Α2 Phase Research Articles

Penggunaan Media Interaktif Berbasis Video Animasi Dalam Peningkatan Bahasa Ekspresif Pada Siswa Autis di SKH Bougenville Kota Tangerang Selatan

The purpose of this study is to provide improvements in expressive language through the use of interactive media with the help of animated videos for autistic students at SKh Bougenville, South Tangerang City. The type of research applied is experimental research with the form of Single Subject Research with an A1-B-A2 design which is included in quantitative research. The problem in this study is the low expressive language ability of autistic individuals. One of the causes is the lack of development and variation of learning media that focuses on expressive language. The subjects in this study were autistic individuals in grade 2 of junior high school at SKh Bougenville, South Tangerang City, namely TC. The target behavior (dependent variable) in this study is expressive language ability, while the free variable (independent variable) is interactive media based on animated videos. From the research produced, it is proven that the application of interactive media assisted by animated videos can improve expressive language skills in autistic students at SKh Bougenville. The mean level of the A1 baseline phase at TC was 40%. The mean level obtained in the intervention phase was 89%, while the A2 baseline obtained was 78%. The resulting research shows that the intervention phase shows a higher percentage compared to the baseline A1 phase. The baseline A2 phase also obtained a higher percentage when compared to the baseline A1 phase. Therefore, the conclusion of the research conducted is that the application of interactive media based on animated videos provides an increase in expressive language skills for autistic individuals at SKh Bougenville, South Tangerang City.

Magnetic and mechanical properties of a sintered Fe-Si alloy with precipitated particles

A sintered Fe-Si alloy with Fe-Ta system particles was fabricated by a synthetic route of sintering via evaporation of an Fe-Si matrix and diffusion of Ta by sintering in high vacuum at high temperature. The Fe-Ta system particles precipitated on the surface and in grain boundaries of the matrix after sintering. The precipitated particles along grain boundaries in particular could contribute to improving mechanical strength by preventing intergranular fracture. The almost full densification observed after sintering and the disordered A2 phase of the matrix could also contribute to improving the strength. The sintered Fe-Si alloy with a controlled Si ratio and precipitation had low magnetic coercivity, low magnetic loss, high magnetic permeability, and high saturation magnetization, but it also maintained high mechanical strength. The fabricated Fe-Si alloy with precipitation showed much better magnetic and mechanical properties than those of conventional sintered alloys and even Si steel sheet (35H300).

Investment casting of Cr–Si alloys with liquidus temperatures up to 1900 °C

AbstractIn previous studies, chromium–silicon-based alloys have shown promising material properties for high-temperature applications. For chromium–silicon alloys to be processed on a large scale, primary shaping processes must be adapted to the requirements of these alloys. In this work, binary chromium–silicon alloys are primarily shaped using an investment casting process. Ceramic shell molds made of hafnium oxide stabilized zirconium oxide are developed to withstand the thermal, mechanical and chemical stresses resulting from pouring melts with liquidus temperatures of up to 1900 °C. The layered construction of the shell molds leads to a sufficient thermal shock stability. Energy-dispersive X-ray spectroscopy shows that chemical interactions between the shell mold and the melt do not occur, nor oxides are formed to a detectable extent. Microstructure investigations reveal that casting binary chromium–silicon alloys lead to a coarse grain structure with grain diameters above 300 µm. Strength-increasing precipitations of the intermetallic phase Cr3Si (A15 phase) can be detected from a silicon content of seven-atom percent in the as-cast state.

Engineering “Meso‐Atom” Bonding: Honeycomb‐Network Transitions in Reticular Liquid Crystals

ABSTRACTA library of rod‐like bolapolyphiles with sticky hydrogen‐bonded glycerol groups at their ends and having highly branched side chains with a carbosilane‐based four‐way branching point, all based on the same oligo(phenylene ethynylene) core, has been synthesized and investigated. For these compounds, a A15‐type Frank–Kasper phase is formed upon side‐chain elongation in the steric frustration range at the transition from the triangular to the much larger square honeycombs. In contrast to the previously known tetrahedral sphere packings the A15 phase is in this case formed by tetrahedral networks of aggregates of parallelly organized π‐conjugated rods. This allows the design of compounds with wide ranges of the A15 network down to room temperature. However, its formation becomes strongly disfavored by core fluorination that is attributed to a changing mode of core–core interaction that also modifies the square honeycombs by deformation of the squares into rectangular or rhombic cells, either with or without emergence of tilt of the rods.

