Al Intermetallic Compounds Research Articles

Some Aspects Regarding the Complex Alloying of the Ni3Al Intermetallic Compound with Substitutional and Interstitial Elements

Research results focussed on the combined influence of iron and boron, in proportions of 0.5 and up to 10 wt.% respectively, in complex alloyed Ni3Al synthesised by Self Propagating High Temperature Synthesis (SHS) in the thermo-explosion mode at two ignition temperatures, 950 and 1150 oC, are presented. By XRD and Mössbauer spectroscopy it was established that for 950 oC ignition temperature, the evolved heat is not high enough for the added Fe to be fully incorporated into the synthesised Ni3Al phase, a temperature of 1150 oC being required. For this temperature, the density of the synthesised alloys, their capacity to be cold deformed by re-pressing, hardness and bending strength variations as a function of B and Fe contents, proved their cumulative effects of the ductility and mechanical properties of complex alloyed Ni3Al enhancing.

High-temperature synthesis of the Ni3Al intermetallic compound under pressure

We investigate by experimental and numerical methods the high-temperature synthesis of the Ni 3 Al intermetallic compound in the thermal explosion mode under the pressure of a powder mixture of nickel and aluminum of a stoichiometric composition. The calculated and experimental thermograms of self-propagating high-temperature synthesis are analyzed depending on the temperature of preliminary heating of the powder mixture and the magnitude of external pressure.

Preparation of W–Al intermetallic compound powders by a mechanochemical approach

Abstract A series of W–Al intermetallic compound powders were synthesized by a novel mechanochemical approach, i.e., solid–liquid reaction ball milling. The XRD analysis showed that the Al 12 W, Al 5 W and Al 4 W intermetallic compound powders were successfully prepared at 953, 1023 and 1163 K, respectively. These fine powders have the average particle size of about 100 nm. Moreover, the solid–liquid reaction mechanism during the milling process was discussed.

Synthesis and characterization of molybdenum aluminide nanoparticles reinforced aluminium matrix composites

Aluminium matrix composites reinforced with molybdenum aluminide nanoparticles were synthesized by ball milling and reactive sintering of the mixture of aluminium and 10 wt% hydrated molybdenum oxide powders. Sintering the as milled powder in air below 750 °C produced MoAl 12 intermetallic compound nanoparticles, at 750 °C produced a mixture of MoAl 5 and MoAl 4 nanoparticles and at 800 °C under Argon atmosphere produced predominantly MoAl 4 intermetallic nano-particles in the Al matrix. The powder compacts sintered in air below 750 °C produced MoAl 12 whereas at 750 °C or above formed the Al matrix composite reinforced with the MoAl 5 nanoparticles. These nanoparticles become agglomerated to take up some irregular shaped flakes in the metal matrix. The reaction between Al and hydrated Mo oxide powders was found to be a favorable way to produce predominantly a particular Mo–Al intermetallic compound at a particular temperature. The Al 2O 3 particles formed as another reaction product, in all the above reactions, remain distributed in these composites. The composites thus formed were characterized by SEM-EDS, DTA, XRD and TEM analysis.

The morphology of coating/substrate interface in hot-dip-aluminized steels

In hot-dip-aluminized (HAD) steels, the morphology and the profile of the interface between the aluminum coating and the substrate steel, are affected both by the composition of the molten aluminum as well as by the composition, and even the microstructure, of the substrate steel. This effect has been investigated using optical and scanning electron microscopy, and X-ray diffraction. The reaction between the steel and the molten aluminum leads to the formation of Fe–Al inter-metallic compounds on the steel surface. The thickness of the inter-metallic compound layer as well as the morphology of the interface between the steel and the interlayer varies with the silicon content of the molten aluminum. In hot-dip-aluminizing with pure aluminum, the interlayer is ‘thick’ and exhibits a finger-like growth into the steel. With a gradually increasing addition of silicon into the aluminum melt, the thickness of the interlayer decreases while the interface between the interlayer and the substrate gradually becomes ‘smoother’. With an increase in the carbon content of the substrate steel the growth of the interlayer into the steel is impeded by the pearlite phase, whereas the ferrite phase appears to dissolve more readily. X-ray diffraction and electron microscopic studies showed that the interlayer formed in samples aluminized in pure aluminum, essentially consisted of orthorhombic Fe 2Al 5. It was further observed that the finger-like grains of Fe 2Al 5 phase exhibited a preferred lattice orientation. With a gradual addition of silicon into the aluminum melt, a cubic phase based on Fe 3Al also started to form in the interlayer and replaced most of the Fe 2Al 5.

