Reflection and refraction of acoustic waves at the boundary between a Heusler ferromagnetic alloy and dielectric

Reflection and refraction of longitudinal and transverse acoustic waves at a planar boundary between a dielectric and a ferromagnetic Heusler alloy Ni_2+x+y Mn_1?x Ga_1?y in the range of premartensitic and martensitic phase transitions is considered. We show the possibility of efficiently controlling the angles of reflection and refraction of both longitudinal and, especially, transverse waves, as well as all four coefficients of conversion of the wave type, by the variation of temperature which induces strong anisotropy of elastic properties of the crystal. Conditions for the appearance of critical angles and accompanying surface vibrations as well as for total reflection are discussed. The possibility is analyzed of emission of the arising wave gliding along the interface between the two media into the bulk of the material with the development of a new complex damped dissipationless wave process in the vicinity of the phase transition. Based on Trivisonno’s experimental data on the temperature dependences of the sound velocity in an Ni₂MnGa single crystal, the conclusions of the theory developed are illustrated by numerical calculations for a concrete Ni₂MnGa-quartz structure.     

Reflection and refraction of acoustic waves at the insulator-ferromagnetic heusler alloy boundary

Reflection and refraction of longitudinal and transverse acoustic waves on a flat boundary between an insulator and a ferromagnetic crystal of a Heusler alloy Ni_{2 + x + y} Mn_{1 − x} Ga_{1 − y} have been considered in the region of premartensitic and martensitic phase transitions. The possibility is shown of using temperature to effectively controlling the angles of wave refraction and the coefficients of transformation of wave modes by changing strong acoustic crystalline anisotropy induced with approaching the point of the phase transition. The conditions of the appearance of critical angles and the angles of total internal reflection, as well as the effect of temperature on them, have been considered. The possibility has been analyzed of emission, in the vicinity of the phase transition, of a wave that propagates along the boundary into the bulk of the material. Based on the experimental data obtained by Trivisonno for the temperature dependences of the sound velocity in the Ni_{2 + x + y} Mn_{1 − x} Ga_{1 − y} crystal, the conclusions of the theory developed are illustrated by numerical calculations for a concrete structure, namely, Ni₂MnGa-quartz.     

Martensite stabilization and thermal cycling stability of two-phase NiMnGa-based high-temperature shape memory alloys

The martensite stabilization and thermal cycling stability of four types of two-phase NiMnGa-based high-temperature shape memory alloy, including Ni_56+xMn₂₅Ga_19?x (x = 0, 1, 2, 3, 4), Ni₅₆Mn_25?yFe_yGa₁₉ (y = 4, 8, 9, 12, 16), Ni₅₆Mn_25?zCo_zGa₁₉ (z = 4, 6, 8) and Ni₅₆Mn_25?wCu_wGa₁₉ (w = 2, 4, 8) alloys, were investigated. It is found that the martensite stabilization is closely related to the strength of the alloy and the volume fraction of γ phase; and increases as the alloy strength decreases. It is also found that in Ni₅₆Mn_25?yFe_yGa₁₉ alloys, with increasing Fe content to 12 and 16 at.%, the volume fraction of γ phase increases and the martensite stabilization decreases. The thermal cycling stability differs among different alloy systems and is related to the microstructural changes during thermal cycling and to the strength of the γ phase. Poor thermal cycling stability is observed in Ni_56+xMn₂₅Ga_19?x (x > 0), Ni₅₆Mn_25?zCo_zGa₁₉ and Ni₅₆Mn_25?wCu_wGa₁₉ alloys due to the formation of the ordered γ′ phase and the high strength of the γ phase. Results further show that Fe addition to Ni₅₆Mn₂₅Ga₁₉ alloy can broaden the (bcc + γ) two-phase region and shift it to the Ni–Ga and Ni–Mn sides, hence stabilizing the two-phase region to lower temperatures. These effects can retard the formation of the ordered γ′ phase in the Ni₅₆Mn_25?yFe_yGa₁₉ system during thermal cycling, thus leading to good thermal cycling stability.     