Phase states and structural phase transition in Fe<sub>73</sub>Ga<sub>27</sub>RE<sub>0.5</sub> alloys (RE = Dy, Er, Tb, Yb) alloys: a neutron diffraction study

New data on phase states and structural phase transitions in alloys Fe73Ga27 alloys doped with Dy, Er, Tb, and Yb in an amount of ~0.5 at% are presented. Structural data were obtained in neutron diffraction experiments performed with high resolution and in continuous temperature scanning mode during heating to 850°C and subsequent cooling at a rate of ±2°C/min. It has been established that both the sequence of forming and disappearing structural phases and the final state of the alloy depend on the type of rare earth element. Phase transitions in the alloy with Dy are similar to those in the initial Fe73Ga27 alloy, excluding the final state. The procedure of doping with Er and Tb leads to the formation of disordered A1 and A3 phases instead of the L12 and D019 ordered close packed phases, respectively. In the case of doping with Yb, neither of the above phases is observed. The formation of the L60 (m-D03) and D022 tetragonal structural phases previously discovered in similar alloys by the electron diffraction method is not confirmed.

Influence of atomic substitution on the structural stability and half-metallicity of Fe2-xCrxCoSi (x = 0 to 1) alloys

Bulk Fe2-xCrxCoSi (x = 0, 0.25, 0.5, 0.75, and 1) Heusler alloys have been prepared by arc melting method. Alloys with 0 ≤ x ≤ 0.75 show a highly ordered phase pure XA structure. However, 17 % of an impurity (A15 phase) was detected in the alloy with x = 1. The saturation magnetization (Ms) and Curie temperature (TC) decreased linearly with an increase in Cr content for alloys with x ≤ 0.75. Ms measured at 5 K followed the Slater–Pauling rule for half-metals. Ab initio calculations with the GGA + U approach revealed that spin polarization (P) increased with an increase in Cr and eventually reached 100 % for the alloys with x = 0.5. Though Fe-Co disorder affects P, it is still high (>98 %) for alloys with x ≥ 0.5. Despite the smaller bandgap (0.61 eV) of Fe1.5Cr0.5CoSi than FeCrCoSi (0.91 eV), it has higher Ms, elevated TC, and 100 % P. These factors, coupled with the challenges associated with obtaining phase pure FeCrCoSi alloy, make Fe1.5Cr0.5CoSi a preferred candidate for spintronic device applications.

Atomic mechanisms for the fracture of AlMo0.5NbTa0.5TiZr refractory high entropy superalloy

Refractory high entropy superalloys (RHESs), known for their excellent high temperature performance, exhibit promising characteristics but are challenged by significant brittleness. Efforts to enhance plasticity through microstructure regulation have achieved only limited success, largely due to the unclear underlying fracture mechanisms of the superstructure. In this study, we systematically investigate the fracture mechanisms of the AlMo0.5NbTa0.5TiZr RHES from microscopic to electronic scales. Interestingly, both experimental and simulation results reveal that the ordered B2 phase demonstrates non-negligible plastic deformation capabilities during fracture, including deformation twinning and amorphization. Despite this, the fracture resistance of the B2 phase is lower compared to the A2/B2 interface and disordered A2 phase, even though the A2 phase shows less twinning and amorphization. Ab initio molecular dynamics simulations, combined with electronic behavior analysis, indicate that bonds involving Al and Zr in the B2 phase often exist in an anti-bonding state, making them more prone to breaking under load. This study provides deeper insights into the fracture mechanisms of the A2/B2 superstructure and its constituent phases at both atomic and electronic levels, offering a systematic approach to improving the fracture properties of such RHESs.

