{'fraction_non_alphanumeric': 0.03381428697884394, 'fraction_numerical': 0.012746746923962113, 'mean_word_length': 5.103727714748785, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 1, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Preparation of the AlTiNiCuCox system high-entropy alloys and structural analysis

This study aimed to explore and develop a new material with high cost-effectiveness, excellent strength, light weight, high hardness, great wear resistance, corrosion resistance, and favorable oxidation resistance. Structural analysis suggested that, with the change in Co addition amount, the surface morphology and structure of the alloy system changed. XRD analysis indicated that, the alloy system was the FCC+BCC mixed structure. In addition, metallographical demonstrated that, with the increase in Co content, the dendritic crystal transformed from big block to dendritic structure, then to snowflake, gradually to petal-like, and finally to petal shape. SEM-EDS analysis revealed that, Cu element was enriched in interdendritic site, while Ti, Ni, Al and Co elements were enriched in dendrite. Besides, TEM and TEM-EDS analysis indicated that, there was nano-size precipitate of small particles in the Cu-enriched block region, along with dislocation; further, there was twin structure inside the dendrite, as well as the second phase with different morphology, and the second phase showed coherency with the matrix. The above analysis suggested that, the intercrystalline structure was the Cu-enriched phase of FCC structure; the internal matrix of grain was the NiTi and TiCo phases of BCC structure; and the second phases inside the grain were the AlCu2Ti,AlNi2Ti,AlCo2Ti and CuNi phases of FCC structure. Taken together, the AlTiNiCuCox system novel alloys have changed phase structures and phase types of the alloy system.


Introduction
The traditional alloy design is associated with limitations and its development tends to be saturated. Scholar Ye Junwei carried out a bold attempt on alloy composition, and proposed a novel alloy in 2004, namely, the multicomponent high-entropy alloy (HEA) [6] . HEA is the alloy that contains at least 5 kinds of elements, and the content of each element is less than 35% (atomic fraction) [7] .
Surprisingly, the HEA breaks through the traditional alloy design concept, and substantially broadens the alloy range. Recent research indicates that, numerous HEAs display superb properties, such as high hardness [8], favorable wear resistance [9], temperature resistance [10], strong acidic and alkali corrosion resistance [11,12], and good oxidative resistance.
Research results reveal that, the multicomponent HEA is the single structure formed by the mutual solid solution of elements at microstructure level [13], most of them form the simple BCC structure and FCC structure, and even the nanocrystal and amorphous phase structure [14,15], but they can hardly form the complicated while fragile intermetallic compound (IMC) [16]. The feature of high entropy and low enthalpy contributes to forming the solid solution; on the one hand, this is because that the formed degree of order of compound atom arrangement is higher than that of solid solution; on the other hand, the high entropy probably reduces the electronegativity difference, hinders compound formation, contributes to blending of components, and forms the simple face-centered structure and body-centered structure.
Besides, according to previous studies, nanophase [17] and even amorphous structure phase precipitation [18][19][20] is observed in the completely annealed or as cast HEA.
The multicomponent HEA displays the nanocrystallization characteristics, which is related to the kinetic theory. To be specific, the atoms are disorderly arranged and at disordered state when the alloy transits from solid state to liquid state. At the time of cooling solidification, the separation of all atoms in multiple elements was blocked, while the atom diffusion of HEA is closely correlated with atom diffusion of all components, the diffusion of component atoms is hindered, and the new phase crystal nucleation and growth are suffocated, thus promoting the formation of small grain nanophase [21]. If the cooling velocity is high enough, the amorphous microstructure will also be generated. The components of HEA are constituted by atoms of various radii, and such atom size differences of the components render lattice distortion around the atoms to various degrees. Actually, the atom radii of HEA components are greatly different from each other, and there is also great lattice distortion effect in the system, which may greatly affect the material properties, such as mechanics, calorifics, and electromagnetism. Each element in HEA is similar to each alcohol in the cocktail, which independently and reciprocally exists in the HEA system. The presence of cocktail effect allows to regulate the HEA structure and performance through controlling the element type and quantity. The above-mentioned effects constitute the four major effects of HEA. At present, the synthetic mechanism of HEA composite material has not been comprehensively understand. Therefore, a large number of novel materials can be synthesized, analyzed and developed, just like the traditional metal-matrix composite materials, so long as the HEA structure is simple and the phase composition can be identified.
To obtain alloy with light weight and superior high temperature oxidation resistance, Ti and Al elements were selected in this study. To improve the strength, Ni, Cu and Co elements were selected, since element Co has high strength under high temperature. HEAs containing Cr or Al can undergo strong acid corrosion, and have superb antioxidation resistance at the temperature of as high as 1100 ℃. In this study, 5 common metal elements, including Ti, Ni, Al, Cu and Co, were selected based on the alloying principle and the electronic structure, and element Co was used as the variable to prepare 5 novel material ingots AlTiNiCuCox (x=0.5,1.0,1.5,2.0,2.5) according to vacuum melting method. The new materials obtained through melting were performed microstructure analysis, phase and energy spectrum analyses, so as to screen the novel material with superb properties. This experimental study is of certain reference value in the field of HEA.

