Parent Alloy Research Articles

Properties of the chalcogenide–carbon nano tubes and graphene composite materials

Composite can deliver more than the individual elemental property of the material. Specifically chalcogenide- multi walled carbon nano tubes and chalcogenide- bilayer graphene composite materials could be interesting for the investigation, which have been less covered by the investigators. We describe micro structural properties of Se55Te25Ge20, Se55Te25Ge20+0.025% multi walled carbon nano tubes and Se55Te25Ge20+0.025% bilayer graphene materials. This gives realization of the alloying constituents inclusion/or diffusion inside the multi walled carbon nano tubes and bilayer graphene under the homogeneous parent alloy configuration. Raman spectroscopy, X-ray photoelectron spectroscopy, UV/Visible spectroscopy and Fourier transmission infrared spectroscopy have also been carried out under the discussion. A considerable core energy levels peak shifts have been noticed for the composite materials by the X-ray photoelectron spectroscopy. The optical energy band gaps are measured to be varied in between 1.2 and 1.3eV. In comparison to parent (Se55Te25Ge20) alloy a higher infrared transmission has been observed for the composite materials. Subsequently, variation in physical properties has been explained on the basis of bond formation in solids.

Investigation of the nugget zone corrosion behavior in friction stir welded lap joints of 6061-T6 aluminum alloy

The corrosion behavior at different positions (top and bottom) of the weld nugget zone along the thickness plates in AA6061-T6 aluminum alloys welded by friction stir lap welding, under the conditions of 1000 rpm-60 mm/min and 900 rpm-40 mm/min in a 3.5 wt% NaCl solution, was investigated by Tafel polarization at ambient temperature. The morphology of the nugget zone corroded surfaces was analyzed by scanning electron microscopy together with energy dispersive spectroscopy (SEM-EDS) as well as atomic force microscopy (AFM). It was found that the top half of the nugget zone has a better corrosion resistance than that of the bottom half for both welding conditions. A localized pit dissolution with combined intergranular corrosion are the dominant corrosion types across different positions of the nugget zone for various welding conditions and in the parent alloy.

Friction stir welding of PM2000 ODS alloy

Friction stir welding has been used to join sheets of a ferritic, oxide dispersion strengthened alloy, PM2000. A stepped spiral probe, polycrystalline cubic boron nitride tool, with a shoulder diameter of 25 mm, was used to weld 4 mm thick plate in a butt joint configuration. The thermomechanically affected zone underwent dynamic recrystallisation during welding; the resultant microstructure consisted of equiaxed ferritic grains containing a dispersion of yttrium aluminium oxides. Microindentation measurements revealed a significant reduction in hardness within the weld zone, when compared to the parent material. The welding process induced an overall coarsening of the yttrium aluminium oxide particles and depletion in their number density. However, the precipitation of secondary phase particles, likely to be oxides, which took place during the welding process, is indicative that an element of mechanical alloying occurs during the welding process. Annealing the welds for 1 h at 1380°C produced a massive recrystallised grain structure in the weld zone and a uniform hardness across the parent and weld was achieved. Transmission electron microscopy showed that, subsequent to annealing, particles were coarser in the weld zone (33 nm mean diameter) than in the parent alloy (24 nm mean diameter). However, electron diffraction and energy dispersive X-ray spectroscopy confirm that the dominant oxide phase, YAlO3 perovskite (YAP), was the same in both regions. Oxide particle size and number densities were not uniform throughout the weld. Focused ion beam prepared surfaces revealed particles within the size range of 50–600 nm diameter in material beneath the tool shoulder/workpiece contact area; the average size of dispersoids in this region was 130 nm.

Nanostructured Co–Cr–Fe alloy surface layer fabricated by combination of laser clad and friction stir processing

Friction stir processing (FSP) was carried out on a laser clad Co–Cr–Fe alloy layer in order to transform the coarse laser clad microstructure into nanostructure and improve the mechanical properties. In the microstructure of the laser clad Co–Cr–Fe alloy, coarse brittle carbides precipitated along the grain boundary and formed networks, along which micro-cracks tended to initiate. After FSP, nanostructured surface layers with 20–100nm grain sizes and 30–65μm thicknesses were obtained. The coarse network carbides were significantly crushed to nanosize particles uniformly distributed in the nanostructured Co matrix. The plastic layer showed a gradient grain size that ranged from tens of nanometers at the top surface to tens of micrometers at the interior. A large number of the deformation nanotwins were found in the plastic zone which revealed the deformation mechanism. Moreover, FSP enabled the closure of micro-cracks in the laser-clad microstructure. The formation of nanostructures increased the hardness up to 819Hv, compared with the 490Hv of the laser parent alloy. The friction coefficients of the laser-clad Co alloy decreased from about 0.35 to 0.1–0.2 after FSP, with enhanced wear performance.