Thermophysical properties of AlxCoCrCuFeNi high entropy alloys

The AlxCoCrCuFeNi (x = 0.25, 0.5, 1, 2) high entropy alloys (HEAs) were prepared by arc melting and spray casting techniques. Their microstructures, hardness, and thermophysical properties such as fusion enthalpy, entropy, thermal diffusion coefficients, thermal expansion coefficients, were investigated. XRD results indicated that AlxCoCrCuFeNi (x = 0.25 and 0.5) alloys were composed of a high-entropy FCC phase and Cu-rich nanophase. As the Al content increased to 1 and 2, the phase structures included the AlNi-rich B2 phase, FeCr-rich A2 phase and Cu-rich nanophase. With the increased Al content, the microstructures of AlxCoCrCuFeNi HEAs transitioned from coarse dendrites to petal-like dendrites, and the grains were continuously refined. Moreover, the Al additions reduced the density whereas increased the Vickers hardness of the alloys. The maximum hardness observed in Al2CoCrCuFeNi HEA was approximately 2.4 times greater than that of the Al0.25CoCrCuFeNi HEA. The thermal diffusion coefficients of alloys initially increased and subsequently decreased as the temperature elevated. The phase transformation induced by Al content was an effective method for rapidly homogenizing the internal temperature of alloys. Furthermore, the crystal structure, elemental segregation, lattice distortion, enthalpy and entropy of fusion, and lattice vibration frequency all mutually affected the thermal diffusion and expansion coefficients of AlxCoCrCuFeNi HEAs.

Phase transformation mechanism and microstructure of a Y-doped TiAl gas-atomized powders

In this study, the phase transformation mechanism of a yttrium-containing β-solidified TiAl alloy (Ti-43Al-9 V-0.3Y at.%), prepared by gas atomization, was systematically investigated. X-ray diffraction, electron backscatter diffraction, scanning electron microscopy, and transmission electron microscopy were utilized to comprehensively analyze the morphology and microstructure of powders with varying sizes as well as the form and distribution of yttrium and its influence on the phase transformation of the powders. The results show that the solidification phase structure of the powders exhibits significant variations: the ultra-fine powder consists of α’ martensite and remaining β phase, while the medium-sized powder is solely composed of β0 phase. The large-sized dendritic powder comprises β0, α’ martensite and α2 phase. With an increase in powder size, there is a corresponding increase in the content of α2 phase, whereas the content of martensite initially rises and subsequently declines. Additionally, yttrium is present in the form of multiscale Y-rich precipitates (YAl2 and Y2O3) within the matrix, and the segregation degree gradually increases with increasing powder size. The primary factors contributing to the disparity in solidification structure include cooling rate and segregation defects. A faster cooling rate and a higher supercooling degree will inhibit the β → α transition, while the Y-rich precipitated phase forms a pre-existing strain zone around it, providing an effective site for martensitic nucleation. In summary, these findings offer novel insights into the mechanism of phase transformation in yttrium-containing β-solidified TiAl alloy, thereby contributing to further advancements in the theory of rapid solidification for TiAl alloys.

In-situ synchrotron high energy X-ray diffraction study on the deformation mechanisms of D019-α2 phase during high-temperature compression in a TiAl alloy

The α2 phase with an ordered hexagonal structure has a strong mechanical anisotropy. The limited plasticity interacting with crystallographic texture formation undoubtedly complicate the deformation mechanisms of the α2 phase. Taking advantage of in-situ synchrotron high energy X-ray diffraction (HEXRD), this study unveils the origin of the α2 texture and its correlation with plastic deformation. Upon loading at 800 °C, the dislocation glide in the γ phase initiates at a stress of 370 MPa and that in the α2 phase at a stress of 670 MPa. Nevertheless, the texture evolution of the α2 phase sets in in parallel with that of the γ phase, and these textures are preliminarily established at a stress of 650 MPa. A main <11 2‾ 0> fiber texture with the c axis of the α2 unit cell aligned vertically to the compression axis has been unexpectedly evolved. This texture forms primarily via rigid body rotation and is correlated with glide and twin activation in the neighboring γ phase. The preferential orientation primarily favors double prismatic glide in α2 and in addition triggers the tensile twin activation. The grain rotation caused by the tensile twin slightly affects the α2 transverse texture evolution. The results unveil a complex interaction between the α2 phase deformability, texture evolution and the combined elastic-plastic deformation of the phases γ and α2 in TiAl alloys.

