Formation and crystallization of an amorphous Al80Fe10Ti5Ni3B2 alloy

In this study, we investigated the crystallization behavior of an Al₈₀Fe₁₀Ti₅Ni₃B₂ amorphous alloy (obtained by mechanical alloying) using X-ray diffraction (XRD), transition electron microscopy (TEM), and differential thermal analysis (DTA) techniques. The obtained results show that an amorphous phase formed during mechanical alloying (for 40 h) of the Al-10%Fe-5%Ti-3%Ni-2%B powder mixture. It was found that the Al₈₀Fe₁₀Ti₅Ni₃B₂ amorphous alloy exhibits one-stage crystallization when heated (amorphous to Al₁₃Fe₄, Al₅Fe₂ and AlFe intermetallic phases). The activation energy for the crystallization, evaluated from the Kissinger equation, was about 242 ± 5 kJ/mol. We also discuss kinetic parameters such as the Avarmi exponent and reaction order (n). The results show that only one three-dimensional diffusion-controlled growth mechanism was working during the amorphous-glass process of the investigated glass.     

Crystallization studies of Al<Subscript>85</Subscript>Y<Subscript>10</Subscript>Fe<Subscript>5−x</Subscript>Ni<Subscript>x</Subscript> (x = 0, 2.5, 5) alloys

The crystallization behavior of melt-spun A₈₅Y₁₀Fe_5−xN_x (x=0, 2.5, 5) amorphous alloys has been investigated by a combination of differential scanning calorimetry (DSC) and x-ray diffractometry (XRD). XRD traces of these alloys consisted of a single broad peak corresponding to fully amorphous structure. Continuous DSC results showed that, the first crystallization peak temperature of Al₈₅Y₁₀Fe₅ amorphous alloy was about 60 K higher than that of Al₈₅Y₁₀Ni₅. The activation energies for the first crystallization peak increased from 210 kJ/mol for Al₈₅Y₁₀Ni₅ to 280 for Al₈₅Y₁₀Fe₅. These results indicate that 5 at.% substitutions Ni by Fe increases the stability of the amorphous phase.     

Peculiarities of ball-milling induced crystalline–amorphous transformation in Cu–Zr–Al–Ni–Ti alloys

An amorphization process in (Cu₄₉Zr_45−xAl_6+x)_100−y−zNi_yTi_z (x = 1, y, z = 0; 5; 10) induced by ball-milling is reported in the present work. The aim was investigation of the effect of Ni and Ti addition to Cu₄₉Zr₄₅Al₆ and Cu₄₉Zr₄₄Al₇ based alloys as well as type of initial phases on the amorphization processes. Also the milling time sufficient for obtaining fully amorphous state was determined. The entire milling process lasted 25 h. Drastic structural changes were observed in each alloy after first 5 h of milling. In most cases, after 15 h of milling the powders had fully amorphous structure according to XRD except for those ones, where TEM revealed a few nanosized crystalline particles in the amorphous matrix. In (Cu₄₉Zr₄₅Al₆)₈₀Ni₁₀Ti₁₀ alloy the amorphization process took place after 12 h of milling and the amorphous state was stable up to 25 h of milling. In the case of (Cu₄₉Zr₄₄Al₇)₈₀Ni₁₀Ti₁₀ alloy the powders have fully amorphous structure between 12 h and 15 h of milling.     

Crystallization behavior in severely cold-drawn Ti50Ni47Fe3 wire

The microstructures and crystallization behavior of Ti–47 at% Ni–3 at% Fe shape memory alloy wire under the condition of severe cold drawing at room temperature and different post-deformation annealing processes were intensively investigated using transmission electron microscope(TEM) and differential scanning calorimetry(DSC). It is indicated that the amorphous phase is dominant in the Ti50Ni47Fe3 wire after the cold drawing of 78 % areal reduction. The critical temperature for recrystalization is determined at about 300 °C. The average grain size grows from 7 up to 125 nm when annealing temperature rises from300 to 500 °C. Post-deformation annealing process exerts significant influence on the crystallization temperature which climbs up with the increase of annealing temperature.     