Reassessment of Ni-Al and Ni-Fe-Al solidus temperatures

Solidus temperatures of the B2 NiAl phase have been determined by high-temperature differential thermal analysis for binary melt compositions Ni_xAl_100?x (45<x<57) and for ternary alloys Fe_yNi_50?yAl₅₀ (0≤y≤50). It was shown that the melting temperature of the stoichiometric Ni₅₀Al₅₀ phase is 1681 °C, which is 43 K higher than some literature data. The solidus line at the Ni-rich side of the Ni-Al phase diagram exhibits a steeper slope than that reported previously. Substituting Fe for Ni, the decrease of solidus temperature along the isoplethal section with 50 at.% Al of the ternary Ni-Fe-Al phase diagram exhibits a steep initial slope of ?13 K/at.% Fe for small Fe-fractions, which changes into a nearly linear decrease with an average slope of ?8.5 K/at.% Fe.     

Modification of the titanium nickelide surface using frictional treatment and subsequent heating in air

The effect of a combined treatment including severe plastic deformation under the conditions of dry sliding friction and heating in air to temperatures of 300?C480°C (holding for 1 h) on the structure and wear resistance of the surface layer of the Ti_49.4Ni_50.6 alloy has been investigated. It has been shown that this frictional treatment results in an amorphous-nanocrystalline structure in the surface layer (of thickness to 10 ??m) of the Ti_49.4Ni_50.6 alloy. Heating to 300°C brings about the complete crystallization of the amorphous phase; as a result, the structure of the deformed surface layer of the alloy becomes single-phase, consisting of nanocrystals of the B2 phase. At 400°C, in this deformed surface layer there arises a nanocrystalline oxide (TiO₂) phase whose amount reaches tens of volume percent. The sizes of crystals of the B2 phase and oxide TiO₂ are in the range of 1?C50 nm. The arising two-phase (B2 + TiO₂) nanocrystalline structure is located just below the oxide TiO₂ film, which is less than 1 ??m thick. With an increase in the heating temperature to 480°C, the deformed surface layer under consideration retains the nanocrystalline two-phase (B2 + TiO₂) structure, but an increase in the amount of the oxide phase and a decrease in the microhardness of this structure are observed. In some cases (heating at temperatures of 430 and 450°C), the presence of the two-phase (B2 + TiO₂) nanocrystalline surface layer leads to a noticeable (to ??25%) enhancement in the adhesive wear resistance of the Ti_49.4Ni_50.6 alloy upon sliding friction in pair with steel 40Kh13.     

Phase transformations during deformation of Fe-Ni and Fe-Mn alloys produced by mechanical alloying

Compositions of Fe_{(100 ? x)}Mn _x (x = 10 and 12 at. %) and Fe_{(100 ? y)}Ni _y (y = 18 and 20 at. %) were produced by combined mechanical alloying of pure-metal powders and annealed in the austenitic field. After annealing and cooling to room temperature, the alloys had a single-phase austenitic structure. During deformation, the γ phase partially transforms into the α ₂ phase (and/or ? phase in Fe-Mn alloys). The phase composition of the alloys after deformation depends on the amount of alloying elements and the predeformation annealing regime. The amount of martensite in the structure of a bulk alloy obtained by powder compacting grows proportionally to the degree of deformation of the sample.     

