Formation Of Intermetallic Phases Research Articles

Thermokinetic study of intermetallic phase formation in an Al/Cu multilayer thin film system

The solid-state reaction process in a multilayer thin film system (Al/Cu)50 has experimentally been studied using the methods of simultaneous thermal analysis (STA) and in situ electron diffraction. A detailed kinetic analysis of the phase formation processes during the solid-state reaction has shown that the observed solid-state transformations can be described by a statistically significant kinetic model where each stage corresponds to the reaction of the n-th order with autocatalysis. The low-temperature stage has been demonstrated to be attributable to the formation of the θ-Al2Cu phase, with the medium-temperature and high-temperature ones corresponding to the α2-AlCu3 and γ1-Al4Cu9 phases, respectively. The kinetic parameters for the formation of the phases θ-Al2Cu, α2-AlCu3 and γ1-Al4Cu9 have been determined. It has been shown that the kinetic model describing the solid-state reaction in the Al–Cu multilayer thin film system is in best agreement with the experimental data in the case of a competition between the formation stages of the α2-AlCu3 and γ1-Al4Cu9 phases.

Gibbs Energy of Formation of U2Mo and U2Ti Determined by EMF Measurements in LiCl-KCl-UCl3 Melt

Gibbs energy of formation of U2Mo and U2Ti intermetallic phases in U-Mo and U-Ti binary systems, respectively was determined employing electromotive force measurements in LiCl-KCl-UCl3 melt. U-Mo and U-Ti alloys corresponding to two-phase field U2Mo+Mo and U2Ti+Ti were prepared by vacuum arc-melting and characterized by X-ray diffraction. Single phase U2Mo and U2Ti intermetallics were also prepared and characterized to support the indexing of Bragg peaks in two-phase alloys. Temperature dependence of ΔfGU2Mo∘ and ΔfGU2Ti∘ were, respectively expressed asΔfGU2Mo∘(kJ/mol-atom)=(−144.9±1.5)+(63±3)×10−3T(K)ΔfGU2Ti∘(kJ/mol-atom)=(−116.2±1.7)+(60±3)×10−3T(K)Since there were no other experimental data available that could be used to compare present correlations, results by DFT calculations from earlier works were compared and discussed. LiCl-KCl-UCl3 melt was analyzed after completion of electromotive force runs by cyclic voltammetry and no identifiable redox features due to Mo or Ti species in melt were observed. This suggested that both alloys remained stable in the melt even after 100 h duration of electromotive force runs and there was no chemical leaching of Mo or Ti from the alloy.

Microstructural evolution and mechanical properties of Ni/Al reactive nanolaminates with different NixAly intermetallic phases

Nanolaminates made up by alternative Ni and Al nanolayers are widely applied to solder structural materials, due to abundant heat releases when supplied with an energetic input. This work studies the microstructural evolution and mechanical properties of Ni/Al nanolaminates with a wide mole ratio of Ni (MNi, 0.18–0.53), to ascertain the role of NixAly intermetallic phases during heat-treatment. To this end, 3 nanolaminates with Al thickness fixed at ≈110 nm and Ni thickness varying 15–75 nm are fabricated and are heat-treated at 400 °C, to trigger formations of NiAl3, Ni2Al3 and NiAl intermetallic phases. The results suggest an enhanced strength of Ni/Al after heat-treatment. However, their evolution with MNi is complex. The nanolaminate with MNi ≈0.18 is the softest after heat-treatment, due to the dominant plasticity of residual Al phases. The maximized strength is achieved when MNi ≈0.40, in which a novel NiAl3/Ni2Al3 nanolaminate structure is formed. Owing to the brittleness of both phases, the nanolaminate after heat-treatment is fractured by shearing upon uniaxial compression. The best strength-ductility synergy is achieved when Ni mole ratio ≈0.53. In the heat-treated nanolaminate a homogenous nanocrystalline NiAl phase is formed. As a result, the nanolaminate exhibits excellent ductility and intermediate strength among the 3 nanolaminates.