Microstructures and Mechanical Properties of NiTiFeAlCu High-Entropy Alloys with Exceptional Nano-precipitates

Three novel NiTiFeAlCu high-entropy alloys, which consist of nano-precipitates with face-centered cubic structure and matrix with body-centered cubic structure, were fabricated to investigate microstructures and mechanical properties. With the increase in Ni and Ti contents, the strength of NiTiFeAlCu alloy is enhanced, while the plasticity of NiTiFeAlCu alloy is lowered. Plenty of dislocations can be observed in the Ni₃₂Ti₃₂Fe₁₂Al₁₂Cu₁₂ high-entropy alloy. The size of nano-precipitates decreases with the increase in Ni and Ti contents, while lattice distortion becomes more and more severe with the increase in Ni and Ti contents. The existence of nano-precipitates, dislocations and lattice distortion is responsible for the increase in the strength of NiTiFeAlCu alloy, but it has an adverse influence on the plasticity of NiTiFeAlCu alloy. Ni₂₀Ti₂₀Fe₂₀Al₂₀Cu₂₀ alloy exhibits the substantial ability of plastic deformation and a characteristic of steady flow at 850 and 1000 °C. This phenomenon is attributed to a competition between the increase in the dislocation density induced by plastic strain and the decrease in the dislocation density due to the dynamic recrystallization.     

Electron irradiation induced nano-crystallization in Zr66.7Ni33.3 amorphous alloy and Zr60Al15Ni25 metallic glass

Electron irradiation induced phase transformation behavior of an amorphous phase in Zr_66.7Ni_33.3 alloy, and an amorphous phase or supercooled liquid in Zr₆₀Al₁₅Ni₂₅ alloy was investigated. The amorphous phase could not maintain the original glassy structure under electron irradiation at 298 K, and f.c.c.-solid solution precipitated under electron irradiation in both alloys. The precipitation of C16-Zr₂Ni, big-cube (metastable f.c.c.-based Zr₂Ni intermetallic compound), Zr₆Al₂Ni and Zr₅AlNi₄ crystalline phases from an amorphous phase was not observed during electron irradiation induced crystallization. The amorphous phase in Zr₆₀Al₁₅Ni₂₅ metallic glass shows the highest phase stability against electron irradiation induced crystallization among Zr_66.7Cu_33.3, Zr_66.7Ni_33.3, Zr₆₅Al_7.5Ni_27.5, Zr₆₀Al₁₅Ni₂₅ and Zr₆₅Al_7.5Ni₁₀Cu_17.5 alloys. In Zr₆₀Al₁₅Ni₂₅ metallic glass, electron irradiation promoted the precipitation of f.c.c.-solid solution and Zr₆Al₂Ni crystalline phases from the supercooled liquid.     

Powder metallurgical production of TiNiNb and TiNiCu shape memory alloys by combination of pre-alloyed and elemental powders

The common Ti₄₄Ni₄₇Nb₉ and Ti₅₀Ni₄₀Cu₁₀ ternary shape memory alloys were produced by sintering techniques and the microstructure, phase structure and phase transformation behaviour were investigated. A combination of pre-alloyed binary TiNi powder and elemental Nb, Ni and Cu, Ti powders, respectively, were used. In contrast to the use of pre-alloyed ternary powders, which have to be produced in each new composition, a higher flexibility in the alloy composition becomes possible. In case of the Ti₄₄Ni₄₇Nb₉ alloy, liquid phase sintering was done to obtain the eutectic phase structure known from cast material. In case of the Ti₅₀Ni₄₀Cu₁₀ alloy, the pore size and porosity can be improved by choosing a two-step sintering process, as a eutectic melt between Ti and Cu is formed at low temperatures which influences the sintering behaviour. Controlling the impurity contents and the resulting secondary phases is necessary for both alloys in the same way as for binary TiNi alloys.     

层叠Ni/Ti热扩散形成金属间化合物的规律

选择Ni和Ti粉末及其机械合金化粉末制备Ni/Ti扩散偶,利用扫描电镜和X射线衍射等手段研究了Ni/Ti扩散偶在固相热处理作用下金属间化合物的形成及生长规律.随着热处理温度的提高,Ni3Ti,Ti2Ni和NiTi金属间化合物的数量增加明显;随热处理保温时间的增加,NiTi金属间化合物呈抛物线规律生长,而对Ni3Ti和Ti2Ni的生长影响不大.结果表明,金属间化合物在形成过程中,Ni3Ti和Ti2Ni优先形成,达到一定厚度后,NiTi金属间化合物开始形成并快速增长.     

