Intermetallic Phase Layer Research Articles

Thermal and Microstructure Characterization of Zn-Al-Si Alloys and Chemical Reaction with Cu Substrate During Spreading

The problems associated with the corrosion of aluminum connections, the low mechanical properties of Al/Cu connections, and the introduction of EU directives have forced the potential of new materials to be investigated. Alloys based on eutectic Zn-Al are proposed, because they have a higher melting temperature (381 °C), good corrosion resistance, and high mechanical strength. The Zn-Al-Si cast alloys were characterized using differential scanning calorimetry (DSC) measurements, which were performed to determine the melting temperatures of the alloys. Thermal linear expansion and electrical resistivity measurements were performed at temperature ranges of −50 to 250 °C and 25 to 300 °C, respectively. The addition of Si to eutectic Zn-Al alloys not only limits the growth of phases at the interface of liquid solder and Cu substrate but also raises the mechanical properties of the solder. Spreading test on Cu substrate using eutectic Zn-Al alloys with 0.5, 1.0, 3.0, and 5.0 wt.% of Si was studied using the sessile drop method in the presence of QJ201 flux. Spreading tests were performed with contact times of 1, 8, 15, 30, and 60 min, and at temperatures of 475, 500, 525, and 550 °C. After cleaning the flux residue from solidified samples, the spreadability of Zn-Al-Si on Cu was determined. Selected, solidified solder/substrate couples were cross-sectioned, and the interfacial microstructures were studied using scanning electron microscopy and energy dispersive x-ray spectroscopy. The growth of the intermetallic phase layer was studied at the solder/substrate interface, and the activation energy of growth of Cu5Zn8, CuZn4, and CuZn phases were determined.

W–steel and W–WC–steel composites and FGMs produced by hot pressing

Tungsten–steel composites and functionally graded materials (FGMs) are being developed for potential application in plasma facing components of fusion devices. Their role is to reduce thermal stresses at the interface between plasma facing tungsten armor and structural material. In this study, uniform composites and graded layers produced from tungsten and steel powders by hot pressing were investigated. Fully dense composites with uniform distribution and good bonding of the phases were formed. A thin layer of Fe2W intermetallic phase was found at the interfaces. To avoid its formation, a third phase (tungsten carbide) was introduced between tungsten and steel. Structure, thermal and mechanical properties of both types of composites in the as-produced and annealed state were characterized.

Microstructural characterisation and mechanical response of laminated Ni-intermetallic composites synthesised using Ni sheets and Al foils

Abstract The laminated Ni–(Ni 2 Al 3 + NiAl 3 ) and Ni–(Ni 3 Al + NiAl) composites have been successfully fabricated by reaction synthesis in vacuum using 400 μm thick Ni sheets and 150 μm thick Al foils. The aluminium layers were completely consumed due to the formation of intermetallics. The final microstructures consisted of alternating layers of intermetallic phases and unreacted nickel could be designed easily because the structures of the composites depend on the treating time and temperature. Reaction synthesis at 620 °C for 2 h resulted in a microstructure consisting of Ni and Ni 2 Al 3 + NiAl 3 layers. At room temperature the Ni–(Ni 2 Al 3 + NiAl 3 ) laminated composites had an ultimate tensile strength of 615 MPa and an elongation of 10%. The fracture behaviour of the composites exhibited a mixture of brittle fracture of Ni 2 Al 3 + NiAl 3 intermetallics and ductile one of Ni layers. Delamination that occurred in the middle of the intermetallic layers was caused by the presence of continuous Al 2 O 3 inclusions. The next thermal aging cycle was employed to change the microstructure of intermetallic layers and to improve mechanical properties of the laminated composites. Heat treatment at 1150 °C for 4 h resulted in a composite comprising Ni and Ni 3 Al + NiAl layers. The Ni–(Ni 3 Al + NiAl) laminated composites had an ultimate tensile strength of 875 MPa and an elongation of 24%. The dislocations in the Ni layers could easily slide through the coherent Ni/Ni 3 Al interfaces, so Ni 3 Al layers co-operatively deformed with the Ni layers during tensile testing. Debonded Ni 3 Al/NiAl interfaces containing spherical Al 2 O 3 inclusions further encouraged the capability of the Ni 3 Al layers for plastic deformation. As a consequence, the Ni–(Ni 3 Al + NiAl) laminated composites at room temperature exhibited significant strain-hardening, a good tensile strength and a high ductility. The effect of temperature on the tensile properties and deformation behaviour of the laminated Ni–(Ni 2 Al 3 + NiAl 3 ) and Ni–(Ni 3 Al + NiAl) composites have been also investigated. With increasing tensile test temperature from room to 700 °C, the ultimate tensile strength decreased gradually for both types of composites. The yield strength of the Ni–(Ni 2 Al 3 + NiAl 3 ) laminated composites decreased and elongation increased with increasing temperature. The abnormal strengthening of the Ni 3 Al phase in the Ni–(Ni 3 Al + NiAl) composites led to a gradual increase of the yield strength and the fracture elongation decrease with increasing the tensile test temperature.

