La2O3-modified YSZ coatings: High-temperature stability and improved thermal barrier properties

Lanthana precursor was coated on yttria-stabilized-zirconia (YSZ) powders by wet chemical infiltration, and was introduced to the crystalline structure and grain boundaries of YSZ after plasma spraying of thermal barrier coatings (TBCs). The microstructural stability and thermal barrier properties of this new kind of TBCs were studied under different annealing conditions. It demonstrates that the La₂O₃ surface coating restrains grain growth of YSZ during both deposition and post-annealing processes, compared to a TBC obtained from commercially available unmodified YSZ powders. According to the composition analysis, lanthana partially dissolved in the zirconia matrix after heat treatment. The thermal diffusivity of YSZ coating significantly decreased after lanthana modification, typically from 0.354 mm² s^− 1 for an unmodified sample to 0.243 mm² s^− 1, reflecting a decrease of 31%. Even after annealed at 1200 °C for 50 h, the thermal diffusivity of modified coatings still shows a reduction of 25% than unmodified samples.     

Factors affecting the microstructure of platinum-modified aluminide coatings during a vapor phase aluminizing process

Platinum (Pt)-modified aluminide coatings were developed by electroplating a thin layer of Pt followed by an industrial vapor phase aluminizing process. The goal of this work was to systematically investigate the effect of critical coating process parameters (such as the electroplated Pt thicknesses, Al contents in Cr-Al nuggets, diffusion heat treatments) and substrates on the final Pt-modified aluminide coatings. Surface morphology and cross-section microstructure of the developed coatings were inspected and compared by using Optical Microscope, Scanning Electron Microscope (SEM) equipped with energy dispersive spectroscopy (EDS). Experimental results showed that the Al and/or Pt increase shall favor the formation of ξ-PtAl₂ phase; transformation of ξ-PtAl₂ into β-(Ni,Pt)Al phase can be obtained via a heat treatment process; Cr, Co elements in the studied Ni-base superalloy substrates did not show significant influence on coating outer layer microstructure; while substrate elements affect the microstructure of the coating interdiffusion layer.     

TEM study of TiN coatings fabricated by mechanical milling using vibration technique

A mechanical milling method was used for the deposition of TiN coatings. The principle of this method is that a substrate and powder were placed along with balls into the vibration chamber that was vibrated by a mechano-reactor. During mechanical milling process, the substrate surface was impacted by a large number of flying balls. The TiN particles trapped in between the balls and the substrate became cold welded to the surface. The repeated substrate-to-ball collisions forged TiN particles into a coating on the substrate surface. The process allowed the thick TiN coatings to be produced at room temperature in an ambient atmosphere. TEM study of the as-fabricated coatings was carried out. The coating formation depended on the size of the initial TiN particles. The 50-nm TiN nanoparticles were more easily cold welded than 1.5-μm microparticles. The nanoparticles had a tendency to consolidate and densify into the bulk material under the applied compressive loading. The TiN particles better consolidated and densified on the hard Ti surface than on the soft Al one.     

Effect of Zn Additions on the Oxidation of Cu–2 at.% Al and Cu–4 at.% Al Alloys in 1 atm O2 at 800 °C

Four ternary Cu–Zn–Al alloys containing 5 or 10 at.% Zn and 2 or 4 at.% Al plus an alloy containing 2 at.% Al and 15 at.% Zn have been oxidized at 800 °C in 1 atm O₂, and their behavior has been compared with that of the corresponding binary Cu–Zn and Cu–Al alloys. For the alloy containing 4 at.% Al, which is already able to form external alumina scales, the addition of Zn is only effective in reducing the mass gain during the fast, initial-oxidation stage. Conversely, the addition of 15 at.% Zn to Cu–2Al is able to prevent the formation of external scales containing mixtures of the Cu and Al oxides, resulting in the formation of external alumina scales after an initial stage of faster rate, producing a limited third-element effect. Finally, the addition of Al to both Cu–5Zn and Cu–10Zn is able to prevent the internal oxidation of Zn, producing a kind of reversed third-element effect. Possible mechanisms for these effects are examined on the basis of general treatments concerning the scaling behavior of ternary alloys.     

