Crack Size and Undermatching Effects on Fracture Behavior of a Welded Joint.

Crack size and undermatching effects on fracture behavior of undermatched welded joints are presented and analyzed. Experimental and numerical analysis of the fracture behavior of high-strength low-alloyed (HSLA) steel welded joints with so-called small and large crack in undermatched weld metal and the base metal was performed, as a part of more extensive research previously conducted. J integral was determined by direct measurement using special instrumentation including strain gauges and a CMOD measuring device. Numerical analysis was performed by 3D finite element method (FEM) with different tensile properties in BM and WM. Results of J-CMOD curves evaluation for SUMITEN SM 80P HSLA steel and its weld metal (WM) are presented and analyzed for small and large cracks in tensile panels. This paper is focused on some new numerical results and observations on crack tip fields and constraint effects of undermatching and crack size keeping in mind previously performed experiments on the full-scale prototype. In this way, a unique combined approach of experimental investigation on the full-scale proto-type and tensile panels, as well as numerical investigation on mismatching and crack size effects, is achieved.

Development of Coated Electrodes with Solid Wire and Flux-Cored Alloyed Wire for Microalloyed Steel Welding.

In this paper, we will present our investigation of the quality of J55 microalloyed steel welds that were formed by a basic flux-cored wire electrodes that were of appropriate quality and alloyed with Ni and Mo. Based on the comparison and analysis of the obtained results related to the testing of the chemical composition, mechanical properties, toughness at test temperatures, and the microstructure of welding joints formed by a classic and specially coated rutile flux-cored electrode, we assessed the justification to switch from solid wire electrodes to flux-cored alloyed wire electrodes of appropriate quality. The research aim for the application of flux-cored wire electrodes instead of solid wire electrodes is based on the advantages pertaining to a flux-cored wire: molten metal from electrode wire is transferred in the form of fine droplets, easy welding and maximum productivity within all spatial positions related to welding, improved properties of welding joints, and increased productivity when compared to a classic solid wire. Our research encompasses the development of the experimental production at the Research and Development Center IHIS Belgrade (Development Institute for Chemical Power Sources), Serbia, of the new type of a coated electrode with improved welding properties when compared to a classic electrode intended for microalloyed steel welding.

Electrochemical and biocompatibility examinations of high-pressure torsion processed titanium and Ti-13Nb-13Zr alloy.

The purpose of this study was to estimate the electrochemical behavior and biocompatibility of ultrafine-grained (UFG) commercially pure titanium (CPTi) and Ti-13Nb-13Zr (TNZ) alloy obtained by high-pressure torsion process. Electrochemical behavior of materials in artificial saliva at 37°C was evaluated by potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS), and the obtained results indicated that UFG TNZ alloy showed corrosion current density (jcorr  = 53 ± 5 nA cm-2 ) which was 2 times lower compared to coarse-grained (CG) TNZ alloy (jcorr  = 110 ± 12 nA cm-2 ) and higher corrosion resistance, while UFG CPTi and CPTi showed approximately the same corrosion rate (mean jcorr ∼ 38-40 nA cm-2 ). Static immersion test in artificial saliva, performed in this study, showed that the released ion concentrations from UFG materials were more than 10 times lower than the permitted concentration (the highest released Ti ion concentration from UFG CPTi and UFG TNZ alloy was 1.12 and 1.28 ppb, respectively, while permitted concentration was 15.5 ppb). The in vitro cytotoxicity tests, as the initial phase of the biocompatibility evaluation, showed that the fraction of surviving cells in all examined materials was much higher compared to the control sample and hence demonstrated absence of cytotoxicity and an increase of fibroblast cells adhesion on UFG materials surfaces. UFG CPTi and UFG TNZ alloy can be considered as promising materials for applications in dentistry due to high corrosion resistance and outstanding biocompatibility which were shown in this study. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1097-1107, 2018.

Surface properties of magnetite in high temperature aqueous electrolyte solutions: A review.

Deposits and scales formed on heat transfer surfaces in power plant water/steam circuits have a significant negative impact on plant reliability, availability and performance, causing tremendous economic consequences and subsequent increases in electricity cost. Consequently, the improvement of the understanding of deposition mechanisms on power generating surfaces is defined as a high priority in the power industry. The deposits consist principally of iron oxides, which are steel corrosion products and usually present in colloidal form. Magnetite (Fe3O4) is the predominant and most abundant compound found in water/steam cycles of all types of power plants. The crucial factor that governs the deposition process and influences the deposition rate of magnetite is the electrostatic interaction between the metal wall surfaces and the suspended colloidal particles. However, there is scarcity of data on magnetite surface properties at elevated temperatures due to difficulties in their experimental measurement. In this paper a generalized overview of existing experimental data on surface characteristics of magnetite at high temperatures is presented with particular emphasis on possible application in the power industry. A thorough analysis of experimental techniques, mathematical models and results has been performed and directions for future investigations have been considered. The state-of-the-art assessment showed that for the characterization of magnetite/aqueous electrolyte solution interface at high temperatures acid-base potentiometric titrations and electrophoresis were the most beneficial and dependable techniques which yielded results up to 290 and 200°C, respectively. Mass titrations provided data on magnetite surface charge up to 320°C, however, this technique is highly sensitive to the minor concentrations of impurities present on the surface of particle. Generally, fairly good correlation between the isoelectric point (pHiep) and point of zero charge (pHpzc) values has been obtained. All obtained results showed that the surface of magnetite particles is negatively charged in typical high temperature thermal power plant water, which indicates the low probability of aggregation and deposition on plant metal surfaces. The results also gave strong evidence on decline of pHiep and pHpzc with temperature in the same manner as neutral pH of water. The thermodynamic parameters of magnetite surface protonation reactions were in good agreement with each other and obtained using one site/two pK and mainly one site/one pK model. All collected data provided evidences for interaction between particles, probability of deposition and eventual attachment to the steel surface at various pH and temperatures and can serve as a foundation for future surface studies aimed at optimizing plant performances and reducing of magnetite deposition. In future works it would be indispensable to provide the surface experimental data for extended temperature ranges, typical solution chemistries and metal surfaces of power plant structural components and thus obtain entire set of results useful in modeling the surface behavior and control of deposition process in power reactors and thermal plant circuits. Moreover, the acquired results will be applicable and greatly valuable to all other types of power plants, industrial facilities and technological processes using the high temperature water medium.