AlCoCrFeNi high entropy alloy (HEA) was synthesized by mechanical alloying (MA). Formation of single-phase solid solution of body centered cubic (BCC) structure (a = 2.88 ± 0.01 Å) was confirmed from ...x-ray diffraction (XRD) and high-resolution synchrotron XRD. The nanostructure nature of the milled powder was observed through transmission electron microscopy (TEM). The milled powder was consolidated through conventional sintering at 900 °C (1173 K) for 2 h. The microstructure of the sintered AlCoCrFeNi HEA showed two types of grain distribution. Coarser size of grains varied in the range of ∼18–22 μm and finer grains of ∼ 2–10 μm sizes that are homogeneously distributed in the matrix. Detailed analysis of the x-ray diffraction pattern of sintered HEA showed the phase transition from parent BCC phase to Al–Ni type B2 phase (cP2) (a = 2.91 ± 0.02 Å) and Ni3Al type L12 phase (cP4) (a = 3.56 ± 0.01 Å) along with Co–Cr type σ phase (tP30) (a = 8.8 Å, c = 4.53 Å). The sintered samples showed high value of microhardness, i.e. 919 ± 18 HV at 300 g load. Alloy shows fascinating soft magnetic property with saturation magnetization of 70.05 A m2/kg (emu/gm) along with effective Curie temperature (TC) of ∼617 °C (890 K).
•Nanocrystalline AlCoCrFeNi HEA forms a single phase BCC structure after 30 h of milling.•Precipitation of B2, L12 and σ phases were observed after conventional sintering.•Alloy had shown the high hardness with better soft magnetic properties.
A newly designed composition of non-equiatomic Fe
40
Cr
25
Ni
15
Al
15
Co
5
medium-entropy alloy (MEA) was produced by induction melting (IM). The as-cast alloy was found to consist of a two-phase ...microstructure of BCC (2.87 ± 0.01 Å) and ordered B2 (2.88 ± 0.02 Å) type phases. The structures of these phases were confirmed through X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It was observed that the Ni-Al-enriched ordered B2 phase of cuboidal shapes (~ 100 to 200 nm) is homogeneously distributed in Fe-Cr-rich BCC matrix with a cube-on-cube orientation relationship. The formation of the columnar dendrites (width 50 to 100
μ
m) was identified through optical microscopy (OM). The structural and microstructural stability of the alloy was investigated by heat-treating the alloy through different schedules. Heat-treated samples at different temperatures (< 1273 K) exhibit a similar type of two-phase microstructure with columnar dendrites. However, compositional rearrangement takes place during long time exposure to develop polymorphically related phases. The alloy was observed to possess a high compressive yield strength and hardness,
i.e.
, ~ 1047 MPa and 391 ± 9 HV, respectively, at room temperature. Heat-treated samples at 600 °C and 900 °C (873 K and 1173 K) showed an increase in yield strength and ultimate strength with a significant increase in plasticity due to the increase in volume fraction of B2 phase and softening of the BCC matrix phase. The thermal stability and high strength of this alloy may open new avenues for high-temperature applications.
In the present investigation, a newly designed composition of equiatomic AlCrFeCoNiZn high-entropy alloy (HEA) has been synthesized by mechanical alloying. The milled powder after 30 h exhibited the ...formation of a single solid solution phase of BCC crystal structure with lattice parameter,
a
= 2.87 ± 0.02 Å. Decomposition of the single-phase BCC structure into the two-phase, tetragonal (Cr–Co)-based σ phase (
a
= 8.81 Å,
c
= 4.56 Å)- and L1
2
(
a
= 3.59 ± 0.02 Å)-type intermetallics was observed at temperature of ~ 800 °C (1073 K). However, after heat treatment of the 30 h milled powder at the temperatures of 300 °C (573 K) and 600 °C (873 K), similar type of phases was also noticed to coexist along with B2 (
a
= 2.87 ± 0.03 Å)-type phase. This behaviour of the alloy confirms the diffusive nature of the phase transformation. The consolidated bulk alloy exhibited similar type of phases after sintering at 950 °C (1223 K).
