Al Intermetallic Phase Research Articles

Synthesis, microstructure and micro-mechanical characterization of metal (Nb, Ti) – MAX phase (Ti2AlC) nanolaminates

We utilize elevated temperature physical vapor deposition (PVD) techniques to design metal/MAX multilayered nanocomposite thin films with alternating nanoscale metallic (Nb, Ti) and MAX phase (Ti2AlC) layer thicknesses. These metal/MAX nanolaminate architectures attempt to exploit a unique hierarchical topology – as interfaces between the layers are expected to be in direct competition with the internal interfaces within the MAX layers, to drive their tunable macroscopic mechanical behavior. Two metal/MAX nanolaminates – Nb/Ti2AlC and Ti/Ti2AlC – were deposited. The Nb/Ti2AlC metal/MAX system showed highly diffused layer interfaces with distinct Ti – rich and Nb–Al – rich layers, with the presence of MAX phase alongside TiC and other Ti–Al and Nb–Al intermetallic phases. The Nb/Ti2AlC system possessed a layered architecture, though the MAX phases were not found to be continuously present in each alternating layer. The second Ti/Ti2AlC system showed a non-lamellar nanocomposite microstructure and the formation of mixed Tin+1AlCn phases (a mix of n = 1, 2), and no indication of layering. Diffusion occurring between the metal/MAX layers in both cases, likely due to the elevated temperatures during the deposition process, is speculated as the likely cause of these resultant microstructures. The mechanical properties of both systems were evaluated using micromechanical (nanoindentation and micro-pillar compression) techniques, which demonstrated high strengths for both systems (Nb system: yield and instability strengths of 4.88 ± 0.1 GPa and 5.57 ± 0.03 GPa, Ti system: yield and instability strength of 5.61 ± 0.28 GPa and 6.21 ± 0.25 GPa). This work highlights the promising mechanical properties of metal/MAX multilayered depositions and summarizes the challenges in PVD synthesis of metal/MAX multilayered nanolaminates.

Fabrication of a Porous Fe–Al Intermetallic Alloy with Ultrahigh Open Porosity

Herein, a porous Fe–Al intermetallic material with ultrahigh open porosity is prepared via the multistep sintering process using a Fe–Al–Mn powder mixture as the raw material. The microstructure, phase composition, Mn sublimation, and open porosity of the sintered Fe–Al–Mn compacts are investigated. The compacts sintered at temperatures ≤700 °C are composed of the newly formed Fe/Mn‐based solid solutions, intermetallic phases, and the original elemental particles without the sublimation of Mn. The open porosities of the 650‐ and 700 °C‐sintered compacts are ≈39.83 and ≈47.19 vol%, respectively. After sintering at 1250 °C, Mn is rarely left in the porous body, and a single Fe–Al intermetallic phase with an even chemical composition is generated. The open porosity of the 1250 °C‐sintered compacts is ≈66.67 vol%, superior to other reported porous Fe–Al materials, and its strength is ≈22.5 MPa, which is competitive as well. This work may open a new strategy to design and optimize the high‐quality porous Fe–Al alloy in future.

Investigations on the Microstructure of an Aluminium Nitride Layer and Its Interface with the Aluminium Substrate (Part I)

In principle, the plasma nitriding of Al based substrates is a well-known process, though it remains extremely challenging from both the technological point of view and the aspect of stress loading conditions. In order to improve the latter, a duplex treatment consisting of plasma nitriding and subsequent surface remelting using electron beam technology was employed. The focus of this paper (part I) was on the characterisation of the initial microstructure after plasma nitriding. This should create the basis for a better understanding of the processes taking place or changes in the subsequent duplex treatment. This was done with the help of high-resolution imaging and analysis tools in the scanning and transmission electron microscope as well as XPS analyses. Special attention was paid to the nitriding mechanism at the interface as a function of the local microstructural constituents of the hypereutectic Al alloy substrate (Al solid solution, primary silicon, and intermetallic phases). While the main part of the nitride layer formed consisted of AlN and small fractions of pure Al in the diffusion paths, other nitrides and oxides could also be detected in the area of the interface.

