Y.X. Wu

Effect of ultrarapid cooling on microstructure of laser cladding IN718 coating

Abstract IN718 alloy clad coating cooled in liquid nitrogen was fabricated by high power diode laser. The microstructure of the coating was investigated using SEM equipped with energy disperse spectroscopy, and the precipitation phase was analysed using TEM after standard heat treatment. The results showed that the liquid nitrogen provided the clad coating an ultrarapid cooling rate during laser cladding. Laves in the ultrarapid cooled clad coating was refined, and Laves concentration and dendritic space were decreased compared with the air cooled clad coating. The ultrarapid cooling rate reduced the constitutional supercooling and restrained Nb segregation in the Laves during solidification. More Nb was distributed in austenite and precipitated as γ″-Ni3Nb during the standard heat treatment to improve the mechanical properties of the clad coating.

Error analyses on some typically approximate solutions of residual stress within a thin film on a substrate

Stoneys equation and subsequent modifications and some approximations are widely used to evaluate the macrostress within a film on a substrate, though some of these solutions are only applicable for thin films. The purpose of this paper is to review the considerable efforts devoted to the analysis of residual stresses in a single-layer film in the last century and recent years and to estimate the errors involved in using these formulas. The following are some of the important results that can be obtained. (1) The exact solution for the residual stress can be expressed in terms of Stoneys equation [Proc. R. Soc. London A82, 172 (1909)] and a correction factor, (1+Ση3)∕(1+η), where Σ,η are the ratios of the elastic modulus and the thickness of the film to those of the substrate, respectively. (2) When the thickness ratio of the film and the substrate is less than 0.1, Stoneys equation and Rolls approximation [J. Appl. Phys. 47, 3224 (1976)] do not cause serious errors. (3) The approximation proposed by ...

Analytical modeling of edge effects on the residual stresses within the film/substrate systems. I. Interfacial stresses

Several analytical models have been developed to derive the closed-form solutions for the residual stresses at the interface when a film was overlaid on a substrate. In these models, the film edge effects on the interfacial stresses were analyzed. However, some of the existing models do not yield good results, and sometimes, they err in a fundamental manner in the prediction of the interfacial stress distribution. In this paper, an analytical model is developed to derive the closed-form solutions for the interfacial stress distributions along the film width. Compared to the existing analytical models, the present model is more rigorous and the analytical results agree better with the finite element results.

Residual stress relaxation in the film/substrate system due to creep deformation

An analytical model is developed to estimate the effect of creep deformation on the stress relaxation and distribution in the film/substrate bilayer structure during prolonged exposure to high temperature. In the model, either the film or the substrate subjecting to high-temperature creep is considered. Closed-form solutions for the residual stresses in the film and the substrate are derived. A relationship between the stress relaxation rate in the film/substrate system and the relaxation time is obtained. Case studies show that the ratios of the biaxial modulus and the thickness of the film to those of the substrate, the creep parameters, and the exposure temperature have significant influence on the residual stress relaxation rate.

Studies of electroslag cladding Inconel 52M multilayer

Abstract The current study investigates Inconel 52M multilayer by electroslag cladding. The four-layer multilayer with good formation is obtained. The experimental results indicate that the microstructure of the multilayer consists of numerous coarse columnar dendrites in the same growth direction. Nb rich carbides, the mixture of Al rich oxides and Nb rich carbides and long chains of eutectic phases are precipitated in the interdendritic regions. The significant composition changes merely occur in the limited interface regions between the substrate and the first layer, while the smooth composition changes occur in the 1st layer. Moreover, the microhardness in single layer decreases from the root to the top. The microhardness decrease in the first layer is more significant than that in the other single layer as a result of the composition transitions by the effect of dilution.

Effect of laser scanning speed on TiN/TiB–Ti based composite

Abstract In situ synthesised TiN and TiB particulate reinforced metal matrix composite coating was formed on Ti–3Al–2V alloy by laser cladding with a Ti/h-BN powder mixture. The phase structure, microstructure, microhardness and wear performance of the clad layer were analysed by optical microscope, X-ray diffraction, scanning electron microscopy, microhardness tester and wear testing machine. In situ TiN and TiB were synthesised in the forms of equiaxed crystal and needle platelet/whisker type microstructures in the clad layers. The scanning speed plays an important role on the microstructure of the TiN and TiB. The microhardness of laser clad layer was 850–1250 HV0·5, which was about five times of the substrate. The wear height loss of the substrate is almost two times of the clad layers.