Role of partial Cu/Co substitution on magnetic and electronic properties of Mn-rich Ni46Mn43In11 alloy

In this investigation we show that the optimum substitution of Ni by Co and Cu can bring the martensite transition temperature (TM = 390 K) of Ni46Mn43In11 alloy close to room temperature as well as greatly influence applicable magnetic and transport properties. In contrast to the parent alloy, a ferromagnetic austenite phase is induced in these substituted alloys. A huge exchange bias field of up to 1615 Oe was observed for a field-cooled hysteresis loop at 5 K in the Ni44Cu2Mn43In11 alloy. A giant magnetic entropy change of 20.8 J kg−1K−1 at a field change of 70 kOe and a giant negative magneto-resistance of 57% at ΔH = 30 kOe was also observed for the Ni44Co2Mn43In11 alloy. Possible reasons for the observed behaviours are comprehensively discussed.

Tuning Fermi level of Cr2CoZ (Z=Al and Si) inverse Heusler alloys via Fe-doping for maximum spin polarization

We report full potential treatment of electronic and magnetic properties of Cr2−xFexCoZ (Z=Al, Si) Heusler alloys where x=0.0, 0.25, 0.5, 0.75 and 1.0, based on density functional theory (DFT). Both parent alloys (Cr2CoAl and Cr2CoSi) are not half-metallic frromagnets. The gradual replacement of one Cr sublattice with Fe induces the half-metallicity in these systems, resulting maximum spin polarization. The half-metallicity starts to appear in Cr2−xFexCoAl and Cr2−xFexCoSi with x=0.50 and x=0.25, respectively, and the values of minority-spin gap and half-metallic gap or spin-flip gap increase with further increase of x. These gaps are found to be maximum for x=1.0 for both cases. An excellent agreement between the structural properties of CoFeCrAl with available experimental study is obtained. The Fermi level tuning by Fe-doping makes these alloys highly spin polarized and thus these can be used as promising candidates for spin valves and magnetic tunnelling junction applications.

Corrosion behavior of friction stir welded lap joints of AA6061-T6 aluminum alloy

In this work, the corrosion behaviors of friction-stir lap welding of 6061-T6 Al-alloy are studied. The friction-stir lap welding was performed under different welding conditions (rotation speed and welding speed). The corrosion behavior of the parent alloy, the weld nugget zone (WNZ), and the heat affected zone (HAZ) of each welded sample working as an electrode, were investigated by the Tafel polarization test in 3.5 wt. (%) NaCl at ambient temperature. The morphology of the corroded surface of each region was analyzed by scanning electron microscopy together with energy dispersive spectroscopy (SEM-EDS). The results showed that the corrosion resistance of the parent alloy was better than the WNZ and the HAZ in both welding conditions. Localized pit dissolution and intergranular corrosion were the dominant corrosion types observed in the parent alloy, WNZ, and HAZ. The parent alloy, WNZ, and HAZ exhibited similar corrosion potentials (Ecorr) after T6 heat treatment. This treatment had a better effect on the corrosion resistance of the welded regions than the parent alloy.

Microstructure and hydrogen storage properties of (Ti0.32Cr0.43V0.25) + x wt% La (x = 0–10) alloys

The composite alloy of Ti0.32Cr0.43V0.25 with x wt% La (where x = 0–10) was prepared by arc melting technique. The effect on hydrogen storage capacity, flatness of the plateau pressure, and residual hydrogen was investigated in La added Ti0.32Cr0.43V0.25. Crystalline phase and microstructure of the prepared composite alloy were investigated and characterized by XRD, SEM and TEM. The crystal structure was refinement using Rietveld analysis. The effective hydrogen storage capacity of the composite alloy was found comparable to the parent alloy, when 5 wt% La was added. The effective hydrogen capacity (∼2.31 wt%) was close to that of the parent alloy (2.35 wt%) and the plateau slope was significantly improved from 30.5 of the parent alloy to 14.6. Appropriate mechanisms associated with the improved flatness by the La addition has been discussed in terms of the refined crystalline structure. Using TG/DTA method we have shown the differences in the interaction of residual hydrogen with the BCC phase of both parent alloy and 5 wt % La mixed alloy.

