Microstructural characterization and amorphous phase formation in Co40Fe22Ta8B30 powders produced by mechanical alloying

In this work, microstructural evolution and amorphous phase formation in Co₄₀Fe₂₂Ta₈B₃₀ alloy produced by mechanical alloying (MA) of the elemental powder mixture under argon gas atmosphere was investigated. Milling time had a profound effect on the phase transformation, microstructure, morphological evolution and thermal behavior of the powders. These effects were studied by the X-ray powder diffraction (XRD) in reflection mode using Cu Kα and in transmission configuration using synchrotron radiation, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results showed that at the early stage of the milling, microstructure consisted of nanocrystalline bcc-(Fe, Co) phases and unreacted tantalum.Further milling, produced an amorphous phase, which became a dominant phase with a fraction of 96 wt% after 200 h milling. The DSC profile of 200 h milled powders demonstrated a huge and broad exothermic hump due to the structural relaxation, followed by a single exothermic peak, indicating the crystallization of the amorphous phase. Further XRD studies in transmission mode by synchrotron radiation revealed that the crystalline products were (Co, Fe)_20.82Ta_2.18B₆, (Co, Fe)₂₁ Ta₂ B₆, and (Co, Fe)₃B₂. The amorphization mechanisms were discussed in terms of severe grain refinement, atomic size effect, the concept of local topological instability and the heat of mixing of the reactants.     

Kinetics and formation mechanism of amorphous Fe52Nb48 alloy powder fabricated by mechanical alloying

A single phase amorphous Fe₅₂Nb₄₈ alloy has been synthesized through a solid state interdiffusion of pure polycrystalline Fe and Nb powders at room temperature, using a high-energy ball-milling technique. The mechanisms of metallic glass formation and competing crystallization processes in the mechanically deformed composite powders have been investigated by means of X-ray diffraction, Mössbauer spectroscopy, differential thermal analysis, scanning electron microscopy and transmission electron microscopy. The numerous intimate layered composite particles of the diffusion couples that formed during the first and intermediate stages of milling time (0–56 ks), are intermixed to form amorphous phase(s) upon heating to about 625 K by so-called thermally assisted solid state amorphization, TASSA. The amorphization heat of formation for binary system via the TASSA, ΔH_a, was measured directly as a function of the milling time. Comparable with the TASSA, homogeneous amorphous alloys were fabricated directly without heating the composite multilayered particles upon milling these particles for longer milling time (86 ks–144 ks). The amorphization reaction here is attributed to the mechanical driven solid state amorphization. This single amorphous phase transforms into an order phase (μ phase) upon heating at 1088 K (crystallization temperature, T_x) with enthalpy change of crystallization, ΔH_x, of −8.3 kJ mol⁻¹.     

Microstructural, thermal and magnetic properties of amorphous/nanocrystalline FeCrMnN alloys prepared by mechanical alloying and subsequent heat treatment

Amorphous FeCrMnN alloys were synthesized by mechanical alloying (MA) of the elemental powder mixtures under a nitrogen gas atmosphere. The phase identification and structural properties, morphological evolution, thermal behavior and magnetic properties of the mechanically alloyed powders were evaluated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM), respectively. According to the results, at the low milling times the structure consists of the nanocrystalline ferrite and austenite phases. By progression of the MA process, the quantity and homogeneity of the amorphous phase increase. At sufficiently high milling times (>120 h), the XRD pattern becomes halo, indicating complete amorphization. The results also show that the amorphous powders exhibit a wide supercooled liquid region. The crystallization of the amorphous phase occurs during the heating cycle in the DSC equipment and the amorphous phase is transformed into the crystalline compounds containing ferrite, CrN and Cr₂N. The magnetic studies reveal that the magnetic coercivity increases and then decreases. Also, the saturation magnetization decreases with the milling time and after the completion of the amorphization process (>120 h), the material shows a paramagnetic behavior. Although the magnetic behavior does not considerably change by heating the amorphous powders up to the crystallization temperature via DSC equipment, the material depicts a considerable saturation magnetization after the transformation of the amorphous phase to the nanocrystalline compounds.     

