The Analysis of the Residual Stress Evolution during Cycling Oxidation of the Ni-base Superalloys at High Temperature

The lifetime of the elements made of Ni-base superalloys can be strongly increased by introducing compressive stresses. Such stresses increase the resistance of cracks nucleation and formation during cyclic loads. Therefore, it is important to know how the stresses in the cold rolled Ni-based superalloys evolve during the service. Ni-base superalloys are dedicated to the usage at elevated temperature. However, exposing the Ni-based superalloys to high temperature results in their oxidation. So far, not a single work on the studies of the residual stress evolution in the Ni-based superalloys during cycling oxidation at high temperature was performed. Thus in the present study the residual stress in the materials in the as-received conditions and the changes in the residual stresses during cycling oxidation of IN 625 and IN 718 at 1273 K in air was investigated and described. The obtained results showed differences in the residual stresses level measured for investigated alloys. It was also found that thermal cycling of studied alloys influences the residual stresses. However even after the end of the test, the measured residual stresses were still compressive. Slightly different oxidation resistance was found for the studied alloys, namely, IN 718 was found to be more prone to oxide scale spallation. The latter was correlated with different alloy chemical composition, which results in formation of δ - phase in IN 718. The dissolution of δ - phase during high temperature exposure resulted in formation of sub-scale enriched with Nb and Ti in the near oxide scale/substrate interface. The latter was claimed to have a negative effect on oxide scale adherence

Effect of Substrate Roughness on Oxidation Resistance of an Aluminized Ni-Base Superalloy

In the present work, it is shown that the surface preparation method used on two Ni-based superalloys prior to aluminizing chemical vapor deposition (CVD) is one of the most important factors determining the oxidation resistance of aluminized Ni-based superalloys. It was found that grit blasting the substrate surface negatively affects the oxidation resistance of the aluminized coatings. For grit blasted and aluminized IN 625, a thicker outer NiAl coating was formed compared to that of IN 738. In contrast, no effect on NiAl coating thickness was found for grit blasted and aluminized IN 738. However, a thicker interdiffusion zone (IDZ) was observed. It was shown that the systems with grit-blasted surfaces reveal worse oxidation resistance during thermal shock tests, namely, a higher mass loss was observed for both grit blasted and aluminized alloys, as compared to ground and aluminized alloys. A possible reason for this effect of remaining alumina particles originating from surface grit blasting on the diffusion processes and stress distribution at the coating/substrate is proposed.Comment: Accepted manuscript Metals 201

Spectral density of generalized Wishart matrices and free multiplicative convolution

We investigate the level density for several ensembles of positive random matrices of a Wishart--like structure, $W=XX^{\dagger}$, where $X$ stands for a nonhermitian random matrix. In particular, making use of the Cauchy transform, we study free multiplicative powers of the Marchenko-Pastur (MP) distribution, ${\rm MP}^{\boxtimes s}$, which for an integer $s$ yield Fuss-Catalan distributions corresponding to a product of $s$ independent square random matrices, $X=X_1\cdots X_s$. New formulae for the level densities are derived for $s=3$ and $s=1/3$. Moreover, the level density corresponding to the generalized Bures distribution, given by the free convolution of arcsine and MP distributions is obtained. We also explain the reason of such a curious convolution. The technique proposed here allows for the derivation of the level densities for several other cases.Comment: 10 latex pages including 4 figures, Ver 4, minor improvements and references updat

The role of adiponectin and leptin in the treatment of ovarian cancer patients

Introduction: Ovarian cancer is most frequently detected in the advanced stage. Although its pathogenesis is not fully elucidated, it is assumed that body susceptibility and hormonal disorders are responsible. The role of some cytokines as predictors in the treatment process is still investigated. The aim of the study was to determine the relationship of adiponectin and leptin with the disease severity and response to chemotherapy. Material and methods: Forty-three ovarian cancer patients were treated by systemic treatment. Patients received 5–7 cycles of chemotherapy — paclitaxel/carboplatin with or without bevacizumab. Using standard ELISA kits before and after chemotherapy, adiponectin and leptin concentrations were determined in the blood serum. Results: The average adiponectin concentration before chemotherapy was found to be 8.83 ± 3.19 μg/ml, as compared to 10.37 ± 4.18 μg/ml (increase by 17.44%, p < 0.001) after treatment. Mean pre-treatment leptin concentration was 16.89 ± 15.54 ng/ml, and 21.77 ± 14.69 ng/ml after chemotherapy (increase by 28.89%, p < 0.01). A positive correlation was found between leptin concentration and age and BMI. There was no relationship of the disease severity with the response to treatment and the concentration of the adipokines. The leptin/adiponectin ratio (L/A) before treatment correlated with better response to chemotherapy. Conclusions: Adiponectin and leptin did not correlate with the stage of ovarian cancer and response to chemotherapy. The L/A ratio may be considered a predictor of clinical response to treatment

Complete diagrammatics of the single ring theorem

Using diagrammatic techniques, we provide explicit functional relations between the cumulant generating functions for the biunitarily invariant ensembles in the limit of large size of matrices. The formalism allows to map two distinct areas of free random variables: Hermitian positive definite operators and non-normal R-diagonal operators. We also rederive the Haagerup-Larsen theorem and show how its recent extension to the eigenvector correlation function appears naturally within this approach.Comment: 18 pages, 6 figures, version accepted for publicatio