Procedia Materials Science最新文献

In this study, the effect of the metal salt generation bonding technique on the strength of a direct-bonded SUS304 stainless steel interface was investigated. SUS304 stainless steel surfaces were modified by boiling in 50% formic acid, and direct bonding was performed at a bonding temperature of 1023-1123 K under a pressure of 147 N (for a bonding time of 900 s). After direct bonding, the specimens were subjected to the peel test for evaluating their strength. As a result of the surface modification, bonded joints were obtained at bonding temperature of 30 K lower than that required for the unmodified surfaces, and the peel strength was comparable to that of the maximum load. On the basis of the experimental results, it was established that metal salt generation processing is effective for removing oxide films on SUS304 stainless steel.

In the present work two techniques are combined to optimize bond coat properties before thermal barrier coating (TBC) application, the cold gas dynamic spraying (CGDS) and electron beam remelting (EB). Results of the work focused on comparison of high velocity oxygen fuel (HVOF) and CGDS CoNiCrAlY bond coats are firstly presented. Than the effect of the electron beam remelting of the CoNiCrAlY coating manufactured by HVOF and CGDS deposition techniques is deeply investigated. The CoNiCrAlY bond coat to Inconel substrate interface displayed locations with very poor bonding, in larger extent for the states prepared by HVOF comparing to CGDS. The bond coats prepared by both ways being EB remelted are typically removal of the defects on the substrate to bond coat interface. The microstructure of the bond coat after this treatment is formed by Inconel fine grain layer being followed by the surface layer consisting of elongated dendritic microstructure. An increased porosity has been observed in interdendritical space in larger extent for CGDS samples.

The characteristics of cyclic bending deformation and fatigue fracture are studied on polycrystalline aluminum and Al-1.0mass%Mg alloy from the metallurgical point of view. It is found that the fatigue life mainly depends on grain size and the kind of materials. Cracks are preferentially formed at grain boundaries inclined 40 – 60°to the tension-compression direction, suggesting that shear stress affects the crack formation. EBSD measurements reveal the inhomogeneity of deformation. Intense development of sub-grain is seen in the grain interior close to a crack. It indicates that the work hardening close to grain boundaries triggers the crack formation.

In this study we focused on antimicrobial nanocomposites based on kaolinite, when two series of nanocomposites were prepared. In the first case, kaolinite (KAO) was used as the carrier for antibacterial drug. Secondly, kaolinite modified with dimethyl sulphoxide (DMSO) was used. In both series, chlorhexidine dihydrochloride (CH) acts as an active antimicrobial component. The resultant samples were characterized by X – ray diffraction (XRD) and infrared spectroscopy (FTIR). The antimicrobial activity of prepared composites against bacteria strains Staphylococcus aureus, Escherichia coli and against yeast Candida albicans were evaluated by finding minimum inhibitory concentration (MIC). It was found that prepared nanocomposites were very effective and they had different effect against bacteria strains and yeast. Important information was that treatment with DMSO had not significant effect on antimicrobial activity. These nanocomposites can be in future used for preparation of drugs for local treatment of oral cavity with long-acting antimicrobial activity.

The Small Punch (SP) test technique is used for the evaluation of actual tensile, fracture and creep characteristics of materials exposed for a long period in operating plant components in order to provide data needed for plant life and integrity assessment.

In the present paper the results of SP tests in the temperature range from -193 °C to +20 °C, carried out in two laboratories on low alloy steel of type 14MoV6-3 in as received state and after long term operation at 540 °C were compared. SP transition temperatures T_SP determined from the temperature dependences of the fracture energy were correlated with the FATT temperatures obtained using standardized Charpy V notch test specimens.

The presented paper is devoted to the study of hydrogen diffusion characteristics in the C-Mn-Si TRIP 800 steel. The steel was tested in three different states: in as-received state after hot and cold rolling and subsequent heat treatment; and furthermore after 5% and 10% tensile deformation. Hydrogen diffusion characteristics were studied by means of electrochemical permeation method. Two build up transients corresponding to lower and higher charging current densities as well as a decay transient were recorded during experiment. The lowest values of hydrogen diffusion coefficient (from 1.10^-7 to 3.5.10^-7 cm².s^-1) were observed during the first build up transient; the value of 3.5.10^-7 cm².s^-1 corresponded to 10% tensile deformation. During the 2^nd build up transient corresponding to the higher charging current density, hydrogen diffusion coefficients increased markedly reflecting thus the fact that hydrogen trapping was less pronounced. For decay transients hydrogen diffusion coefficients were situated between values obtained for the 1^st and 2^nd build up transients. In all studied states, rather high sub-surface hydrogen concentration was observed during the 1^st build up transient rising to 12.6 ppm of hydrogen in as-received state. The obtained results are explained taking into account steel microstructure and hydrogen trapping.

The non-reciprocity of magneto-optical reflection response by surface plasmon excitation in the planar Au/Fe/Au/glass nano-systems with prism coupling is studied. In order to simulate diffraction response to external magnetic field theoretical matrix model based on rigorous coupled waves algorithm is applied that allows to simulate both the influence of metallic layer thicknesses and external magnetic field. The two new response factors related to response function are introduced and tested from the point of view of their applicability. Obtained theoretical results are compared with experiment realized using the measuring device Multiskop (Optrel GbR, Germany).

Numerous WWER-440 steam generators showed a very serious problem of cracking in weld joints which are connecting primary collectors to the steam generator's vessel. As a cause of this cracking was determined stress corrosion cracking mechanism. The weld is connecting austenitic steel collector to the carbon steel vessel, so it is a dissimilar metal weld. There are two approaches how to lower the possibility of stress corrosion cracking in the weld. First one is to improve the secondary water chemistry in the weld's surrounding to stop the corrosion and second one is to decrease presented stresses in weld's area. It is better to combine both approaches. This paper deals with the second approach of possibilities to decrease presented stresses. Inspired by Russian study of external cooling on WWER-1000 steam generators, it was an attempt to adapt the external cooling idea on the WWER-440 steam generators and their problem of weld cracking. It was shown that by using the external cooling it is possible not just lower the presented tensile stresses but to change the tensile stresses into compressive stresses. This will of course result in significant reduction of stress corrosion cracking possibility in the steam generator primary collector weld's area.

Microstructure of the base metal, the multilayer welding seam and the two-layer cladding was characterized through the thickness of the WWER 440 reactor pressure vessel wall. Mechanical properties were determined by performing a series of instrumented indentations across the weld at room temperature. The results were treated by so-called automated ball indentation technique. Mechanical properties obtained by instrumented indentation from the local stress-strain behavior were compared with minimum values required by the standard.