Parent Alloy Research Articles

Characterization of Alloy 600 joints exposed to a high-temperature supercritical-carbon dioxide environment

Two types of Alloy 600 joints, such as diffusion-bonded joint and Alloy 182 fusion-weld, were exposed to supercritical-CO2 environment at 550 and 650 °C (20 MPa) for 1000 h. The diffusion-bond region showed similar oxidation characteristics as parent Alloy 600, but the migration of diffusion bond line below oxide layer was observed due to the Cr-depletion induced recrystallization. For Alloy 182 fusion-weld, outer Mn-rich oxides (Mn3O4 and MnCr2O4) and a small amount of inner SiO2 mixed with chromia were formed due to high Mn and Si contents. The presence of SiO2 in chromia suppressed carburization at the oxide/matrix interface, which resulted in the formation of an amorphous C layer between the outer Mn-rich oxide and inner Cr-rich oxide. For Alloy 182 fusion-weld, tensile property changes after exposure to supercritical-CO2 environment were negligible.

Evolution of phase transformation and magnetic properties with Fe content in Ni55−xFexMn20Ga25 Heusler alloys

A series of Ni55−xFexMn20Ga25 (0 ⩽ x ⩽ 5) Heusler alloys was prepared to investigate their phase transitions and magnetic properties. At room temperature, these alloys present various crystal structures, and the unit cell volume enlarges with increase of Fe content in both austenite and martensite. Multiple magneto-structural transformations were observed in the parent alloy (x = 0). In the process of cooling, it undergoes martensitic transformation (MT) from L21-type paramagnetic austenite to L10-type ferromagnetic martensite, accompanying an intermartensitic transformation (IMT, 7M → L10). By establishing a detailed phase diagram, we found that both MT and IMT shift to lower temperature simultaneously, while the ferromagnetic (FM) transition of austenite moves to higher temperature as Fe increases. With the further increase of Fe content beyond a critical value, both the IMT and the FM transitions split off from MT, and the former follows with the transforming sequence of 7M → 5M. Based on the experimental data, some key magnetic parameters have been obtained in this system. The calculated magnetocrystalline anisotropy constant () of martensite quickly increases as Fe increases, and then it almost reaches a saturated value (~5.5 × 105 J m−3) for the alloys with x > 3. However, the spontaneous magnetic moment () attains a peak value of about 4.2 μB/f.u. in the alloy with x = 4, which is not consistent with the linear increasing of effective magnetic moment (). Further magnetic measurements with hydrostatic pressure indicate that such a discrepancy could be ascribed to the competition between the magnetic exchange interaction and the volume change of unit cell governed by the dopant Fe content.

Near total magnetic moment compensation with high Curie temperature in Mn2V0.5Co0.5Z (Z = Ga,Al) Heusler alloys

Mn2V1−xCoxZ (Z = Ga,Al and x = 0, 0.25, 0.5, 0.75, 1) Heusler alloys have been synthesized to investigate the effect of Co substitution at the V site on the magnetic moment and Curie temperature of half-metallic ferrimagnets Mn2VGa and Mn2VAl. Near total magnetic moment compensation was achieved with high Curie temperature for x = 0.5 composition. The Co substituted alloys show a non linear decrease in lattice parameter without altering the crystal structure of the parent alloys. The end members Mn2VGa and Mn2CoGa have the saturation magnetization of 1.80 µB/f.u. and 2.05 µB/f.u. respectively whereas for the Mn2V0.5Co0.5Ga alloy, a near total magnetic moment compensation (0.10 µB/f.u.) was observed due to the ferrimagnetic coupling of Mn with parallelly aligned V and Co. The Co substituted Mn2VAl has also shown a similar trend with compensated magnetic moment value of 0.06 µB/f.u. for x = 0.5. The Curie temperatures of the alloys including the x = 0.5 composition are well above the room temperature (more than 650 K) which is in sharp contrast to the earlier reported values of 171 K for the (MnCo)VGa and 105 K for the (MnCo)VAl (substitution at the Mn site). The observed TC values are highest among the Mn2V based fully compensated ferrimagnets. The magnetic moment compensation without significant reduction in TC indicates that the V site substitution of Co does not weaken the magnetic interaction in Mn2VZ (Z = Ga,Al) alloys which is contrary to the earlier experimental reports on Mn site substitution.