Microstructure of a newly developed γ′ strengthened Co-base superalloy

The microstructure of a newly developed Co-base superalloy with enhanced high-temperature strength has been investigated using transmission electron microscopy (TEM) and three-dimensional atom probe (3DAP) techniques. It mainly consists of a typical γ/γ′ (FCC/L1 2) structure and a plate-shaped AB 3-type ( Ni , Co , Cr ) 3 ( Ti , Al ) intermetallic compound with hexagonal structure ( a∼5.1 Å and c∼12.5 Å). γ′ is formed with a bimodal distribution and fine γ′ has a cuboidal morphology. Cr and Co are enriched in the γ phase, while Ti, Al and Ni are enriched in the γ′ phase. W and Mo are more or less uniformly distributed in both γ and γ′. Chemical composition analysis by 3DAP suggests that the plate-shaped phase has a higher Ti and lower Al content compared to that of γ′ phase, and the concentration of Ti, Co and Ni has a periodic variation along c-axis with a period of 12.5 Å in the plate-shaped phase.

Improving the wear resistance of AA 6061 by laser surface alloying with NiTi

To improve the wear resistance of a popular aluminum alloy AA 6061, a 1.5 mm thick hard surface layer consisting of Ni–Al and Ti–Al intermetallic compounds was synthesized on the alloy by laser surface alloying technique. NiTi powder was preplaced on the aluminum alloy substrate and irradiated with a high-power CW Nd:YAG laser in an argon atmosphere. With optimized processing parameters, a modified surface layer free of cracks and pores was formed by reaction synthesis of Al with Ni and Ti. X-ray diffractometry (XRD) confirmed the main phases in the layer to be TiAl 3 and Ni 3Al. The surface hardness increased from below 100 HV for untreated AA 6061 to more than 350 HV for the laser-treated sample. Accompanying the increase in hardness, the wear resistance of the modified layer reached about 5.5 times that of the substrate.

Role of Ti in the reversible dehydrogenation of Ti-doped sodium alanate

The role of Ti in the reversible dehydrogenation of NaAlH4 has been the subject of debate for many years. The authors resolve this controversy by calculating the phase stability diagram of Na–Al–H–Ti and defect formation enthalpy of Ti doped NaAlH4 from first principles. The calculations show that Ti substitutes Al in NaAlH4 and forms a defect pair with interstitial H under H-rich and Al-poor conditions. However, the defect pair is not stable under H-poor and Al-rich conditions resulting in the formation of a Ti–Al intermetallic compound. The doped Ti reduces the Al–H bonding via additional Al 2p and Ti 3d hybridizations. The results give a picture why and how doped Ti acts to enhance hydrogen storage related solid phase transitions.

Reactive brazing of Al alloy to Mg alloy using zinc-based brazing alloy

According to the feature of Mg–Zn eutectic reaction, Al alloy was bonded to Mg alloy by contact reaction brazing using a zinc-based brazing alloy successfully. The experimental observations showed that Mg–Al intermetallic compounds were avoided for the addition of the zinc-based brazing alloy. The Mg substrate and the remanent brazing alloy were bonded with the reaction zone that formed along the zinc rich and magnesium poor interface. Only a few Mg–Zn intermetallic compounds (MgZn2) existed homogeneously in the reaction zone. The substrate and the remanent brazing alloy were bonded with a thin Al–Zn solution. The average tensile-shear strength of the final joints was a little lower than that of the zinc-based brazing alloy owning to some pores at the interface between the reaction zone and the remanent brazing alloy layer.

Phase formation sequence of Cr 2AlC ceramics starting from Cr–Al–C powders

The reaction process of Cr 2AlC ceramics was analyzed, in which the samples were prepared for composition Cr:Al:C = 1:1.2:1 by hot-pressing in argon in the range of 850–1450 °C using Cr, Al and graphite powders as the starting materials. X-ray diffraction (XRD), electron probe microanalysis (EPMA) and energy dispersive spectrum (EDS) were employed for identification of phase assembly and analysis of reaction route of the samples. The phase formation sequence of Cr 2AlC was finally analyzed based on phase diagram of the Cr–Al binary system combined with the results of differential thermal analysis (DTA) and XRD. It was found that Cr 5Al 8, Cr 2Al and Cr 7C 3 were the intermediate phases appearing in turn in the heating process. The amount of Cr 2AlC phase was gradually increased with increase in temperature by the reaction between Cr–Al intermetallic compounds, un-reacted Cr and graphite, and it became a pure phase in the sample with disappearance of intermediate phases above 1250 °C.

