Abstract
The exploration of microstructures in high temperature alloy melts is important for manufacturing of metallic components but extremely challenging. Here, we report experimental evidence of ...the disruption of Si-rich microstructure in engineering-lightweight Al–12.2at.%Si alloy melt at 1100 °C, via melt-spinning (MS) of Al
1−x
Si
x
(x = 0.03,0.07,0.122,0.2) alloy melts from different initial melt temperatures, 800 °C and 1100 °C, under the super-high cooling rate of ~ 10
6
°C/s, in cooperation with the small angle neutron scattering (SANS) measurement. Si particles in 1100 °C MS alloys are abnormally smaller and increased in number at Al–12.2at.%Si, compared with 800 °C MS alloys, which demonstrates the disruption of Si-rich microstructure in Al–12.2at.%Si alloy melt at 1100 °C. SANS experiment verifies that large quantities of small (0–10 nm) Si-rich microstructures and small quantities of large (10–240 nm) Si-rich microstructures exist in Al–12.2at.%Si alloy melt, and the large Si-rich microstructures disrupt into small Si-rich microstructures with increasing of melt temperature from 800 to 1100 °C. Microstructure analysis of the MS alloys indicates that the large Si-rich microstructures in Al–12.2at.%Si alloy melt are probably aggregates comprising multiple small Si-rich microstructures. This work also provides a pathway for the exploration of microstructures in other high temperature alloy melts.
The structure of FeCoNiCrAl1.8Cu0.5 high-entropy alloys (HEA) obtained by two different routes has been studied. The selection of the composition has followed the Hume–Rothery approach in terms of ...number of itinerant electrons (e/a) and average atomic radius to control the formation of specific phases. The alloys were obtained either from a mixture of elemental powders or from gas-atomised powders, being consolidated in both cases by uniaxial pressing and vacuum sintering at temperatures of 1200 °C and 1300 °C. The characterization performed in the sintered samples from both types of powder includes scanning electron microscopy, X-ray diffraction, differential thermal analysis, and density measurements. It was found that the powder production techniques give similar phases content. However, the sintering at 1300 °C destroys the achieved phase stability of the samples. The phases identified by all techniques and confirmed by Thermo-Calc calculations are the following: a major Co-Ni-Al-rich (P1) BCC phase, which stays stable after 1300 °C sintering and homogenising TT treatments; a complex Cr-Fe-rich (P2) B2 type phase, which transforms into a sigma phase after the 1300 °C sintering and homogenising TT treatments; and a very minor Al-Cu-rich (P3) FCC phase, which also transforms into Domain II and Domain III phases during the heating at 1300 °C and homogenising TT treatments.
•Average magnetic field variations of HEA are similar to those of corresponding binary Fe alloys.•Influence of cobalt and nickel on the hyperfine field on iron is small in HEA.•Lattice parameter of ...FeCoNiPdx changes with x, not affecting Mossbauer spectra.•All the spectra present simultaneous hyperfine field and quadrupole splitting distributions.•The random direction of observation causes the average QS value to be close to zero.
Two series of FeCoNiPdx and CrxFeCoNiPd high entropy alloys were investigated using SEM-EDX, XRD technique and Mössbauer spectroscopy. Increasing of Pd content in the FeCoNiPdx samples only slightly influenced the Mössbauer spectra. They were analysed assuming simultaneous presence of hyperfine field and quadrupole splitting distributions, however random direction of observation relative to Bhf and EFG caused the average QS value to be close to zero. Increasing of Cr content in the CrxFeCoNiPd samples resulted in strong decrease of the hyperfine field, its distribution becomes wide and influence of Bhf,ISBhf and EFG on the Mössbauer spectra can not be separated unambiguously. The decomposing of the HEAs compositions into binary artificial Fe-dopant systems, namely FeCoNi-Pd and FeCoNiPd-Cr, allowed to interpret the magnetic structure of the two investigated series.
According to a recent Hume-Rothery approach, the electron concentration, e/a, and the average radius can be used to identify the domain of stability of HEAs and to estimate the phases that may occur ...in the alloy. The present study investigates the influence of the electronic polymorphism of nickel on the efficiency of the classification and on the design of HEAs for magnetic applications. Many different compositions were used, based on 4 to 7 elements out of a total 13 different elements (Co, Cr, Fe, Ni, Al, Cu, Pd, Ti, Mn, V, Nb, Sn, Ru). Phases have been determined by X-ray and neutron diffraction as well as in some cases high energy X-ray diffraction. The e/a for the constituent elements is calculated according to Massalski. The two polymorphic electronic structure of nickel, namely (e/a)Ni = 1 or (e/a)Ni = 2 are considered. The average e/a for the alloy is calculated assuming a solid solution case. The electronic structure Ar 3d9 4s1 seems to be more appropriate for the classification of HEAs. Based on a Self-organising Map predictions are made for the average magnetic moment at saturation for this electronic structure of Ni. Non-saturated values and data from the literature are compared with the predictions. The consequences of such results when modelling the structure and properties of Ni containing HEAs are presented, in particular the consideration of the shape and transformation of the Brillouin zone.
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•The Ni electronic structure Ar 3d9 4s1 should be considered for Ni containing HEAs.•The HEA phases Domains are: I-fcc e/a<1.53; II-mixed 1.53<e/a<1.88; III-bcc e/a>1.88.•The Brillouin zone of HEAs has to be investigated in calculations and modelling.•The average magnetic moment at saturation and the phases can be predicted for HEAs.
The microstructure evolution of impulse atomized powders of Al-0.61 wt pct and Al-1.90 wt pct Fe compositions have been investigated with a scanning electron microscope, transmission electron ...microscope, neutron diffraction, and backscattering electron diffraction (EBSD). Both hypoeutectic and hypereutectic compositions demonstrated similar macrostructure (
i.e.
, primary
α
-Al dendrites/cells with eutectic Al-Fe intermetallics decorated at the dendritic/cellular walls). Selected area electron diffraction (SAED) analysis and SAED pattern simulation identified the eutectic Al-Fe intermetallic as Al
m
Fe (
m
= 4.0-4.4). This is verified by neutron diffraction analysis. Cubic texture was observed by EBSD on the droplets with dendritic growth direction close to 〈111〉. The possible reasons are discussed.
The 7th JournCes de la Diffusion Neutronique (JDN7) arranged by the SFN (Société Française d e la Neutronique) was held from May 13-15. 1998 at Albé, which is situated in a beautiful part of the ...Vosges in Alsace, France. The very successful meeting was locally organized by Monique Calvo-Dahlborg, Ecole des Mines, Nancy, Jean-Georges Gasser, chairman, and Benoit Grosdidier, both from the University of Metz.
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