Material preparation, alloy structure and phase analysis methods
In this project, 5 common metal elements, including Ti, Ni, Al, Cu and Co, were selected to prepare the HEAs. All the adopted materials were the high-purity alloy elements, with the purity of 99.9%. 5 HEAs were prepared according to the AlTiNiCuCox(x=0.5,1.0,1.5,2.0,2.5) system. Then, the test specimens were conducted XRD test using the X'Per Pro multifunctional X-diffractometer (PANalytical), at the scanning speed of 4°/min, the scanning angle from 20° to 120°, and the Cu target wavelength λ of 1.54. Then, the corroded test specimens were placed into the OLYMPUS-PM3 optical metallographical microscope, JEOLJSM-6480A scanning electron microscope (SEM) (equipped with energy disperse spectroscope EDS), and JEM-2100 transmission electron microscope (TEM), respectively, to take photos of test specimens at various magnifications. Later, the SEM was used in combination with electron probe for point analysis and regional analysis on the special points and regions in the scanned images, so as to obtain the elemental compositions of corresponding points and regions.    The microstructures of the as cast AlTiNiCuCoX (x=0.5,1.0,1.5,2.0,2.5) system

Metallographical structural analysis of the AlTiNiCuCoX system
HEAs were analyzed through the metallographical images, the results suggested that, with the increase of Co content, the dendrite shape changed from line and filiform to the regular dendritic shape, then to snowflake-like shape, to petal-like shape, and finally to petal shape gradually. It was observed from the metallographical images that, when the Co content was ≥1.0, the structure showed the obvious 3D perspective, and dendrite projection was observed on the surface. Moreover, with the increase in Co addition amount, the relative area in intergranular region increased, while that in intragranular region decreased, and the grain size gradually became coarse.     The black phase increased inside the structure morphology were that, the grains were first refined, then the dendrite arm length became shorter, the width became wider, and the filiform shape changed into the regular dendrite crystal structure. With the further increase in Co, the dendrite crystal structure changed into the coconut branch shape, and then gradually into the petal shape dendrite crystal structure. Besides, it was seen from the locally magnified scanned images of the system AlTiNiCuCox HEAs that, with the increase in Co addition amount, the black little dot phase gradually decreased; the contrast began to occur in the microstructure when the Co addition amount (molar ratio) was >1.5, and the contrast was not obvious at the Co addition amount of 2.5, with the production of the block black phase.        Table 3.9 Area where each phase of the AlTiNiCuCox(ｘ＝0.5,1.0,1.5,2.0,2.5)system HEAs locates       There was second phase precipitation inside the grains, which showed coherency with the matrix. With the increase in Co content, the second phase shape in dendrite regions rich in Ti, Ni, Al and Co elements changed from the multilayer black alternating with white elliptical shape to the multilayer black alternating with white round shape, then to the black granular shape, the number of light alternating with dark layer at second phase first increased and then decreased, and finally turned into the black phase. The second phase size first decreased, then increased, and then decreased; the intragranular second phase of Co2.5 was the CuNi phase, while those in remaining alloys were the close AlNi2Ti, AlCu2Ti and AlCo2Ti phases. With the increase in Co content, the dislocation lines gradually increased and formed the dislocation network, while the dislocation was generated due to the stress during the alloy cooling process.

Conclusions
The effect of Co element on the microstructure and phase composition of the alloy was investigated by metallographic microscope, scanning microscope, transmission electron microscope, EDS and XRD analysis in a multicomponent high-entropy alloy AlTiNiCuCox (x =0.5, 1.0, 1.5, 2.0, 2.5) system.
(１)From the analysis of AlTiNiCuCox system high entropy alloy phase, we can find that with the increase of Co element content, alloy system FCC and BCC structure changed. The Cu phase of the FCC structure in the alloy system always exists. When the molar ratio of Co element is at 1.0, 1.5, 2.0, 2.5, the new BCC structure TiCo phase and the NiTi phase disappeared and the FCC2 structure phase changed.
(２)The microstructure of AlTiNiCuCox high-entropy alloy was analyzed by means of metallographic and SEM images. With the increase of the amount of Co element, the shape of the dendrites changed from the line filaments to the regular dendrites, and the dendrite arms began to expand laterally to the snowflake-like transition.
(３)Combined with XRD, SEM-EDS and TEM to analyze the high entropy alloy of AlTiNiCuCox system, the intergranular region consisted of Cu-rich phase of FCC structure, the inner grain was rich in Ti, Ni, A1 and Co elements, and the inner matrix of the grain was mostly in the colattice form with the second phase.