Strengthening in a DS casting Ni3Al base alloy IC6

A unidirectionally solidified casting base alloy IC6, with the chemical composition (at.%) 16.3–17.6% Al, 8.0–8.3% Mo, 0.16–0.78% B, Ni balance has been developed for advanced gas turbine blades and vanes. The experimental results show that this alloy has high yield strengths from room temperature to 1100°C, excellent creep resistance at temperatures up to 1100°C. The microstructural observations and analysis indicate that the superior mechanical properties of this alloy may be attributed to solid solution hardening by the large molybdenum addition, second phase strengthening by phase and other minor phases that precipitate in various temperature ranges, the formation of a raft structure during creep, and to the existence of high density misfit dislocation networks at / interface areas due to a high value of / misfit.Abbreviations BSE back scattered electron - DS unidirectionally solidified - EDS energy dispersive spectroscopy     

Sputter deposited nanocrystalline Ni-25Al alloy thin films and Ni/Ni3Al multilayers

Thin films of nominal composition Ni-25at%Al have been sputter deposited from a target of the intermetallic compound Ni₃Al at different substrate deposition temperatures. The film deposited on an unheated substrate exhibited a strongly textured columnar growth morphology and consisted of a mixture of metastable phases. Nanoindentation studies carried out on this film exhibited a strong strain hardening tendency. In contrast, the film deposited at 200 °C exhibited a recrystallized non-textured microstructure consisting of grains of a partially ordered Ni₃Al phase. At higher deposition temperatures (∼400 °C), larger grains of the bulk equilibrium, long-range ordered, Ll₂ Ni₃Al phase were observed in the film. Unlike the film deposited on an unheated substrate, the films deposited at elevated temperatures did not exhibit any dependence of the hardness on the indentation depth and, consequently no strain hardening. The average hardness of the film deposited at 200 °C was higher than the one deposited at 400 °C. In addition to monolithic Ni-25Al thin films, multilayered Ni/Ni3Al thin films were also deposited. Multilayers deposited non-epitaxially on unheated substrates exhibited a strong {111} fiber texture while those deposited epitaxially on (001) NaCl exhibited a {001} texture. Free-standing multilayers of both types of preferred orientations as well as of different layer thicknesses were deformed in tension untill fracture. Interestingly, the {111} oriented multilayers failed primarily by a brittle fracture while the {001} multilayers exhibited features of ductile fracture.     

On the tensile creep behaviour of a directionally-solidified Ni3Al-based alloy

High temperature tensile creep behaviour of a directionally-solidified Ni₃Al-based alloy is presented. The study involved selection of nine alloy systems based on Ni₃Al. The alloys contained varying amounts of Cr and Ta, fixed amounts of 1·5 at.% Hf and 0·5 at.% Zr and doped with 0·2 at.% each of C and B. The alloys were vacuum arc-melted into buttons and homogenized at 1050°C for 68 h. The test pieces of the alloys were hot compression tested at 600, 700, 800 and 900°C. The yield strength data of some of the alloys were superior to conventionally cast Mar-M 200, a cast nickel-base superalloy widely used in gas turbine structural applications. The best alloy system was chosen based on consistent performance in the hot compression studies. The alloy so chosen was directionally solidified and vacuum-homogenization-treated for 20 h at various selected temperatures. Optimum creep properties were observed at 1120°C, 20 h treatment. The minimum creep rate data of the DS alloy showed relatively higher values even at lower temperatures and stress levels as compared to Mar-M 200. Hence, the alloy is less promising in replacing nickel-based superalloys used as structural materials in gas turbine applications.     

Effect of Cr and Ni on diffusion bonding of Fe3Al with steel

Microstructure at the diffusion bonding interface between Fe₃Al and steel including Q235 low carbon steel and Cr18-Ni8 stainless steel was analysed and compared by means of scanning electron microscopy and transmission electron microscopy. The effect of Cr and Ni on microstructure at the Fe₃Al/steel diffusion bonding interface was discussed. The experimental results indicate that it is favourable for the diffusion of Cr and Ni at the interface to accelerate combination of Fe₃Al and steel during bonding. Therefore, the width of Fe₃Al/Cr18-Ni8 interface transition zone is more than that of Fe₃Al/Q235. And Fe₃Al dislocation couples with different distances, even dislocation net occurs at the Fe₃Al/Cr18-Ni8 interface because of the dispersive distribution of Cr and Ni in Fe₃Al phase.     