Laser-Mig Hybrid Welding Of Aluminium To Steel — Effect Of Process Parameters On Joint Properties

Laser MIG hybrid welding was recently suggested as a feasible process for joining of aluminium to steel for both structural as well as tailored blank applications. To promote an understanding of the process and the effect of process parameters on joint properties, laser MIG hybrid welding experiments were performed to join aluminium alloy AA6016 to DC05 zinc-coated steel sheets, in the thickness range of 1 mm, in a butt joint configuration. Among the process parameters varied were laser power, MIG arc power, wire feed rate, welding speed and arc position relative to the abutting edges. By metallographic cross-sections and tensile tests, the effect of these process parameters on joint properties such as wetting length, intermetallic phase layer thickness and tensile strength could be elucidated. Based on these results, a process parameter envelope resulting in adequate and reproducible joint properties (sound weld bead, sufficient and regular wetting, thin intermetallic phase layer, tensile strength exceeding 180 MPa) was established. Within this parameter envelope, corrosion behaviour was rated not critical, and forming behaviour showed promising results.

Structure of Nitride and Nitride/Oxide Layers Formed on NiTi Alloy

The present work summarises the results, which were obtained from studies carried out on the structure of the nitride and nitride-oxide surface layers with use of the electron transmission microscopy. The layers were formed using glow discharge technique at relatively low temperature (300°C). It has been shown that low temperature nitriding or nitriding/oxiding process produced a thin layer ~30 nm thick. They were formed from titanium nitride as well as titanium oxides. The structure revealed that nanoparticles were surrounded by high amount of amorphous phase. Especially, electron microscopy was useful method for studying the phase boundary between the layer and the NiTi matrix. During deposition process, which was carried out at temperature above 300°C, the intermediate layer of Ni3Ti intermetallic phase appeared between titanium oxides and/or nitrides. Lowering deposition temperature down to 300°C or below resulted in absence of such sublayer. Moreover, thickness, structure of layers, absence of sublayer formed during glow discharge process, can significantly influence deformation during inducing of the shape memory or superelasticity effect.

Modeling the role of sources and sinks for vacancies on the kinetics of diffusive phase transformation in binary systems with several stoichiometric phases

The formation and growth of layers of intermetallic phases at joints of different metals is a common problem with many aspects. One of them is also the kinetics of growth of the layers. The present model based on application of the thermodynamic extremal principle accounts for the intensity of sources and sinks for vacancies in the interfaces and in the bulk. Simulations indicate that the sources and sinks influence the kinetics of the system significantly.

Effect of tool travel and rotation speeds on weld zone defects and joint strength of aluminium steel lap joints made by friction stir welding

In this study, Al-5083 and St-12 alloy sheets were friction stir lap welded at different travel (7–23 cm min−1) and rotation (750–1125 rev min−1) speeds of the welding tool. The welded joints were characterised by various methods including shear tensile and Vickers microhardness tests, optical and scanning electron microscopies and X-ray diffraction analysis. The results showed that the weld zone defects decreased, and the joint strength also improved significantly with the reducing tool travel speed from 23 to 7 cm min−1. The travel speed of 11 cm min−1 was an optimum speed within the travel speeds investigated in this work. Additionally, raising the tool rotation speed enhanced the joint strength slightly. The microhardness results confirmed the formation of intermetallic phase layer with the hardness of ∼335 HV at the swirl layered structure.