Studies on salt fog corrosion behavior of friction stir welded AA7075–T651 aluminum alloy

Abstract High strength aluminum alloy 7075 is used in aerospace applications. This alloy is considered unweldable using fusion welding processes. Friction stir welding being a solid state process has been proved to be a suitable process for obtaining sound welds of these materials. Although no solid–liquid phase transformation occurs during friction stir welding, relatively high temperatures, up to 475 °C for AA7075 aluminum alloy, are generated by friction between the tool and the workpiece. This produces modified microstructures that may be more susceptible to corrosion than the parent alloy. In the current study, 16 mm thick rolled AA7075–T651 aluminum alloy plates were joined using friction stir welding. The corrosion behavior of base material and friction stir welds was investigated using the Salt fog test (ASTM B117). It was observed that the corrosion resistance of the welds in the basic solution is better than that in the acidic and neutral solutions. In contrast, no significant difference has been found in the corrosion resistance of the base material with change in pH value. It was also found that the corrosion rate decreases with increase in time of exposure. It has been observed that corrosion attack is greater in the weld region than in the parent material and within the weld, the heat-affected zone has been found to be more susceptible to corrosion compared to the weld nugget and thermo-mechanically-affected zone regions. Transmission electron microscopy studies showed coarser precipitates and wider precipitate-free zones in the heat-affected zone which are concluded to be reasons for more susceptibility to corrosion.

Investigation of Precipitation Behavior in Age-Hardenable Cu-Ti Alloys by an Extraction-Based Approach

We investigated the precipitation processes in Cu-4 mol pct Ti alloy specimens aged at 723 K (450 °C), by means of X-ray diffraction and chemical analyses of the precipitates extracted from the parent alloy specimens. Aging-induced precipitate particles of a spinodally decomposed disorder, α′; those of a metastable order, β′-Cu4Ti; and those of a stable order, β-Cu4Ti, were continuously formed in the aged specimens. The extraction of the precipitate particles from the aged specimens by submergence in a nitric solution allowed for not only the structural analyses of the constituent precipitate phases but also the quantitative evaluation of their chemical compositions and volume fractions. Early during the aging process, the supersaturated Cu solid solution decomposes spinodally in a continuous manner, and an unstable disorder, α′, appears. Then, fine needle-shaped β′-Cu4Ti particles, which have a Ti content of approximately 37.5 mol pct, form in the Cu matrix. During prolonged aging, coarse cellular components composed of the terminal Cu solid solution and stable β-Cu4Ti particles which have a Ti content of 20.5 mol pct nucleate and grow, primarily in the grain boundaries, at the expense of the metastable β′-Cu4Ti particles. The volume fraction of the β′-Cu4Ti particles in the alloy reaches a maximum of approximately 1.7 pct after aging for 24 hours, while that of the β-Cu4Ti particles increases steadily to more than 18 pct after 480 hours. The volume fraction of the fine β′-Cu4Ti particles in the alloy specimens remained constant throughout the age-hardening, indicating that the hardening is primarily owing to the fine dispersion of the β′-Cu4Ti particles and not because of the large volume fraction of coarse β-Cu4Ti particles.

Failure of pyrolysis coils coated with anit-coking film in an ethylene cracking plant

This paper presents a specific kind of failure in ethylene cracking coils coated with anti-coking film. It investigates a case in which the coils made of 35Cr 45Ni high temperature alloy failed within two years of operation. The damage occurred due to heavy oxidation in localized regions of the coil resulting in the formation of blisters, which eventually failed by cracking. The mechanism involved was determined by studying the oxidized samples under a scanning electron microscope with an energy dispersive system and is attributed to the presence of rare earth metals in the anti-coking film and inherent casting defects in the base alloy. The cerium present in the anti-coking film diffused preferentially to a defect site in the parent alloy thereby resulting in its segregation which further led to embrittlement.

