiple regression analysis, to obey the equation

Full-size image

. Thus, the effect of Mn on γ formation followed a non-linear function, containing an interaction term including the Cr and Mn contents, and first- and second-order terms involving the Mn concentration. This indicates the ranges over which Mn is a γ-former or an -former. Iso-austenitic lines, constructed on the basis of this new equation, are nearly orthogonal to those in the Schaeffler diagram for Cr–Mn steels so that use of the latter for prediction of the austenite content in the present case would be inappropriate.     

Thermodynamic analysis of alloys Ti–Al, Ti–V, Al–V and Ti–Al–V

Thermodynamic analysis of three binary Ti-based alloys: Ti–Al, Ti–V, and Al–V, as well as ternary alloy Ti–Al–V, is shown in this paper. Thermodynamic analysis involved thermodynamic determination of activities, coefficient of activities, partial and integral values for enthalpies and Gibbs energies of mixing and excess energies at four different temperatures: 2000, 2073, 2200 and 2273 K, as well as calculated phase diagrams for the investigated binary and ternary systems. The FactSage is used for all thermodynamic calculations.     

Corrosion behavior of wrought Mg–6%Zn–1%Mn–XSi–YCa alloy

Different quantities of silicon and calcium were added to Mg–6%Zn–1%Mn alloy and its effect on corrosion behavior investigated. AC and DC polarization were carried out on the extruded rods, which contain different quantities of silicon and calcium. The phases present in the alloys have been identified by optical microscopy and TEM. Four different phases were found, i.e., intermetallics containing Si–Mn, Mg–Si, Mg–Zn, and Mg–Si–Ca phase. The corrosion behavior of the studied alloys were influenced by the amount and distribution of the second phases.     

Prediction of the formation enthalpies of Bi–Cd–Ga–In–Pb–Sn–Zn liquid alloys by binary infinitely dilute enthalpies

The molecular interaction volume model (MIVM) is used to predict the formation enthalpies of Bi–Cd–Ga–In–Sn–Zn and Bi–Cd–Ga–In–Pb–Sn–Zn liquid alloys, using only the infinitely dilute enthalpies of binary systems and the coordination numbers of the constituent elements in liquid alloys. In addition, the infinitely dilute enthalpies of binary system were obtained by Miedema's theory without requiring experimental data. The results are compared with the experimental data and calculated values using the Hoch–Arpshofen model (HAM), the results indicate that the model is reliable as well as being convenient.     

Influence of oxygen content on grain growth in Pr–Fe–B/Nd–Fe–B sintered magnets

An investigation into the effects of intermediate/variable final oxygen contents, in relation to the resultant microstructures and final magnetic properties of Pr–Fe–B- and Nd–Fe–B-type magnets in the as-sintered state has been undertaken. For low oxygen contents the Pr–Fe–B and Nd–Fe–B sintered magnets exhibited excessive grain growth on sintering. A high oxygen content resulted in the elimination of abnormal grain growth for both materials, on sintering, where the level of oxygen contamination appeared to affect the grain growth process, although not the grain growth mechanism. Differences, however, in grain growth behaviour for the Pr–Fe–B and Nd–Fe–B sintered magnets have been observed. A changing oxygen content resulted in a variable grain size and grain size distribution for both the Pr–Fe–B and Nd–Fe–B sintered magnets, resulting in a progressive change in intrinsic coercivity, with oxygen content.     

Crystallization processes and phase evolution in amorphous Fe–Pt–Nb–B alloys

Fe–Pt system is nowadays widely studied due to its potential applications as magnetic recording media. The hard magnetic FePt L1₀ phase has extremely promising potential as permanent magnet with high magnetocrystalline anisotropy. Of recent interest is also the developing of the hard magnetic phase from an amorphous precursor by appropriate crystallization processes. The melt-spun amorphous Fe₆₈Pt₁₃Nb₂B₁₇ alloy has been submitted to dynamical annealing and its phase transformation during the process has been monitored by differential scanning calorimetry and in situ energy-dispersive X-ray diffraction of the synchrotron radiation. In the first stage of crystallization, -Fe and cubic FePt phases are formed from the amorphous precursor. At around 600 °C superlattice Bragg reflections corresponding to tetragonal FePt are indexed in the XRD spectra and -Fe phase diminishes drastically. Finally, between 900 °C and 975 °C the tetragonal superlattice peaks disappear and cubic FePt phase is formed again. This reversible order–disorder transformation is accompanied by a strong uniaxial lattice expansion of the cubic FePt unit cell. The system show promising features for the co-existence of hard and soft exchange coupled magnetic phases crystallized from FePt-based amorphous precursors.     