Influences of additional alloying elements (V,Ni, Cu,Sn, B) on structure and mechanical properties of high-strength hypereutectic Ti–Fe–Co bulk alloys

High-strength nonequilibrium hypereutectic bulk alloys were obtained recently in the Ti–Fe and Ti–Fe–Co systems by arc-melting. Following these results, the influences of the additional alloying elements (V, Ni, Cu, Sn, B) on high strength hypereutectic Ti–Fe–Co bulk alloys are studied and analyzed in the present work. The structure of the hypereutectic quaternary Ti₆₇Fe₁₄Co₁₄Sn₅, Ti₆₇Fe₁₄Co₁₄V₅, Ti₇₀Fe₁₇Co₇Cu₆, Ti₇₀Fe₁₇Co₇Ni₆, and Ti_69.4Fe_14.8Co_14.8B₁ alloys obtained in the form of arc-melted ingots of about 20–30 mm diameter and 10–15 mm height was studied by X-ray diffractometry and scanning electron microscopy. The mechanical properties were tested by an Instron-type machine. Ti₆₇Fe₁₄Co₁₄Sn₅ alloy exhibits a high ultimate compressive strength of 1830 MPa and a large plastic strain of 24% which exceeds the ductility values obtained for Ti–Fe and Ti–Fe–Co alloys. The addition of Sn causes formation of a relatively rough eutectic structure which is preferable for the high strength hypereutectic alloys. Rough primary dendrites and eutectic rods of the cP2 intermetallic phase act as efficient barriers for shear strain and cracks propagation while fine eutectic rods of submicron size are quite effortlessly cut by deformation bands and cracks.     

Crystallization of amorphous Zr60Al15Ni25 alloy

The phase formation and crystallization kinetics during the thermal treatment of amorphous Zr₆₀Al₁₅Ni₂₅ alloy were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). By lowering the isothermal annealing temperatures, it is revealed that the crystallization of the amorphous Zr₆₀Al₁₅Ni₂₅ alloy consists of a primary transformation followed by a polymorphic transformation, corresponding to the precipitations of hexagonal Zr₆Al₂Ni and the Zr₅AlNi₄ with a U₃Si₂-typed superstructure. The primary phase being Zr₆Al₂Ni rather than Zr₅AlNi₄ in the crystallization is because the latter has a complex structure and its formation requires the diffusion of Al and Zr atoms on a large scale.     

Structural and Mössbauer spectroscopic investigation of Fe substituted Ti–Ni shape memory alloys

In the present investigation the effect of Fe substitution in Ti₅₁Ni₄₉ alloy has been studied. The alloys were synthesized through radio frequency induction melting. The alloy was characterized through X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Mössbauer spectroscopy and positron annihilation techniques. It was found that the Fe substitution stabilized the TiNi type cubic (a = 2.998 Å) phase. The microstructure and presence of the oxide phase in Ti₅₁Ni₄₅Fe₄ alloy have been investigated by scanning electron microscopy. The positron annihilation measurements indicated a similar bulk electron density in both the as-cast and annealed (1000 °C for 30 h) alloys, typically like that of bulk Ti. Mössbauer spectroscopy studies of as-cast and annealed iron substituted samples showed regions in the samples where nuclear Zeeman splitting of Fe levels occurred and an oxide phase was found to be present in as cast Ti₅₁Ni₄₅Fe₄ alloy, while annealed sample indicated the presence of bcc iron phase.     

Kinetics of crystallization process for bulk glass forming Zr-base alloys

The crystallization kinetics of Zr₆₅Ni₁₀Cu_17.5Al_7.5 (alloy I) and Zr_52.5Ni_14.6Cu_17.9Al₁₀Ti₅ (alloy II) are investigated. Two-stage crystallization takes place during continuous heating of the glassy alloy I, resulting in the transformation of the glass to the metastable α-Zr-solid solution and Zr-base quasicrystals with an activation energy of 309 KJ/mol in the first-stage and the formation of Zr₂Cu compound and the stable α-Zr-solid solution with an activation energy of 227 KJ/mol in the second-stage. For alloy II, one-stage crystallization with an activation energy of 333 KJ/mol occurs during continuous heating of the glass, resulting in the formation of Zr₃Al and α-(Zr,Ti)-solid solution. Based on the DSC data and calculations, both the alloys go through with three stages of crystallization mechanism during isothermal annealing, i.e. (1) surface nucleation and growth, (2) three-dimensional nucleation and growth, and (3) crystal growth. The TEM observation on Zr_52.5Ni_14.6Cu_17.9Al₁₀Ti₅ alloy is in good agreement with the calculations.     