Magnetism-Structure Correlations during the ε→τ Transformation in Rapidly-Solidified MnAl Nanostructured Alloys

Magnetic and structural aspects of the annealing-induced transformation of rapidly-solidified Mn55Al45 ribbons from the as-quenched metastable antiferromagnetic (AF) ε-phase to the target ferromagnetic (FM) L10 τ-phase are investigated. The as-solidified material exhibits a majority hexagonal ε-MnAl phase revealing a large exchange bias shift below a magnetic blocking temperature TB~95 K (Hex~13 kOe at 10 K), ascribed to the presence of compositional fluctuations in this antiferromagnetic phase. Heat treatment at a relatively low annealing temperature Tanneal ≈ 568 K (295 °C) promotes the nucleation of the metastable L10 τ-MnAl phase at the expense of the parent ε-phase, donating an increasingly hard ferromagnetic character. The onset of the ε→τ transformation occurs at a temperature that is ~100 K lower than that reported in the literature, highlighting the benefits of applying rapid solidification for synthesis of the rapidly-solidified parent alloy.

Primary and Secondary Dealloying of Au(Pt)-Ag: Structural and Compositional Evolutions, and Volume Shrinkage

Systematic study of the dealloying of Au-Ag and Au(Pt)-Ag alloys shows that the dealloying occurs by two processes: a primary dealloying process that selectively dissolves Ag from the parent alloy and creates a nanoporous (np) structure, and a secondary dealloying process that occurs behind the corrosion front and further dissolves the residual Ag from the nano-ligaments. The secondary dealloying can occur during coarsening, and/or when a more anodic potential is applied. With suppressed np structure coarsening in Pt-containing samples, we found that the intrinsic np structure created by the primary dealloying contains small ligament diameter (3–7 nm) and high concentration of residual Ag (∼50 at.%), irrespective of the dealloying potentials. Dilatometry experiments show that the volume shrinkages are rather small during primary dealloying and are large during secondary dealloying. The primary dealloying can be explained by the percolation dissolution mechanism. Although the mechanism of the secondary dealloying (without coarsening) remains unclear, we point out that the kinetics of the secondary dealloying is decisive to some important characters of np metals, such as the crack formation and the final residual Ag concentrations.

Fabrication of Porous and Nanoporous Aluminum via Selective Dissolution of Al-Zn Alloys

Porous and nanoporous aluminum have been fabricated via selective dissolution. Al-Zn alloys were dealloyed in an aqueous solution of nitric acid to selectively dissolve zinc. Fast solidification methods permitted to adjust the precursor microstructure of the parent alloy in order to induce supersaturation of zinc in aluminum. An electric potential applied during corrosion affected the final morphology of porosity. Electronic imaging evinced the presence of regions with less than 100 nm diameter pores. This nanoporosity was only present in electrochemically dealloyed samples. We observed two types of porosity in dealloyed samples: a primary porosity resulting from the selective removal of zinc-rich interdendritic phases and a secondary porosity resulting from nanoporosity evolution inside zinc-supersaturated dendrites.

Changes in magnetic state of Y2(Fe,Mn)17-H systems: Regularities and potentialities

Abstract A systematic study is made of the magnetic properties of the hydrides of Y2Fe17−xMnxHy intermetallic alloys (0 ⩽ x ⩽ 8 and 0 ⩽ y ⩽ 4.4 at.H/f.u.) and the exchange interaction parameters of these compounds are estimated. It is found that hydrogen atoms enhance the ferromagnetic interactions. The decrease of the Curie temperature observed in both hydrides and parent alloys with substitution of manganese for iron gives an indication of the reinforcement of negative exchange interactions. As a result the magnetic order of the compounds under study is subject to change at high (x > 6) manganese concentration. The transformation of magnetic state in the Y2Fe17−xMnx-H system is explained on the basis of molecular field theory connecting the Curie temperatures with the value and sign of exchange interaction integrals (AFeFe, AMnMn, and AFeMn) for magnetoactive atoms: iron and manganese.

Synergistic alloying effect on microstructural evolution and mechanical properties of Cu precipitation-strengthened ferritic alloys

We report the influence of alloying elements (Ni, Al and Mn) on the microstructural evolution of Cu-rich nanoprecipitates and the mechanical properties of Fe–Cu-based ferritic alloys. It was found that individual additions of Ni and Al do not give rise to an obvious strengthening effect, compared with the binary Fe–Cu parent alloy, although Ni segregates at the precipitate/matrix interface and Al partitions into Cu-rich precipitates. In contrast, the co-addition of Ni and Al results in the formation of core–shell nanoprecipitates with a Cu-rich core and a B2 Ni–Al shell, leading to a dramatic improvement in strength. The coarsening rate of the core–shell precipitates is about two orders of magnitude lower than that of monolithic Cu-rich precipitates in the binary and ternary Fe–Cu alloys. Reinforcement of the B2 Ni–Al shells by Mn partitioning further improves the strength of the precipitation-strengthened alloys by forming ultrastable and high number density core–shell nanoprecipitates.