Fabrication of Ti-Cu-Ni-Al amorphous alloys by mechanical alloying and mechanical milling

Ti-based amorphous alloy powders were synthesized by the mechanical alloying (MA) of pure elements and the mechanical milling (MM) of intermetallic compounds. The amorphous alloy powders were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Scanning electron micrographs revealed that the vein morphology of these alloy powders shows deformation during the milling. The energy-dispersive X-ray spectral maps confirm that each constituent is uniformly dispersed, including Fe and Cr. The XRD and DSC results showed that the milling time required for amorphization for the MA of pure elements was longer than that of the MM for intermetallic compounds. The activation energy and crystallization temperature of the MA powder are different from those of the MM powder.     

Amorphization of Al---Cu---Fe quasicrystalline alloys by mechanical milling

The amorphous phase is formed from as-solidified Al---Cu---Fe alloy powder, which is mainly composed of the quasicrystalline phase, by mechanical milling. The structure and morphology of the milled powders were monitored by X-ray diffraction, scanning electron microscopy, and transition electron microscopy respectively. Experimental results indicate that quasicrystalline alloys are more easily amorphized than the corresponding crystalline alloys. No intermediate metastable phase appeared during the whole process. The crystallization behavior of the amorphous powders has been examined by thermal annealing and differential thermal analysis.     

A comparative study of mechanical alloying and mechanical milling of Nd8Fe88B4

A comparative study was made of structure and magnetic properties of Nd₈Fe₈₈B₄ prepared by mechanical alloying (MA) using elemental powders as starting materials and by mechanical milling (MM) of the alloy. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) combined with transmission electron microscopic (TEM) studies revealed that both milling procedures resulted in a mixture of α-Fe and an amorphous phase. The thermal stability of the as-milled powders produced by MA was comparable to that of the as-milled powders produced by MM. Heat treatment of the milled powders above the crystallization temperature resulted in the formation of a nanocrystalline mixture of Nd₂Fe₁₄B and α-Fe, but annealed MA powders demonstrated a somewhat coarser structure in comparison with annealed MM powders. Therefore, higher remanences and coercivities were obtained by MM.     

Structure and crystallization kinetics of a Cu50Zr45Ti5 glassy alloy

The crystallization kinetics and structure changes in a melt-spun Cu₅₀Zr₄₅Ti₅ glassy alloy on heating were investigated by X-ray diffractometry, transmission electron microscopy, differential scanning calorimetry and differential isothermal calorimetry. The glassy phase in the Cu₅₀Zr₄₅Ti₅ alloy was crystallized forming Cu₁₀Zr₇ and CuZr₂ phases upon thermal annealing. The activation energy for crystallization obtained by the Arrhenius equation was 435 kJ/mol. The crystallization process took place by nucleation and growth mechanism, and an Avrami exponent of about 3.3 may indicate a three-dimensional interface-controlled growth of nuclei with a decreasing nucleation rate.     

Partial martensitic transformation of nanocrystalline NiAl intermetallic during mechanical alloying

Nanocrystalline NiAl intermetallic powders were synthesized by mechanical alloying (MA) in a planetary ball mill. Microstructural characterization was accomplished using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The nanocrystalline NiAl powders were formed by a gradual exothermic reaction mechanism during MA. Prolonged milling resulted in partial martensitic transformation of B2-NiAl to tetragonal L1₀-NiAl structure. It is believed that the martensitic transformation is induced by mechanical stress during MA.     

Microstructures and transformation behavior of Ti-Ni-Cu shape memory alloy powders fabricated by ball milling method

Ti-Ni and Ti-Ni-Cu alloy powders have been fabricated by ball milling after which their microstructures and transformation behaviors were investigated by means of scanning electron microscopy, X-ray diffraction, energy dispersive X-ray analysis, transmission electron microscopy and differential scanning calorimetry. The powders of as-milled Ti-Ni-Cu alloys whose Cu-content is less than 5 at.% were mixtures of crystal and amorphous, whereas those alloy powders whose Cu-content is more than 10 at.% were crystalline. The B19’ martensite is formed in the Ti-Ni-Cu alloy powders whose Cu-content is less than 10 at.%, whereas the B19 and B19’ martensites coexist in those whose Cu-content is more than 10 at.%. The martensitic transformation range became wider with increasing rotating speed, and so endothermic and exothermic peaks obtained from differential scanning calorimetry were indiscernible.     