A study on the hot workability of a cast Ti–Al intermetallic compound

The hot deformation behavior of a cast Ti–45Al–2Cr–4Nb–0.4B (numbers indicate at.%) intermetallic compound under hot-working conditions in the temperature range of 1100–1300 °C and strain rate range of 0.01–5 s −1 has been studied by performing a series of hot compression tests. The dynamic materials model (DMM) has been employed for developing the processing maps, which show variation of the efficiency of power dissipation with temperature and strain rate. Also the Kumar's model has been used for developing the instability map, which shows variation of the instability for plastic deformation with temperature and strain rate. The efficiency of power dissipation increased with decreasing strain rate and increasing temperature. High efficiency of power dissipation over 40% was obtained at a finite strain level of 0.2 under the conditions of strain rate lower than 0.1 s −1 and temperature higher than 1200 °C. Plastic instability was expected in the regime of strain rate higher than 0.1 s −1 and temperature lower than 1200 °C.

Double glow plasma surface alloying and plasma nitriding

Based on plasma nitriding technique, Double Glow Plasma Surface Alloying Technology (DG Technique) was developed in 1980. This technique breaks the restriction of traditional plasma nitriding and successfully applies solid alloying elements, such as Ni, Cr, W, Mo, Ti, Al, Nb et al., to realize plasma surface alloying. Numerous experiment results concerning the DG technique have demonstrated that various alloys and alloy steels, such as high speed steel, nickel base alloy and wear resistant alloys et al., have been produced upon the surfaces of carbon steels, titanium alloys, Ti–Al intermetallic compounds and copper. This paper is written in hope that the differences between plasma nitriding and DG technique will become more apparent. Some new development and experiment results of the double glow plasma surface alloying are also shown in this paper. For example, Ti–Al–Nb–C alloy has been produced on the surface of TiAl and Ti–Cu and Ti–Cr burn-resistant alloys have been formed on the surfaces of titanium and Ti6Al4V alloy by using this process; When solid graphite is used as carbon supplier, hydrogen-free carburizing has been carried out in order to avoid hydrogen embrittlement of titanium materials; Co–W–Mo–Fe age hardened high speed steel has been produced on the surfaces of carbon steels.

Electrodeposition of Ho and Electrochemical Formation of Ho–Al Alloys from the Eutectic LiCl–KCl

The electrochemistry of a melt at inert and reactive electrodes has been studied at temperatures between 673 and . At a W electrode the electroreduction of Ho(III) proceeds in a single step and electrocrystallization plays an important role. Experimental current-time transients followed the theoretical models based on instantaneous nucleation with three-dimensional growth of the nuclei whatever the applied overpotential. Mass transport toward the electrode is a diffusion process, and the validity of the Arrhenius law was verified. For an Al electrode, the electroreduction of Ho(III) takes place at less cathodic potential values than at the inert W electrode which indicated the formation of Ho–Al intermetallic compounds. Ho–Al alloy films were obtained by potentiostatic electrolysis, and the samples were characterized by X-ray diffraction and scanning electron microscopy. The activity of Ho in the aluminium phase as well as the standard Gibbs energy of formation for were estimated from open-circuit chronopotentiometric measurements.

Fabrication of cold sprayed Al-intermetallic compounds coatings by post annealing

A cold spray coating technique for thick Al coating with finely dispersed intermetallic compounds was tested by post annealing. The powder composition of Al:Ni and Al:Ti was fixed at 75:25 wt.%. The hard Ni and Ti powders have been successfully coated with the soft metal of Al at low gas pressure condition. Also, the Ni and Ti particles were embedded in the Al matrix. In the post annealing of coatings, the intermetallic compounds were observed in the cold sprayed Al–Ni and Al–Ti composites coatings. Above 450 °C of post annealing temperature, the Al 3Ni and Al 3Ni 2 phases were observed in the cold sprayed Al–Ni coatings. The Ni particles in the Al matrix were fully consumed via compounding reaction with Al at the 550 °C of the annealing temperature. In the case of Al–Ti coatings, the Ti particles still existed in the Al matrix up to 630 °C of annealing temperature.

Interfacial Microstructure of Magnetic Pressure Seam Welded Al-Fe, Al-Ni and Al-Cu Lap Joints

A new welding method, magnetic pressure seam welding, was used to lap join dissimilar metals (Al-Fe, Al-Ni and Al-Cu). The circuit for magnetic pressure seam welding consists of a capacitor, an electric discharge gap switch, and a plate-type coil. The overlapped metal plates are placed over the coil. When an impulse current from an energy-storage capacitor bank passes through the coil, a high-density magnetic flux is suddenly generated around the coil. The generated high-density magnetic flux lines cross the end of the overlapped plates. Eddy currents are induced mainly inside the Al plate because it has a high electrical conductivity. Both the Joule heat generated in the plates and the magnetic pressure applied from the Al side promote the joining of the lapped plates. The welding is normally achieved within 10 μs. This results in very little microstructural change in the parent plates aside from the area around the weld interface. Strong lap joints were obtained for every metal combination and no tensile fracture took place in the weld region. A characteristic wavy morphology was observed at the weld interface. An intermediate phase layer was also observed at the weld interface. TEM observation revealed that the intermediate layer consisted of fine Al grains and intermetallic compound particles dispersed among the Al grains. The growth direction of the wave, the welding condition dependency of the wavelength and the amplitude of the interfacial wave were intensively investigated in order to clarify the welding mechanism of this method.