Characterization of Fe–Al intermetallic phases formed during hot-dip Al coating on carbon steel C45

Characterization of Fe–Al intermetallic phases formed during hot-dip Al coating on carbon steel C45

Revisiting selective nucleation at heterophase interfaces in Fe–Al solid-liquid reaction

The reaction between solid Fe and liquid Al occupies the important position due to its wide application in industrial processes. However, it is still unclear now which intermetallic compounds will form and the formation mechanism of Fe–Al intermetallic phases. In present work, the Fe–Al solid-liquid reaction by using iron wire as Fe resource is traced by in-situ synchrotron powder X-ray-diffraction. With Fe4Al13 as the dominant phase, two intermetallic phases named Fe4Al13 and Fe2Al5 are found. This phenomenon is different with the result obtained from the diffusion couple of Fe block and melt Al. Thermodynamic calculation and molecular dynamics simulation are performed to verify the underlying mechanism. Related events such as interfacial diffusion and nucleation driving force are analyzed and discussed.

The effect of homogenization on microstructure and hardness of a large-scale high-aluminum Al4.4Co26Cr18Fe18Ni26Ti5.5 Compositionally Complex Alloy cast

Abstract As any largescale cast material, specific Compositionally Complex Alloys or High Entropy Superalloys contain segregations, leading to unideal, inhomogeneous properties. This work presents the effects of a homogenization heat treatment at 1 150°C for 6 h of a large-scale cast Al4.4Co26Cr18Fe18Ni26Ti5.5 alloy. In order to reveal these effects, homogenized specimens were analyzed and compared to the as-cast state with regard to chemical homogeneity as well as the homogeneity of elemental solution by means of scanning electron microscopy, energy dispersive X-ray spectroscopy as well as X-ray diffraction and hardness measurements. Despite the increased Al content, intermetallic phases and segregations, observable in the as-cast state, dissolve during homogenization. Improved, but not full homogeneity of elemental distribution after annealing can be determined. The improved state of solution and homogeneity agrees with the increasing lattice parameter from 3.572 Å to 3.594 Å and the decreasing hardness from 320.3 HV10 to 245.2 HV10 during homogenization.

Strengthening of novel TiC–AlN ceramic with in-situ synthesized Ti3Al intermetallic compound

5 wt% AlN was added to TiC-based samples spark plasma sintered at 1900 °C under 40 MPa for 10 min. XRD and microstructural assessments confirmed the in-situ formation of Ti3Al during the sintering process. The densification behavior and mechanical properties of the undoped and doped samples were studied to evaluate the impact of AlN addition and Ti3Al in-situ formation on the properties of TiC ceramics. AlN had a significant influence on the relative density of TiC due to the formation of molten Al and Ti3Al intermetallic phase, yielding a fully dense material. Reinforcing TiC with AlN and Ti3Al led to a limited drop by around 2% in the Vickers hardness of the doped sample, but improved significantly the flexural strength up to 688 MPa. The reason for such an improvement in the flexural strength of SPSed ceramic was owing to the formation of strong diffusion bonds between secondary phases and the matrix.

The Poisoning Effect of Al and Be on Mg—1 wt.% Zr Alloy and the Role of Ultrasonic Treatment on Grain Refinement

AAddition of Al – Be master alloy to a Mg – Zr alloy reduces melt oxidation, however, it has a detrimental grain coarsening effect that is believed to be caused by an unknown interaction of Be with the Zr nucleant particles. However, this study found that Al is the major cause of grain coarsening. By analysis of intermetallic phases and chemical analysis for solute Zr, it was revealed that Al reacts with the undissolved α – Zr particles forming Zr – Al intermetallic phases and reducing the amount of solute Zr both of which lead to a decrease in the grain refinement efficiency of the master alloy. Despite this negative effect of Al on grain refinement, application of ultrasonic treatment produces significant grain refinement of the Mg – Zr – Al – Be alloy demonstrating the potential for developing ignition-proof and grain refined Mg alloys.