Effect of alloying elements on mechanical behaviour of Cu-Zn-Sn bronzes

Abstract The effect of Fe, P and Mn on microstructure and fatigue properties of CuZnSn bronzes investigated with optical microscopy and scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, hardness, tensile and fatigue tests. The addition of Fe, Mn and P to Cu-Zn-Sn bronzes formed Cu31Sn8, Cu6Sn5, ZnSn2, PbSnS2, ZnS, Cu2S, FeZn9 and FeZn21 phases. These phases were deposited between the dendrite arms and were dissolved in the matrix in small amounts. Especially, these precipitated phases were effective in fatigue properties. The formation of Cu-Sn, Cu-Zn and Zn-Sn intermetallic phases emitted due to the addition of Fe, Mn and P increased the fatigue strength. The spread of ferrous phases caused an increase in mechanical properties. The beneficial effect of P addition on the fatigue life far surpassed that of Mn and Fe additives.

Influence of refractory and platinum group metals on the microstructure and thermo-physical properties of Co-Al-W-based superalloys

The influence of various alloying elements on Co-Al-W based superalloys has been investigated in detail since the discovery of the Co3(Al,W) phase. However, a full picture on the role of the refractory and platinum group elements is still lacking. Accordingly, this work covers the microstructural changes and phase stability in Co9Al9W-X superalloys with 2 at% Zr, Ru, Rh, Pd, Hf, Re, Ir, and Pt. The experimental findings are compared with thermodynamic calculations. Generally, alloying with refractory and platinum group elements preserves γ/γ′ microstructures, but causes the formation of additional intermetallic phases. Electron backscatter diffraction and energy dispersive X-ray spectroscopy reveal that Ru, Ir, and Pt cause discontinuous formation of β (B2) and χ (D019) phases whereas in the Re-containing alloy β and µ (D85) precipitates are present along the grain boundaries. Also unidentified Hf- and Zr-rich phases form in the alloys containing these elements. Additionally, differential scanning calorimetry measurements and scanning electron microscopy analysis indicate an increasing γ′ solvus temperature as well as γ′ volume fraction for most of the refractory and platinum group elements. This can be explained by their γ′/γ partitioning behavior, which has been examined by atom probe tomography.

Evaluating some design criteria for TiFe-based ternary hydrogen storage alloys

Elemental substitution is widely practised to fabricate TiFe-based alloys with enhanced hydrogen storage characteristics. While some hydrogen storage properties can be improved others are usually adversely affected by this method. Hence, establishing sensible alloying design criteria is important for further developing Ti-Fe-based alloys. Here, the effects of substitutional elements in Ti-Fe-based ternary alloys are assessed based on several factors such as hydrogen bond dissociation energy, lattice parameters, interstitial site size, and intermetallic phase formation. Our calculations show that all the substitutional elements studied in this work (except Ni and Co) increase the lattice parameter compared to the TiFe alloy, while they have a diverse effect on the interstitial site sizes. The thermodynamic stability of the alloys could not be adequately described based on the lattice parameter and factors such as interstitial site sizes along the local atomic environment should be also considered. Hydrogen storage capacity of the Ti-Fe-based ternary alloys also appears to be influenced by the metal-hydrogen bond dissociation energy of the substitutional elements and their capability to form intermetallic phases with Ti. TiFe-based ternary alloys were modified by V and Zr substitutions according to the above criteria. The modified alloys were mostly composed of the B2 TiFe phase, offering significantly easier activation and a higher reversible hydrogen storage capacity compared to the binary alloy.

Process optimization and property of Ti-Al-Cr-Nb coating on titanium alloy surface by laser in-situ synthesis

Ti-6Al-4V alloys are popular structural materials for the production of critical components. However, its poor surface properties, such as friction and high-temperature oxidation, further limit its application scope. Ti-Al-Cr-Nb coating was deposited on the Ti-6Al-4V alloy through laser cladding. The tendency of cracks was low when the laser energy density was 14.33-8.19 kw · s · cm −2, the corresponding effective process parameters were the laser power of 1600-1800 W matching the scanning speed of 4-6 mm/s. Due to the formation of Ti3Al intermetallic compound phase, and the lattice distortion caused by adding a small amount of Cr and Nb playing a role in solid solution strengthening, average vickers hardness of the coating was about 583.3 HV0.1, which was about 1.7 times that of the substrate.