Influence of anisotropy, the latent heat and the thermal history of alloy on martensitic transformation strain in Ni3Ta single crystal

Transformation characteristics in the single crystal of Ni₃Ta shape memory alloy were studied by the dilatation measurement in the temperature range of room temperature up to 500 °C. The transformation strains were positive in the direction of the b-axes and the c-axes and negative in the direction of a-axes. The martensitic phase transformation takes place without volume change of the sample. Thermal diffusivity of the single crystal measured in two directions b-axes and a-axes was higher than that for polycrystalline material.The latent heat of the martensitic phase transformation influences the temperature distribution inside sample. Absorption (releasing) of the latent heat during heating (cooling) leads to cooling (heating) of the sample in place where the phase transformation takes place. This decrease (increase) of the temperature in the interface between both phases leads to stopping of the phase transformation. This effect is visible on the temperature dependence of the dilatation characteristics. The martensitic phase transformation in Ni₃Ta single crystal took place with hysteresis of 30 °C. This hysteresis changes depending on the thermal history of the sample. Hysteretic behaviour of the Ni₃Ta single crystal was analyzed and compared with behaviour of Ni_53.6Mn_27.1Ga_19.3 alloy where no hysteresis was found.     

Thermal stability and crystallization of Zr–Al–Cu–Ni based amorphous alloy added with boron and silicon

The amorphous Zr_65−x−yAl_7.5 Cu_17.5Ni₁₀Si_xB_y alloy ribbons, x=1–4 and y=1–2, with 0.1 mm thickness were prepared by melt spinning. The thermal properties and microstructure development during the annealing of amorphous alloys were investigated by the combination of differential thermal analysis, differential scanning calorimetry, X-ray diffractometry, and TEM. Both of the glass transition temperature and the crystallization temperature for Zr_65−x−yAl_7.5 Cu_17.5Ni₁₀Si_xB_y alloys increases with the silicon and boron additions and reaches 674 and 754 K, respectively for Zr₆₀Al_7.5 Cu_17.5Ni₁₀Si₄B₁ alloy. The highest T_rg (0.62) and γ value (0.43) occurred at the Zr₆₀Al_7.5Cu_17.5Ni₁₀Si₄B₁ alloy. In addition, the Zr₆₀Al_7.5Cu_17.5Ni₁₀Si₄B₁ alloy was revealed to have the highest activation energy of crystallization (about 370 kJ/mol as determined by the Kissinger plot). This value is about 20% higher than the activation energy of crystallization for the Zr₆₅Al_7.5Cu_17.5Ni₁₀ based alloy (314 kJ/mol). In parallel, the alloy 4Si1B also performs a longer incubation time at higher isothermally annealing temperature. All of the evidence implies that Zr₆₀Al_7.5 Cu_17.5Ni₁₀Si₄B₁ alloy exhibits the highest thermal stability among those alloys in this study. The crystallization behavior for the alloy 4Si1B isothermally annealed at the supercooled temperature region for different time has also been examined by TEM and discussed.     

Measurement of phase equilibria in Ti-Ni-Sn system

Phase relations of the Ti-Ni-Sn ternary system were investigated via alloy sampling assisted with X-ray diffractometry (XRD) and electron probe micro-analysis (EPMA). A new binary phase with composition of TiSn₄ (molar fraction, %) was detected at 508 K. In addition, a supplementary phase (Ti_1–x–yNi_xSn_y)Ni₃ (τ, AuCu₃-type) was observed at 873 and 973 K. According to the characterised microscopic structure in various annealed alloys, four ternary phases were detected in Ti-Ni-Sn ternary system: TiNiSn, TiNi₂Sn, Ti₂Ni₂Sn and (Ti_1–x–yNi_xSn_y)Ni₃. Additionally, isothermal sections of Ti-Ni-Sn ternary system at 508, 873 and 973 K were constructed. By comparing three isothermal sections, a peri-eutectic reaction, L+TiNi₂Sn→Ni₃Sn₄+TiNiSn, was deduced, which occurs at a temperature between 873 and 973 K. Furthermore, the solubility of Sn in TiNi and Ni in Ti₅Sn₃ was detected.     