Study of Modified Layer on Exterior Surface of Superheater Tubes

Renewal of overhaul period of power plants equipment, especially superheater tubes, is important problem in energy sector of every country. Investigation of processes on tube’s surfaces is necessary to obtain information of equivalent temperature during maintenance. In this work the austenitic chrome-manganese steel 10Cr13Mn12Si2Ni2Cu2Nb (DI59) and chrome-nickel steel 12Cr18Ni12Ti were studied. Application of these steels provides the desired heating resource of the steam superheater (100000 h) and reliable exploitation of the boilers at high temperature (~650°C). Between the oxide layer and the base metal layers with different crystal structure compared with matrix are observed. Qualitative and quantitative electron microscopic techniques, optical metallography and X-ray phase analysis are employed to investigate the morphological evolution, elemental redistribution in the alloy system and formation and growth of discovered layers. In steel DI59 the discovered layer had a ferrite structure. In steel 12Cr18Ni12Ti it was first shown that this layer is consist of different sulfides which disposed in FeNi3 matrix. This intermetallic phase and ferrite layer are ferromagnetic. Changes in the structure of steel on its surfaces are caused by high exploitation temperature and type of fuel which is used in power plants (combination of natural gas and mazut). This opens the possibility to use connection between thermal irregularity in metal and thickness of discovered layers in order to search most damaged part of tubes with ferrite meter.

Processing, Microstructure and Properties of Laminated Ni-Intermetallic Composites Synthesised Using Ni Sheets and Al Foils

Processing, Microstructure and Properties of Laminated Ni-Intermetallic Composites Synthesised Using Ni Sheets and Al FoilsThe laminated Ni-(NiAl3+Ni2Al3) and Ni-Ni2Al3intermetallic composites were fabricated by reaction synthesis in vacuum using Ni sheets and Al foils. The aluminium layers were completely consumed due to the formation of intermetallic phases. The Ni-Al reaction at 620°C was studied by interrupting in steps the reaction process to observe the microstructural changes. The final microstructure consisted of alternating layers of intermetallic phases and unreacted nickel can be designed easily because the stable structures of the composites depend only on the treating time. Microstructural examinations using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray microprobe analysis (EDX) demonstrated that after 1h of treatment Ni2Al3is the predominant intermetallic phase. The formation of the Ni2Al3phase is thermodynamically favoured over the formation of the other phases and can be understood from the steps occurred through a series of solid state reactions. The tensile strength of the laminated composites increases with an increase of the volume fraction of the intermetallic products. However, it decreases after long heat treatment because the Ni2Al3/Ni2Al3interfaces can very easily delaminate due to a very weak bonding caused by continuous Al2O3inclusions. Observations show that the laminated composites exhibit a mixture of brittle fracture of intermetallics and ductile one of residual Ni layers.

Analysis of Morphology and Growth Kinetics of Zn-Mn and Zn-0.2wt.%Al-Mn Hot-Dip Galvanizing Coatings

The influence of manganese in Zn-Mn and Zn-0.2wt.%Al-Mn bath on the morphology and growth kinetics of the galvanizing coatings has been studied using scanning electron microscopy equipped with energy dispersive spectroscopy. When galvanized in zinc bath, the coating consists mainly h and ζphase. When manganese is added in zinc bath, the morphology of ζ phase changes from fragmental to compact. Manganese favors the formation of the δ phase and inhibits the growth of the ζ phase.When galvanized in Zn-0.2wt.%Al bath, the coating consists only δ and h phase. With the addition of manganese in Zn-0.2wt.%Al bath, the morphology of δ phase changes from fragmental to compact The thickness of the Fe-Zn intermetallic phase layer in coatings decreases obviously when manganese is added into zinc and Zn-0.2wt.%Al bath, and the thickness increases slowly with the increase of immersion time.

Effect of Thermal Cycle on the Formation of Intermetallic Compounds in Laser Welding of Aluminum-Steel Overlap Joints

The intermetallic compound (IMC) (or intermetallic phase layer) has a significant influence on the mechanical properties ofjoints between dissimilar metals obtained by thermal processes such as laser welding. Its formation is basically affected by thermal cycles in the joining or contact zone, where the IMC is formed. Within this study, the influence of the thermal cycle on the formation of the IMC during laser welding of an aluminum-steel (Al99.5-DC01) overlap joint was investigated. The temperature was measured directly by a thermocouple, and the weld seam was analyzed by scanning electron microscope (SEM). The influence of peak temperature, cooling time and the integral of the thermal cycle on the thickness of the IMC was identified and discussed. It was identified that cooling time has the biggest influence on the thickness of the IMC.