Role of Ti-6Al-4V addition in modulating crack sensitivity, solidification microstructure and mechanical properties of laser powder bed fused γ-TiAl alloys

Solidification cracking is still the primary challenge for laser powder bed fusion (LPBF) without high-temperature preheating of γ-TiAl alloys. Circumventing the peritectic reaction and promoting β-solidification by adding the β-stablizing elements have been proved to be an effective way to suppressing the crack formation. In this work, we attempted a more economic method to realize β-solidification via the addition of Ti-6Al-4V (TC4) pre-alloyed powder. The results showed that the TC4 addition successfully changed the solidification path from L→L+β→L+α→α→α+γ→α2+γ to L→L+β→β→α+β→α2+β/B2. As a result, the solidified microstructure was mainly comprised of primary α2 phase and small amount of retained β/B2 (8.5 %) phase distributed along the molten pool boundary. What's more important was that the TC4 addition led to a 44.6 % decrease in crack density. Contributions to low hot cracking sensitivity were found to mainly origin from the relatively lower cooling rate, higher fraction of low-angle grain boundaries (LAGBs) and smaller dendrite coalescence undercooling induced by the TC4 addition. Besides, the smaller temperature interval (10.63K) in the final solidification stage (0.90<fs < 0.94) for the TC4/TiAl alloy was also conducive to facilitate the liquid feeding and dendrite coalescence.

Microstructure evolution and nitriding mechanism of Ti‐6Al‐4 V alloy in alumina‐based refractories

AbstractThe aims of this study were to explore the nitriding mechanism of Ti‐6Al‐4 V alloy in Al2O3‐based refractories. Al2O3‐based composite refractories were fabricated using Ti‐6Al‐4 V and sintered alumina as main materials, followed by nitriding at different temperatures in a nitrogen atmosphere. Phase and microstructure evolution of the products was analyzed by X‐ray diffraction and field‐emission scanning electron microscopy equipped with energy‐dispersive X‐ray spectroscopy. The results reveal a multi‐stage nitridation process of Ti‐6Al‐4 V at different temperatures. At 900°C, nitridation of the Ti‐6Al‐4 V surface results in the formation of a (Ti,V)N solid solution, while Al and V migrate inward, forming intermetallic compounds Ti3Al and a‐Ti (Ti1‐x‐yVxAly) with rich Al and V. At 1100°C, nitridation of Ti3Al produces intermediate products like Ti2AlN or Ti3AlN, with continued inward migration of Al or V to form the intermetallic α2 phase of (Ti1‐xVx)3yAly in the center of the alloy particles. At 1300°C, decomposition of Ti2AlN or Ti3AlN results in the outward migration of Al atoms and the presence of AlN on the outer layer of Ti‐6Al‐4 V particles, thus forming a hollow structure. Finally, at 1500°C, the (Ti,V)N solid solution grains grow as a result of further diffusion and dissolution of nitrogen.

Mechanical behavior of powdered iron aluminide Fe – 28Al manufactured by direct powder forging

This study examines the impact of direct powder forging of powders on the composition, structure, and mechanical properties of iron aluminide Fe–28 at. % Al. During the synthesis and forging of Fe3Al powders, a homogeneous A2 phase is formed at a temperature of 1100 °C. Porosity after forging is 2–2.5 %. Residual pores are predominantly planar in shape and are located at the boundaries of the powder particles. Annealing at 1300 °C improves the quality of interparticle boundaries and all samples exhibit transcrystalline fracture mechanism. Samples forged at 1100 °C and annealed at 1300 °C show maximum strength σbend = 1050 MPa and fracture toughness K1c = 32.3 MPa·m1/2. The yield strength demonstrates anomalous temperature sensitivity with a maximum of 400 °C and at 500 °C. Samples tested at 600 °C show a decrease in yield strength, but a high enough yield point σy ∼400 MPa and a high strengthening rate are very important for high-temperature creep resistance. In creep experiments at a load of 120 MPa at 600 °C, the strain rate varies in the range of 10−7–10−6 s−1, the value of the rate sensitivity n ≈ 4. The main mechanism of creep is dislocation glide.