Corrosion behavior of mechanically alloyed A6005 aluminum alloy composite reinforced with TiB2 nanoparticles

Corrosion susceptibility of the A6005 alloy reinforced with n-TiB₂ was studied through electrochemical tests. The mechanical alloying (MA) technique was used as the processing route and a posterior hot extrusion was employed to consolidate the powders. Bulk samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and microhardness tests. The combination of both MA processing and 5 wt% n-TiB₂ addition in the aluminum matrix produced 61% increase of microhardness. Electrochemical tests were performed in 3.5 wt% NaCl solution to assess the effect of MA processing and TiB₂ presence on corrosion behavior. The corrosion resistance of the samples processed by MA increased slightly compared with the base A6005 alloy. The amorphous Al₂O₃ phase formed during MA processing was the cause of this increase, providing continuity to the passive layer. Furthermore, the addition of TiB₂ on the sample processed by MA did not significantly affect corrosion resistance. Polarization tests confirmed that the reinforced sample had similar i_corr to that of the unreinforced alloy, and cyclic polarization tests revealed that pit nucleation sites were localized in the interface between Al₂O₃ and the aluminum matrix.     

Zr-Ti-Cu-Ni-Be大块非晶合金等温晶化过程相分离研究

利用差示扫描量热法(DSC)和透射电镜(TEM)对Zr41.2Ti13.8Cu12.5Ni10Be22.5(at％)大块非晶合金的等温晶化过程和析出相进行了研究。结果表明，大块非晶合金在等温晶化过程中表现出多阶段相析出行为，并且在不同的晶化阶段，析出相也有所不同。在第1个晶化阶段，析出相主要是体心四方(b.c．t)结构的Zr2Cu相；而在晶化的第2个阶段，晶化相主要为简单六方结构的ZrBe2相。从一定程度上证实了Zr41.2Ti13.8Cu12.5Ni10Be22.5大块非晶合金在发生晶化时会形成富Zr区和富Be区，即有相分离的趋势。XRD测试的结果也证实了非晶合金在发生完全晶化时，主要的晶化产物为Zr2Cu和ZrBe2相。     

Mechanically induced crystalline–glassy phase transformations of mechanically alloyed Ta55Zr10Al10Ni10Cu15 multicomponent alloy powders

New multicomponent Ta-based glassy alloy powder was synthesized by mechanical alloying (MA) the elemental powders of Ta₅₅Zr₁₀Ni₁₀Al₁₀Cu₁₅ at room temperature, using a low-energy ball milling technique. During the early stage of milling the agglomerated crystalline powders are mechanically crushed and fresh surfaces are rapidly created. Kneading of such ground powders enhances the atomic diffusion and leads to local alloying. As the MA time increases, the number of vacancies in the Ta lattice (base material) increases so that the atoms of the alloying elements for Zr, Al, Ni and Cu tend to migrate to the open defected lattice of metallic Ta. The number of atoms of the alloying elements that migrate to the bcc lattice of the base material are increasing with increasing MA time and this leads to a monotonic expansion of the Ta lattice. Further milling time (86–130 ks) plays an important role in increasing the rate of diffusion and this leads to an increase in the number of migrated atoms of the alloying elements that pass into the Ta lattice. The a₀ of the yielded solid solution at this stage does not change anymore with increasing MA time and a homogeneous supersaturated bcc-solid solution is obtained after 130 ks of MA time. This solid solution, which is subjected to continuous imperfections, is gradually transformed into a glassy phase upon increasing the MA time. The glassy powders of the final-product (1080 ks) in which its glass transition temperature (T_g) lies at a high temperature (834 K), crystallize through a single sharp exothermic peak at 1004 K (T_x). The total enthalpy change of crystallization (ΔH_x) is −10.32 kJ/mol. The width of the supercooled liquid region before crystallization (ΔT_x) of the synthesized glassy powder shows the largest value (170 K) of any reported metallic glassy system.     

