Volume 112, Issue 9

The solidification microstructure evolution of Ni-25 at.% Cu alloys under different undercooling degrees were studied by the cladding method and cyclic superheating method. Two grain refinement phenomena were observed in the obtained undercooling. In the low undercooling condition, dendrite remelting is the main reason for grain refinement in the recalescence process, while in the high undercooling condition, the stress accumulated in the recalescence process leads to recrystallization in the later stage of recalescence. Under the condition of high undercooling, the solidification structure is composed of complete equiaxed grains with relatively uniform grain size, which indicates that grain boundary migration occurs during grain growth.

To determine the weldability of SUS445 ferritic stainless steel, two welding approaches, tungsten inert gas and fiber laser welding processes, were used and compared. After the welding processes, the microstructure, mechanical properties, and corrosion resistance of the welds were investigated. In the weld fusion zones of these two welding approaches, different morphologies of the grains were obtained. No obvious precipitation formed in these zones. In the heat affected zone of the tungsten inert gas welds, more volume fraction and larger grain sizes of the Laves phase and larger matrix grains were observed, which significantly affected its corrosion resistance and mechanical properties. However, in the heat affected zone of the fiber laser welds, only small amounts Laves phases and a relatively narrow matrix grain growth area were observed, which offers better corrosion resistance and mechanical properties.

This paper presents the results of research on material and microstructural effects in a hypoutectic Al–Mg– Si–Mn–Fe alloy, modified by the addition of Ti and Ti + P, in two series of castings, gravity and pressure. It has been found that the use of high pressure die casting technology allows for significant improvement of mechanical properties, especially tensile strength and plasticity of the examined alloy. On the other hand, the addition of Ti and Ti + P caused different material effects. In gravity castings, the addition of Ti and Ti + P caused a decrease in strength and plasticity, while in high-pressure castings, an increase in the values of these parameters was observed. The microstructural effects related to the foundry technology and those caused by Ti and P additions were revealed, such as differences in the phase composition of the interdendritic eutectics and in the morphology and dispersion of their phase constituents: Mg 2 Si and α-Al(Fe,Mn)Si.

The present work investigated the influence of Zr and Sc on the evolution of α-Al(FeMn)Si dispersoids (“α-dispersoids") in Al–Mg–Si alloys. Both the individual addition of Zr and the combined additions of Sc and Zr increased the size but decreased the number density of the α-dispersoids, indicating the reduction in the formation of α-dispersoids. However, the reduction levels were the most significant when heat-treated at 350 °C in the alloy with both Sc and Zr and at 400 ° C in the alloy with only Zr, which were likely related to the different interactions between intermediate B’ precipitates and α-dispersoids with the addition of Zr and Sc. Although the α-dispersoids were suppressed in the Zr/Sc-containing alloys, their microhardness was generally higher than the base alloy, which can be attributed to the strengthening contribution induced by Zr and Sc either from their solid solution hardening or the precipitation hardening of Al 3 Zr/Al 3 (Sc, Zr) dispersoids.

This study reports on silicon nitride (Si 3 N 4 ) and graphene nanoplatelets binary powder reinforced hybrid titanium composites obtained by a powder metallurgy method. Si 3 N 4 powder was added at 3 wt.% and graphene nanoplatelets were added in various amounts (0.15, 0.30, 0.45, 0.60 wt.%) in the titanium matrix. Density, micro-Vickers hardness, compressive behavior, wear properties and microstructure of the hybrid composites were evaluated. Addition of different percentages of graphene nanoplatelets and 3 wt.% Si 3 N 4 to the titanium matrix composites significantly enhanced mechanical properties. The highest hardness (634 HV) and compressive strength (1458 MPa) values were measured for 0.15 wt.% graphene nanoplatelets and 3 wt.% Si 3 N 4 added titanium hybrid composite. The lowest mass loss and wear rate (Δm = 4 mg, W = 6.1×10 –5 mm 3 (N m) –1 ) values were measured for the same 0.15 wt.% graphene nanoplatelets and 3 wt.% Si 3 N 4 added titanium hybrid composite compared with pure Ti.

The Fe-rich corner of the Ce–Nd–B–Fe quaternary system at 773 K has been experimentally investigated by means of X-ray powder diffraction and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy techniques. No quaternary compound was observed in this system. Ce 2 Fe 14 B and Nd 2 Fe 14 B were found to form the continuous solid solution (Ce,Nd) 2 Fe 14 B. Ce-Fe 4 B 4 and NdFe 4 B 4 also form the solid solution (Ce,Nd)-Fe 4 B 4 . The isothermal section consists of 8 three-phase regions and 2 four-phase regions.

The enthalpies of mixing in liquid alloys of the ternary Al–Gd–Mn system were determined over a wide range of compositions by means of isoperibolic calorimetry at 1650 K. The measurements of the partial enthalpies of components were performed along five sections: for the Δ H̅ Al (sections with x Gd / x Mn = 0.30/0.70 and 0.65/0.35 for x Al changed from 0 up to 0.30); for the Δ H̅ Gd ( x Al / x Mn = 0.80/ 0.20 and 0.50/0.50 for x Gd changed from 0 up to 0.30); for the Δ H̅ Mn ( x Al / x Gd = 0.29/0.71 for x Mn changed from 0 up to 0.26). The enthalpies of mixing in the ternary system were found to be exothermic and steadily increasing in absolute values from the Mn corner towards the Al–Gd constituent binary system, reaching the minimum value of approximately – 37 kJ · mol –1 in the vicinity of the Al 0.6 Gd 0.4 composition, evidently related to the formation of stable Al 2 Gd phase.

Gold-rich rare earth intermetallic compounds (viz. Ce 2 Au 2 Cd and CeAu 4 Cd 2 ) show unusual magnetic and physical properties, and they have extensive applications in electronic and mechanical industries due to their good electronic and thermal behavior with high mechanical strength. In the present research article, to take full advantage of technological importance of these materials, we have investigated the structural, electronic and thermodynamic properties of Ce 2 Au 2 Cd and CeAu 4 Cd 2 ternary intermetallic compounds using density functional theory (DFT). The electronic band structure and density of state calculations show that Ce-f orbital electrons provide metallic character to both the compounds with strong hybridization of Au-p and Cd-p orbitals at the Fermi level. The effect of temperature has been studied on the various thermodynamic parameters using the quasi-harmonic Debye model. Thermodynamic properties show that CeAu 4 Cd 2 compound has larger mechanical resistance (or high mechanical strength or hardness) and smaller randomness compared to Ce 2 Au 2 Cd with respect to temperature.

Perovskite structured LaTi x Fe 1-x O 3 ( x = 0, 0.05, 0.15, 0.25) lanthanum ferrites were synthesized by conventional solid-state reaction. The structural Rietveld refinement and Raman analysis were conducted and confirmed that single-phase orthorhombic phase with Pbnm symmetry formed. The positions of the ions and their bonds of these ferrites were investigated. The spherical shaped morphology of these ferrites was examined. The quantitative chemical composition and distribution of these ferrites were confirmed. The excitonic absorption edge was observed at 590 nm; ascribed to the electronic transition from O 2p →Fe 3d and optical band gap values increased from 1.85– 2.02 eV as Ti concentration increased. The dielectric and magnetic behavior of these ferrites was studied. It is suggested that synthesized LaTi x Fe 1x O 3 powders with different properties could be tailored for different requirements.