The influence of tool flank wear on residual stresses induced by milling aluminum alloy

The machining processes could induce residual stresses that enhance or impair greatly the performance of the machined component. Machining residual stresses correlate very closely with the cutting parameters and the tool geometries. In this paper, the effect of the tool flank wear on residual stresses profiles in milling of aluminum alloy 7050-T7451 was investigated. In the experiments, the residual stresses on the surface of the workpiece and in-depth were measured by using X-ray diffraction technique in combination with electro-polishing technique. In order to correlate the residual stresses with the thermal and mechanical phenomena developed during milling, the orthogonal components of the cutting forces were measured using a Kistler 9257A type three-component piezoelectric dynamometer. The temperature field of the machined workpiece surface was obtained with the combination of infrared thermal imaging system and finite element method. The results show that the tool flank wear has a significant effect on residual stresses profiles, especially superficial residual stress. As the tool flank wear length increases, the residual stress on the machined surface shifts obviously to tensile range, the residual compressive stress beneath the machined surface increases and the thickness of the residual stresses layer also increases. The magnitude and distributions of the residual stresses are closely correlated with cutting forces and temperature field. The three orthogonal components of the peak cutting forces increase and the highest temperature of the machined workpiece surface also increases significantly with an increase in the flank wear. The results reveal that the thermal load plays a significant role in the formation of the superficial residual stress, while the dominative factor that affects thickness of residual stresses layer is the mechanical load in high-speed milling aluminum alloy using worn tool.     

Precipitation-hardenable Mg–2.4Zn–0.1Ag–0.1Ca–0.16Zr (at.%) wrought magnesium alloy

A new precipitation-hardenable wrought magnesium alloy based on the Mg–Zn system with an excellent combination of high tensile yield strength, good ductility and low tensile-compression anisotropy has been developed. The Mg–2.4Zn–0.1Ag–0.1Ca(–0.16Zr) (at.%) alloys show significantly higher age-hardening responses compared to that of the binary Mg–2.4Zn alloy due to the increased number density and refinement of rod-like MgZn₂ precipitates. The addition of Zr to the Mg–2.4Zn–0.1Ag–0.1Ca alloy resulted in a significant refinement of the grain size. A high number density of precipitates was observed in the Mg–2.4Zn–0.1Ag–0.1Ca–0.16Zr alloy in both the as-extruded condition and following isothermal ageing at 160 °C. The tensile yield strength of the as-extruded and aged alloys was 289 and 325 MPa, with an elongation of 17% and 14%, respectively. These alloys show relatively low compression and tensile anisotropy. The origins of these unique mechanical properties are discussed based on the detailed microstructural investigation.     

Structural processes that initiate shear localization in metallic glass

For crystalline metals, the structural carriers (dislocations and twins) of plasticity have been well characterized. In contrast, the structural processes responsible for the localized shear flow in amorphous metals remain poorly understood. Using molecular dynamics simulations, we illustrate here how the shear localization initiates in a Cu–Zr metallic glass. We identify the breakdown of full icosahedral clusters as a structural signature of the initiation of shear localization, which is demonstrated to be a spontaneous and autocatalytic instability propagating with a velocity close to the speed of sound. Structural disorder induced softening precedes thermal softening as the origin of the shear banding. Once the deformation band penetrates across the entire sample, the already-rejuvenated structure inside allows the entire band to collectively slip as a whole, to grow the shear offsets on both sides of the sample.     

Development of in-vessel components of the microfission chamber for ITER

Microfission chambers (MFCs) will measure the total neutron source strength in ITER. The MFCs will be installed behind blanket modules in the vacuum vessel (VV). Triaxial mineral insulated (MI) cables will carry signals from the MFCs. The joint connecting triaxial MI cables in the VV must be considered because the MFCs and the MI cables will be installed separately at different times. Vacuum tight triaxial connector of the MI cable has been designed and a prototype has been constructed. Performance tests indicate that the connector can be applied to the ITER environment. A small bending-radius test of the MI cable indicates no observed damage at a curvature radius of 100 mm.     

Development and irradiation test of lost alpha detection system for ITER

We developed a lost alpha detection system to use in burning plasma experiments. The scintillators of Ag:ZnS and polycrystalline Ce:YAG were designed for a high-temperature environment, and the optical transmission line was designed to transmit from the scintillator to the port plug. The required optical components of lenses and mirrors were irradiated using the fission reactor with the initial result that there was no clear change after the irradiation with a neutron flux of 9.6×10(17)?nm(-2) s(-1) for 48 h. We propose a diagnostic of alpha particle loss, so-called alpha particle induced gamma ray spectroscopy. The initial laboratory test has been carried out by the use of the Ce doped Lu(2)SiO(5) scintillator detector and an Am-Be source to detect the 4.44 MeV high energy gamma ray due to the (9)Be(α,nγ)(12)C reaction.