Further investigation on phase relation and microstructures in Ni3Si–Ni3Ti–Ni3Nb pseudo-ternary alloy system

The isothermal phase diagram at 1323 K in the Ni₃Si–Ni₃Ti–Ni₃Nb pseudo-ternary alloy system was re-investigated by scanning electron microscopy (attached with a wavelength dispersive spectroscope), X-ray diffraction and transmission electron microscopy (TEM), focusing on the phase relation among possible geometrically-close-packed (GCP) Ni₃X phases. The prepared alloys exhibited widely different microstructures, depending on alloy compositions whether they exist in a single phase, a two- or a three-phase region, and also on the constituent GCP Ni₃X phases. The L1₂(Ni₃Si), D0₂₄(Ni₃Ti) and D0_a(Ni₃Nb) phases were directly equilibrated one another or each other when keeping Ni content 79.5 at.%. On the other hand, the D0₁₉(Ni₃Ti_0.7Nb_0.3) phase was identified to exist when keeping Ni content 75 at.%. The phase stability and existing region of each GCP Ni₃X phase identified in the Ni₃Si–Ni₃Ti–Ni₃Nb pseudo-ternary alloy system were discussed, based on the electron concentration (e/a) and the atomic size factor (R_x/R_Ni) of the constituent atoms.     

Structural changes in a model alloy after irradiation of Fe62Ni35Ti3 with fast neutrons and isochronous temperature annealing

The experimental results of neutron diffraction studies of the crystal structure of the Fe₆₂Ni₃₅Ti₃ alloy after irradiation with fast neutrons and postradiation isochronous annealing are presented. It is shown that the structural state of the Fe₆₂Ni₃₅Ti₃ alloy for all external forces is determined by two competing processes: the creation or annealing of radiation defects and precipitation or dissolution of the metastable ?á? phase Ni₃Ti.     

Microstructures,Martensitic Transformation,and Mechanical Behavior of Rapidly Solidified Ti-Ni-Hf and Ti-Ni-Si Shape Memory Alloys

In this work, the microstructure and mechanical properties of rapidly solidified Ti_50?x/2Ni_50?x/2Hf _x (x = 0, 2, 4, 6, 8, 10, and 12 at.%) and Ti_50?y/2Ni_50?y/2Si _y (y = 1, 2, 3, 5, 7, and 10 at.%) shape memory alloys (SMAs) were investigated. The sequence of the phase formation and transformations in dependence on the chemical composition is established. Rapidly solidified Ti-Ni-Hf or Ti-Ni-Si SMAs are found to show relatively high yield strength and large ductility for specific Hf or Si concentrations, which is due to the gradual disappearance of the phase transformation from austenite to twinned martensite and the predominance of the phase transformation from twinned martensite to detwinned martensite during deformation as well as to the refinement of dendrites and the precipitation of brittle intermetallic compounds.     

Structure analysis of the constitutional phases in liquid phase sintered W–Mo–Ni–Fe heavy alloys

The crystal structures of constitutional phases in two different tungsten heavy alloys processed via different conditions were examined. The compositions of these two alloys were W–11.9Mo–17.0Ni–7.7Fe and W–29.6Mo–17.0Ni–7.7Fe (at.%), which were liquid phase sintered at 1500 °C for 5 or 240 min, and followed by either furnace-cooling or water-quenching. Increase in isothermal hold caused increased concentration of Mo but decreased concentration of W in the matrix phase, which did not affect the lattice parameter of the matrix phase to a significant extent. Quenching the specimen in water caused increase in the concentrations of both W and Mo in the matrix phase, and, consequently, increases in the lattice parameter of the matrix phase. A tungsten heavy alloy with a high alloying concentration of Mo was prone to induce the precipitation of an intermetallic phase during cooling, which was enhanced by increasing the isothermal hold at the liquid phase sintering temperature and decreasing the cooling rate. The structure of this intermetallic phase is analogous to that of MoNi, and can be designated as (W_xMo_1−x)(Fe_yNi_1−y). The composition of this intermetallic phase varied with the composition of the alloy and its cooling rate subsequent to sintering. For a furnace-cooling condition, the atomic ratio of W to Mo (x/1−x) in this intermetallic phase was about 0.47 times the atomic ratio of W to Mo of the original alloy composition. Such a proportional constant decreased to about 0.30 when the specimen was water-quenched.     

