Nanocrystalline Intermetallic Compounds Research Articles

Ball milling synthesis and effects of infrared heat treating on the nanocrystalline Ti/Zr/Cu/Ni system

A Ti/Zr based solid solution with a nominal wt. % composition of 37.5Ti-37.5Zr-15Cu-10Ni (eutectic) has been successfully synthesized by mechanical alloying using a high-energy planetary ball mill and it was performed at 250 rpm and different milling periods of 5, 10, and 15 h. Scanning electron microscopy revealed that the powder experienced severe deformation from the milling process. The powder was heat treated using an indigenous infrared tube furnace at a heating rate of 200 °C/min. X-ray diffraction results showed the presence of several nanocrystalline intermetallic compounds after infrared heat treating at 750 °C for 15 min in an argon atmosphere. The feature of infrared radiation ensured that the nanocrystalline size of the produced powder remained almost intact during the milling process. The crystal size, lattice parameter, and lattice strain at the optimal milling period (10 h) were determined to be 13 nm, 2.7 Å, and 0.4 %, respectively.

Tribological behavior of Ni-Nb amorphous coating fabricated by mechanical alloying method

In this study, the microstructure, microhardness and tribological behavior of the Ni-Nb amorphous coating fabricated by mechanical alloying method were investigated at three annealing timepoints (30, 120, 240 min) at 650 °C. Annealing of amorphous coating for 30 min led to a reduction in microhardness. However, as annealing continued, the microhardness demonstrated significant growth. The changes were attributed to the formation of Ni3Nb and Ni6Nb7 nanocrystalline intermetallic compounds embedded in the amorphous matrix. The wear resistance of the coatings up to 120 min of annealing showed a similar trend with microhardness but no longer followed the microhardness trend after 240 min of annealing. The delamination and oxidative wear mechanisms were the dominant wear mechanisms for the as-prepared and annealed coatings.

Ball milling for the formation of nanocrystalline intermetallic compounds from Ni-Ti elemental powders

Abstract In the present research work nickel (Ni) and titanium (Ti) elemental powder with an ostensible composition of 50% of each by weight were mechanically alloyed in a planetary high energy ball mill in diverse milling circumstances (10, 20, 30 and 60 h). The inspection exposed that increasing milling time leads to a reduction in crystallite size, and after 60 h of milling, the Ti dissolved in the Ni lattice and the NiTi (B2) phase was obtained. The lattice strain of ball milled mixtures augmented from 0.15 to 0.45 at 60 h milling. With increase in milling time the morphology of pre-alloyed powder changed from lamella to globular. Annealing of as-milled powders at 1100 K for 800 s led to the formation of NiTi (B19′), grain growth and the release of internal strain. The result indicated that this technique is a powerful and highly productive process for preparing NiTi intermetallic compounds with a nano-crystalline structure and appropriate morphology.

Mineralogical characterization of scalings formed in geothermal sites in the Upper Rhine Graben before and after the application of sulfate inhibitors

Scale formation processes in the surface installations of geothermal power plants may have a negative effect on power plant performance. In addition, scales formed within the geothermal water circuit frequently accumulate natural radionuclides. Consequently, scale formation may lead to radiation dose rates, which are of radiological concern, and deposits, which may have to be disposed as radioactive waste. In order to minimize these problems and to foster geothermal power plant availability, it is of major interest to understand scale formation processes and to develop methods for their inhibition. One important pre-requisite towards this goal is a sound mineralogical and geochemical characterization of the formed material.Geothermal brines at sites in the Upper Rhine Graben are in general highly mineralized and become, upon cooling in the heat exchanger, supersaturated with respect to sulfate solid-solutions, e.g. (Ba,Sr)SO4, and other mineral phases. Some geothermal power plants very successfully tested the application of sulfate scaling inhibitors. Here we present mineralogical analyses of scale samples from geothermal power plants in the Upper Rhine Valley deposited in absence and presence of sulfate scaling inhibitors. Solid samples are investigated using wet-chemistry (after digestion), XRPD, SEM-EDX, XPS, EA-IRMS, Raman spectroscopy, and XANES (for explanation of abbreviations, see main text).Samples of scales deposited in the absence of a sulfate scaling inhibitor mainly consist of two phases. The largest part is made up of a barite type (Ba,Sr,Ca)SO4 solid-solution. Traces of Ra occurring in the scaling are assumed to be incorporated in the barite type solid solution. Further minor phases are sulfide phases, either an X-ray amorphous nano-particulate phase or galena (PbS).Since the application of the sulfate inhibitor, sulfate minerals are no longer detectable in the scale samples. Subsequent scalings are Pb-dominated and consist mainly of galena (PbS), elemental lead (Pb), arsenic (As) and antimony (Sb). As and Sb are likely present as a nanocrystalline intermetallic mixed compound ((Sb, As) or Pb3(Sb,As)2S3). The absence of barite-type minerals demonstrates the success of the application of the sulfate inhibitor. The precipitation of elemental Pb, As, and Sb, which are more noble than iron, may enhance the corrosion of mild steel pipes in the geothermal water circuit. Elution tests and oxidation of the scalings upon storage at atmospheric conditions demonstrate that proper disposal of the toxic heavy metal and metalloid containing scalings may be challenging.