Structure and phase-composition of Ti-doped gas atomized Raney-type Ni catalyst precursor alloys

Raney-type Ni precursor alloys containing 75 at.% Al and doped with 0, 0.75, 1.5 and 3.0 at.% Ti have been produced by a gas atomization process. The resulting powders have been classified by size fraction with subsequent investigation by powder XRD, SEM and EDX analysis. The undoped powders contain, as expected, the phases Ni₂Al₃, NiAl₃ and an Al-eutectic. The Ti-doped powders contain an additional phase with the TiAl₃ DO₂₂ crystal structure. However, quantitative analysis of the XRD results indicate a far greater fraction of the TiAl₃ phase is present than could be accounted for by a simple mass balance on Ti. This appears to be a (Ti_xNi_1−x)Al₃ phase in which higher cooling rates favour small x (low Ti-site occupancy by Ti atoms). SEM and EDX analysis reveal that virtually all the available Ti is contained within the TiAl₃ phase, with negligible Ti dissolved in either the Ni₂Al₃ or NiAl₃ phases.     

The compositional range of amorphous phase formation and thermal stability of Al90−xFe5Ni5Cex

The effects of Ce-substitution for Al in the Al_90−xFe₅Ni₅Ce_x (x = 0, 2, 5, 7, 8, 9, and 10) system on the mechanical alloying process were investigated. The structural evolution in these powders was characterized by scanning electron microscopy, differential thermal analysis and X-ray diffraction techniques. The compositional range of amorphous forming was obtained and it extended from 5 to 9 at.% Ce. With increasing Ce content, the crystallization temperature of amorphous alloys increases. The crystallization temperature versus concentration of Ce was reproduced well by applying an extension of a relationship between the crystallization temperature and the vacancy formation energy of constituents with smaller atomic radius. The crystallization product phases were analyzed by XRD after annealing the milled powders at temperature over the crystallization temperature.     

The effect of Si addition on crystallization behavior of amorphous Al-Y-Ni alloy

This article reports the effect of silicon (Si) addition upon the crystallization behavior and mechanical properties of an amorphous AlYNi alloy. An amount of 1 at.% Si was added to a base alloy of Al₈₅Y₅Ni₁₀ either by substitution for yttrium (Y) to form Al₈₅Y₄Ni₁₀Si₁, or by substitution for nickel (Ni) to form Al₈₅Y₅Ni₉Si₁. Differential scanning calorimetry (DSC) of all three alloys showed three exothermic peaks. Comparing the peak temperature for the first exothermic peak, a significant shift occurs toward the lower temperature. This indicates that 1 at.% substitutions of Y or Ni by Si decreases the stability of the amorphous phase. DSC study of these amorphous alloys during isothermal annealing at temperatures about 5–15 K lower than their first crystallization peaks showed that the formation of α-Al nanocrystals via primary crystallization occurred without an incubation period. The Avrami time exponent (n) of the primary crystallization from the amorphous structure was determined to be 1.00–1.16 using the Johnson-Mehl-Avrami (JMA) analysis. This suggested a diffusion-controlled growth without nucleation. However, a DSC study of these amorphous alloys during isothermal annealing at higher temperatures between 585 and 605 K showed a clear incubation period during the formation of the Al₃Ni and Al₃Y intermetallic phases. An n value of 3.00–3.45 was determined using JMA analysis. This suggested that the transformation reaction involved a decreasing nucleation rate and interface-controlled growth behavior. The tensile strength σ_f and Vickers hardness for these amorphous alloys are in the range 1050–1250 MPa and 380–398 diamond pyramid hardness number (1 diamond pyramid hardness number=1 kg/mm²=9.8 MPa), respectively.     

Microstructural analysis of Zr55Cu30Al10Ni5 bulk metallic glasses by laser surface remelting and laser solid forming

The crystallization behavior of Zr₅₅Cu₃₀Al₁₀Ni₅ bulk amorphous alloy during laser solid forming (LSF) was analyzed. Since laser surface remelting (LSM) is a key process for the LSF, the crystallization behavior of as-cast Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glasses (BMGs) during LSM was also investigated. It was found that the amorphous state of the as-cast BMGs was maintained when they were repeatedly remelted four times in a single-trace LSM, and as for the LSF of Zr₅₅Cu₃₀Al₁₀Ni₅ bulk amorphous alloy, the crystallization primarily occurred in the HAZ between the adjacent traces and layers after the two layers were deposited. The as-deposited microstructure exhibited a series of phase evolutions from the molten pool to the HAZ as follows: the amorphous → NiZr₂–type nanocrystal + amorphous → NiZr₂–type equiaxed dendrite + amorphous → Cu₁₀Zr₇–type dendrite + NiZr₂–type nanocrystal. Among these microstructural patterns, the NiZr₂–type nanocrystals and equiaxed dendrites primarily formed from the rapid solidification of the remelted liquid in the laser processing process, and the Cu₁₀Zr₇–type dendrites in the HAZ primarily formed by the crystallization of pre-existed nuclei in the already-deposited amorphous substrate.     