Effect of high temperature preoxidation treatment on the oxidation behavior of MoSi2- and WSi2–Al2O3 composites

Composites of 30 vol% MoSi2-70 vol% Al2O3 and 30 vol% WSi2-70 vol% Al2O3 were prepared via sintering at 1600 °C in argon. The high-temperature preoxidation treatments were applied at 1000°-1200 °C for 10–120 min in air. The non-isothermal oxidation tests were conducted in air at temperatures ranging between 50° and 870 °C to study and understand the influence of the alumina phase and preoxidation process on the low-temperature oxidation behavior. The optical and scanning electron microscopy, X-ray diffraction, X-ray photoelectron and Raman spectroscopy were used to characterize the surface layers formed. The oxidation-induced mass gains were substantially reduced by 82.1–99.8%, implying their enhanced oxidation resistance. This was due to the formation of highly dense, protective surface layers with a sufficient thickness (3.1–14.2 μm). The structural and surface analyses revealed their complex chemistries, since the ternary (Mo–Si–Al, W–Si–Al) intermetallic, mullite, alumina and silica phases with high oxidation resistances were identified within these surface features. In addition, the high-temperature electrical properties of the composites were highly preserved after the preoxidation treatment, and their electrical conductivities were measured as 45.1–78.6 S/cm at 800 °C and 40.1–69.1 S/cm at 900 °C.

Formation sequence of Fe–Al intermetallic phases at interface between solid Fe and liquid Zn–6Al–3Mg alloy

In the present study, we characterized the Fe–Al intermetallic phases formed in interstitial-free (IF) steel hot-dipped in a Zn–6Al–3Mg (wt.%) alloy melt at different temperatures (400, 460 and 500 °C) and dipping times (from 2 to 3600 s). Chemical composition analyses indicated Fe dissolution into the Zn alloy melt even after 2 s of dipping. Microstructural characterization revealed the initial formation of a continuous θ-Fe4Al13 phase layer, followed by the local growth of η-Fe2Al5 phase toward both steel and Zn alloy melt sides during the hot-dipping process. After long-term hot-dipping, further growth of the η phase was accompanied by significant dissolution of Fe into the Zn alloy melt, resulting in the loss of thickness of the IF steel sheets. Altogether, we rationalized the formation mechanism of Fe–Al intermetallic phases and their associated growth at the interface between solid Fe and liquid Zn alloy in terms of a Zn–Al–Mg–Fe quaternary phase diagram, calculated according to thermodynamic database available in the literature.

Influences of mechanical activation and heating rate on reaction processes in combustion synthesis of NiAl-Al2O3 composites

This paper investigates the combustion synthesis of NiAl-Al2O3 composites by the heating of Ni, NiO and Al powder mixture from 20 °C to 1300 °C. The influence of mechanical activation (without and with 1 h) and heating rate (20 °C/min and 40 °C/min) on thermal events in combustion synthesis process are investigated. Thermal events are assessed by Differential Thermal Analysis (DTA), X-Ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM). By heating the sample without mechanical activation, exothermic reaction of NiO reduction by Al and Ni-Al intermetallic phases (Al3Ni, Al3Ni2, AlNi and AlNi3) production happened in the presence of molten Al at 870 °C as one DTA peak. Mechanical activation causes occurrence of these reactions more separately at lower temperatures (590 °C and 630 °C). By decrement in the heating rate, these reactions happened in a more dispersed way at lower temperatures (590 °C and 630 °C). The reaction temperature for nickel aluminides formation in the presence of eutectic melt of AlNi3-Al is constant regardless of heating rate in mechanically activated powder. A seven-stage mechanism for reactions in a mechanically activated sample at a heating rate of 40 °C/min is proposed. Initially, by heating of the powder, an exothermic reaction between nickel oxide and aluminum and also nickel and aluminum occurs at 590 °C in solid state. NiO is consumed totally and Al2O3 is produced from the nickel oxide reduction by aluminum. Nickel aluminide phases are formed from reactions between aluminum and primary nickel and also from aluminum and nickel formed by aluminothermic reduction of nickel oxide. With continuation of heating process, Al-Al3Ni eutectic transition happens at 630 °C and results in the liquid phase formation. Presence of the molten phase accelerates the exothermic nickel aluminides formation reactions. Aluminum is consumed totally in this stage and more intermetallic phases are developed. By increasing the temperature, diffusion is enhanced. The remaining Al3Ni melts at 856 °C. This small amount of molten phase slightly enhances exothermic reactions between nickel aluminides and leads the system towards the equilibrium phase. After this event, reactions progresses gradually. The nickel core shrinks by the diffusion progressively and the whole nickel aluminides system undergoes a gradual evolution towards the NiAl equilibrium phase.