Titanium alloys developed on the basis of the addition of cheap strong eutectoid β-stabilisers

Historically, titanium alloys have been developed disregarding the addition of eutectoid β-stabilisers as they generally lead to the formation of brittle intermetallic phases upon solidification of the alloy. However, such phenomenon can be prevented using powder metallurgy. Thus, this study considered the concurrent addition of cheap strong eutectoid β-stabilisers, namely Mn and Fe, for the development of new ternary Ti–Mn–Fe alloys, reducing the intrinsic cost of Ti alloys. It is found that the progressive addition of Mn and Fe in equal concentration enhances the densification of Ti during sintering, leading to lower amount of residual porosity, the transformation of the microstructure from purely lamellar to metastable, and the associated refinement of the microstructural features (grains and lamellae), as well as the stabilisation of a greater amount of β phase, and the formation of the metastable α″ phase. Such microstructural changes result in the strengthening (higher yield and ultimate tensile strength and hardness) and embrittlement of the alloy by changing the fundamental strain hardening mechanism of the ternary Ti–Mn–Fe alloys.

Thick functionally-graded W-316L composite coatings for nuclear fusion applications

Nuclear fusion is a potential pathway to finding a sustainable, carbon-free energy source. Some critical components of the fusion reactors are planned to be coated by tungsten. For the task, thermal spraying in vacuum or protective atmosphere can be employed, offering several advantages such as easy preparation of advanced feedstock for deposition of functionally graded composites. Such coatings could be a viable approach to avoid the thermal expansion coefficient mismatch between the W coating and the steel components. In this study, radio-frequency inductively-coupled plasma spray method was used to deposit W-steel composite coatings of three different W ratios, as well as a functionally graded coating consisting of the three composites and a pure W top coat. The coatings exhibited a high-quality microstructure, without intermetallic or oxide phases formation. Thermal diffusivity and conductivity of the coatings was measured at 100 °C and 600 °C, with the values falling into range between the bulk steel and plasma sprayed W. In conclusion, we have shown that the RF-ICP technology is suitable for preparation of tungsten-steel graded deposits and the outputs are now prepared for other testing and a following upscaling to the industry-relevant size.

Laser surface alloying of titanium alloy with silver: Microstructure, hardness and corrosion property

In this study, silver (Ag) was surface-alloyed in TC4 alloy (Ti6Al4V) with a high-power diode laser (HPDL). The Ag content in the alloyed layers were controlled to be 5 to 24 wt%. The microstructure, hardness and corrosion properties of the alloyed layers are affected by the Ag content. The hardness of TC4 alloy, when laser surface-alloyed with 14 wt% Ag increased from 381 HV0.2 to a maximum value of 569 HV0.2, caused by the formation of hard intermetallic phases (Ti2Ag and TiAg) in the α-Ti matrix. However, with the increase of Ag content to 24 wt% the hardness of the alloy was lowered to 456 HV0.2, result of the formation of a soft Ag-rich phase. In addition, observing a decrease in corrosion resistance of the laser surface-alloyed TC4 with a high Ag content, which is attributed to micro-galvanic effect between the α-Ti and Ti2Ag, TiAg and Ag-rich phase.