410 Ti-Al基金属間化合物の組織と被削性(OS-13 先端材料・難削材の加工)

Machinability of Ti-47.7at%Al intermetallic compound having TiAl-Ti_3Al full lamellar structure is investigated by orthogonal cutting test using cemented carbide tool K10. Defects such as cracks, peelings due to brittle fracture along with the direction of lamellar were observed on the machined surface. The larger brittle cracks were occurred in cutting by tool with the rake angle of +5°. For machining in the rake angle of -5°, the depth of crack occurrence was independent on the direction of lamellar. On the other hand, for machining in the rake angle of +5°, it increased rapidly at the lower angle between lamellar direction and cutting direction than 90°.

Ignition and reaction mechanism of Co–Al and Nb–Al intermetallic compounds prepared by combustion synthesis

The ignition and propagation mechanism of the self-propagating high-temperature synthesis of several cobalt and niobium aluminides was investigated. Two propagation mechanisms were identified depending on the stoichiometry of the starting mixture. Al-rich compositions propagate through a dissolution–precipitation mechanism while Al-poor mixtures require solid state diffusion. The ignition temperatures were measured by means of microthermocouples in quasi-adiabatic conditions through experiments carried out in thermal explosion mode. Ignition temperatures were found to be characteristic of each system and to depend strongly on reactants particle size. Ignition energies for all compositions were evaluated through a mathematical model.

Orientation control of a lamellar microstructure in a Ti−Al intermetallic compound by high-temperature compression in an alpha single-phase and/or in a two-phase region and the alpha re-heat treatment

In order to control the spatial Ti−Al distribution of the α2+γ γ lamellar microstructure in Ti−Al alloys, processes consisting of a high-temperature deformation in an alpha single-phase region, and an annealing and deformation in the α2+γ ψ region were examined. The compression deformation temperatures and strain rates were from 1573 to 1623 K and from 1.0×10−4 to 5.0×10−3 s−1, respectively. Dynamic recrystallization occurred during the compressive deformation in the alpha single-phase region. The uniaxial compression resulted in the formation of a fiber texture. It was found that more than half of the lamellar microstructure can be arranged within 30 degrees from the specimen surface by these processes. It was also shown that the orientation control of the lamellar microstructure in a polycrystalline Ti−Al intermetallic compound is effective in improving the creep resistance of this material.

Diode laser brazing of aluminium alloy to steels with aluminium filler metal

Diode laser brazing of aluminium alloy (A5052) to interstitial free steel (IF steel) or type 304 stainless steel (SUS304) was conducted using aluminium filler metal (BA4047) with Nocolock flux. The processing parameters of laser power, wire feed rate and travel speed were varied. The strength of lap joints of A5052 on steels was evaluated by tensile shear test. The joint strength of A5052/steels was increased with increasing laser power and reached the maximum strength, more than approximately 80% of the A5052 base metal strength, at a laser power of 1300 W. Voids and incomplete penetration of filler metal were observed at the A5052/braze layer interface when the laser power was below 1100 W. The Fe–Al intermetallic compounds were formed at the steel/braze layer interfaces and grew drastically when the laser power exceeded 1300 W. Superior brazability of A5052/steels was found at brazing conditions corresponding to a temperature of filler metal droplet of 1050–1250 K.

The thermophysical properties of KhN55VMTKYu nickel-based heat-resistant alloy

New experimental data are given for the KhN55VMTKYu industrial nickel-based heat-resistant alloy on its heat capacity at temperatures from 300 to 1000 K and on the thermal conductivity coefficient at T = 380-1450 K. The newly obtained and previously available data are used to construct approximating equations and tables of smoothed values in the range from 300 to 1200 K for heat capacity, enthalpy, average heat capacity, thermal conductivity, average coefficient of thermal expansion, density, and thermal diffusivity of the alloy. The effect of disordering of the Ni3 (Ti, Al) intermetallic compound on the properties of the alloy is examined. The activation energy of disordering of the alloy Q = 0.93 eV and the temperature dependence of the enthalpy of disordering are estimated, as well as the concentration of intermetallic compound in the alloy.