Structures and superparamagnetic properties of overaged Fe–Al–Mn–C alloys

Microstructures and superparamagnetic properties in aged-hardened Fe–9%Al–30%Mn– (x)C,Si alloys, resulting from overaging at a temperature of 823 K for 48 h to 313 days, have been investigated by transmission electron microscopy (TEM), X-ray diffraction patterns, and vibrating sample magnetometry (VSM). The results reveal that the precipitate κ-phase [(Fe,Mn)₃AlC] decomposition in this alloy, overaged at 823 K for one week, resulted from two separate mechanisms: (1) wetting of the antiphase boundary segment (APBs) of D0₃ [(Fe/Mn)₃Al] domains by the B2 [(Fe/Mn)Al] phase; and (2) precipitation of the B2 [(Fe/Mn)Al] phase within the domain. A superparamagnetic behaviour was discovered when the alloy was overaged at 823 K for ≈120–313 days. The super-soft magnetic property was mainly attributable to the ferromagnetic spinel-ordered (B2 [(Fe/Mn)Al]+D0₃ [(Fe/Mn)₃Al]) phases and ordered B2 with monoclinic ′Mn structures.     

Variables on the precipitation of an intermetallic phase for liquid phase sintered W–Mo–Ni–Fe heavy alloys

The concentration of Mo in the liquid phase of W–Mo–Ni–Fe heavy alloys during isothermal hold dictates the precipitation of an intermetallic phase during cooling. If the concentration of Mo atoms in the matrix phase exceeds an equilibrium value (between 8 and 9 at.%), Mo atoms have a strong tendency to precipitate along with W, Ni and Fe from the matrix phase onto the solid matrix phase interface during cooling. The coprecipitation of W, Mo, Ni, and Fe results in the formation of an intermetallic phase in the interface between the solid grains and the matrix phase, (W₄Mo₆)(Ni₇Fe₃), which possibly has the same structure as MoNi. This intermetallic phase is difficult to eliminate by a fast water-quench practice.     

A contribution to the Al–Pd–Mn phase diagram

A part of the Al–Pd–Mn phase diagram in the vicinity of the icosahedral phase was refined. Partial isothermal sections of 710, 850, 870 and 880°C are presented. The overall compositional range of the icosahedral phase was found to be between 5.8 and 10.5 at.% Mn and between 69.5 and 71.5 at.% Al at these temperatures. It shifts to lower Mn concentration at lower temperatures. It was confirmed that the phase usually designated Al₃Pd has a lower Al concentration in the binary alloys than that according to the formula. It extends to the ternary compositions up to about 5 at.% Mn. The increase of the Mn content results in an increase of the Al concentration of this phase.     

The microstructures and mechanical properties of cast Mg–Zn–Al–RE alloys

The microstructures and mechanical properties of cast Mg–Zn–Al–RE alloys with 4 wt.% RE and variable Zn and Al contents were investigated. The results show that the alloys mainly consist of α-Mg, Al₂REZn₂, Al₄RE and τ-Mg₃₂(Al,Zn)₄₉ phases, and a little amount of the β-Mg₁₇Al₁₂ phase will also be formed with certain Zn and Al contents. When increasing the Zn or Al content, the distribution of the Al₂REZn₂ and Al₄RE phases will be changed from cluster to dispersed, and the content of τ-Mg₃₂(Al,Zn)₄₉ phase increased gradually. The distribution of the Al₂REZn₂ and Al₄RE phases, and the content of β- or τ-phase are critical to the mechanical properties of Mg–Zn–Al–RE alloys. The Mg–6Zn–5Al–4RE alloy with cluster Al₂REZn₂ phase and low content of β-phase, exhibits the optimal mechanical properties, and the ultimate tensile strength, yield strength and elongation are 242 MPa, 140 MPa and 6.4% at room temperature, respectively.     

Thermodynamic properties of liquid glass-forming Ca–Mg alloys

The complex formation model was used to investigate the thermodynamic properties of liquid Ca–Mg glassy alloys. Our expressions reproduce the thermodynamic functions such as free energy of mixing, enthalpy of mixing, entropy of mixing and activity ratio. The study of long wavelength concentration–concentration fluctuations (S_CC(0)) provides structural information about liquid glass-forming Ca–Mg alloys. Chemical short range order parameter (₁) was obtained from S_CC(0) to quantify the degree of order. The study reveals that the formation of more than one type of complex may be related to the process of glass formation.     

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.     

A novel Al–Ti–B alloy for grain refining Al–Si foundry alloys

Al–Ti–B refiners with excess-Ti (Ti:B > 2.2) perform adequately for wrought aluminium alloys but they are not as efficient in the case of foundry alloys. Silicon, which is abundant in the latter, forms silicides with Ti and severely impairs the potency of TiB₂ and Al₃Ti particles. Hence, Al–Ti–B alloys with excess-B (Ti:B < 2.2) and binary Al–B alloys are favored to grain refine hypoeutectic Al–Si alloys. These grain refiners rely on the insoluble (Al,Ti)B₂ or AlB₂ particles for grain refinement, and thus do not enjoy the growth restriction provided by solute Ti. It would be very attractive to produce excess-B Al–Ti–B alloys which additionally contain Al₃Ti particles to maximize their grain refining efficiency for aluminium foundry alloys. A powder metallurgy process was employed to produce an experimental Al–3Ti–3B grain refiner which contains both the insoluble AlB₂ and the soluble Al₃Ti particles. Inoculation of a hypoeutectic Al–Si foundry alloy with this grain refiner has produced a fine equiaxed grain structure across the entire section of the test sample which was more or less retained for holding times up to 15 min.     