Oxidation Behavior of Non-Modified and Rhodium- or Palladium-Modified Aluminide Coatings Deposited on CMSX-4 Superalloy

Rhodium-modified as well as palladium-modified and non-modified aluminide coatings on CMSX-4 Ni-based superalloy were oxidized in air atmosphere at 1100 °C. Uncoated substrate of CMSX-4 superalloy was also oxidized. The microstructure of coatings before oxidation consists of two layers: an additive and an interdiffusion one. The NiAl intermetallic phase was found in the microstructure of non-modified coatings, while the (Ni,Rh)Al intermetallic phase was observed in the microstructure of rhodium-modified aluminide coatings before oxidation. The (Ni,Pd)Al phase of palladium-modified aluminide coatings in the additive layer was observed before oxidation. The microstructure of the oxidized non-modified coatings consists of the γ’-Ni3Al phase. The oxide layer (10 µm thick) consists of the NiAl2O4 phase and porous Ni-rich oxide. The oxide layers (5 µm thick) formed on the surface of rhodium or palladium-modified coatings consist of the α-Al2O3 phase and the top layer of the NiAl2O4 phase. Al-depleted (30 at. %) β-NiAl grains besides the γ’-Ni3Al phase were found in the rhodium-modified coating, while only the γ’-Ni3Al phase region was revealed in the palladium-modified coating, Rhodium-modified coatings with small rhodium content (0.5 µm rhodium layer thick) can be an alternative for palladium-modified ones with bigger palladium content (3 µm thick palladium layer).

Effects of the process parameters on the formability of the intermetallic zone in two-layer Mg/Al materials

This paper discusses experimental results concerning the plastic deformation of the bonding zone in a two-layer AZ31/Al material subjected to compression loads. The specimens were fabricated by diffusion bonding method. The 50μm thick transition zone at the AZ31/Al interface contained Mg–Al intermetallic phases. The physical modelling of the deformation behaviour of the intermetallic zone was performed using a Gleeble 3800 system. The compression tests were carried out at two temperatures (300 and 400°C), two strain rates (0.1 and 1.0s−1) and a true strain of 0.15 applied in one or two stages. The metallographic examinations and microhardness measurements were performed to assess the influence of the selected process parameters on the forming behaviour of the intermetallic zone. The experiments revealed that the main factors affecting the formability of the intermetallic zone in the two-layer AZ31/Al material were the strain rate and the temperature. It was found that when the deformation occurred at a strain rate of 0.1s−1 and a temperature of 400°C, there was no loss of continuity of the intermetallic transition zone; such conditions induced its plasticization.

Synthesis and Dry Sliding behaviour of LM24-TiB₂ Reinforced Particulate Composite

The existing effort deals with synthesis of (LM24) composite developed by reinforcing 3wt % and 5wt % TiB2 particles in the size range of 20-60 μm in the LM24 matrix. Hardness of the alloy and the composites were evaluated to see the changes in the hardness of the materials. The sliding wear tests were performed using pin on disc machine to study the wear properties. Effect of various experimental parameters like sliding distance, and applied pressure were studied on sliding wear response of the alloy and the composite. Micro structural examination of the alloy and composite was done to see the structural changes and distribution of the particles in the matrix. Worn surfaces were examined to see the mechanism of material removal. Results show that reinforcement of TiB2 particles in LM24 alloy increases the hardness and wear resistance. Microstructural study of the base alloy LM24 and composites were performed having special attention to the dispersion of TiB2 particles in LM24 base alloy matrix and interface closeness between TiB2 particles and LM24 alloy matrix. The microstructure of aluminium alloy shows primary Al dendrites and intermetallic phases around in the inter-dendrites region. The TiB2 particles were noted to be more or less uniformly distributed within the metallic matrix and these particles were trapped within the primary aluminium dendrites instead of inter-dendritic region.The importance of this work is to study the importance of TiB2 particles in enhancing the properties of the base alloy. In general, the properties of unreinforced materials show poor mechanical as well as wear properties and there is a need to improve the properties to a certain level so that the material can be extended to a certain level for its usefulness. In the present work, it has been observed that after reinforcing TiB2 particles to the base alloy considerable amount of enhancement in the properties can be achieved. It is quite sure that this project work will certainly help in designing of the various parts.