Mechanical and Microstructural Characterization of Al-5083/St-12 lap joints made by friction stir welding

Al-5083 and St-12 alloys sheets were friction stir lap welded at various traveland rotation speeds of the welding tool. Microscopic examinations indicate that the joint strength is due to the macroscopic and microscopic mechanical lockings and also atomic diffusion. The reaction zone of the welded joints consists of mixed layers of ultra-fine grains and the intermetallic compounds. The microhardnessand nano indentationresults prove that the intermetallic phase layer is more brittle in comparison to base metals and ultra-fine grain region. The fracture surfaces are a combination of brittle and ductile fractures. The fracture loads show that the joint strength improves significantly by decreasing the travel speed of the tool.

最大で2.2 GPaの引張強度を持つCu-Zr合金線材の開発とそのミクロ組織

Round bar ingots of hypoeutectic Cu-4 and -5 at% Zr alloys cast into copper mold were wire-drawn (WD) with drawing ratio η=5.9 and more, and the relationship between the mechanical and electrical properties and microstructures of those wires was investigated. As a result, it became obvious that the WD Cu-5 at% Zr alloy with η=8.6, which was 40 μm in diameter, reached 2234 MPa of ultimate tensile strength (UTS), 1873 MPa of 0.2% proof stress, 4.2% of total strain to failure, 126 GPa of Young's modulus and 16%IACS of electrical conductivity (EC). As for the WD Cu-4 at% Zr alloy, it was able to be wire-drawn down to 27 μm in diameter with η=9.4. Both UTS and Young's modulus increase linearly with the drawing ratio η. One of the reasons to indicate the high strength will be the development of nano-sized lamellar structure of α-Cu and Cu9Zr2 inter-metallic compound phase. Furthermore it was observed that nano-sized amorphous phase was formed within the nano-sized layer of Cu9Zr2 inter-metallic compound phase. Increase of the strength for heavily WD of Cu-4 and -5 at% Zr alloy wires will be due to the synergistic effect of deformation twins developed in the α-Cu phase and the formation of the nano-sized lamellar structure consisting of α-Cu and Cu9Zr2 inter-metallic compound phases. The highly EC of 16%IACS obtained for the WD Cu-5 at% Zr alloy wire can be explained by few dislocations in the high conductive α-Cu phase.

Investigation on the diffusion bonding of tungsten and EUROFER97

Due to its advantages, tungsten is selected as armor and structural material for use in future fusion power plants. To apply tungsten as structural material, a joint to EUROFER97 is foreseen in current divertor design for which the diffusion bonding is considered in this work. The joining must have acceptable strength and ductility without significant change in microstructures. So far, numerous diffusion bonding experiments without and with post bonding heat treatment (PBHT) are performed at 1050°C for various bonding duration. For the bonding processes without PBHT, the bonding seams obtained are defect free and have a very high tensile strength. However they are brittle due to a thin layer of FeW intermetallic phase and metal carbides. For the bonding processes with PBHT, the bonding specimens fail at the bonding seam.

STUDI LAPISAN INTERMETALIK Cu3Sn PADA UJUNG ELEKTRODA DALAM PENGELASAN TITIK BAJA GALVANIS

Intermetallic Cu3Sn Phase Layer on Electroders Tip of Galvanized Resistance Spot Welding. A resistance spotwelding method is commonly used in automotive industries application. In a resistance spot welding method, the copperelectrode has a significant role as an electric current carrier for joining thin metal sheet. This research was focused onstudying the effect of tin layer at the electrode tip for joining galvanized steel sheet. The main variable of this researchis in the thickness of the intermetallic Cu3Sn layer. The result showed that the introduction of tin layer less than 1 mm inthickness on the electrode tip gives a comparable shear strength and nugget diameter distribution with the unplatedelectrode tip.

He ion irradiation damage in Al∕Nb multilayers

We investigate the evolution of microstructure and mechanical properties of sputter-deposited Al∕Nb multilayers with miscible fcc/bcc type interface and individual layer thickness, h, of 1–200nm, subjected to helium ion irradiations: 100keV He+ ions and a fluence of 6×1016∕cm2. Helium bubbles, 1–2nm in diameter, are observed. When h is greater than 25nm, hardnesses of irradiated multilayers barely change, whereas radiation hardening is more significant at smaller h. Transmission electron microscopy and scanning transmission electron microscopy studies reveal the formation of a thin layer of Nb3Al intermetallic phase along the Al∕Nb interface as a consequence of radiation induced intermixing. The dependence of radiation hardening on h is interpreted by using a composite model considering the formation of the hard Nb3Al intermetallic layer.