Development of hybrid aluminium metal matrix composite and study of property

Hybrid metal matrix composites are advanced materials used for light weight high strength applications in aerospace and automobile sector. Among the various techniques employed in fabricating hybrid metal matrix composites stir casting technique is simple and economical. The metal matrix choice was Aluminium 6061and the reinforcements are Zirconium di oxide (ZrO2) and Aluminium oxide (Al2O3) respectively. Aluminium 6061 was chosen due to its excellent cast ability, compatibility and application in aerospace and automotive sector. The key objective of exploiting zirconium di oxide as one of the reinforcement was, ZrO2adopts amonocliniccrystal structureat room temperature and transitions totetragonalandcubicat higher temperatures and holds very high refractory property. The key cause of selecting Aluminium oxide as one of the reinforcement includes that it possess a very high wear resistant property. The composite comprises of 90% of aluminium 6061, 5% of ZrO2 and 5% of Al2O3 which was restricted to 10 weight percentage in order to prevent cluster formation and to reduce weight. The average size of the reinforcing particle was 55-65 microns in order to attain good bonding with metal matrix. The developed composite casting was cut using wire EDM and test specimens were prepared .The various test consist of, micro graph study, tensile strength test, micro hardness test wear test and corrosion behaviour test. Micro graph study was carried and the images reveal the availability of reinforcement particles in the metal matrix phase. Tensile strength test specimens were cut as per ASTM- E8 standard, and the readings were tabularized. The tensile value show significant improvement. The hardness test was performed using Vickers micro hardness tester and its maximum value is 82.9 at 200kgf load. This accounts 70% increase when evaluate with parent alloy. Wear test was performed using pin on disc Ducom wear test device and the result shows significant increase in wear resistant property when compare with ground alloy Al6061. This is due to the excellent tribological property of ZrO2 and Al2O3. This research work comprises of successful invention of hybrid metal matrix composite with elevated property.

Dendritic Boundary Corrosion of AA2198 Weld Using Fiber Laser Welding with Al–Cu Filler Wire

The microstructures and corrosion behaviors of AA2198–T851 alloy and weld were analyzed under corrosive conditions. Weld was formed using an innovative fiber laser welding process with AA2319 Al–Cu filler wire. The metallurgic morphology and distribution of the chemical compositions were determined using imaging techniques such as optical micrograph, scanning electron micrograph, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. Corrosion was evaluated using an immersion test and electrochemical impedance spectroscopy in 3.5% NaCl solution at room temperature. Results indicate that the parent alloy suffered from pitting corrosion during the initial 4-h immersion which was caused by the inhomogeneous distribution of its chemical components and the different intermetallics formed during the rolling process. The weld experienced dendritic boundary corrosion under the same conditions due to the addition of the Al–Cu filler and rapid solidification during laser welding, which led to the precipitates Cu enrichment along the grain boundary. When a welding joint was immersed in the solution for 5 days, a big crack was observed across the center of the weld. In comparison, there was good corrosion resistance in the heat-affected zone with a compact protective film.

Glassy magnetic ground state and Kondo-like behaviour in Mn10FeGe8 alloy

We report a detailed investigation of the ground-state magnetic properties of newly synthesized alloy. The sample can be thought of being derived by substituting one Mn atom by Fe of the parent compound . Fe-substitution leads to a drastic change in the magnetic ground state as well as to the magneto-transport properties of the parent alloy. On cooling below 250 K, undergoes a transition from paramagnetic phase to a state having significant ferromagnetic correlations. The ground state is found to be canonical spin glass (CSG) type in nature as evident from the dc magnetization and ac susceptibility measurements. Interestingly, the resistivity data shows an upturn at low temperature below about 30 K, mimicking Kondo-like behaviour. turns out to be a rare example among 3d transition metal alloys, where a Kondo-like state coexists within a CSG phase.