Calorimetric study of peculiar hydrogenation behavior of nanocrystalline TiFe

Thermodynamic analysis of hydrogen interaction with TiFe nanocrystalline intermetallic compound produced by mechanical alloying has been carried out using microcalorimetric titration technique. The boundary of the phase regions and H2 absorption/desorption reaction enthalpies have been defined in comparison with conventional as-cast alloy. It has been concluded that specific microstructure and oxygen contamination determine the system features within the α solid solution region and play a key role in formation of β2 and γ, but does not affect the thermodynamic parameters of the main β → α transformation.

Solid solution and amorphous phase in Ti–Nb–Ta–Mn systems synthesized by mechanical alloying

This work discusses the formation of Ti–30Nb–13Ta–xMn (x: 2, 4 and 6 wt%) solid solution by mechanical alloying using a shaker mill. A solid solution was formed after 15 h of milling and an amorphous phase was formed after 30 h of milling, according to X-ray diffraction results. Disappearance of strongest X-ray diffraction peaks of Nb, Ta and Mn indicated the formation of solid solution, while, X-ray diffraction patterns of powders milled for 30 h showed an amorphous hump with crystalline peaks in the angular range of 35–45° in 2θ. TEM image analysis showed the presence of nanocrystalline intermetallic compounds embedded in an amorphous matrix. Mn2Ti, MnTi and NbTi4 intermetallic compounds were detected and revealed crystallites with size ranging from 3 to 20 nm. The Gibbs free energy for the formation of solid solution and amorphous phase of three ternary systems (Ti–Nb–Ta, Ti–Nb–Mn and Ti–Ta–Mn) was calculated using extended Miedema's model. Experimental and thermodynamic data confirmed that solid solution was first formed in the alloy with 6wt% Mn followed by the formation of an amorphous phase as milling time increases. The presence of Mn promoted the formation of amorphous phase because the atomic radius difference between Mn with Ti, Nb and Ta.

Effect of Mo Addition on Nanostructured Ni50Al50 Intermetallic Compound Synthesized by Mechanical Alloying

The mechanical alloying process was used to synthesize the Ni50Al50−xMox nanocrystalline intermetallic compound using pure Ni and Al elemental powder. This process was carried out in the presence of various Mo contents as a micro-alloying element for various milling times. Structural changes of powder particles during mechanical alloying were studied by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Results showed that mechanical alloying in various combinations was completed after 48 h of milling time. Minimum crystallite size of the as-milled powders (∼10 nm) was achieved after introducing Mo and milling for 128 h. Also, lattice strain decreased with increasing milling time up to 48 h and again increased after 48 h of milling time. On the other hand, the presence of Mo significantly affected variation intensity of the lattice parameter and morphology of the powder particles.

Superior electrochemical hydrogen storage properties of binary Mg–Y thin films

Mg–Y thin films capped with Pd have been prepared by direct current magnetron co-sputtering system. It is found that Mg alloyed with Y in film state forms ultrafine nanocrystalline intermetallic compounds. The structure together with the catalytic effect of Y gives rise to a high electrochemical hydrogen storage capacities and superior activation properties. It is worthy to note that Mg78Y22 film achieves a high discharge capacity of 1590 mAh g−1 without requiring activation process. Moreover, Mg alloyed with Y effectively improves the cyclic stability of Mg-based films ascribing to the anti-corrosion role of Y. For Mg37Y63 film, more than 92％ of the maximum discharge capacity can be maintained after 100 charge–discharge cycles.

Mechanical alloying of nanocrystalline intermetallic compound TiFe doped with sulfur and magnesium

A series of nanostructured alloys based on TiFe intermetallic compound were synthesized from the metallic elements in a planetary ball mill by solid state mechanical alloying. Mg and S were added as doping components to a Fe–50%(at.) Ti powder mixture. Phase and structure transformations during mechanical alloying and subsequent annealing as well as hydrogen interaction with the alloys prepared were studied. It was shown that reversible hydrogen sorption capacities of the nanostructured alloys based on TiFe intermetallic compound were of 0.6 and 0.7wt.% at room temperature for the alloys with S and Mg, respectively. The alloys studied demonstrated a simplified activation of hydrogenation, especially for the S-containing one.