Twin-Roll Cast Al-Clad Magnesium Alloy

An attempt has been made to clad Mg alloy with Al by twin-roll casting. This was done by inserting an Al sheet between the roll and the Mg alloy melt during twin-roll casting. Microstructural investigation across the transverse section of the as-cast Al-clad Mg alloy sheet reveals a very good interfacial bonding between Al and the base Mg alloy. Annealing of the Al-clad Mg alloy sheet results in the formation of layers of various intermetallic phases along the Mg/Al interface. Subsequent rolling of the as-annealed sheet significantly improves the formability of the reaction zone, as evidenced by the cracking of the base Mg alloy before the cracking of the reaction zone.

In Situ Combustion Synthesis of Ti-Al Intermetallic Compounds in Al Alloy Casting Process

Ti-Al intermetallic compounds are regarded as promising materials for the hightemperature structural and coating applications. We focused on the joining of Al casting alloy with Ti-Al intermetallic compounds by in-situ combustion synthesis to improve the surface properties of Al casting components. Microstructures and phase formation behavior of Ti-Al based intermetallic compounds synthesized by combustion reaction were analyzed using scanning electron microscope(SEM) equipped with energy dispersive x-ray spectroscopy (EDS) and x-ray diffractometer(XRD) in Ti-Al intermetallic compounds. Three kinds of titanium aluminides of Ti3Al, TiAl and TiAl3 were synthesized by the heat from the Al molten metal and a coating layer of intermetallic phase were formed simultaneously on solidifed Al alloy surface. The shapes and microstructures of reacted compacts were varied by mixing ratio of elemental powders. The TiAl3 intermetallic compound was observed in the compacts regardless of the mixing ratio of elemental powders. And the unreacted Ti powders were remained in the reacted compacts due to the big size of Ti powder and low exothermic heat of reaction between Ti and Al powders. The zone that poured Al alloy diffused into the reacted Ti-25at.%Al compact of about 200 μm thickness was formed at the interface by the reaction between liquid molten Al alloy and solid Ti powders in green compact.

In-Situ Joining of Combustion Synthesized Ni-Al Alloys with Al Casting Alloy

We focused on the surface reinforcement of Al casting alloys with Ni-Al intermetallic compounds by in-situ combustion reaction to improve the surface properties of Al casting components. Microstructure and phase formation behavior of Ni-Al based intermetallic compounds synthesized by combustion reaction were investigated in terms of thermal and phase analysis using scanning electron microscope(SEM) equipped with energy dispersive x-ray spectrometer (EDS) and x-ray diffractometer(XRD) in Ni-Al intermetallic compounds. Three kinds of nickel aluminides, NiAl3, NiAl and Ni3Al, were synthesized by emission heat from the Al molten metal in order to form a coating layer of intermetallic phase simultaneously on the solidifed Al alloy surface. The synthesized shapes and microstructures of nickel aluminides were varied by casting temperature, Si contents, and the mixing ratio of elemental powders. The synthesized reaction products formed in nickel aluminides were observed to be different depending on the mixing ratio of elemental powders. The reaction layer of about 25m thickness was formed at the interface, and it mainly consisted of NiAl3 phase by the reaction between liquid molten Al alloy and solid Ni powders in green compact. With this information, we successfully produced a coating layer of Ni3Al intermetallic compound onto the casting Al alloy surface using molten metal heat without any additional process. These findings led us to conclude that a near-net shaped nickel aluminide coating layer can be formed using this unique process.

Development of multilayer oxidation resistant coatings on niobium and tantalum

In order to improve the high temperature oxidation resistance of refractory metals, multilayers Al–Si composite coatings of about 50 μm and 40 μm thickness were formed on niobium and tantalum metals, respectively, by pack cementation technique. Substrate metals embedded in the pack consisting of Al, Si powders and activator NH 4F intimately mixed in the prescribed proportions were heat treated at 1300 K for 16 h. Coated samples were characterized by SEM, XRD, Optical microscopy and EPMA. Mainly two layers of different intermetallic phases were formed in coating of both niobium and tantalum. The inner layers were thicker than the outer layers and comprise of NbSi 2 and TaSi 2 for niobium and tantalum, respectively. Outer layers were ternary phases of Al, Si, Nb and Al, Si, Ta. From EPMA analysis, the presence of a ternary phase is a possibility for the outer layer of the coating on niobium. The outer layer of the coating on tantalum consisted of a compound that contained Ta, Si and Al. All the coated layers were adherent and no cracks were observed in any layer of coating. Coated samples exhibited good resistance to oxidation during heating up to 1300 °C in air for 8 to 10 h.