An equiatomic quinary MgAlMnFeCu high-entropy alloy (HEA) has been synthesized successfully by mechanical alloying (MA). Phase evolution of MgAlMnFeCu HEA has been studied using X-ray diffraction ...(XRD), transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS/XEDS). Milling up to 60 h leads to the formation of a mixture of two phases consisting of a BCC phase (
a
= 2.87 ± 0.02 Å) and ϒ-brass-type phase (
a
= 8.92 ± 0.03 Å), with ~ 2 μm powder particle size. The as-milled alloy after spark plasma sintering (SPS) at 900 °C exhibits an experimental density of 4.946 ± 0.13 g cc
−1
, which is 99.80% of the theoretical density. SPS leads to the formation of C15 Laves phase (MgCu
2
-type; a = 7.034 ± 0.02 Å) and B2 (AlFe-type; (
a
= 2.89 ± 0.02 Å) intermetallic along with the ϒ-brass-type phase. The SPSed sample has exceptional hardness value (~ 5.06 GPa), high compressive strength (~ 1612 MPa) and appreciable failure strain (~ 6.4%) coupled with relatively low density. Various thermodynamic parameters have been considered for understanding the phase evolution and their stability during MA.
An equiatomic Mg
20
Al
20
Si
20
Cr
20
Fe
20
(at.%) low-density high-entropy alloy (LDHEA) was synthesized by mechanical alloying (MA) and consolidated by spark plasma sintering (SPS) techniques. The ...phase identification, chemical composition, fine microstructural features and thermal stability of the mechanical alloyed powder and the spark plasma sintered (SPSed) compacts were discerned through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) techniques. The LDHEA powder after mechanical alloying for 60 h exhibited a nanocrystalline BCC phase (
a
= 0.2887 ± 0.005 nm) as a major one along with the minor fraction (~ 3%) of undissolved Si. The 60-h milled powder was consolidated through SPS at 800 ℃ (1073 K). The SPSed sample exhibited the presence of a major B2-type AlFe phase (cP2;
a
= 0.2889 nm) along with a parent disordered BCC phase and a minor amount of Al
13
Fe
4
(mC102;
a
= 1.549 nm,
b
= 0.808 nm,
c
= 1.248 nm),
β
-Al
3
Mg
2
(cF1168;
a
= 2.824 nm) and Cr
5
Si
3
(tI32;
a
= 0.917 nm,
c
= 0.463 nm) phases. Attempts were made to explore the mechanical properties of the LDHEA through microindentation techniques. The hardness and yield strength were evaluated to be ~ 7 GPa and ~ 2100 MPa respectively. The density of the sintered sample was found to be around 4.38 g cm
−3
, which is around 99.98% of the theoretical density. The phases evolved during MA and SPS were explained with the help of the thermodynamic parameters and property diagrams generated through the CALPHAD approach using Thermo-Calc software.
The present work deals with powder metallurgical processing of Sn-reinforced Al-Cu-Fe icosahedral quasicrystalline (IQC) composites processed through mechanical milling (MM) followed by hot pressing ...and pressureless sintering. The structure, microstructure and toughening behavior of the nanocomposite powders and bulk samples were investigated through X-ray diffraction (XRD), optical metallography (OM), scanning electron microscopy (SEM) and indentation techniques. The XRD pattern suggested the coexistence of IQC and λ-Al13Fe4 (mC102; a = 1.549 nm, b = 0.808 nm, c = 1.248 nm) and B2-type Al (Cu, Fe) (cP2; a = 0.29 nm) crystalline phases in milled as well as sintered samples. The face-centered icosahedral (FCI) ordering was persistent even after 40 h of milling and sintering. The structural transformation during MM influences the indentation behavior of IQC-Sn nanocomposite powders, and the microhardness was found to be in the range of ~5.3 to 7.3 GPa. Further, efforts were made to study the indentation behavior of IQC-Sn composite prepared by pressureless sintering and hot pressing. The fracture toughness of the IQC-10Sn hot-pressed sample was found to be ~1.92 MPa.√m, which is ~22% higher than that of the as-cast and annealed IQC. The enhancement in the fracture toughness resulted mainly from the inhibition of cracks by Sn reinforcement particles. This suggests that powder metallurgical processing can produce the IQC-Sn composite with an optimal combination of microhardness and fracture toughness.
Scanning electron microscopy (SEM), combined with energy-dispersive spectroscopy (EDS), is an extensively used technique for in-depth microstructural analysis. Here, we present the EDS-Phase ...Segmentation (EDS-PhaSe) tool that enables phase segmentation and phase analysis using the EDS elemental map images. It converts the EDS map images into estimated composition maps for calculating markers of selective elemental redistribution in the scanned area and creates a phase-segmented micrograph while providing approximate fraction and composition of each identified phase. EDS-PhaSe offers two unique advantages. Firstly, it enables the direct processing of EDS elemental map images without requiring any raw or proprietary data/software, thereby allowing the analysis of EDS results available in the published literature as images. Secondly, it enables segmentation and analysis of phases even when the phase contrast is missing in backscattered micrographs, assisting in correlating the XRD and SEM-EDS data as shown in this work for a AlCoCrFeNi high-entropy alloy.
