Li-ion batteries are widely used as energy storage devices due to their excellent electrochemical performance. The cubic Li7La3Zr2O12 (c-LLZO) compound is regarded as a promising candidate as a ...solid-state electrolyte for lithium-ion batteries due to its high bulk Li-ion conductivity, excellent thermal performance, and chemical stability. The standard manufacturing procedure involves the high-temperature and lengthy annealing of powders. However, the formation of the tetragonal modification of LLZO and other undesired side phases results in the deterioration of electrochemical properties. The mechanical milling of precursor powders can enhance the powders’ reactivity and can result in an easier formation of c-LLZO. The aim of this work was to study the influence of selected milling and annealing parameters on c-LLZO compound formation. The starting powders of La(OH)3, Li2CO3, and ZrO2 were subjected to milling in various ball mills, under different milling conditions. The powders were then annealed at various temperatures for different lengths of times. These studies showed that the phase transformation processes of the powders were not very sensitive to the milling parameters. On the other hand, the final phase composition and microstructure strongly depended on heat treatment conditions. Low temperature annealing (750 °C) for 3 h produced 90% of c-LLZO in the powder structure.
A number of non-equimolar refractory high entropy alloys (RF HEAs) from the Al–Ti–Mo–Nb–V system are synthesized, with the selected compositions aimed to balance the conflicting requirements of the ...low-temperature ductility and high-temperature corrosion protection. Based on the thermodynamic modeling and experimental results, all the obtained alloys are characterized by the single-phase B2 structure with V acting as the main phase stabilizer. The microstructure and mechanical properties appear to be controlled mainly by the Al content, which is especially visible on the example of hardness, with a maximum value of 545 HV for Al
20
Ti
5
Mo
25
Nb
25
V
25
composition. For the selected Al
20
Ti
5
Mo
25
Nb
25
V
25
and Al
10
Ti
30
Mo
20
Nb
20
V
20
alloys, the measured stress–strain curves indicate the highly coveted, ductile room temperature behavior, with the values of ultimate strain measured under compression mode being 9.17 and 9.00 pct, respectively, and compressive fracture strain of 13.38 and 13.25 pct, respectively. The obtained results suggest that it is possible to include Al as a vital component of refractory HEAs without compromising their low-temperature ductility. The next intended step will be the characterization of the high-temperature corrosion behavior in order to investigate the potential selective oxidation capabilities of such materials.
The paper describes an attempt to obtain harmonic structure (HS) in AISI308L steel. Harmonic structure is the term related to the microstructure fabricated by mechanical milling of metallic powders ...under soft milling conditions, resulting in the formation of plastically deformed, grain-refined shell and unchanged core. This microstructure can be preserved after successful powder compaction. The powders of AISI308L steel were milled under soft condition up to 50 h and then compacted by pulse plasma sintering at 900–1100 °C. For powders and compacts XRD, SEM and hardness measurements were applied as characterization techniques. The milling process resulted in austenite transformation into nanocrystalline ferrite and formation of grain refined outer layer. The applied pulse plasma sintering parameters allowed preservation of this microstructure and manufacturing of compacts with homogeneous distribution of elements, relative density above 95% and hardness in the range 167–185 HV, depending on sintering temperature. Simultaneously, the starting phase composition was restored, i.e., austenite with 12% contribution of ferrite. The crystallite size of austenite was about 20 nm and was significantly smaller then in starting powders.