Mechanical and magnetic characterisation of SiC whisker reinforced Fe–Co alloy composites

SiC whisker reinforced Fe–Co composites containing up to 3vol% of bare, copper, Ni–P and cobalt plated whiskers were prepared in a spark plasma sintering furnace at 900°C, applying a pressure of 80MPa for 5min. The influences of the bare and the coated whisker additions on the magnetic and mechanical properties of the brittle matrix were assessed and correlated using their microstructural and fractographic observations. The bare whiskers played dual and contradicting roles on the grain growth behaviour of Fe–Co. The insulating fibres, which promoted grain growth of Fe–Co by concentrating the sintering current in the regions away from them, reduced the grain growth kinetics by pinning the boundaries. The grain growth was more pronounced in all the materials with more than 2vol% of whiskers. Among the coatings investigated, the amorphous Ni–P coating aided to achieve maximum improvements in both strength and ductility by forming nanocrystalline intermetallic compounds with Fe–Co and by promoting dispersion of the whiskers in the matrix alloy. The copper and cobalt coatings were not beneficial in improving the mechanical properties of the composites because of their inability to promote homogeneous dispersion of the whiskers and to form new intermetallic compounds with the matrix alloy, respectively.

Nanocrystalline intermetallic compounds in the Ni–Al–Cr system synthesized by mechanical alloying and their thermodynamic analysis

Mechanical alloying (MA) of the ternary Ni–Al–Cr mixtures having the Ni50Al50, Ni25Cr25Al50 and Ni50Cr25Al25 compositions was investigated. The structural changes of powder particles during mechanical alloying were studied by X-ray diffractometry (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show that for all three compositions the gradual interdiffusion of elements during MA leads to the development of different phases. The final structures for the Ni50Al50 and Ni25Cr25Al50 compositions are nanocrystalline NiAl and (Ni, Cr)Al intermetallic compounds, respectively. However MA of the Ni50Cr25Al25 composition led to the formation of a Ni3Al intermetallic compound as well as Cr which transformed to the (Ni, Cr)3Al intermetallic compound after subsequent heat treatment. The structural transition upon annealing was investigated. Furthermore, thermodynamic analysis using the Miedema model for all three systems is carried out and discussed in detail.

Mechanical alloying of nanocrystalline intermetallic compound TiFe doped by aluminum and chromium

Abstract A series of nanostructured alloys based on TiFe intermetallic compound were synthesized from the metallic elements in a planetary ball mill by solid state mechanical alloying. Al and Cr were added as doping components to a Fe-50% (at.) Ti powder mixture. Phase and structure transformations during mechanical alloying and subsequent annealing as well as hydrogen interaction with the alloys prepared were studied. It was shown that reversible hydrogen sorption capacity of the nanostructural alloys based on the TiFe intermetallic compound was of 0.7 wt.% at room temperature. The alloys studied demonstrated a simplified activation of hydrogenation. A correlation between the alloys behavior in their reactions with hydrogen and structure parameters of the hydrogenated samples has been discussed.

Mechanochemical synthesis of a TiFe nanocrystalline intermetallic compound and its mechanical alloying with third component

The method of solid-phase mechanochemical synthesis is used to obtain nanostructured ternary alloys based on a TiFe intermetallic compound with manganese, copper and zirconium as alloying components. The phase and structural transformations in the process of the synthesis are determined by x-ray diffraction analysis. The interaction between the resulting compounds and hydrogen is studied, isotherms of absorption and desorption of hydrogen are plotted, and the hydration products are subjected to x-ray phase analysis. It is shown that the use of mechanical activation and the presence of a third component permits activation under less rigid conditions as compared to TiFe obtained by metallurgical alloying.

Effects of milling and annealing on formation and structural characterization of nanocrystalline intermetallic compounds from Ni–Ti elemental powders

Nickel and Titanium elemental powders with a nominal composition Ni–50at.%Ti were mechanical alloyed in a planetary high-energy ball mill in different milling conditions (5, 10, 20, 40 and 60h). The investigation revealed that increasing milling time leads to a reduction in crystallite size, and after 60h of milling, the Ti dissolved in Ni lattice and NiTi (B2) phase was obtained. With milling time, morphology of pre-alloyed powders changed from lamella to globular. Annealing of as-milled powders at 1173K for 900s led to formation of nanocrystalline NiTi (B19′), grain growth and release of internal strain. The results indicated that this technique is a powerful and high productive process for preparing NiTi intermetallic compound with nanocrystalline structure and appropriate morphology.