Hydrogenation of Zr–Cu–Al–Ni–Pd metallic glasses by electrochemical means

Amorphous materials of Zr–Cu–Ni–Al systems have shown attractive electrochemical hydrogen absorption properties. A comparison between Zr₆₀Cu₁₅Al₁₀Ni₁₀Pd₅ and Zr₆₅Cu_17.5Al_7.5Ni₁₀ reveals that the palladium (Pd) increases the hydrogen absorption capacity. Charging melt-spun Zr₆₀Cu₁₅Al₁₀Ni₁₀Pd₅ ribbons electrochemically to different hydrogen-to-metal (H/M) ratios and following the effusion of hydrogen by thermal desorption analysis (TDA) reveals hydrogen desorption from interstitial sites of high energy levels at temperatures below 630 K. Zirconium hydrides are formed above 630 K. At higher temperatures partial desorption of hydrogen occurs. The thermal stability observed with differential scanning calorimetry (DSC) of the amorphous phase has been significantly deteriorated by hydrogen absorption. After hydrogenation, the crystallization behaviour shows suppression of the characteristic quasicrystalline phase and depends on the hydrogen content. Therefore, at low hydrogen concentrations H/M = 0.3, Cu and/or Cu-rich phases are primarily formed while at high hydrogen concentrations H/M ≥ 0.9 Zr-hydride phase(s) are mainly formed.     

In situ composite formation in the Ni–(Cu)–Ti–Zr–Si system

In situ composites were synthesized by arc melting Ni–(Cu)–Ti–Zr–Si alloys. The X-ray diffraction patterns of rapidly cooled cast strips show a primary Ni(Ti, Zr) B2 structure superimposed on the diffuse scattering maxima from the amorphous phase. Compression test results show that the composite starts to yield at 1200 MPa and fractures at 1900 MPa.     

The electrochemical behavior of Mg–9Al–0.5Zn,Mg–9Al–0.7Zn,and Mg–9Al–1.0Zn in a NaCl solution

In this study, the electrochemical behavior of Mg–9Al–0.5Zn, Mg–9Al–0.7Zn, and Mg–9Al–1.0Zn electrodes in a 0.7 mol L^?1 NaCl solution is evaluated by using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and potentiostatic oxidation. The utilization efficiencies of these materials are also determined. The results show that the Mg–9Al–1.0Zn alloy has the highest corrosion resistance and that Mg–9Al–0.5Zn displays the largest discharge current in the 0.7 mol L ^?1 NaCl solution at 25°C. In addition, the utilization efficiencies of the alloys decrease as follows: Mg–9Al–1.0Zn > Mg–9Al–0.7Zn > Mg–9Al–0.5Zn. This study illustrates that doping Zn into Mg‐Al electrodes increases the corrosion resistance and utilization efficiency but decreases the discharge activity of Mg–Al–Zn anodes when the Zn content is between 0.5% and 1.0%.     

Das Kunststoff–Stahl–Verbundrohrsystem

Composite pipes of steel and plastics The reasons for developing a complete pipe system combining the advantages of steel pipes with those of plastic pipes are surveyed. The advantages of such composite pipes compared with similar products are discussed, and attention is drawn to the technical and economic limitations. A special chapter deals with the comprehensiveness of this pipe system which comprises all the necessary components from the simple pipe to the pump; with its adaptability to the building site and to different working conditions; with the different types of joints and sizes; with the ease of handling the system, and with its safety. In conclusion, the price situation is surveyed, and a number of applications in the United States and in Europe are listed. Technical data are appended.     

Structural evolution during crystallization in phase separated Ti–Y–Al–Co metallic glass

Structural evolution during heat treatment of melt spun Ti₃₆Y₂₀Al₂₄Co₂₀ alloy was studied using differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. The as-melt spun Ti₃₆Y₂₀Al₂₄Co₂₀ specimen showed a hierarchical complex microstructure consisting of Ti-rich and Y-rich amorphous phases and crystallized with two-step process. Crystallization in the phase separated two phase mixture took place in a confined mode due to different thermal stability and complex microstructure, resulting in various nano-scaled microstructural formation ranging from fine distribution of crystalline particles in amorphous matrix to fine distribution of amorphous particles in crystalline matrix.     

Impedance spectroscopy studies of electroless Ni–P matrix,Ni–W–P,Ni–P–ZrO2, and Ni–W–P–ZrO2 coatings exposed to 3.5% NaCl solution

Ni–P matrix, ternary Ni–W–P and Ni–P–ZrO₂ coatings, and quaternary Ni–W–P–ZrO₂ coatings were deposited using electroless method from a glycine bath. Their corrosion resistance was evaluated by electrochemical impedance spectroscopy (EIS) for various immersion times in a 3.5% NaCl solution. From among the investigated coatings, the ternary Ni–W–P coatings show the highest resistance to corrosion in the first hour of exposure to the 3.5% NaCl medium. An addition of ZrO₂ adversely affects the performance of both the Ni–P coatings and the Ni–W–P coatings. For all the coatings, including the ones containing tungsten, a marked decrease in pore resistance (R_por) over time is observed. This means that their corrosion resistance and capacity to protect the substrate decline. On the other hand, after 24 h immersion in the 3.5% NaCl solution the Ni–W–P coating shows the highest low‐frequency impedance modulus (|Z|_{f = 0.01 Hz}). As regards corrosion resistance, the Ni–P coatings and the Ni–W–P coatings perform best.     