Effects of the adjustable ring-mode laser on intermetallic formation and mechanical properties of steel to aluminium laser welded lap joints

Research has confirmed a positive effect of laser beam shaping on controlling weld profiles and keyhole stabilisation, with significant reductions of porosity in weldments. However, few attempts with scattered results have studied the impact of laser beam shaping on intermetallicphase formation. This paper implements the adjustable-ring mode (ARM) laser and studies the impact of the core/ring power ratio to explore the impact on intermetallic phase formation and mechanical properties during remote laser welding of IF steel to 1050 aluminium. It was found that in conduction mode, the core/ring power ratio of 0.2 provided a larger surface area for bonding at the weld interface, and this was translated through the maximum lap-shear strength of 97.6 N/mm2 (joint efficiency 71%). Furthermore, this significantly reduced the Fe2Al5 intermetallic compound (IMC) thickness by 62% and total IMC thickness by 40% in contrast to a core-dominant beam (power ratio greater than one). In keyhole mode, cracking and lower lap-shear strengths were observed compared to the conduction mode. Notably, with a core/ring power ratio of 0.5 a significant grain refinement in the steel side of the weld was observed.

Combustion Synthesis and Reactive Spark Plasma Sintering of Non-Equiatomic CoAl-Based High Entropy Intermetallics

The present work reports the direct production of a high-entropy (HE) intermetallic CoNi0.3Fe0.3Cr0.15Al material with a B2 structure from mechanically activated elemental powder mixtures. Fast and efficient combustion synthesis (CS), spark plasma sintering (SPS), and reactive SPS (RSPS) methods were used to synthesize the HE powders and bulks. The formation of the main B2 phase along with some amounts of secondary BCC and FCC phases are reported, and L12 intermetallic (CS scheme) and BCC based on Cr (CS + SPS and RSPS schemes at 1000 °C) were observed in all samples. The interaction between the components during heating to 1600 °C of the mechanically activated mixtures and CS powders has been studied. It has been shown that the formation of the CoNi0.3Fe0.3Cr0.15Al phase occurs at 1370 °C through the formation of intermediate intermetallic phases (Al9Me2, AlCo, AlNi3) and their solid solutions, which coincidences well with thermodynamic calculations and solubility diagrams. Compression tests at room and elevated temperatures showed that the alloy obtained by the RSPS method has enhanced mechanical properties (σp = 2.79 GPa, σ0.2 = 1.82 GPa, ε = 11.5% at 400 °C) that surpass many known alloys in this system. High mechanical properties at elevated temperatures are provided by the B2 ordered phase due to the presence of impurity atoms and defects in the lattice.

Compound Casting of Aluminum with Sheet Steel in 3D Sand Casting Using an Inductive Heating System

Compound casting is a process in which a single component is made from two metallic materials, such as aluminum and steel. Solid-liquid bimetallic compounds can be produced by suitable process control. This technology can reduce the number of joining processes, and the specific properties of the respective metal component can be used for specifically designed product properties, for example, where lightweight and high strength are needed. This paper presents an experimental methodology for producing a purely material-bonded bimetallic joint from cast aluminum and zinc-coated sheet steel in 3D sand casting using an inductive heating system. The process-related temperature characterisation in the compound zone is described using a heating test rig and temperature measurements. It shows that inductive preheating can only produce a material bond between the aluminum casting and the coated steel sheet. Shear tensile tests showed strengths between 15 MPa and 22 MPa. Laser surface pre-treatment using laser ablation cutting on the coated steel sheet was carried out to investigate the benefit of possible microform-locking. The results show a strength-reducing influence on the tensile shear tests. Micrographs showed the formation of Al4.5FeSi and Al7Fe2Si, as well as the formation of other undefined intermetallic phases. The thickness of the compound zone is 10 µm.

Processing and Properties of Sintered W/Steel Composites for the First Wall of Future Fusion Reactor

Functionally graded tungsten/steel composites are attractive to be used as an interlayer to join tungsten (W) and steel for the first wall of future fusion reactor to reduce the thermally induced stresses arising from the different coefficient of thermal expansion (CTE) of W and steel. W/steel composites, with three W contents: 25, 50 and 75 vol% W, will serve as individual sublayers of this functionally graded material. Therefore, the present work exploits an emerging sintering technique, field-assisted sintering technology, to produce these composites. Firstly, a systematic parameter study was conducted aiming to reduce the residual porosity to a minimum while keeping the formation of intermetallic phases at the W/steel interface at a low level. The optimized composites 25, 50 and 75 vol% W achieved a relative density of 99%, 99% and 96%, respectively. Secondly, mechanical tests at elevated temperatures reveal that these composites are ductile above 300 °C, which is the minimum operating temperature of the first wall. Lastly, the measured CTE, specific heat capacity and thermal conductivity were consistent with the theoretically expected values.