Effect of Cr on nano-indentation Young's modulus and hardness of the β-Ti phase in equilibrium with α2-Ti3Al and γ-TiAl phases in Ti-Al-Cr alloys

Young's modulus and hardness of the constituent phases of β-Ti (bcc or B2), in equilibrium with α2-Ti3Al (D019) and γ-TiAl (L10) phases in Ti-Al-Cr ternary alloys were quantitatively evaluated in terms of the chemical composition analysis and nano-indentation method, in order to identify the Cr concentration dependence on the mechanical properties of the β phase. An alloy with a nominal composition of Ti-43Al-3Cr (at.%) decomposes into the three phases of β, α2, and γ by equilibrium heat treatment at 1373 K, with chemical composition of Ti-37.2Al-5.2Cr, Ti-38.9Al-2.2Cr, and Ti-47.4Al-1.4Cr, respectively. The β phase shows a Young's modulus of 141 ± 5 GPa, smaller and less orientation dependent than the other two phases of α2 (174 ± 9 GPa) and γ phases (164 ± 15 GPa). In contrast, the β phase has a hardness of 5.9 ± 0.3 GPa, slightly softer than the α2 phase (6.4 ± 0.8 GPa) but much harder than the γ phase (3.7 ± 0.6 GPa). The alloys Ti-44Al-4Cr and Ti-45Al-6Cr consist of two phases of β and γ phases, and the chemical composition of the β phase in these two alloys is Ti-36.5 Al-8.5 Cr and Ti-36.3 Al-13.9 Cr, respectively, with nearly the same Al concentration. The Young's modulus and hardness of the β phase with the latter composition become 158 GPa and 6.7 GPa, respectively, with increasing Cr content. These results found that the effect of solid solution Cr on the Young's modulus for β phase is relatively weak, and that on the hardness is strong, in comparison with that for the other two phases.

Effect of Er2O3 and Y2O3 on microstructure and mechanical properties of Ti2AlNb alloy

Rare earth oxides can significantly refine the microstructure of the cast alloys and improve their mechanical properties. In this study, Er2O3 and Y2O3 particles were chosen to add into the Ti2AlNb-based alloy with vacuum non-consumable arc melting method. For the Er2O3 particles, it has obvious dissolution and re-precipitation characteristics during melting. While for the Y2O3 particles, they are more stable, and aggregated and grew up during melting. These two kinds of Er2O3 or Y2O3 both have obvious refinement effects on the B2 grains due to their heterogeneous nucleation. Specially, adding Er2O3 particles can promote the decomposition of the B2 and α2 phases and the increases of the O-phase content. But adding the Y2O3 particles can inhibits the B2 decomposition and just only promotes the α2 decomposition into the O-phase. Additionally, the TAC-Er2O3 ingot shows the worst mechanical properties at room-temperature due to its large size and grain boundary segregation of the Er2O3 reinforcements. Conversely, the TAC-Y2O3 alloy exhibits excellent strength and ductility whatever at room- and high- temperatures owing to its fine grain strengthening and effective strengthening of the second precipitated Y2O3 phases.

Complex topological close-packed phase of rapidly cooled chromium

The topological close-packed phases have attracted extensive attention due to their high packing density and excellent properties. However, it is difficult to identify topological close-packed phases by using numerical methods. In this work, the cooling of pure chromium at a rate of 1010 K/s was studied by molecular dynamics simulation, and the structure evolution was analyzed by the largest standard cluster analysis and visualization technique. It was found that the rapid cooling resulted in a complex topological close-packed solid, which contains A15 phase, Z phase, σ phase, and H phase. The atomic connection characteristics in the A15 and Z units are also detailed. And a method for quick and preliminary identification of σ phase and H phase based on Z15-Z15 bonds is proposed. This work enriched the understanding of topological close-packed phases, and demonstrated the advantage of the largest standard cluster analysis in identifying complex phases.

