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•The dependence between the BC-surface condition and the α-Al2O3 phase formation.•Low-temperature α-Al2O3 formation in the pre-oxidation treatments.•Influence of the grit-blasting on ...the oxidation kinetics of β-(Ni, Pt)Al System.•In the grit-blasted samples, oxidation stable-state is reached less than 2 h.•Stifle the growth of metastable θ-Al2O3 and accelerate θ- to α-Al2O3 at > 1000 °C.
The effect of surface modification by grit-blasting of β-(Ni,Pt)Al bond coats on the growth of α-Al2O3 is here presented. Thermogravimetry tests at 1000 °C, 1050 °C, 1100 °C, and 1150 °C were performed on as-aluminized and as-grit-blasted specimens under the same oxygen partial pressure (pO2 = 2.1 × 10-1 atm), where the parabolic rate constant (kp) was calculated. The oxide phase fraction was obtained from the fitting of the photo-stimulated luminescence spectroscopy (PSLS) results. A strong dependence between the surface condition of the bond coat and the α-Al2O3 phase formation was observed. The thermally treated grit-blasted samples achieved faster the steady-state (1.6 h) of the thermal growth oxide (TGO), while a treatment 2.7 times longer (4.25 h) was required for the as-aluminized specimens. This result contributes to the general understanding of the effect of the surface condition on the TGO formation during pre-oxidation treatment to promote the growth of the α-Al2O3 phase at low temperature and less time without affecting the lifetime of thermal barrier coating systems.
The effect of isothermal pre-oxidation treatments on the β-(Ni,Pt)Al + IDZ + René N5 system degradation is reported here. The pre-oxidation treatments were carried out from 900 °C (mostly θ-Al2O3 ...growing conditions) to 1200 °C (mainly α-Al2O3 growing conditions) for 5 h, under an Ar-stream with pO2 = 1 × 10−5 atm. The correlation between the structural, microstructural, and chemical properties of the β-(Ni,Pt)Al BC show that pre-oxidation parameters have an important effect on the multi-elemental counter diffusion phenomena along the BC. Heat treatments performed above 1100 °C resulted in loss of stability of the BC, partially disordering of the β phase promoting the β → β + L10 and β → β + L12 transformations. A significant BC + IDZ thickness increase of 55% at 1200 °C was observed with respect to the as-received specimen resulting in a severe BC degradation. Multi-elemental inward diffusion is the main mechanism responsible for BC degradation at high temperatures.
•BC microstructural degradation is highly dependent on the pre-oxidation temperature.•An unbalanced diffusivity due to TGO formation promotes an excessively TGO/BC-interfacial voids and a BC Pt-enrichment.•The two-sublattice model adequately describes the elemental distribution within the β phase.•A partially disordering and phase transformations β → β + L10 and β → β + L12 take place for pre-oxidation above 1100 °C.
Cu/Sn soldering alloys have emerged as a viable alternative to Pb-based solders, and thus have been extensively explored in the past decade, although the fine-scale behavior of the resulting ...intermetallic compounds (IMCs), particularly during the early stages of interface formation, is still a source of debate. In this work, the microstructural evolution of Cu6Sn5, in a Cu/Sn soldering reaction at 523K, was experimentally investigated by dipping a single Cu sample into molten Sn at a near-constant speed, yielding a continuous set of time evolution samples. The thickness, coarsening and morphology evolution of the Cu6Sn5 layer is investigated through the use of scanning electron microscopy. The experimental results are also compared to phase-field simulations of the microstructural evolution of the Cu6Sn5 layer. The influence of model parameters on the kinetics and morphological evolution of the IMC layer was examined. In general, good qualitative agreement is found between experiments and simulations and for a limited parameter set there appears to be good quantitative agreement between the growth kinetics of the Cu6Sn5 layer, the grain boundary (GB) effect on grain coarsening, and the substrate/IMC interface roughness evolution. Furthermore, the parametric investigations of the model suggests that good agreement between experiments and simulations is achieved when the dominant transport mechanism for the reacting elements (Cu and Sn) is GB diffusion.