Novel Mechanically-Alloyed Cu–La–P Ternary Alloy Electrocatalysts for the Alkaline Hydrogen Evolution Reaction

Transition metal phosphides, such as Cu3P, are of research interest as hydrogen evolution electrocatalysts due to a combination of good intrinsic activity and good stability. Rare earth-transition metal alloying is known to improve electrocatalytic performance, especially by the formation of intermetallic phases. Current transition metal phosphide electrocatalyst manufacturing methods are not capable of forming these intermetallic phases. Mechanical alloying is a promising technique to synthesize these intermetallic phases. Alloy powders of Cu3P, Cu19La5P12, and a novel multi-phase Cu74La4P22 composition were prepared using mechanical alloying and evaluated as electrocatalysts for the alkaline hydrogen evolution reaction on a geometric and intrinsic area basis. On an intrinsic basis, the novel Cu–La–P composition demonstrated excellent Tafel performance of 69.4 mV dec−1. Tafel slope, exchange current density, and overpotential data demonstrated the importance of spillover effects in multiphase Cu3P/Cu19La5P12 surface structures. These results suggest that Cu–La–P alloys are promising potential catalysts for electrochemical hydrogen production, and mechanical alloying of rare earth elements is an effective technique for improving the electrochemical performance of transition metal phosphides.

Photocatalytic activity of Zn-Cu-S alloy for the removal of dye pollutant: Synthesis, characterization, optimization and DFT insights

This study synthesized Zn-Cu-S alloy powder using mechanical alloying to eliminate EBT dye pollution. Multiple techniques were used to characterize the alloyed materials. The formation of intermetallic phase, Cu5Zn8, was realized, after 35 h milling process. After light irradiation, both the adsorption and photocatalytic activity of the alloyed material were observed. The EBT removal process was optimized by varying pH, lamp power, and alloy dosage (g/L) parameters. Response surface plots were employed to investigate the removal percentage of dye. Isotherm and kinetic models were utilized to investigate EBT uptake. The maximum adsorption capacity (qmL) of 222.8 mg/g was significantly higher than previously reported values. The maximum removal rate was determined to be approximately 87%. DFT calculations estimated the optimized geometry of the ground state of a semiconductor alloy by frontier molecular orbitals and explained the origin of the alloy photocatalyst's electronic transitions.

Experimental study on aluminium bronze coatings fabricated by low pressure cold spraying and subsequent heat treatment

Among bronze alloys, strength and corrosion resistance are the distinguishing features of aluminium bronzes. CuAl alloys coatings are commonly prepared using thermal spraying technologies, but low-pressure cold spray, unpopular for this purpose so far, seems to be a good alternative in terms of manufacturing and facility costs. The research studies the effect of aluminium addition on low-pressure cold spray deposition of mixed CuAl feedstock powders (up to 30 wt% of Al) instead of bronze particles. Additionally, hard alumina particles (of the same weight as CuAl feedstock powders together) were added to lower coating porosity, provide good adhesion, and tailor the mechanical properties of coatings. After the implementation of thermal treatment, fine mixing of feedstock powders within the coating facilitated the formation of copper-rich solid solution and Cu4Al9 intermetallic phase for high amounts of Al (≥25 wt%). The coatings were characterized through light and scanning electron microscopy to examine cross-section morphology; energy-dispersive X-ray spectrometry and X-ray diffraction to investigate elemental and phase composition before and after thermal treatment. Additionally, to quantify the individual phases in sprayed coatings Rietveld refinement was performed. For coatings after thermal treatment were bronze formation was observed, the maximum solubility of aluminium in the copper structure was also determined using Vegard's linear dependence.