铝镁合金等离子喷涂复相陶瓷涂层微观组织

为解决铝镁合金表面耐磨性差的问题,利用机械球磨法和PVA造粒技术制备复合陶瓷粉末,采用等离子喷涂技术在XGFH-3铝镁合金表面制备了反应复相陶瓷涂层,利用扫描电镜(SEM)、X射线衍射仪(XRD)分析了喷涂复合粉末和复相陶瓷涂层的形貌及组成.结果表明,复合粉末随着球磨时间的延长明显趋于扁平化和均匀化,并且生成了Al₃Ti,Ni₄Ti₃等新相.而在喷涂过程中Al₃Ti和Ni₄Ti₃中间相又会消失,涂层中出现了MgAl₂O₄和Ti₅Si₃等新相,基体和涂层之间有元素扩散,这使得涂层有良好的结合强度.     

Influence of powder size on the crystallization behavior during laser solid forming Zr55Cu30Al10Ni5 bulk amorphous alloy

The Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glasses (BMGs) were prepared using laser solid forming (LSF) process from the plasma rotating electrode process (PREP) powder. The effect of the powder size on the crystallization behavior of the remelted zone (RZ) and heat affected zone (HAZ) was investigated. It was found that the as-prepared powders were composed of the amorphous phase and Al₅Ni₃Zr₂-type phase. The RZ mainly kept the amorphous state after LSF. The residual Al₅Ni₃Zr₂-type phase could be observed in RZ only if the powder size was larger than 106 μm. Meanwhile, the NiZr₂-type nanocrystals at the boundary of RZ primarily formed from the solidification of remelted liquid. With the increase of the powder size, the lower overheating temperature and shorter existing time of the molten pool enhanced the heredity of Al₅Ni₃Zr₂ clusters and other intermetallic clusters in remelted alloy melt, which decreased the thermal stability of the already-deposited layer. The volume fraction of crystallization in the deposit increased with the increase in powder size. There was no crystallization occurred in the HAZ between the adjacent tracks and layers for the deposit prepared by the powder with the size range of 53–75 μm. However, the wide crystalline band with Al₅Ni₃Zr₂-type faceted phase, CuZr-type dendrite, CuZr₂-type spherulite and NiZr₂-type nanocrystal were observed in the entire HAZ for the deposit prepared by the powder with the size range of 106–150 μm. The finer powder was benefit to prepare the BMGs by LSF.     

Nanocrystalline Al–Fe intermetallics – light weight alloys with high hardness

Nanocrystalline Al–Fe alloys containing 60–85 at.% Al were produced by consolidation of mechanically alloyed nanocrystalline or amorphous (Al85Fe15 composition) powders at 1000 °C under a pressure of 7.7 GPa. The hardness of the alloys varied between 5.8 and 9.5 GPa, depending on the Al content. The specific strength, calculated using an approximation of the yield strength according to the Tabor relation, was between 544 and 714 kNm/kg. Based on the results obtained, we infer that application of high pressure affected crystallisation of amorphous Al₈₅Fe₁₅ alloy, influencing the phase composition of the crystallisation product, and phase changes in nanocrystalline Al₈₀Fe₂₀ alloy, inhibiting them.     

Effect of Gd on microstructure and refinement performance of Al-5Ti-B alloy

Al-5Ti-B and Al-5Ti-B-Gd master alloy refiners were fabricated by fluorine salt casting method. The microstructure and phase constitution of the master alloys were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that Al-Ti-B alloy refiner consists of Al₃Ti phase and TiB₂ phase. After Gd is introduced into the intermediate alloy, Ti₂Al₂₀Gd phase appears in the alloy, the size of Al₃Ti is significantly reduced, and Ti-Al-Gd phase is found in the edge of Al₃Ti phase. At the same time, some independent Ti-Al-Gd phases appear in local areas, which are Ti₂Al₂₀Gd phase determined by micro-area electron diffraction analysis. Analysis and calculation results of the high-resolution images of the Ti₂Al₂₀Gd/Al structure show that there is no other compound at the junction between the Ti₂Al₂₀Gd phase and Al, and Ti₂Al₂₀Gd phase has a great difference in atomic space with the α-Al, which cannot be directly used as heterogeneous nucleus. But, after being decomposed in the aluminum melt, the Ti₂Al₂₀Gd phase can promote the refinement effect of the refiner. In the Al-Ti-B-Gd master alloy, there are many dispersed Al₃Ti particles with a size of less than 1 µm, which can promote the Al-5Ti-B refining effect.