Solute diffusion during high-temperature plastic deformation in alloys

Solute volume diffusion during high-temperature plastic deformation in a substitutional solid solution alloy is analyzed theoretically. Both deformation-induced supersaturated vacancy enhanced diffusion effect and dislocation pipe diffusion effect are considered in the model. The model is applied to the prediction of deformation-enhanced phosphorus diffusion in γ-Fe. Deformation-induced supersaturated vacancy enhanced diffusion and pipe diffusion can both enhance the overall phosphorus diffusion coefficient, but the former effect plays a predominant role. At a certain temperature, the deformation-enhanced phosphorus diffusion coefficient is mainly dependent on strain and strain rate, and at each strain rate there is a steady state value for the enhanced diffusion coefficient.     

Effect of Nb,Mo, V contents on oxidation resistance of Ti3Al based alloys

In the present paper, the effect of the contents of Nb, Mo, V on the oxidation properties (700°C, in air) of Ti₃Al based alloys has been studied. It has been shown that the alloys were oxidized rapidly as exposed at 700°C in the air. After 100 h exposure, oxygen-affected alloy surface layer of about 10 thickness has been formed on account of the poor protection of the oxide film. An addition of (11–13%)¹ Nb enhanced the oxidation resistance. The addition of Mo and V in the Ti₃Al–Nb system alloy reduced the oxidation resistance significantly.     

Effect of Ni-modified α-Al2O3 prepared by sol–gel and solvothermal methods on the characteristics and catalytic properties of Pd/α-Al2O3 catalysts

In the present study, Ni-modified α-Al₂O₃ with Ni/Al ratios of 0.3 and 0.5 were prepared by sol–gel and solvothermal method and then were impregnated with 0.3 wt.% Pd. Due to different crystallization mechanism of the two preparation methods used, addition of nickel during preparation of α-Al₂O₃ resulted in various species such as NiAl₂O₄, mixed phases between NiAl₂O₄ and α-Al₂O₃, and mixed phases between NiAl₂O₄ and NiO. As revealed by NH₃-temperature programmed desorption, formation of NiAl₂O₄ drastically reduced acidity of alumina, hence lower amounts of coke deposited during acetylene hydrogenation was found for the Ni-modified α-Al₂O₃ supported catalysts. For any given method, ethylene selectivity was improved in the order of Pd/Ni–Al₂O₃-0.5 > Pd/Ni–Al₂O₃-0.3 > Pd/Ni–Al₂O₃-0  Pd/α–Al₂O₃-commercial. When comparing the samples prepared by different techniques, the sol–gel-made samples showed better performances than the solvothermal-derived ones.     

Ultra-fast boriding of nickel aluminide

In this study, we explored the possibility of ultra-fast electrochemical boriding of nickel aluminide (Ni₃Al) in a molten borax electrolyte. Electrochemical boriding was performed at 950 °C for 15 min and at current densities ranging from 0.1 to 0.5 A/cm². The boride layers formed on the test samples were 50 to 260 μm thick depending on the current density. The mechanical, structural, and chemical characterization of the boride layers was carried out using a Vickers micro-hardness test machine, optical and scanning electron microscopes, and a thin film X-ray diffractometer. The hardness of boride layer was in the range from 800 to 1200 ± 50 HV depending on the load and the region from which the hardness measurements were taken. X-ray diffraction studies confirmed that the boride layers were primarily composed of Ni₃B, Ni₄B₃ and Ni₂₀AlB₁₄ phases. Structurally, the boride layer was very homogenous and uniformly thick across the borided surface area.     

Hydrothermal synthesis and characterization of monodisperse α-Fe2O3 nanoparticles

Monodisperse α-Fe₂O₃ nanoparticles have been successfully prepared by hydrothermal synthetic route using FeCl₃, CH₃COONa as reagents and reacted at 200 °C for 12 h. The morphology and structure of products were characterized by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the α-Fe₂O₃ nanoparticles were single-crystalline hexagonal structure and average diameters were about 80 nm. Magnetic properties have been detected by a vibrating sample magnetometer at room temperature. The nanoparticles exhibited a ferromagnetic behavior with the coercive force (Hc), saturation magnetization (Ms) and remanent magnetization (Mr) was 185.28 Oe and 0.494 emu/g, 0.077 emu/g.     