Solubility of boron in Mo5+ySi3−y

Using X-ray analysis, optical microscopy, chemical analysis, and electron probe microanalysis (EPMA) it has been determined that the level of boron solubility in Mo_5+ySi_3−y at 1800°C reaches a maximum value of approximately 2 at% in a narrow region within the homogeneity range of −0.08⩽y⩽0.04. Both the B doped and undoped Mo_5+ySi_3−y (T1) have the tetragonal W₅Si₃ crystal structure, which corresponds to the I4/mcm space group. Within the single phase Mo_5+ySi_3−yB_x (T1) region there is a contraction in the lattice volume with increasing boron concentration while there is an increase in cell volume with an increase in Mo:Si ratio.     

Effects of annealing at 800 and 1000 °C on phase precipitates and hardness of Al7Cr20FexNi73−x alloys

The effects of Fe content on the microstructure, phase constituents and microhardness of the as-cast, 800 °C- or 1000 °C-annealed Al₇Cr₂₀Fe_xNi_73?x (x=13?66) alloys were investigated. Not all these alloys are composed of the single FCC phase. The BCC and B2 phases are found. It is confirmed that the BCC phase in the Al₇Cr₂₀Fe₆₆Ni₇ alloy is transformed from the FCC phase at about 900 °C during cooling. While in the 800 °C-annealed Al₇Cr₂₀Fe₆₀Ni₁₃ alloy, the FCC phase is stable and the hardness decreases. After annealing at 1000 °C, for the precipitation of the B2 particles, the Al content in the FCC phase decreases, which results in decreasing of the alloy hardness. Moreover, after annealing at 800 °C, a small amount of Al-rich B2 particles precipitate at the phase boundary and some nanocrystal BCC phase precipitates in the FCC matrix, which increases the hardness of the Al₇Cr₂₀Fe_xNi_73?x (x=41?49) alloys. These results will help to the composition design and processing design of the Al?Cr?Fe?Ni based high-entropy alloys.     

The ductility and shape-memory properties of Ni–Mn–Co–Ga high-temperature shape-memory alloys

Ni–Mn–Co–Ga alloys with Ni/Mn or Ni and Mn substituted by Co were investigated as candidates for high-temperature shape-memory alloys. Ni_56?xCo_xMn₂₅Ga₁₉ alloys with x < 8 consist of single phase martensite, whereas Ni_56?xCo_xMn₂₅Ga₁₉ (x ? 8), Ni₅₆Mn_25?yCo_yGa₁₉ (y = 4, 8) and Ni_56?z/2Mn_25?z/2Co_zGa₁₉ (z = 4, 6) alloys consist of a two-phase mixture of martensite and γ phase. The mechanical and shape-memory properties of Ni₅₆Mn_25?yCo_yGa₁₉ and Ni_56?z/2Mn_25?z/2Co_zGa₁₉ alloys, which were hot-rolled into 0.5 mm thin plates by conventional hot rolling process, were investigated. The ductility and hot-workability of Ni–Mn–Co–Ga alloys were greatly improved by increasing the amount of ductile γ phase. Dynamic tensile tests and scanning electron microscopy observations of fracture surfaces confirm that the existence of γ phase plays a key role in improving the ductility of Ni–Mn–Co–Ga alloys.     

Microstructure and plastic deformation behavior of Ni3(Ti,X) (X = Nb,Al) single crystals with long-period geometrically closely packed crystal structures

The crystal structure, phase stability and plastic deformation behavior of Ni₃(Ti_1−xNb_x) [x = 0, 0.01, 0.03, 0.05 or 0.10] and Ni₃(Ti_1−yAl_y) [y = 0.16 or 0.28] single crystals were investigated. The substitution of Ti by Nb in Ni₃Ti induced the formation of various long-period stacking ordered (LPSO) structures with 18-fold, 10-fold or 9-fold stacking sequences of closely packed plane (CPP) depending on the Nb content. In compression tests, the yield stress anomaly (YSA) appeared in ternary LPSO crystals as well as in binary Ni₃Ti by slip on the CPP. The change in stacking sequence of CPP in the LPSO phases strongly affects the YSA behavior due to the change in APB energy on the non-closely packed plane.     