A study on intermetallic compound formation in Ag–Al system and evaluation of its mechanical properties by micro-indentation

In electronic packaging in recent years, silver (Ag) alloy wires have been widely adopted in wire-bond processes. The bond pads on the device chips are mostly aluminum (Al). Thus, the bonding interface is mainly Ag–Al. In recent Ag alloy wire-bond publications, it is unclear what intermetallic phases form at the interface. In this research, experiments were designed to understand the Ag–Al intermetallic compound (IMC) formation in the Ag–Al system and evaluate its mechanical properties. First, the Ag–Al alloys with compositions from 19 to 43 at.% Al were evaluated to identify the phase equilibrium and crystal structure of the Ag–Al intermetallic phases. Microstructures and phase compositions of the designed Ag–Al alloys are presented. To further study the intermetallic compound formation at the Ag/Al interface, the interfacial reaction of the Ag/Al joints at 200 °C was investigated. The µ-Ag3Al and δ-Ag2Al IMC were identified to form at the Ag/Al interface and stabilize after long-time annealing at 200 °C. At last, deformation and fracture behaviors of the bulk µ-Ag3Al and δ-Ag2Al were analyzed by the micro-indentation. The measured results reveal that µ-Ag3Al exhibits significantly higher hardness and lower fracture toughness as compared to δ-Ag2Al. Indentation crack propagation in µ-Ag3Al demonstrates the fracture characteristics of brittle materials. In the case of δ-Ag2Al, the presence of slip bands exhibits the ductility of δ-Ag2Al to endure plastic deformation prior to fracture. The effect of the mechanical properties of the µ-Ag3Al and δ-Ag2Al IMC on the Ag–Al joint reliability is discussed. New information obtained in this research is important for future study of the joint reliability and failure mechanism of Ag–Al wire bonds.

Porous Ti–Al Intermetallic Based Alloys Fabricated by Pressure-Sintering Elemental Powders with a Space Holder Powder

ABSTRACTIn the present study, we have attempted to produce the porous Ti–Al intermetallic based alloys by pressure-sintering of the elemental powders of Ti and Al through a combustion reaction, with a NaCl space holder to achieve the development of a highly porous structure. The powders of Ti (particle size: <45 μm) and Al (particle size: <45 μm) were mixed to various total compositions of Ti–0-40 Al (at.%), and NaCl (particle size: 300-400 μm) was mixed with the Ti/Al powder to give a highly porous structure. The mixed powder was sintered at 700 oC under a constant pressure of 30 MPa to form cylindrical specimens with a diameter of 20 mm. The soaking of the specimens in pure water allows for the removal of NaCl (with a volume fraction of 60 %) and the formation of the pores to achieve a controlled relative density of 0.4. The present process can produce porous Ti–Al alloys with various compositions. In as-sintered Ti–Al specimens, an inhomogeneous microstructure consisting of Ti particles surrounded by the a Ti–Al alloy layer (various Ti–Al intermetallic phases) was observed. The as-sintered specimens exhibited the brittle behavior under compression, which is independent of their Al content. However, in a Ti–20Al alloy heat-treated at 1300 °C, a nearly Ti3Al single-phase microstructure appeared in the porous specimen. The heat-treated porous Ti–20Al alloy shows both a high plateau-strength level of approximately 100 MPa and a high plateau-end strain over 50%, resulting in a high absorption energy. The present results demonstrate that controlling the microstructure for the formation of the Ti3Al single-phase would be an effective method to achieve high energy absorption capacity of the porous Ti–Al alloy.