The effect of Y additions on the oxidation behavior in furnace cyclic tests and its correlation with thermogravimetric analysis of sintered NiAl alloys is here reported. Part of the samples got an ...EB-PVD 7YSZ coating on top. Highly ordered B2-NiAl intermetallic powder was obtained by self-propagating high-temperature synthesis (SHS) during ball milling of elemental precursors with Y additions in amounts between 0 and 1.5 at.%. The SHS process was optimized to identify the combination of milling parameters that leads to a sharp increase in the reaction temperature for intermetallic synthesis. The tested samples consisted of NiAl-Y buttons densified by spark plasma sintering (SPS). Furnace cyclic testing of the SPS- buttons at 1100 °C showed high resistance to spallation of the 7YSZ top-coat and a significant decrease in its oxide growth kinetics attributed to Y-additions. Contents below 0.5 at.% Y reduce the oxidation kinetics of NiAl exposed to thermal cycles at 1100 °C, while higher Y contents are favorable for a longer TBC life.
•SHS process parameters by ball milling to prepare highly ordered NiAl-Y powder.•7YSZ coated NiAl-Y model alloys to evaluate their furnace cyclic oxidation behavior at 1100 °C.•0.1–0.5 at.%Y reduce the oxidation kinetics to one third of undoped NiAl mass gain.•Longest TBC lives and lowest spallation rates were achieved on NiAl-1.0 - 1.5 at.%Y/7YSZ.•Y-additions improved oxidation behavior and TBC live respective to undoped NiAl.
Aliment Pharmacol Ther 2010; 32: 244–253
Summary
Background Obesity increases the risk for severe acute pancreatitis, although abdominal obesity may be a better prognostic marker.
Aim To determine ...if a single anthropometric parameter best predicts severe acute pancreatitis and correlates with intra‐abdominal fat.
Methods Ninety‐nine patients with acute pancreatitis were studied prospectively. Anthropometry included body mass index (BMI) and girths (umbilical/minimum waist, iliac/trochanter hip, thigh). Several waist‐to‐hip/waist‐to‐thigh ratios (WHR/WTR) were constructed. A CT‐scan with calculation of cross‐sectional abdominal fat areas was obtained in 37 cases.
Results Severe acute pancreatitis occurred in 25 patients. Waist circumference (WC), WHR and WTR – all using the umbilical reference – most accurately predicted severe acute pancreatitis. Only umbilical WC was retained in multivariate analysis: the risk for severe acute pancreatitis increased 16% with every 1 cm (OR 1.16, 95%CI: 1.1–1.3). Abdominal obesity caused a 6‐fold increase in risk. Umbilical WC correlated best with subcutaneous fat area (r = 0.791, P < 0.001), whereas WHR with intra‐abdominal (r = 0.594, P < 0.001).
Conclusions Abdominal obesity according to umbilical WC is a better predictor for development of severe acute pancreatitis than BMI, minimum WC, WHR and WTR. The protocol for anthropometry must be standardized as it may affect results. Both subcutaneous and intra‐abdominal fat appears to affect the likelihood of a severe outcome.
IN718 is a Ni-based superalloy usually manufactured by conventional processes such as wrought or casting. However, recently additive manufacturing (AM) technologies, such as Powder bed fusion (PBF), ...are used to produce IN718 parts. Heat treatments, also designed for conventional processes, are usually used in AM parts to improve mechanical properties. Unlike traditional techniques, AM processes involve rapid cooling rates, large thermal gradients, and multiple reheat cycles, which might cause high residual stresses and elemental segregations in the printed parts affecting their final mechanical properties. In this work, a detailed comparative study of microstructural features was carried out in both wrought- and PBF-produced IN718. It was found differences in size, shape, and location of MC carbides. According to experimental results and the phase fraction diagram obtained from Thermo-Calc, these MC carbides cannot be dissolved in a conventional solution heat treatment. In consequence, these carbides continue their evolution during complete aging heat treatment, affecting the material hardness. Nevertheless, similar hardness in the wrought and AM sample was obtained after applying a modified aging treatment proposed in this work.
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