Transient Liquid Diffusion Bonding of AISI304 Stainless Steel with a Nickel Base Interlayer

AISI304 stainless steel was bonded by a nickel base interlayer, using a TLP bonding method at 1150 °C with different holding times. The microstructure of the joint region was studied by optical and scanning electron microscopes. The results showed that 20 minutes holding time is sufficient for complete isothermal solidification. At the bonding times of 4, 10, 15 minutes, a eutectic structure was formed at the joint region. The distribution of alloying elements within the joint region and diffusion affected zone were detected using EDS. The results showed that the eutectic microstructure consists of Fe and Cr borides and the isothermal solidified zone consists of solid solution of Fe and Ni at the bonding temperature. Samples with complete isothermal solidified joint were homogenized at 950°C for different times from 30 to 360 minutes to study the distribution of alloying elements between joint region and parent alloy. The results showed more uniform distribution of alloying elements with increasing the homogenization time due to the diffusion of alloying elements between the joint region and the parent alloys. Microhardness and shear strength of joined samples were measured and compared to that of the parent alloy at the same heat treatment condition. The joint shear strength of TLP bonded samples was about 82% that of the parent alloy at the homogenization time of 180 minutes.

Alloy Design Criteria for Solid Metal Dealloying of Thin Films

Liquid metal dealloying is a promising route for making metal nanocomposites with a wide range of microstructure morphologies. However, it is not well suited for synthesizing nanocomposites in thin-film form. We propose a new route to fabricating fully dense nanocomposite thin films by dealloying a binary parent alloy in a unary solid metal solvent. We fabricated and tested three thin-film diffusion couples to understand the alloy design criteria for synthesizing dealloyed thin films free of cracks and voids. We find that the best-quality dealloyed thin films may be obtained from alloys that do not undergo large volume changes upon dealloying and that exhibit minimal net vacancy flux during interdiffusion.

Nanoporous Cu Thin Films for Electrochemical CO2 Reduction

Copper catalysts have been extensively researched as catalysts for electrochemical reduction of CO2 (CO2RR) due to their capability to catalyze production of hydrocarbons. The selectivity and activity of Cu catalysts for CO2RR are greatly dependent on the surface structure of the catalysts, and due to this dependence, many forms of Cu (ranging from high quality single crystals to densely populated arrays of supported nanostructures) have been investigated as CO2RR catalysts. Nanoporous (np) metals, which are produced through selective dissolution of an element from a parent alloy or compound, have inherent properties not typically present in other nanostructured materials that can strongly affect their catalytic properties, including concave surfaces with unique surface structures and open porosity that can cause mass transport effects during catalysis. Nanoporous Au and Ag, have been demonstrated as efficient and selective catalysts for oxidation of CO and reduction of CO2 to CO relative to their bulk metals. However, np-Cu has yet to be comprehensively studied as a CO2RR catalyst. To date, np-Cu has been primarily produced from homogeneous bulk materials which are not well suited for practical use as a potential CO2RR catalyst due to long dealloying treatments required to produce np-Cu that remains stable, without continued dealloying of the non-noble metal, at low CO2RR overpotentials. In this work, we demonstrate new electrochemical methods for producing fully dealloyed thin films of high-quality, crack-free np-Cu on inert substrates in significantly shorter processing times compared to bulk samples. We examine the activity and selectivity of np-Cu film catalysts produced by several dealloying methods for CO2RR. These results are presented in relation to other Cu catalysts with focus on the catalytic effects of the unique structural properties of np-Cu and the effects of post dealloying treatments to tune pore and ligament sizes of the np-Cu films. In addition to np-Cu films, we discuss how the presented techniques offer a path for production of stable thin films of other nanoporous metals on complex geometries. This work is supported by the Department of Energy award number DE-SC0008686.

Mechanical Behaviour and Morphology of A356/SiC Nanocomposites Using Stir Casting