Composite powders of pre-alloyed 316 L austenitic stainless steel with yttria (Y
2
O
3
) powder in various compositions (0.3, 1.0, 1.5 and 2 wt%) were synthesized by mechanical alloying using a high ...energy ball mill. The 25-h milled powder has shown no changes other than exhibiting an austenite phase of FCC (
a
= 3.54 Å) structure. Milled powders were found to contain nano-yttria dispersed in the austenitic stainless steel matrix of nano-crystallite size and with high lattice strain. Milled powders were cold pressed and sintered at 1100 °C (1373 K) in a controlled atmosphere. It can be inferred that nano-yttria dispersion restricts grain growth of matrix even during conventional sintering. The present yittria dispersed austenitic alloy showed the low physical density and increase in compressive strength (194–374 MPa) and hardness (477–528 HV). The compressive strength and hardness enhancement can be attributed primarily to the dispersoids of nano-yttria in the austenitic matrix by dispersion strengthening/hardening mechanisms.
•Nanocrystalline MgAlSiCrFeNi LDHEA was synthesized by mechanical alloying with a major BCC phase.•LDHEA is stable upto ~ 400 °C and start transforming into minor intermetallics and silicides.•The ...SPSed LDHEA showed the retention of major BCC phase along with B2 type phase.•These LDHEA showed high hardness and modulus of elasticity of 9.98 GPa and 229 GPa respectively.
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Equiatomic MgAlSiCrFeNi low-density high-entropy alloy (LDHEA) was prepared by mechanical alloying followed by spark plasma sintering (SPS). The phase evolution, chemical composition, and thermal stability of the alloy were analyzed by X-Ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) techniques. Formation of a BCC phase having a lattice parameter of 0.2876±0.03 nm and undissolved Si (~3 at%) was observed after milling of 60 h. DSC experiment up to 1200 °C (1473 K) shows five exothermic heating events corresponding to various phase transformations, which were matched with the results obtained from XRD experiments. It has been found that the alloy after high temperature annealing led to the evolution of a major B2 phase (a=0.289 nm) and also BCC phase along with small amounts of FCC Al-Mg solid solution phase, FCC 1 (a= 0.4082 nm) and FCC 2 (a= 0.4215 nm), monoclinic Al13Fe4 (a= 1.549 nm, b= 0.808 nm, c= 1.248 nm, α = β = 90˚), Mg2Si (a= 0.6351 nm), Cr5Si3 (a=b= 0.9165 nm, c= 0.4638 nm). The spark plasma sintered (SPS) sample also exhibited BCC and B2 phases coexisting with minor amounts of other phases observed for 800 °C (1073 K) annealed sample. The co-exsistence of minor phases with parent BCC phase in SPSed alloy (having relative density of ~99.40%) has led to significantly high hardness and modulus of elasticity of ~9.98 ± 0.3 GPa and 229 ± 0.3 GPa respectively. Various thermodynamics parameters were calculated in order to correlate with the experimental findings of phase evolution and stability of the annealed powder and spark plasma sintered alloy.
The outstanding properties of the high entropy alloys (HEA) are attributed to various factors like composition, microstructure, phase formation, synthesis route etc. In this regard, the present ...investigation deals with phase evolution, microstructure, thermal stability and microhardness properties of an equiatomic quinary Cr-Mn-Fe-Co-Mo high entropy alloy synthesized by mechanical alloying followed by pressure-less sintering. The structure and phase evolution with milling time was studied by x-ray diffraction technique. After completion of 40h of milling, two simple solid solution phases with BCC structure (a= 3.146 ± 0.002Å and 2.873 ± 0.002Å) along with a minor amount of undissolved α-Mn were identified. Phase formation, chemical composition, thermal stability etc. were also evaluated using electron microscopy and differential thermal analysis (DTA) methods as well as in-situ high temperature x-ray diffraction technique. In the sintered sample, four phases consisting of two BCC solid solution, σ (sigma) and μ (mu) phases are observed to coexist and to be stable up to the melting point. The phase formation was predicted by Thermo-Calc approach and was compared with the experimental observation as well as other calculated results. The sintered samples were tested by instrumented hardness tester for evaluation of mechanical properties and was found to exhibit high hardness (9.3 ± 0.3GPa) and Young’s modulus (~245 ± 6GPa).
•A new equiatomic quinary CrMnFeCoMo HEA has been prepared by mechanical alloying followed by pressure less sintering.•Two BCC solid solution phases along with minor α-Mn is formed after 40h of milling. The sintered alloy consists of a major σ-type phase along with a μ-type phase and two BCC solid solution•The alloy is thermally stable upto 400 °C and beyond that intermetallics start to form.•The sintered pellet possesses excellent hardness value of 9.3GPa