Nanocrystallization of Pd74Si18Au8 metallic glass

The crystallization process of Pd₇₄Si₁₈Au₈ amorphous alloy has been investigated by transmission electron microscopy, small angle X-ray scattering and three-dimensional atom probe techniques. Although literature suggests that the alloy decomposes into two glassy phases prior to the crystallization, we found that the crystallization occurs directly from a single amorphous phase by the primary crystallization of fcc Pd–Au solid solution, followed by the polymorphous crystallization of the remaining amorphous phase to a Pd₃Si phase.     

Phase transformation behaviours of Ti-Ni-Cu shape memory alloy powders fabricated by mechanical alloying

In our research, Ti-Ni and Ti-Ni-Cu alloy powders were fabricated by mechanical alloying, and then phase transformation behaviours were investigated by means of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and transmission electron microscopy. The size of the Ti-Ni-Cu alloy powders decreased as Cu-content increased. The powders of as-milled Ti-Ni and Ti-Ni-Cu alloys with Cucontents less than 5at.% were amorphous, whereas those of as-milled Ti-Ni-Cu alloys with Cu-content more than 10at.% were crystalline. These characteristics indicate that Cu addition tends to suppress amorphization of Ti-Ni based alloy powders. The monoclinic B19’ martensite is formed in the Ti-Ni-Cu alloy powders with Cu-content less than 10 at.%, whereas the orthorhombic B19 martensite is formed in the Yi-Ni-Cu alloy powders Cu-content more than 10 at.%. The Fe contamination is reduced by decreasing rotation speed from 350 rpm to 250 rpm.     

放电等离子烧结-非晶晶化法合成Ti7oNb7.8Cu8.4Ni7.2Al6.6复合材料

采用机械合金化制备不含和含2%(体积分数)B4C的钛基非晶合金粉末,随后采用放电等离子烧结-非晶晶化法合成不含／含(TiB+TiC)的Ti7oNb7.8Cu8.4Ni7.2Al6.6超细晶／细晶钛基复合材料;运用X射线衍射分析(XRD)、差示扫描量热分析(DSC)、扫描电子显微镜(SEM)和万能材料试验机等对制备的钛基非晶粉末和超细晶／细晶钛基复合材料进行表征.结果表明高能球磨80h的钛基粉末中主要为非晶相,B4C颗粒的加入对钛基粉末的玻璃转变温度、晶化温度和晶化焓有显著的影响.另外,不含／含(TiB+TiC)的复合材料的显微硬度分别为5.47和5.33GPa;以50K/min升温到1223K并保温10min获得的Ti70Nb7.8Cu8.4Ni7.2Al6.6块体试样的断裂强度和断裂应变分别为2098MPa和11.5%.     

Formation of NiAl Intermetallic Compound by Cold Spraying of Ball-Milled Ni/Al Alloy Powder Through Postannealing Treatment

Ni/Al alloy powders were synthesized by ball milling of nickel-aluminum powder mixture with a Ni/Al atomic ratio of 1:1. Ni/Al alloy coating was deposited by cold spraying using N₂ as accelerating gas. NiAl intermetallic compound was evolved in situ through postspray annealing treatment of cold-sprayed Ni/Al alloy coating. The effect of annealing temperature on the phase transformation behavior from Ni/Al mechanical alloy to intermetallics was investigated. The microstructure of the mechanically alloying Ni/Al powder and NiAl coatings was characterized by scanning electron microscopy and x-ray diffraction analysis. The results show that a dense Ni/Al alloy coating can be successfully deposited by cold spraying using the mechanically alloyed powder as feedstocks. The as-sprayed alloy coating exhibited a laminated microstructure retained from the mechanically alloying powder. The annealing of the subsequent Ni/Al alloy coating at a temperature higher than 850 °C leads to complete transformation from Ni/Al alloy to NiAl intermetallic compound.     