Influence of Nd-Co Substitution on Structural,Electrical, and Dielectric Properties of X-Type Hexagonal Nanoferrites

A series of single phase X-type hexagonal ferrites with concentration Sr_2?x Nd _x Ni₂Fe_28?y Co _y O₄₆ (x = 0.02, 0.04, 0.06, 0.08, 0.10 and y = 0.1, 0.2, 0.3, 0.4, 0.5) has been prepared by sol-gel method sintered at 1250 °C for 6 h. The x-ray diffraction analysis reveals the single phase of X-type hexagonal ferrites. The particle size was calculated by using SEM and TEM. The ferrite substituted with Nd³⁺ and Co²⁺ has average particle size in the range of 40-50 nm. The room temperature electrical resistivity experiences the significant enhancement from a value of 1.1 × 10⁷ to 2.03 × 10⁸ Ωcm with the increase in Nd³⁺ and Co²⁺ concentration. The dielectric constant exhibits high value at low frequencies and decreases with the increase of frequency. The tangent dielectric loss shows the abnormal behavior which can be explained on the basis of hopping between the Fe²⁺ and Fe³⁺ ions on octahedral sites. The maximum value of tangent loss at low frequencies reflects the application of these materials in medium frequency devices (MF).     

High strength and good ductility of casting Al-Cu alloy modified by PrxOy and LaxOy

A modified Al-Cu alloy with high tensile strength and ductility of about 574.0 MPa and 10.4%, respectively, was obtained by adding multiple rare earth oxides (Pr_xO_y and La_xO_y) as modifier. Compared with the unmodified Al-Cu alloy, the tensile strength and ductility of the modified sample were increased by 24.3% and 42.5%, respectively. The improvement both in the strength and ductility may attribute to the finer crystal grains and dendrites, more homogeneously distributed θ′ phase precipitates and the intermetallic compounds formed at the crystal grain boundaries as well as in the space of the dendrites.     

The Effects of Strain-Annealing on Tuning Permeability and Lowering Losses in Fe-Ni-Based Metal Amorphous Nanocomposites

Fe-Ni-based metal amorphous nanocomposites with a range of compositions (Fe_100?x Ni _x )₈₀Nb₄Si₂B₁₄ (30 ≤ x ≤ 70) are investigated for motor and transformer applications, where it is beneficial to have tunable permeability. It is shown that strain annealing offers an effective method for tuning permeability in these alloys. For an Fe-rich alloy, permeability increased from 4000 to 16,000 with a positive magnetostriction. In a Ni-rich alloy, permeability decreased from 290 to 40 with a negative magnetostriction. Significant elongations (above 60%) are observed during strain annealing at high stress. Crystallization products have been determined in all alloys heated to 480°C. γ-FeNi is formed in all alloys, while (Fe₃₀Ni₇₀)₈₀Nb₄Si₂B₁₄ also undergoes secondary crystallization at temperatures of approximately 480°C to form a phase with the Cr₂₃C₆-type structure and a likely composition of Fe₂₁Nb₂B₆. Toroidal losses have been measured for (Fe₇₀Ni₃₀)₈₀Nb₄Si _y B_16?y (0 ≤ y ≤ 3) at various annealing temperatures. At an induction of 1 T and frequency of 400 Hz and 1 kHz, the toroidal losses obtained are W_{1.0T, 400 Hz} = 0.9 W/kg and W_{1.0T, 1 kHz} = 2.3 W/kg, respectively. These losses are lower than losses recently reported for state of the art 3.0% and 6.5% silicon steels, a Metglas Fe-based amorphous alloy, and some Fe-based nanocomposites.