Internal friction of γ-TiAl-based alloys with different microstructures

A Ti–46.5 at.% Al–4 at.% (Cr, Nb, Ta, B) intermetallic alloy with different microstructures (fine-grained primary annealed (PA) and coarse-grained fully lamellar (FL)) was examined by internal friction experiments. The influence of microstructure on the internal friction properties was studied by high-temperature (300–1270 K) mechanical loss experiments using a low frequency subresonance apparatus (0.01–10 Hz). The mechanical loss spectra show two phenomena: (i) a loss peak of Debye type at about 1000 K (1 Hz) which occurs only in samples with fully lamellar microstructure. The activation enthalpy, determined from the frequency shift, is 3.0 eV. The peak is assigned to thermally activated reversible local movement of dislocations that are part of the mismatch structure of semicoherent lamellar interfaces. (ii) A high-temperature damping background above 1000 K which is controlled by an activation enthalpy of 3.8–3.9 eV. The activation enthalpy agrees well with that of creep and strain rate cycling tests (3.5–3.7 eV) and is in the range of values reported for self-diffusion indicating that both properties (high-temperature background (HTB) and creep) are controlled by volume diffusion assisted climb of dislocations.     

High-strength Mg95Y3Zn1Ni1 alloy with LPSO structure processed by hot rolling

Microstructures and mechanical properties of Mg₉₅Y₃Zn₁Ni₁ alloy containing long period stacking ordered (LPSO) phase processed by hot rolling were systematically investigated in the present work. The results showed that the as-cast alloy was mainly composed of α-Mg and network 18?R LPSO phase. The thermal stability of 18?R LPSO phase in the as-cast alloys decreased with the decrease of Ni content. After solution treatment at 773?K for 40?h, network 18?R phase at grain boundary dissolved, while fine lamellar phase identified as 14H LPSO precipitated in the interior of grains. When the solid-solution alloy was hot rolled at 723?K with six passes and thickness reduction of 62%, some LPSO phases broke down and kinking of varying degrees occurred in LPSO phase. Meanwhile, the as-rolled α-Mg and LPSO phase redistributed aligned along the rolling orientation. The alloy exhibited excellent mechanical properties: yield strength of 282?MPa, ultimate tensile strength of 383?MPa, and elongation to failure of 16% at ambient temperature along the rolling orientation. The remarkable improvement of strength was ascribed to the refined microstructure induced by the deformation kinking and the crush of LPSO phase.     

Optoelectronic properties of β-Fe2O3 hollow nanoparticles

The effect of hollow structure on the optoelectronic properties of β-Fe₂O₃ hollow nanoparticles (HNPs) was determined. Spectrophotometry showed that the optical transmittance of the β-Fe₂O₃ HNPs was less than 40% in the visible-light region. This opaqueness was suggested to be an optical characteristic, commonly found in the authors' previous studies of TiO₂ and δ-Al₂O₃ HNPs. In addition, β-Fe₂O₃ HNPs had a band gap (1.86 eV) between amorphous (1.73 eV) and polycrystalline (1.97 eV) β-Fe₂O₃ thin films, which was a 5–7 nm thick shell that embraced an intermediate volume of the crystal phase, in-between the two thin films.     

Determination of the chemical diffusion coefficient of lithium in Li3V2(PO4)3

The chemical diffusion of lithium ion in Li₃V₂(PO₄)₃ were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. The CV results show that there exists a linear relationship between the peak current (i_p) and the square root of the scan rate (ν^1/2). The impedance spectrum exhibits a single semicircle and a straight line in a very low frequency region. A linear behavior was observed for every curve of the real resistance as a function of the inverse square root of the angular frequency in a very low frequency region. The obtained chemical diffusion coefficient from EIS measurements varies within 10^− 9 to 10^− 8 cm²·s^− 1, in good agreement with those from CV results.     

Chemical diffusion coefficient of lithium ion in Li3V2(PO4)3 cathode material

The kinetic properties of monoclinic lithium vanadium phosphate were investigated by potential step chronoamperometry (PSCA) and electrochemical impedance spectroscopy (EIS) method. The PSCA results show that there exists a linear relationship between the current and the square root of the time. The D?_Li values of lithium ion in Li_3-xV₂(PO₄)₃ under various initial potentials of 3.41, 3.67, 3.91 and 4.07 V (vs Li/Li⁺) obtained from PSCA are 1.26 × 10^− 9, 2.38 × 10^− 9, 2.27 × 10^− 9 and 2.22 × 10^− 9 cm²·s^− 1, respectively. Over the measuring temperature range 15-65 °C, the diffusion coefficient increased from 2.67 × 10^− 8 cm²·s^− 1 (at 15 °C) to 1.80 × 10^− 7 cm²·s^− 1 (at 65 °C) as the measuring temperature increased.     

