Transition from spin glass to paramagnetism in the magnetic properties of PrAu2Si2

It is unexpected that a spin-glass transition, which generally occurs only in system with some form of disorder, was observed in the ThCr2Si2-type compound PrAu2Si2 at a temperature of 3 K. This puzzling phenomenon was later explained based on a novel dynamic frustration model that does not involve static disorder. We present the results of re-verification of the reported spin-glass behaviors by measuring the physical properties of three polycrystalline PrAu2Si2 samples annealed under different conditions. Indeed, in the sample annealed at 827 ◦C for one week, a spin-glass transition does occur at a temperature of T f~2.8 K as that reported previously in the literature. However, it is newly found that the spin-glass effect is actually more pronounced in the as-cast sample, and almost completely disappears in the well-annealed (at 850 ◦C for 4 weeks) sample. The annealing effect observed in PrAu2Si2, that is, spin glass to paramagnetism transition is discussed by comparing with earlier results reported on the same system and other isomorphic compounds.

Microstructure Evolution of AS41 Magnesium Alloy in ECAP

ECAP is a continuous multi-pass extrusion process that enables the specimen to obtain considerable cumulative deformation to refine the grain. In this paper, ECAP was used to deform AS41 magnesium alloy at 350°C, and the microstructure was observed and analyzed. The results show that the ECAP process has excellent effect on grain refinement and uniform microstructure. The grain size of AS41 decreases from 200μm to 20μm, and the microstructure is more uniform than that of as-cast sample. The reason is that the original grain is broken and refined under the action of shear force, and dynamic recrystallization occurs at the same time, resulting in small recrystallized grains. The Mg2Si particles were redistributed during ECAP and uniformly distributed in the crystal in rod shape.

INFLUENCE OF THE POURING DIRECTION ON THE QUALITY OF THE MELT ENTERING THE MOLD AND OBTAINING A GOOD STANDARD CAST IRON SAMPLE

The paper presents the results of computer simulation (on the example of grey cast iron of SCH 20 grade) of the influence of melt pouring direction on the degree of defects of shrinkage origin in the axial zone of the neck of a tensile sample when filling the mold cavity with a standard cast sample for optimal values of melt mass flow rate.

Kappa Carbide Precipitation in Duplex Fe-Al-Mn-Ni-C Low-Density Steel

The microstructural evolution of a Fe-Mn-Al-Ni-C low-density steel was studied. The lightweight low-density steels are a promising material for the transportation industry, due to their good mechanical properties and low density. The base microstructure of the investigated steel consists of ferrite and austenite. Thermo-Calc calculations showed the formation of an ordered BCC (body-centred cubic) B2 phase below 1181 °C and kappa carbides below 864 °C. The steel was produced in a vacuum induction furnace, cast into ingots and hot forged into bars. The forged bars were solution annealed and then isothermally annealed at 350, 450, 550, 650, 750, and 850 °C. The microstructure of the as-cast state, the hot forged state, solution annealed, and isothermally annealed were investigated by optical microscopy and scanning electron microscopy. The results showed the formation of kappa carbides and the ordered B2 phase. The kappa carbides appeared in the as-cast sample and at the grain boundaries of the isothermally annealed samples. At 550 °C, the kappa carbides began to form in the austenite phase and coarsened with increasing temperature.

RESULTS OF SHRINKAGE ORIGIN DEFECTS DISTRIBUTION COMPUTER SIMULATION IN STANDARD CAST SAMPLE VOLUME OF GREY CAST IRON

For cast iron grades SCH 15 and SCH 20, using the computer modeling system of casting processes in the environment of the LVMFlow software package, the possibility of predicting defects of shrinkage origin when obtaining a standard cast sample that determines the grade and quality of the castings of responsible purpose poured simultaneously with it is considered

Гомогенизационный отжиг и магнитные свойства образца фазы Лавеса GdNi-=SUB=-2-=/SUB=-

The paper shows the effect of homogenization annealing on the ferromagnet-paramagnet phase transition in the GdNi2 alloy. In the cast sample, at the Curie point, a temperature hysteresis is observed, which in an external magnetic field of 13.5 T can be at least 3 degrees. The data of scanning electron microscopy of the electropolished samples showed a decrease in the impurity phase of GdNi and practically no temperature hysteresis of the phase transition in the annealed GdNi2 sample. The value of the isothermal change entropy DSm = - 18.931 J/(kg*K) for an annealed sample of the GdNi2 alloy at the Curie point of 75 K in a magnetic field of 13.5 T.

Corrosion Behaviour of Passive Layer Growth by Controlling Additives of Nano-Metals-Phosphate to Pure Aluminum

This study investigates how microstructure and chemistry effects by Nano-Metal-Phosphate and the kinetics of growth passive layer and passivity breakdown. Additionally, the passive layer germination behavior on aluminum alloy 1050 with anticorrosive properties. The passive layer is an alloying method which allows an aluminum oxide to germinate. Morphologically and structurally, the aluminum oxide films were characterized using microscopy analyzes and XRD analysis. Results indicated that the reinforcements are well distributed and the grin size is downy. Corrosion behavior tested by Cyclic polarization exam and done at room temperature in (3.5 per cent NaCl) solution. The reinforcement increased the hardness for processed aluminum from Hv81.1 to HV=120.492 as castings. The parameter Nano-Metal-Phosphate has attenuated the current density of corrosion (7.15μA / cm2) compared to the as-cast sample results.

Effect of Heat Treatments on the Microstructural Evolution of a Single Crystal High-Entropy Superalloy

The effect of solution heat treatment as well as primary and secondary aging treatment conditions on the microstructural evolution of a high-entropy superalloy was investigated. The as-cast sample shows coarsened γ′ precipitates and other extra phases at interdendrite region due to microsegregation. This microsegregation makes γ′ solvus unclear and decreases the solidus. After conducting the solution treatment determined in this study, primary aging conditions showing an aligned cubic γ′ phase at 1050 °C for 4 h and random spherical γ′ precipitates at 950 °C for 20 h in similar size were found. By using both samples, secondary aging conditions showing coarsened secondary γ′ precipitates and γ particles inside the γ′ precipitates at 800 °C for 20 h and fine secondary γ′ precipitates at 850 and 870 °C for 20 h were found.

INDENTATION SIZE EFFECT IN HIGH PRESSURE TORSION PROCESSED HIGH ENTROPY ALLOY

High entropy alloy HfNbTaTiZr in as cast conditions and after high pressure torsion straining was characterized by nanoindentation. The length-scale dependent material response (indentation size effect) was characterized by indentation at various indentation depths. Hardness dependence on the characteristic length (depth of penetration) indicated decomposition of disordered high entropy alloy in the as cast sample, which probably occurred during slow cooling after casting. Subsequent severe plastic deformation by high pressure torsion led on the other hand to the short-range disorder of (originally partially decomposed as cast) structure. Further hardening was generated during high pressure torsion by the mechanisms of grain refinement and increasing dislocation density.

SHAPING OF DUCTILE CAST IRON DEDICATED FOR SLAG LADLE

In industrial conditions, ductile iron was prepared and two molds were made, in which a 600mm thick plate was formed. Filling system for one mold was placed vertically and for the second -horizontally. In order to obtain cooling curves, "S" type thermocouples have been placed in the mold. After cooling the casts, the samples from the fixing points of thermocouples were cut by the trepanning method. In the "vertical" cast sample shrinkage porosity was observed, while in the "horizontal" cast sample no porosity was detected. A significant difference in the recorded temperature in the center of the casts was discovered, indicating a defect in "vertical" cast.