Magnetic anisotropy of Ho–Fe–Co–Cr intermetallic compounds

Starting with a Ho₃(Fe_1−xCo_x)_29−yCr_y, (x,y) = (0.6,4.5) and (0.8,5.5) nominal stoichiometry, a disordered variant of the hexagonal 2:17 phase (Th₂Ni₁₇-type, S.G. P6₃/mmc) occurs, since both the monoclinic 3:29 and the transition-metal-rich disordered Th₂Ni₁₇-type hexagonal compounds have the same rare earth to transition metal ratio, 1:9.7. The magnetic properties and the magnetocrystalline anisotropy of these compounds have been investigated. The anisotropy constant, K's, and the anisotropy field, μ₀H_A, values have been deduced from the magnetization curves measured on powder samples magnetically aligned in a rotating magnetic field. The compound with (x,y) = (0.8,5.5) shows a compensation point at about 55 K. The magnetic anisotropy of both compounds is that of easy-plane from room temperature to low temperatures down to 5 K.     

Growing ledge structures of AlN crystals in a Fe–Mn–Al–C alloy

The Fe–30.4Mn–8.7Al–1.0C (wt.%) alloy was nitridized at 1000 °C. The AlN formed into a Widmanstätten side-plate shape. The side-plate of the AlN is parallel to the basal plane of the HCP crystal. There are three possible growing riser planes; namely ()_AlN, ()_AlN, and ()_AlN planes. The angle for growing riser planes met on the (0 0 0 1) terraces is 120°.     

Phase transformations in the Zn–Cd–Sb system

Phase equilibria of the Cd–Sb–Zn system have been investigated by metallographic examinations, DSC, XRD and WDS measurements. At 250 °C, the ternary diagram shows two three-phase fields, (Zn)+(Cd)+Zn₄Sb₃ and (Cd)+ Zn₄Sb₃+(Zn,Cd)Sb. Continuous solid solution has been found between ZnSb and CdSb. Solubility of Cd in Sb₃Zn₄ was determined to be about 43 at.%. A variant of the reaction scheme is proposed for the Cd–Sb–Zn system to understand phase relations observed at 250 °C.     

H NMR spectra and echoes in Pd–H and Pd–Ag–H alloys

The paper presents the experimental results of rigid-lattice proton magnetic resonance spectra and second moments in Pd–H, Pd_0.90Ag_0.10–H, Pd_0.80Ag_0.20–H, Pd_0.75Ag_0.25–H, and Pd_0.65Ag_0.35–H alloys at T = 2.4 K in a wide hydrogen concentration range. Free induction decay (FID), solid and inhomogeneous echoes were detected and interpreted. The interpretation based on dipole–dipole interaction of homogeneously distributed proton spin system is satisfactory at high hydrogen concentration, but an inhomogeneous field of paramagnetic origin (most probably coming from Fe impurities) plays the dominant role at small hydrogen content. An unexpected correlation was found between the macroscopic magnetic susceptibility and the second moment coming from the inhomogeneous internal field.     

Hydrogen absorption properties of Li–Mg–N–H system

Isothermal hydrogen absorption properties of the ball milled mixture of 3Mg(NH₂)₂ and 8LiH after dehydrogenation at 200 °C under high vacuum were investigated at two different temperatures of 150 and 200 °C. The pressure–composition isotherm (PCT) curve at 200 °C revealed a two-plateaus-like behavior, while the PCT curve at 150 °C showed a single-plateau-like behavior. The hydrogenated phases were composed of LiH and Mg(NH₂)₂ under 9 MPa at 200 °C, while those were observed as mixed phases of LiH and LiNH₂ at 150 °C without any trace of Mg(NH₂)₂ in XRD measurements. These results indicate that there are two-step hydrogenation processes corresponding to high and low pressures at 200 °C, but the kinetics at 150 °C is too slow to proceed with the second hydrogenating step at high pressure region.     

Phase transformations in iron-rich Tb–Fe–Si alloys

RRhO₃ (R=rare earth except Ce and Pm) was prepared by a solid-state reaction, and its crystallographic, magnetic, and electric properties were investigated. RRhO₃ has an orthorhombic perovskite-type structure of the space group Pbnm. RRhO₃ shows Curie–Weiss paramagnetism above 5 K. On the other hand, EuRhO₃ shows antiferromagnetic behavior. The Rh³⁺ ion, which seems to be in the low-spin state, has a very small effective magnetic moment (P_eff=0.295 μ_B/ion). The P_eff value of the RRhO₃ compounds shows the same dependence on the number of 4f electrons as the gJ value of the rare-earth ions. The rare-earth ions make a major contribution to the magnetic moment of RRhO₃. The resistivity of all RRhO₃ shows an activation-type (or semiconductor-like) temperature dependence.     

Tetragonal phase in the Mg–Ni–Sn system

Complementary metallographic and crystallographic characterisations of the Mg-rich corner of the Mg–Ni–Sn system are presented. In particular the Mg₇₅Ni₁₅Sn₁₀ phase, previously reported by Arcondo et al. [Hyperfine Interact. 66 (1991) 359] has been identified as a tetragonal phase by transmission electron microscopy and X-ray diffraction studies. The influence of this new phase, called Y-phase, on the glass forming ability of alloys with nearby composition is discussed.