The newly discovered competitive growth behavior of γ and α2 phases

This study reports a new phenomenon of competitive growth between TiAl alloy structures. By annealing the β-solidified Ti-44Al-8Nb-0.1B alloy for a short time, a new phenomenon of repeated competitive growth between α2 and γ phases is found. Finally, the (α2 + γ) lamellar structure engulfs other structures and grows, transforming into a full lamellar structure.

Microstructure and mechanical properties of Ti60–Ti2AlNb functionally graded materials fabricated by laser directed energy deposition

The increasing demands for materials that service under high temperature environments in advanced aero-engines with high thrust-to-weight ratios have led to the exploration of functionally graded materials, which can offer unique advantages for addressing these challenges, such as the ability to achieve multiple properties at different positions of the components. In this study, Ti60–Ti2AlNb functionally graded materials were fabricated via laser directed energy deposition (L-DED) with 20% compositional step and various step widths in the transition zone. The distribution of chemical composition, microstructure, and microhardness in the transition zone of functionally graded materials with different compositional paths along the deposition direction were investigated. Meanwhile, the mechanical properties and fracture mechanisms were also evaluated. Smooth composition transition has been achieved in the joint zone between Ti60 and Ti2AlNb. By decreasing the width of each composition zone in the transition area or removing the Ti60-60% Ti2AlNb zone, the precipitation of the hard and brittle α2 phase can be effectively suppressed, thereby enhancing the tensile strength of the graded material. Through this approach, Ti60–Ti2AlNb functionally graded material with a tensile strength of 1030.9 MPa and elongation of 2.0% was fabricated.

In-situ synchrotron high energy X-ray diffraction study on the compressive creep behavior of an extruded Ti-45Al-8Nb-0.2C alloy

Wrought high Nb containing (high Nb-TiAl) alloys are potential materials for low pressure turbine blades in aero-engines. The performance and microstructure evolution under high temperature creep condition is of importance to the service stability of these materials. In this study, the internal strain and FWHM evolution of an extruded TNB-based high Nb-TiAl alloy during compressive creep are characterized by in-situ high energy X-ray diffraction (HEXRD) technique for the first time. The compressive creep test was conducted under a constant load of 300 MPa at 900 °C for 10 h in vacuum. The final creep strain is approximately 1.72 %. The microstructure and phase constitution after creep shows little difference from that before creep. Lattice strain analysis shows that γ phase is plastically deformed while the α2 phase deforms elastically due to the low creep strain. The lattice strain of α2 grains is dependent upon the deformation of surrounding γ grains. Creep induces dynamic recovery, exerting a softening effect. A high number of dislocations are visible in the γ lamellae while almost no dislocations exist within the α2 lamellae. α2 lamellae are partially decomposed and refined via the α2→γ transformation.

Exploring the brittle-to-ductile transition and microstructural responses of [formula omitted]−TiAl alloy with a crystal plasticity model incorporating dislocation and twinning

γ−TiAl alloy, with its high specific strength and creep resistance, is ideal for aerospace engines and gas turbines, but its brittleness poses significant manufacturing and processing challenges. To address these issues, this study employs a crystal plasticity finite element method incorporating dislocation and twinning to analyze the brittle-to-ductile transition behavior of γ−TiAl alloy at different temperatures. Additionally, the Bayesian optimization methods are employed to efficiently and accurately obtain parameters related to numerical calculations of crystal plasticity. The results indicate that at room temperature, the high activation resistance of the slip systems in the α2 phase leads to limited slip activity, resulting in poor plasticity. However, at 750 °C and 850 °C, the strength of the slip systems decreases significantly, allowing more α2 phase lamellae in the γ-TiAl alloy to undergo greater plastic deformation. This enhancement in the plastic deformation capacity of the α2phase lamellae reduce the overall deformation incompatibility in the TiAl alloy, thereby improving the overall ductile of the γ-TiAl alloy.