[Determination of perfluorinated compounds in human urine by ultra high performance liquid chromatography-tandem mass spectrometry].

A method for the analysis of 12 perfluorinated compounds (PFCs) in human urine by ultra high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed and validated. One mL 2% formic acid in methanol was added into the urine. After ultrasonication and centrifugation, the samples were purified by a solid phase extraction column and examined by UPLC-MS/MS. The target compounds were quantified by stable isotope dilution technique. The linear range was 0.05 -50 microg/L for the 12 PFCs and the correlation coefficient > or = 0.992. The limits of detection of 12 PFCs were in the range of 0.44 - 3.47 ng/L. The matrix recoveries of the method for the 12 PFCs in three spiked levels (20, 100, 500 ng/L) ranged from 80.3% to 116.2%. The relative standard deviations (RSDs, n = 5) were between 5.5% and 13.8%. The sensitive and accurate method was successfully applied to the analysis of PFCs in human urine.

[Development of two-dimensional micro strong cation exchange liquid chromatography/reversed phase pressurized capillary electrochromatography and its application on Cortex Phellodendri extract].

Pressurized capillary electrochromatography (pCEC) combines capillary electrophoresis (CE) with high performance liquid chromatography (HPLC), resulting in high separation efficiency, high selectivity, high resolution and fast speed. In addition, it provides a solvent gradient capability. Based on pCEC, a two-dimensional chromatography was constructed using micro strong cation exchange liquid chromatography and reversed phase pressurized capillary electrochromatography (micro-SCXLC/RP-pCEC) for the analysis of Cortex Phellodendri extract. A sample was separated by the first dimensional SCX column with a linear salt gradient elution into 11 plugs. Each plug was collected and injected into the second dimensional RP-pCEC column with a linear gradient for further separation. Compared with one-dimensional liquid chromatography, it has higher resolution and larger peak capacity. The two-dimensional chromatographic system is suitable for the separation and analysis of complex samples.

[Effect of alcoholic strength on the determination of ethyl carbamate in Chinese spirits by high performance liquid chromatography-fluorescence detection].

A high performance liquid chromatography-fluorescence detection (HPLC-FLD) method was established for rapid determination of ethyl carbamate (EC) in Chinese spirits. Through the analysis and comparison of the EC peak areas in different alcoholic strengths determined by HPLC-FLD, the effect of alcoholic strength on the determination of the content of EC was found. The alcoholic strength and the peak area of EC showed good linearity in the range of 5% to 65% (v/v) alcohol content, and the correlation coefficients (R2) were higher than 0.98. Furthermore, the conversion between the peak area of EC with different alcoholic strengths was established by the relative correction coefficient. The method showed a good linearity in the range of 10 to 500 microg/L for EC with the average recoveries of 98.9%-108.2% and RSDs of 0.6%-4.9%. The reliability of the established HPLC-FLD method was evaluated by comparison with GC-MS method. The results showed that the results of two methods were not significantly different. The developed method is simple, sensitive, accurate, and suitable for the rapid determination of EC in Chinese spirits.

[Simultaneous determination of 8 polybrominated biphenyls in human serum using gas chromatography-mass spectrometry].

A comprehensive analytical method based on gas chromatography-mass spectrometry (GC-MS) has been developed for the simultaneous determination of 8 polybrominated biphenyl congeners (PBBs: BB-15, 18, 52, 101, 153, 180, 194 and 206) in human serum. After the protein was removed, the sample was cleaned-up by an Oasis HLB solid-phase extraction (SPE) cartridge, then purified further by a two-layer cartridge containing activated silica gel and a mixture of silica gel and sulfuric acid, in which elution solvent was optimized. The eluent was evaporated to about 100 microL by a gentle nitrogen stream for GC-MS analysis. The separation was performed on a DB-5ms column (15 m x 0.25 mm x 0.1 microm) and the qualitative and quantitative analyses were carried out in electron impact (EI) selected ion monitoring (SIM) mode, in which isotope was used as internal standard. The limits of detection (LODs, 3.14 times of standard deviation) and the limits of quantification (LOQs, 10 times of standard deviation) were 0.002-0.029 ng/mL and 0.008-0.092 ng/mL respectively for the 8 PBBs. The average recoveries for all PBBs at three spiked levels were 74.24%-119.49% with the relative standard deviations in the range of 1.23%-12.02%. The method was verified by accurate analysis of BB-153 in organic contaminant standard reference materials (SRM) 1957 and 1958. This method is simple, rapid, accurate, precise and fit for the determination of PBBs in human serum.