Effects of Elements on the Microstructure and Mechanical Properties of AlCoCrFeNiTi High-Entropy Alloys

AlCoCrFeNiTi high-entropy alloys (HEAs) have attracted much attention because of their excellent mechanical properties. Here, we systemically studied the effects of elements on the microstructure and mechanical properties of AlCoCrFeNiTi HEAs. The results showed that the phase composition and morphology are significantly affected by the elements. With increasing Ti addition, the lattice parameters of the solid solution phase increased slightly, and lattice distortion occurred. Al changes the crystal structure of FCC to BCC and reduces the lattice distortion energy of the alloy. The BCC phase obviously increases with increasing Al content. However, excessive Al, Ti and Cr promote the formation of intermetallic compound phases, while Ni, Fe and Co promote the transformation of the alloy into a solid solution. The properties of AlCoCrFeNiTi HEAs are closely related to their phase composition and morphology. When HEAs consist only of FCC and BCC phases, their ductility and strength are greatly improved. The presence of an intermetallic compound phase in the microstructure can significantly reduce the configurational entropy of adjacent solid solutions, thus reducing the strengthening effect of solid solutions. Additionally, the AlCoCrFeNiTi HEAs with different microstructures show different deformation mechanisms. The deformation of FCC + BCC HEAs with cellular structures is uniform and presents great plasticity and strength. When the cellular-structure HEAs contain equiaxed BCC, thick lamellar BCC/FCC or intermetallic compound phases, cracks tend to occur and propagate along the phase boundary due to the local nonuniform deformation. For AlCoCrFeNiTi HEAs with dendrite structures, after initiation at the phase boundary, the crack does not easily spread to the dendrite FCC phase but causes the interdendritic BCC phase to crack.

Micro‐Particle Induced X‐ray Emission Study of Lead‐Free and Lead‐Based Solders and Interactions with Copper Wires

Pb‐free electrical solders, such as Cu–Sn alloys, work well for reflow soldering under tightly controlled conditions. Hand soldering, however, often results in poor quality joints compared to conventional Pb–Sn solders. To investigate this under realistic workshop conditions, micro‐particle induced X‐ray emission (micro‐PIXE) with 2 MeV protons has been employed. Commercial flux‐cored Cu–Sn and Pb–Sn solder wires are studied. Solder blobs under two cooling conditions as well as tinning Restriction of Hazardous Substances (RoHS)‐compliant and legacy component wires are investigated. The results show that the long heating and slow cooling of Cu–Sn solder blobs lead to formation of an acicular precipitate that can be ascribed to Cu6 Sn5. Pb–Sn solder under the same conditions shows phase separation with regions of high Sn and regions with high Pb. In the case of rapidly cooled blobs where a shiny surface is produced, no phase separation in either solder is observed. Tinning of RoHS‐compliant and legacy Cu component wires with the two solders produce significantly different interfacial depth profiles with varying degrees of grading, indicative of intermetallic phase formation.

Fatigue analysis of a progressive secondary A357 alloy with higher iron content in a chloride environment

This paper investigates the fatigue behavior of secondary A357.0-T6 alloy with higher Fe content as a result of the usage of recycled metals. Commercial secondary Al-alloys contain Fe, often as an undesirable impurity negatively affecting plasticity, tensile strength, and so on due to the formation of brittle intermetallic phases. A common unwanted intermetallic phase is β-Al5FeSi in form of brittle platelets. This plate-like morphology acts as a stress concentrator, leading to a decrease in the strength, ductility, and dynamic fracture toughness of the castings. Moreover, promoting casting defects such as porosity. In addition to structural and mechanical properties, the corrosive environment also influences fatigue lifetime. The effect of corrosion damage on fatigue failure is a problem for engineers in the aerospace, automotive, and gas or oil industries. The corrosion reactions or their products can interact with the fatigue process accelerating crack initiation or propagation. Therefore, the aim of this study is to investigate chemical-mechanical interactions during the simultaneous application of cyclic stress and exposure to a corrosive environment.