Element distribution and phase constitution of Al2O3-TiC/W18Cr4V vacuum diffusion bonded joint

Vacuum diffusion bonding between Al₂O₃-TiC ceramic composites and W18Cr4V tungsten-based tool alloy has been carried out by using Ti/Cu/Ti multi-interlayer. Element distribution near the Al₂O₃-TiC/W18Cr4V interface was discussed and fracture morphology was analyzed using electron probe microanalysis. Additionally, phase constitutions of the Al₂O₃-TiC/W18Cr4V joint were determined by X-ray diffraction. The results indicate that Ti-rich layers are formed near both Al₂O₃-TiC and W18Cr4V. The Ti-rich layer near Al₂O₃-TiC helps to wet the Al₂O₃-TiC surface. The Ti-rich layer near W18Cr4V can restrain the formation of Fe-Ti intermetallic compounds in the diffusion transition zone. Residual Cu in the diffusion transition zone can act as a stress releasing zone. The structures of interfacial phases are identified as follows: Al₂O₃-TiC/TiO + Ti₃Al/Cu + CuTi/TiC layer/mixed layer of Fe₃W₃C, Cr₂₃C₆ and α-Fe/W18Cr4V. The fracture morphology of Al₂O₃-TiC/W18Cr4V joint appears brittle features and the failure occurs within the Al₂O₃-TiC ceramic.     

Analysis of the microstructure and phase constitution of the Fe3Al/18-8 diffusion interface after re-heating

The existence of coarse precipitation blocked the diffusion of the atoms and caused the uneven distribution of elements at the Fe₃Al/18-8 interface zone. Especially, the brittle precipitation could induce welding cracks directly. Consequently, it was one of the main factors that caused the failure of the joint. The Fe₃Al/18-8 diffusion-bonded joint was re-heated and the precipitation and phase constitution of the interface were analysed by means of scanning electron microscope (SEM), energy dispersive spectrum (EDS) and X-ray diffraction (XRD). The results indicated that the precipitation became tiny and regular and distributed evenly due to re-heating. The brittle precipitation zone was liquified to become a smooth and homogeneous diffusion zone. There were no high-microhardness brittle phases such as FeAl₂ and Fe₂Al₅ near the Fe₃Al/18-8 diffusion interface after re-heating.     

Diffusivity of Al and Fe near the diffusion bonding interface of Fe3Al with low carbon steel

The distribution of elements near the Fe₃Al/Q235 diffusion bonding interface was computed by the diffusion equation as well as measured by means of EPMA. The results indicated close agreement between the two for iron and aluminium. Diffusion coefficient in the interface transition zone is larger than that in the Fe₃Al and Q235 steel at the same temperature, which is favourable to elemental diffusion. The diffusion distance near the Fe₃Al/Q235 interface increased with increasing heating temperature,T , and the holding time, t. The relation between the width of the interface transition zone,x , and the holding time,t , conformed to parabolic growth law: x bd² = 4.8 × 10⁴ exp(-133/RT) bdt -t ₀bd. The width of the interface transition zone does not increase significantly for holding times beyond 60 min.     

Effects of hydrolysis on dodecyl alcohol modified β-CaSiO3 particles and PDLLA/modified β-CaSiO3 composite films

In this research, β-CaSiO₃ particles were surface modified with dodecyl alcohol, and Poly-(DL-lactic acid) (PDLLA)/modified β-CaSiO₃ composite films were fabricated with a homogenous dispersion of β-CaSiO₃ particles in the PDLLA matrix. The aim of the study was to investigate the properties of the composite films before and after hydrolytic treatment. SEM images showed retained homogenous dispersion of β-CaSiO₃ particles after hydrolysis and tensile test also showed maintained mechanical property. Simulated body fluid (SBF) incubation experiment suggested that hydrolytic treatment did not affect the formation of hydroxyapatite on the surface of the composite films. The hydrophilicity of the composites was greatly recovered (from 69.82° to 50.28°) after hydrolysis. In addition, cells cultured on composite films after hydrolysis presented the highest cell proliferation rate and differentiation level. All of these results suggested that the surface modification of silicate particles with dodecyl alcohol along with reversible hydrolytic treatment was an effective and feasible approach to fabricate polymer/silicate composite materials with improved properties.