In this research an attempt has been made to explore the experimental investigation of A356/SiC nanocomposites using two step stir casting process. A356 alloy ingot was selected for the matrix and the reinforcement (aluminium fine powder (99.9%) plus nano size SiC mechanically forged by using ball mill at 100 rpm for duration of 10 hours). Ball milling process enhances the wettability of the particles. Reinforcement was varied from 1% to 5% with a step of 1% by weight. The stirring process was carried out at 500±50 rpm with stirring duration 10 minutes in two steps. The melt composites were poured at 680±20° C into the die to fabricate the composites. In this process of fabrication, less oxides/segregations were depicted. Tensile strengths of fabricated composites were evaluated by using UTM and toughness was calculated from area under stress-strain curve. To identify the involvement and presence of the nanoreinforcement into the matrix alloy (A356), fractured surfaces of the fabricated nanocomposites were examined using SEM and EDX. Tensile test results have shown the fracture mechanism and enhanced mechanical properties with the addition of forged nanoreinforcements. Yield tensile strength (YTS) and ultimate tensile strength (UTS) of A356 parent alloy found as 212.76 MPa and 219.90 MPa respectively. The improvement of 41% in YTS and 45% in UTS in case of A356/SiC nanocomposites were investigated. Decrease in % elongation and toughness with increase in forged nanoreinforcement were predicted. Proper distribution of reinforcement was attributed by SEM micrographs. EDX spectrum disclosed the presence of the constituents in the parent alloy (A356) and stir cast nanocomposites.

Effect of the catalyst concentration, the immersion time and the aging time on the morphology, composition and corrosion performance of TEOS-GPTMS sol-gel coatings deposited on the AZ31 magnesium alloy

The aim of the present work was to evaluate the effect of the catalyst (acetic acid) concentration, the immersion time and aging time during the synthesis and deposition of TEOS-GPTMS hybrid sol-gel coatings on the AZ31 magnesium alloy and to analyse how these synthesis parameters affect the morphology, composition and corrosion performance of the coating resultant. The hydrolysis and condensation reactions occurred within the sols were monitored by rheological test and Fourier Transform Infrared (FTIR) Spectroscopy. In order to evaluate the corrosive power of the sols synthesised and their interaction with the magnesium surface, both the catalyst concentration and the immersion time using during deposition were varied from 2.5 to 10vol%, and from 15 and 120s respectively. Additionally, the effect of the aging time on the composition, morphology and corrosion performance of the hybrid coatings was analysed by employing different aging times up to 15days. Characterisation of the coatings was carried out using Scanning Electron Microscopy (SEM), Attenuated Total Reflection Infrared Spectroscopy (ATR-IR), and contact angle measurements. On the other hand, corrosion resistance was evaluated by potentiodynamic anodic polarisation test in aerated 0.1M NaCl solution. The experimental results showed that by suitable control of synthesis parameters studied it was possible to mitigate surface corrosion processes on the AZ31 magnesium alloy during the sol deposition. This allowed obtaining continuous, homogeneous coatings without cracking. Further, their corrosion evaluation revealed a decreasing the corrosion current density by about one order of magnitude with regard to the parent alloy providing, simultaneously, a protection range up to 150mV.

An experimental approach for estimating the effect of heat affected zone (HAZ) microstructural gradient on fatigue crack growth rate in aluminum alloy FSW

The microstructural gradient of the heat affected zone (HAZ) in aluminum alloy FSW has been simulated experimentally by subjecting the parent alloy to a controlled aging process. The purpose of the simulation is to estimate the effect of the HAZ microstructural gradient on fatigue crack propagation rate by excluding the effect of weld residual stresses. The microstructure in the gradient material produced by aging was evaluated against the actual FSW heat affected zone by comparing microstructural features and microhardness variation. Fatigue crack growth tests were conducted on the gradient material to evaluate its influence on crack propagation rate. The results showed that the gradient has a negative influence on fatigue crack propagation rate, accelerating crack growth with regard to the conditions at onset of the gradient. The impact on crack growth rate is dependent on the slope of the gradient with regard to the direction of fatigue crack propagation. The results of the study suggest that independent from the effect of weld residual stresses the micostructural influence in fatigue crack growth analysis of welded joints should not be neglected.

Thermal stability of excimer laser melted films formed on the AA2024-T351 aluminium alloy: Microstructure and corrosion performance