Kinetic study of non-isothermal crystallization in Al80Fe10Ti5Ni5 metallic glass

This study investigated the crystallization behavior of a kinetically metastable Al₈₀Fe₁₀Ti₅Ni₅ amorphous phase. The Al₈₀Fe₁₀Ti₅Ni₅ amorphous phase was synthesized via the mechanical alloying of elemental powders of Al, Fe, Ti, and Ni. The microstructures and crystallization kinetics of the as-milled and annealed powders were characterized using X-ray diffraction, transition electron microscopy, and non-isothermal differential thermal analysis techniques. The results demonstrated that an Al₈₀Fe₁₀Ti₅Ni₅ amorphous phase was obtained after 40 h of ball milling. The produced amorphous phase exhibited one-stage crystallization on heating, i.e., the amorphous phase transforms into nanocrystalline Al₁₃(Fe,Ni)₄ (40 nm) and Al₃Ti (10 nm) intermetallic phases. The activation energy for the crystallization of the alloy evaluated from the Kissinger equation was approximately 538±5 kJ/mol using the peak temperature of the exothermic reaction. The Avrami exponent or reaction order n indicates that the nucleation rate decreases with time and the crystallization is governed by a three-dimensional diffusion-controlled growth. These results provide new opportunities for structure control through innovative alloy design and processing techniques.     

Formation, properties and microstructure of amorphous/crystalline composite Ag20Cu30Ti50 alloy using miscibility gap

The aim of the work was to produce the amorphous/crystalline composite with uniform distribution of fine crystalline soft phase. Silver–copper–titanium Ag₂₀Cu₃₀Ti₅₀ alloy was prepared using 99.95 wt% Ag, 99.95 wt% Cu, 99.95 wt% Ti that were arc-melted in argon atmosphere. Then the alloy was melt spun on a copper wheel with linear velocity of 33 m/s. Investigation of the microstructure for both arc-melt massive sample and melt-spun ribbons was performed with use of scanning electron microscope (SEM) with EDS, light microscope (LM) and X-ray diffraction. The thermal stability was evaluated by differential scanning calorimetry (DSC). The properties such as Young modulus and Vickers hardness number before and after crystallization of the amorphous matrix were measured with use of nanoindenter. The microstructure was investigated by transmission electron microscope (TEM). It was found, that the alloy has a tendency for separation within the liquid state due to the miscibility gap which resulted in segregation into Ti–Cu–Ag matrix and Ag-base spherical particles after arc-melting. During rapid cooling through the melt spinning the Ag₂₀Cu₃₀Ti₅₀ alloy formed an amorphous/crystalline composite of fcc silver-rich spherical particles within the amorphous Ti–Cu–Ag matrix.     

Calorimetric and structural analysis of the new phase Al33Ni16Zr51 produced by direct synthesis and mechanical alloying

A new phase has been synthesized in the ternary phase diagram Al–Ni–Zr: its nominal composition is Al₃₃Ni₁₆Zr₅₁. For the Al₃₃Ni₁₆Zr₅₁ compound obtained by mixing the three components in suitable proportions, a study has been carried out by direct synthesis (calorimetry) and mechanical alloying in our laboratory. With the first method we know directly the enthalpy of formation of this alloy. For the amorphous alloys prepared by mechanical alloying we can determine the crystallisation enthalpy with the differential scanning calorimetry (DSC) method. So it is possible to determine a fundamental piece of information: the amorphous alloy formation enthalpy.     

Structure and magnetic properties of nanostructured MnNi alloys fabricated by mechanical alloying and annealing treatments

A nearly equiatomic MnNi alloy was fabricated from the elemental powders by means of mechanical alloying in a planetary ball milling apparatus. X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and measurements of magnetization were conducted to identify the structural states and properties of the prepared alloys. After ball milling for 20 h, a disordered face-centered cubic (f.c.c.) solid solution was formed which increased in lattice parameter by further milling up to 50 h. An exothermic reaction took place at around 300–400°C during continuous heating of the disordered f.c.c. solid solution. This reaction is attributed to a structural ordering leading to the formation of a face-centered tetragonal (f.c.t.) phase with L1₀ type ordering. Examination of the magnetic properties indicated that the structural ordering increases remnant magnetization and decreases coerecivity.