Hydrogen storage properties of Ti2−xCrVMx (M = Fe, Co, Ni) alloys

In this work, quaternary alloys having compositions Ti1.9CrVM0.1 and Ti1.8CrVM0.2 (M = Fe, Co and Ni) have been studied in detail for their structural aspects and hydrogen absorption–desorption properties. All the alloys form bcc phase solid solutions and after hydrogen absorption the structures change to fcc. The pressure composition isotherms, hydrogen storage capacities and hydrogen absorption kinetics were studied using Sievert's type of volumetric setup. The Ti1.9CrVFe0.1, Ti1.9CrVCo0.1 and Ti1.9CrVNi0.1 alloys are found to absorb maximum 3.80, 3.68 and 3.91 wt.% of hydrogen respectively; whereas, Ti1.8CrVCo0.2 and Ti1.8CrVNi0.2 alloys show 3.52 and 3.67 wt.% of hydrogen at room temperature. All the alloys show fast hydrogen absorption kinetics at the room temperature. From differential scanning calorimetric measurements, it has been found that Fe, Ni and Co substitution in place of Ti decreased the hydrogen desorption temperature drastically compared to the parent alloy.

Changes in Precipitate Distributions and the Microstructural Evolution of P24/P91 Dissimilar Metal Welds During PWHT

The effect of post-weld heat treatments (PWHTs) on the evolution of precipitate phases in dissimilar metal welds made between 9 pct Cr P91 alloy and 2.25 pct Cr T/P24-type weld metal has been investigated. Sections of multi-pass fusion welds were analyzed in their as welded condition and after PWHTs of 2 and 8 hour duration at 1003 K (730 °C). Thin foil specimens and carbon extraction replicas have been examined in transmission electron microscopes in order to identify precipitate phases and substantiate their distributions in close proximity to the fusion line. The findings of these studies confirm that a carbon-depleted region develops in the lower alloyed weld material, adjacent to the weld interface, during thermal processing. A corresponding carbon enriched region is formed, simultaneously, in the coarse grain heat affected zone of the P91 parent alloy. It has been demonstrated that carbon depletion from the weld alloy results in the dissolution of M7C3 and M23C6 chromium carbides. However, micro-alloying additions of vanadium and niobium which are made to both the P24 and P91 alloys facilitate the precipitation of stable, nano-scale, MX carbonitride particles. This work demonstrates that these particles, which are of key importance to the strength of ferritic creep resistant alloys, are retained in carbon-depleted regions. The microstructural stability which is conferred by their retention means that the pernicious effects of recrystallization are largely avoided.

Onset of magnetic order in U2(Ni1−x Fe x )2Sn-H

We present specific heat and magnetic studies as a function of temperature and magnetic field for U2(Ni1−x Fe x )2Sn alloys (x = 0.0, 0.05, 0.1, 0.15, 0.2, 0.4, 0.6 and 0.8) and their hydrides (absorption of ≈ 2 H/f.u.). For the parent alloys, antiferromagnetic order is rapidly suppressed with increasing Fe concentration and non-Fermi-liquid behavior was found for x = 0.2. Hydrogenation of the parent alloys causes a substantial increase of T N in Fe-low hydrides (x < 0.2), while Fe-rich hydrides show an unexpected appearance of ferromagnetism in the range 0.4 ≤ x ≤ 0.8. Some of the findings are compared with similar studies in U2Co2Sn and U2Co2InH1.9.

Hydrogenation studies on structural and magnetic properties of antiferromagnetic Kondo lattice Ce2Cu2In

Hydrogenation studies were carried out on an antiferromagnetic dense Kondo system Ce2Cu2In. Single-phase hydrides Ce2Cu2InHx were obtained for the hydrogen content 2.17<x<2.8. These compounds form with the crystal lattice of the parent alloy, yet with a strongly expanded unit cell, especially along the crystallographic c-axis. For x<2.17 mixtures of Ce2Cu2In and Ce2Cu2InH∼2.2 were observed, while for x>3 amorphous material was obtained. The single-phase hydrides Ce2Cu2InH2.37 and Ce2Cu2InH2.78 are Curie–Weiss paramagnets due to stable Ce3+ ions. For both compounds, near 11–13K, some tiny features were observed in the magnetic susceptibility data, which might reflect weak magnetic ordering.