Excimer UV laser radiation sources have recently employed for surface modification of aluminium alloys to provide melted layers with highly refined microstructure and superior pitting corrosion resistance. Moreover, the resultant rough appearance might be an excellent base for the later paint application. Unfortunately, during the paint baking process and depending on the exposure time, the temperature of the alloy may raise up to 200°C, thus affecting the stability of the melted film. In the present work, the excimer KrF laser source was employed to create a melted film on the aerospace AA2024-T351 aluminium alloy, which was subsequently evaluated under different heat treatments with the aim to evaluate its thermal stability in terms of microstructure and corrosion performance. Microstructural modification was analysed by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), whereas the corrosion performance was evaluated by anodic polarisation and immersion testing in deaerated 0.1M NaCl solution. The experimental results showed that above 160°C, heat treatment of the melted layer resulted in the precipitation of the strengthening Al2CuMg phase as well as the nucleation and coarsening of the Al(Cu,Fe,Mn) secondary phase from the solute segregation bands originally formed during laser surface melting (LSM). The formation of these particles influenced the pitting corrosion resistance in two different ways: diminishing the pitting potential (Epit), and increasing both corrosion and passivation current densities. Nevertheless, this reduction was relatively negligible for all the heat treatment conditions studied, when compared to the parent alloy.

The effect of the discharge rate on the electrochemical properties of AB3-type hydrogen storage alloy as anode in nickel–metal hydride batteries

In this work, the ternary CeY2Ni9 alloy was prepared and served as anode materials in the Ni–MH battery system. The effect of the discharge rate on the electrochemical proprieties of CeY2Ni9, such as activation capability, polarization, discharge capacities, hydrogen atomic diffusion capability and redox parameters, were also investigated systematically during activation and long cycling. Charge–discharge measurement showed that this alloy is characterized by fast activation and requires only three cycles to be activated regardless of the discharge rate, the maximum discharge capacity was obtained for the medium discharge rate (C/10). An important correlation was observed between the evolution of the electrochemical parameters and that of the kinetic parameters, such as the hydrogen atomic diffusion capability and the exchange current density.The total substitution of La by Ce in LaY2Ni9 parent alloy enhanced its activation, polarization and stability despite the decrease of its discharge capacities, especially at high rates.

Mechanical behaviour of hybrid composite (AA6351+Al2O3+Gr) fabricated by stir casting method

In the current scenario, particulate reinforced aluminium matrix composites present a plenty of applications to aircraft, marine, structural, transportation and automobile industries. This article deals with the fabrication of hybrid AA6351 aluminium matrix composites which incorporates stir casting route. In the process of fabrication AA6351 is reinforced in which Al2O3 and Gr are the hybriding materials.The microstructure and the mechanical behavior of the parent alloy and the produced composites were studied. The reinforcing effect of Al2O3/Gr combined with the parent alloy is studied wherein the investigation went into the intensity of macrohardness, microhardness, tensile strength and flexural strength. Optical microscope was adapted for characterizing the composites. Optical microscope observed the particle distribution of the produced composites. Optical microphotographs depict the nearly homogeneous distribution of the reinforcement particles in the base metal matrix. The hardness, thetensile strength and the flexural strength are found to increase in the AA6351 base matrix alloy with the increase in reinforcement. The mechanical properties of the AA6351 alloy are significantly improved after the dispersion of Al2O3/Gr particles.

Magnetic properties of Nd(Fe1-xCox)10.5M1.5 (M=Mo and V) and their nitrides

In this work, alloys of Nd(Fe1-xCox)10.5M1.5 (M=Mo and V) were prepared via arc melting and heat treatment. The nitrides of these alloys were synthesized using a gas-solid state reaction method. The influence of Co substitution for Fe in NdFe10.5Mo1.5 and NdFe10.5V1.5 alloys and their nitrides were investigated. It was found that the lattice parameters a, c, and unit cell volume V decrease with increasing Co content x for Nd(Fe1-xCox)10.5Mo1.5. As compared to their parent alloys, the lattice parameters and unit cells volume increase after nitrogenation, which gives rise to higher Curie temperature, magnetization and magnetocrystalline anisotropy field for nitrides. A small amount of Co substitution for Fe (x≤0.3) can enhance the magnetic properties including Curie temperature, saturation magnetization and magnetocrystalline anisotropy field of the alloys and their nitrides, while higher concentration of Co (x>0.3) will deteriorates these magnetic properties, especially for the nitrides, due to the modification of the band structure by Co atom. As a result, Nd(Fe1-xCox)10.5Mo1.5Ny and Nd(Fe1-xCox)10.5V1.5Ny with x≤0.2 become promising candidates for permanent magnet applications. A coercivity of 4.6 kOe and maximum energy product BHmax of 20 MGOe were achieved for NdFe9.45Co1.05Mo1.5Nx.