Interfacial Reactions between Alumina and Carbon Refractories and Molten Iron at 1,823 K

AbstractHigh temperature interactions of alumina–carbon refractories with molten iron were investigated at 1,823 K in argon atmosphere. These studies were specifically focussed on the decomposition of alumina in the simultaneous presence of carbon and iron, and associated refractory degradation. Refractory mixtures were prepared by blending 90 wt% alumina with 10 wt% synthetic graphite; 5–15 wt% iron powder was then mixed with the refractory mixture. Using phenol formaldehyde as a binder, pellets were prepared from various blends; these were heat treated at 1,823 K for 30 min in Ar atmosphere. The presence of molten iron significantly enhanced the decomposition of alumina resulting in an enhanced refractory degradation as well as the formation of a new reactant product. This product was identified as a Fe–Al intermetallic phase from SEM/EDS (scanning electron microscopy/energy-dispersive spectroscopy) and x-ray microdiffraction investigations.

The use of titanium aluminides to form electric-spark coatings

Titanium aluminides (TiAl3, TiAl, Ti3Al) fabricated by powder metallurgy were used as alloying electrodes for the formation of electric-spark coatings. Intermetallic coatings were deposited on steel substrates in argon or nitrogen. The microstructure and composition of fabricated coatings were investigated by scanning electron microscopy, X-ray structural analysis, and electron probe microanalysis. It is established that initial Ti–Al intermetallic phases are present in fabricated coatings; however, the ratio between Ti and Al concentrations is shifted to aluminum compared with the stoichiometric one. When depositing titanium aluminide in the nitrogen medium, titanium nitride is additionally formed in surface layers. Thermal and tribotechnical tests showed that the Ti3Al coating deposited in nitrogen possesses high wear resistance and heat resistance.

Thermo-kinetic analysis of Ni–Al intermetallic phase formation in powder system

Thermo-kinetic analysis was carried out to determine the kinetics of Ni–Al intermetallic phase formation from powder mixture of Ni and Al. The kinetic data were generated using dynamic temperature program at 5, 10, 15, 20 K min−1 in a differential scanning calorimeter. The phase formation was studied with the help of both qualitative and quantitative powder X-ray diffraction using Rietveld refinement. The activation energy for the reaction was calculated from model-free isoconversional technique employing both differential (Friedman’s method) and integral (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose method) methods. The result shows that formation of NiAl from elemental powders is multi-step in nature involving $$\hbox {Ni}_2\hbox {Al}_3$$ as a major intermediate. The appropriate kinetic model for the reaction was evaluated by means of Malek’s method (model selection technique). Sestak Breggren (auto-catalytic model) was found to be in good agreement with the experimental data. The corresponding kinetic parameters and rate expression were determined for the reaction system involving solid–solid reaction between Ni and Al in the powder form.

Effect of nickel pre-plating on high-temperature oxidation behavior of hot-dipped aluminide mild steel

An aluminide/nickel duplex coating was prepared on mild steel by nickel pre-plating before hot-dip aluminizing. The isothermal and cyclic oxidations of the hot-dipped aluminide mild steel were performed at 750 °C in a static atmosphere. The effect of nickel pre-plating on the high-temperature oxidation behavior of the aluminide mild steel was studied. The results from the aluminide steel after isothermal oxidation show that the phase transformation in the aluminide layer was dominated by Ni/Al interdiffusion, leading to the aluminide layer being composed of Ni–Al intermetallic phases. Meanwhile, the aluminide layer was void-free. The result from the aluminide steel after cyclic oxidation is similar to that after isothermal oxidation. The aluminide layer has excellent thermal shock resistance, which did not form any cracks during cyclic oxidation. The oxidation kinetic result from the aluminide steel, after high-temperature oxidation, is consistent with the microstructure and phase constitution of the aluminide layer. The low oxidation rate of the aluminide steel proves that nickel pre-plating before hot-dipping can improve the oxidation resistance of the hot-dipped aluminide steel, especially under condition of cyclic oxidation.