Synthesis of Nanocrystalline Fe<sub>25</sub>Al<sub>57.5</sub>Ni<sub>17.5</sub> by Mechanical Alloying

Nanostructured Fe25Al57.5Ni17.5intermetallics was prepared directly by mechanical alloying (MA) in a high-energy planetary ball-mill. The phase transformations and structural changes occurring in the studied material during mechanical alloying were investigated by X-ray diffraction (XRD). Thermal behavior of the milled powders was examined by differential thermal analysis (DTA). Disordered Al(Fe,Ni) solid solution was formed at the early stage. After 50 h of milling, Al(Fe,Ni) solid solution transformed into Al3Ni2，AlFe3，AlFe0.23Ni0.77 phase. The power annealed at temperature 500 results in forming of intermetallics AlFe3 and FeNi3 after 5h milling. The nanocrystalline intermetallic compound was obtained after 500h milling.

Effect of micro-alloying chromium on the corrosion resistance of nanocrystalline nickel aluminide intermetallic produced by mechanical alloying process

In this study, Ni 50Al 50 − x Cr x nanocrystalline intermetallic compound was synthesized by using the high energy mechanical milling of pure Ni, Al and Cr elemental powders for 16 h. The morphological investigation was done by using the optical and scanning electron microscope. The corrosion behavior of the samples was studied by using the electrochemical impedance spectroscopy in 3.5% NaCl solution. The results showed that when the micro-alloying Cr content is increased, the particles distribution is modified and the size of particles is decreased. Therefore the passive film which is formed on the surface of samples is less porous, so the corrosion resistance is increased.

A Nanocrystalline Ni2(Cr,Mo) Intermetallic with Potentially Useful Combination of Properties for Gas Turbine Seal Ring Applications

Seal rings are installed for each turbine stage in gas turbine engines to minimize the loss in gas pressure and maintain engine efficiency. During service, seal rings become susceptible to failure by thermal fatigue as demonstrated by a case study. Therefore, a lower coefficient of thermal expansion is among the most important requirements for these applications. We show that long-range ordering in a Ni-Cr-Mo alloy can be used to synthesize a nanocrystalline intermetallic compound combining high strength, high ductility, low coefficient of thermal expansion, and an adequate oxidation resistance up to at least 700 °C. Twinning rather than slip is found to be the predominant deformation mechanism of the intermetallic compound, which is correlated with the crystallography of the disorder-to-order transformation and microstructure evolution. This could explain the enhanced plasticity of the intermetallic compound. The combination of enhanced plasticity, low-thermal expansion, and nano-sized crystals is expected to improve the resistance to thermal fatigue failure.

Synthesis and Characterization of Ultrafine Nanocrystalline Ti-Al Nanoparticles

Ti-Al nanoparticles and have been synthesized by the flow-levitation (FL) method. The morphology, crystal structure and chemical composition of Ti-Al nanoparticles obtained were investigated by transmission electron microscopy, X-ray diffraction and induction-coupled plasma spectroscopy. Results showed that the average grain size of these nanoparticles is about 30 nm, and it can be controlled availably by altering procedure parameters. The structure of powder is mainly double phase Ti-Al particulate composite. In addition, there are certain corresponding relation between the compositions of evaporate source master material and phase composition of alloy compound nanoparticle. The expected nanoparticle, which is mainly composition of nanocrystalline intermetallic compound, can be obtained through changing the compositions of evaporating source mastermaterial.

The interfacial amorphous double layer and the homogeneous nucleation in reflow of a Sn-Zn solder on Cu substrate

To illustrate the interfacial reaction mechanism, the Sn-Zn[Sn–8.5Zn–0.5Ag-0.01Al-0.1Ga (wt%)] solder was reflowed on Cu substrate at 250 °C for 15 s followed by immediate quench in liquid nitrogen. The frozen interfacial microstructure was investigated with high resolution transmission electron microscope. An amorphous double layer was formed at the interface which consists of a 5 nm pure Cu region and a Cu-Zn diffusion region. Nanocrystalline intermetallic compound (IMC) Cu5Zn8 were observed in the Cu-Zn diffusion region. These nanocrystalline IMCs are suggested to form via a homogeneous nucleation process.

Investigation of chromium effect on synthesis behavior of nickel aluminide during mechanical alloying process

The mechanical alloying process was used to synthesize the Ni 50Al 50− x Cr x nanocrystalline intermetallic compound using the pure Ni and Al elemental powder. The mechanical alloying was carried out in the presence of various Cr contents as a micro-alloying element for various milling times. The synthesis behavior of final product was investigated by using XRD, SEM and EDS. Results confirmed that synthesis behavior of nickel aluminide intermetallic depends on the Cr content and milling time. The results revealed that for an inadequate milling time, the intermetallic phase is generated after opening the vial lid. The EDS results depict that the samples synthesized in the air atmosphere, i.e. after opening the vial lid, include a considerable value of oxygen. The X-ray map results reveal that, after opening the vial lid, the oxidation of milled aluminum particles will result in the generation of final product in the air atmosphere. According to XRD results, when the milling time is constant, increasing the Cr content leads to acceleration in the nickel aluminide formation in the air atmosphere.