Heusler alloys constitute an interesting group of materials with wide applications. The purpose of the present study was to use the mechanical alloying method to synthesize Fe2CrSi Heusler alloy and ...learn about its structure and magnetic properties. Pure metal elements were ground for various periods of time in a planetary ball mill, and the process of alloy formation was monitored using X-ray diffraction and Mössbauer spectroscopy. It was found that after 20 h of milling, the disordered BCC solid solution was formed, with an average crystallite size ~11 nm. After thermal treatment, the desired Fe2CrSi Heusler alloy was obtained, with a small amount of secondary phases. Detailed XRD analysis showed the coexistence of two varieties of Heusler phase, namely Fm-3m and Pm-3n. The main result of this work is the detection of the hyperfine magnetic field distribution using Mössbauer spectroscopy. The occurrence of this distribution proves atomic disorder in the crystalline structure of the obtained Heusler alloy. Macroscopic magnetic measurements revealed soft magnetic properties of the alloy, with a magnetic moment of ~2.3 μB/f.u., only slightly larger than the theoretically predicted value.
Mechanical alloying method was applied to prepare nanocrystalline Co
40Fe
40Ni
20, Co
50Fe
40Ni
10, Co
52Fe
26Ni
22 and Co
65Fe
23Ni
12 alloys. X-ray diffraction, Mössbauer spectroscopy and ...magnetization measurements were used as complementary methods to obtain structural data and to determine magnetic properties of the as-milled as well as the thermally treated samples. X-ray diffraction proved that during mechanical alloying process the Co–Fe–based solid solution with BCC lattice was formed in the case of Co
40Fe
40Ni
20 and Co
50Fe
40Ni
10, while for Co
52Fe
26Ni
22 and Co
65Fe
23Ni
12 systems the Co–Ni–based solid solutions with FCC lattice were obtained. Mössbauer spectroscopy revealed hyperfine magnetic field distributions, which reflect the different surroundings of
57Fe isotopes by Co, Fe and Ni atoms, depending on the chemical composition of the alloy. The most probable atomic configurations were determined on the basis of the local environment model. Thermal treatment of the mechanosynthesized alloys led in some cases to decomposition of the suitable solid solution into the mixture of two solid solutions. In other cases, the phase composition of the alloys was stable or the type of the crystalline lattice was changed during annealing. Moreover, thermal treatment led to an increase in the grain size and a decrease in the level of internal strains that influenced the magnitudes of the effective magnetic moments and Curie temperatures of the investigated alloys.
•High entropy WMoNbZrV alloy was successfully synthesized by mechanical alloying.•Nanocrystalline single phase bcc solid solution was formed.•High thermal stability of nanostructure was confirmed.
...The aim of this work was to apply mechanical alloying technique for synthesis of high entropy multicomponent equimolar WMoNbZrV alloy and to investigate the phase composition after milling and after heat treatment, as well as to characterize the observed changes of crystallite size, lattice strain and lattice parameter of solid solution formed. It was found that nanocrystalline bcc solid solution was characterized by crystallite size of 10 nm, lattice strain of 0.58% and lattice parameter of 3.1687 Å. Heating the sample up to 700 °C resulted in decrease of lattice strain down to 0.20%, while the crystallite size remained not changed, testifying good thermal stability of nanocrystalline bcc solid solution obtained.
Alloys from the CoCrFeMnNi family remain the most studied austenitic high-entropy alloys. In this study, four alloys, i.e., Cantor alloy, A3S (modified nonequiatomic Cantor composition), both “pure” ...or doped with carbon (200 wt. ppm) and niobium (1.3 wt.%), were investigated. Firstly, alloys were induction cast using a cold-crucible method. The obtained ingots were molten, and rapidly solidified by melt-spinning at two cooling rates to obtain “ribbons”, typical of such processing. The effects of the solidification rate and the presence of carbon and niobium on the microstructure and hardness were studied. All the studied alloys show an fcc structure. The lattice parameter of the fcc phase increases with the increasing cooling rate, and with the addition of niobium and carbon, which confirms at least a partial presence of these elements in solid solution. Yet, TEM observations revealed the formation of nanometric NbC precipitates. The microstructure of melt-spun ribbons consists of equiaxed grains of a few micrometers in size. The higher cooling rate led to a small decrease in the grain size and a slight increase in hardness. Moreover, the hardness of doped alloys can be further improved by annealing (500°C for 24 h) through NbC precipitation.
PDF