Softening behaviour of nanostructured Al–14 wt% Zn alloy during mechanical alloying

Al and Zn elemental powder mixtures were subjected to high-energy milling to produce Al–14 wt% Zn alloy. The milled powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness measurement. The Al and Zn grain sizes were estimated from broadening of XRD peaks using Williamson–Hall formula. The results showed that in early stage of milling the solubility of Zn in Al is extended compared to the equilibrium value which is accompanied by a decrease in lattice parameter of the Al matrix. However, after longer milling times, decomposition of Al(Zn) supersaturated solid solution appeared to occur leading to an increase in Al lattice parameter and also a decrease in hardness value of as-milled powder. The final product of milling includes both Al and Zn phases having a grain size of 40 nm and 20 nm, respectively.     

Response to annealing treatments of twin-roll cast thin Al–Fe–Si strips

The new generation twin-roll casters are able to cast strips down to 1 mm and offer a notable increase in the casting speed and caster productivity. The thin strips, however, experience profoundly different temperature and deformation gradients in the caster roll gap and may thus require different down stream processing cycles. An attempt was made in the present work to identify the structural features of the thin-cast AlFeSi strip and its response to high temperature annealing treatments. The deformation introduced to the thin AlFeSi strip in the caster roll gap was largely restored by dynamic processes before coiling, producing recrystallized surface layers. When annealed as-cast, the grain structure was rearranged by an ordinary growth process at the surface and via recrystallization in the interior. The entire process was retarded due to the precipitation reactions, particularly in the immediate vicinity of the surface where the supersaturation of the aluminium matrix was the highest and the boundary mobility was severely impaired. The final strip structure was a coarse one. The entire section of the thin strip underwent recrystallization when the thin strip was annealed after a rolling pass. While some improvement appeared to be possible in this practice, a heterogeneous through thickness structure with relatively coarser surface grains prevailed.     

Macrosegregation induced sedimentation in liquid phase sintered Ni–W alloys

In this study, liquid phase sintering of Ni–W alloys containing a low W solid volume fraction was conducted. A solid-plus-liquid (mushy) zone forms at the compact bottom. A liquid head above this zone demonstrates macrosegregation. With increasing sintering time, macrosegregation is reduced concurrent with a decrease in the volume fraction of W particles and mushy-zone sedimentation.     

Surface tension and mass density of liquid Cu–Ge alloys

We report a study on the mass density and surface tension of liquid Cu–Ge alloys in the temperature range between the liquidus line and 1373 K. The experiments have been carried out by means of the sessile-drop method. The temperature dependences of both properties are given in terms of linear relations for all alloys under investigation. Both, density and surface tension show remarkable deviations from linear mixing: The density is increased, and the surface tension reduced due to Ge acting as surfactant. The composition dependence of the surface tension is discussed in terms of a simple compound formation model which is well able to relate the results to previous findings on the short-range order of the alloys under investigation.     

Phase diagram of the Nb–Al–Si ternary system

A high-efficiency diffusion-multiple approach was employed to map the phase diagram of the Nb–Al–Si ternary system which is very valuable for the design of niobium silicide-based composites. These composites have high potential as a replacement for Ni-base superalloys for jet engine applications. Aluminum is an alloying element for these composites, thus the Nb–Al–Si phase diagram, especially solubility of Al in Nb₅Si₃, is important information for the composite design. An isothermal section at 1000 °C was constructed from the results obtained from a diffusion multiple using scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). A ternary phase Nb₃Si₅Al₂ was observed. The solubility data of Al in Nb₅Si₃ and NbSi₂ as well as Si solubility in Nb₃Al, Nb₂Al and NbAl₃ were obtained. The new isothermal section helps to judge the reliability of the existing literature results and to add new data to the Nb–Al–Si phase equilibria.     

TEM observations of a rapidly solidified Al–20 Sb alloy

In the present work, the microstructural characterization of a melt-spun Al–20 Sb alloy has been carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The phases present in the melt-spun Al–20 Sb alloy were determined to be -Al and AlSb, identical to those in the ingot-cast alloy. The microstructure of the melt-spun Al–20 Sb alloy is dominantly composed of primary AlSb dendrites embedded in the -Al matrix, different from that of the ingot-cast alloy composed of primary AlSb plates within an -Al/AlSb eutectic matrix. In addition, some areas comprise primary AlSb particles within the -Al matrix in the melt-spun alloy.     

Phase relations in the Al–Pr–Sb system at 773 K

The isothermal section of the phase diagram of the Al–Pr–Sb ternary system at 773 K over the whole concentration region has been investigated mainly by powder X-ray diffraction (XRD) with the aid of scanning electron microscopy (SEM). A new ternary compound Al₁₁Pr₂₄Sb₆₅ has been found.     

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°.     

Preparation of Ti–Al–Si alloys by reactive sintering

The isothermal section of the Dy–Co–Ti system at 500 °C has been investigated in the whole composition range by means of X-ray diffraction, thermal analysis, scanning electron microscopy and energy dispersive X-ray spectroscopy. The only ternary phase DyTi_xCo_12−x is of ThMn₁₂-type structure, space group I4/mmm, and shows a small homogeneity range of 1 ≤ x ≤ 1.6. The lattice parameters for DyTi_xCo_12−x with 1 ≤ x ≤ 1.56 are a = 0.8336(4)–0.8402(1) nm and c = 0.4691(3)–0.4727(1) nm. Along a constant Dy concentration, the solid solubilities of Ti in the compounds Dy₂Co₁₇, DyCo₃, DyCo₂ and Dy₃Co are about 2.0, 2.0, 3.0 and 4.0 at.%, respectively. The TiCo phase has a homogeneity range of 50–54 at.% Co at 500 °C and dissolves up to 2.0 at.% Dy.