Structural, electronic and magnetic properties of the Mn54−xAl46Tix (x = 2; 4) alloys

The structural, electronic and magnetic behavior of the as-cast and annealed Mn52Al46Ti2 and Mn50Al46Ti4 alloys have been studied through electronic band structure calculations, X-ray diffraction and magnetic measurements in the temperature range 4–850 K and magnetic field up to 7 T. Band structure calculations show a preference for Ti atoms to occupy the Mn sites in the plane of Al atoms with their magnetic moments (−0.68 μB/Ti) coupled antiparallel relative to the Mn magnetic moments in the plane of Mn atoms (2.33 μB/Mn). The as-cast and annealed samples were phase mixtures with different values of the hard ferromagnetic τ phase content. Except the as-cast and annealed at 1050 °C Mn52Al46Ti2 alloys, all the analyzed samples include, along with the τ and γ2 phases, a soft κ phase (CsCl - structure type) with TC around 530 K. The best magnetic characteristics were obtained for Mn52Al46Ti2 alloy annealed at 470 °C for 6 h: MS = 116 A m2/Kg at 4 K and TC = 668 K, in good agreement with the values reported in the literature for the τ phase of the MnAl system. The effects of the composition and of the preparation route on the electronic and magnetic properties are discussed in comparison with the properties of Mn54Al46 parent alloy.

Laser Cladding of <i>In Situ</i> Al-AlN Composite on Light Alloys Substrate

In situ metal matrix composites are novel composites in which the reinforcement is formed within the parent alloy by controlling chemical reactions during the composite fabrication. In recent years, there have been attempts to produce AlN composites utilizing the reactions between molten Al and a reactive gas. However, the conventional processing methods are sub-optimal and result in porosity, interface matrix-reinforcement deterioration, and high processing costs. The aim of this research is to develop a methodology to manufacture good-quality in situ Al-AlN composites in a cost effective way. In situ Al-AlN composite was synthesized with a laser cladding equipment. This composite powder can be directly deposited as coating on aluminum alloys conventionally used in the transport sector. The increase in the coatings tribological properties was demonstrated.

Structural and magnetocaloric properties in hexagonal MnNiGa alloys with Co doping

Hexagonal MnNiGe-based alloys are a series of novel functional materials with potential magnetostructural transitions (MSTs). Accordingly, it was investigated the magnetic features of bulk hexagonal MnNiGa alloy and attempted to partially substitute Mn by Co atoms to tailor its structural and magnetic properties. Nonetheless, the introduction of magnetic Co atom fails to bring about the first-order phase transition and gives rise to the emergence of second phase with cubic structure instead. For ternary MnNiGa parent alloy, the second-order nature of transition is confirmed by both the absence of thermal hysteresis and the standard Arrott plot. To the end, the values of isothermal entropy change are determined by Maxwell relation, and the maximal values follow the trend predicted by the mean-field theory. Its broad transition region (~53 K) leads to only a very small value of entropy change (~2.4 J·kg−1·K−1 at a field change of 3 T). In turn, the wide transition ensures a relative large refrigerant capacity (~89.4 J·kg−1), which is comparable to that of MnNiGe-based systems. Although the substitution of Co for Mn site is unsuccessful, the chemically modified MnNiGa is still a promising candidate for the application of magnetocaloric effect (MCE) with merits of higher magnetization and better mechanical performance than MnNiGe-based systems.

Magnetic Properties and Phase Diagram of Ni50Mn $$_{50-x}$$ 50 - x Ga $$_{x/2}$$ x / 2 In $$_{x/2}$$ x / 2 Magnetic Shape Memory Alloys

Ni50Mn50-x Ga x/2In x/2 magnetic shape memory alloys were systematically prepared, and the magnetic properties as well as the phase diagram, including atomic ordering, martensitic and magnetic transitions, were investigated. The B2–L21 order–disorder transformation showed a parabolic-like curve against the Ga+In composition. The martensitic transformation temperature was found to decrease with increasing Ga+In composition and to slightly bend downwards below the Curie temperature of the parent phase. Spontaneous magnetization was investigated for both parent and martensite alloys. The magnetism of martensite phase was found to show glassy magnetic behaviors by thermomagnetization and AC susceptibility measurements.