Fracture mechanical investigation of steel grade S890 used in Cleuson–Dixence hydropower plant shaft

Abstract

As a consequence of the accident at the Cleuson–Dixence hydropower plant in December 2000, several investigations were started. In a material qualification programme for the steel S890, as applied in the Cleuson–Dixence plant, strength investigations and small scale fracture mechanic tests in weld metal, heat affected zone and base metal have been performed. Additionally, wide plate tests were performed to verify the results. With the obtained material properties, a fracture mechanics assessment of the critical crack size of the shaft in the area of the pipe rupture was performed using the R6 procedure. This procedure was verified for the given conditions, i.e. material strength and toughness including the welding quality, by the comparison of the calculational and experimental results of the tested wide plates with cracks in base metal and weld metal.     

High speed fusion weld bead defects

Abstract

A comprehensive survey of high speed weld bead defects is presented with strong emphasis on the formation of humping and undercutting in autogenous and non-autogenous fusion welding processes. Blowhole and overlap weld defects are also discussed. Although experimental results from previous studies are informative, they do not always reveal the physical mechanisms responsible for the formation of these high speed weld bead defects. In addition, these experimental results do not reveal the complex relationships between welding process parameters and the onset of high speed weld bead defects. Various phenomenological models of humping and undercutting have been proposed that were based on observations of events in different regions within the weld pool or the final weld bead profile. The ability of these models to predict the onset of humping or undercutting has not been satisfactorily demonstrated. Furthermore, the proposed formation mechanisms of these high speed weld bead defects are still being questioned. Recent welding techniques and processes have, however, been shown to be very effective in suppressing humping and undercutting by slowing the backward flow of molten metal in the weld pool. This backward flow of molten weld metal may be the principal physical phenomenon responsible for the formation of humping and undercutting during high speed fusion welding.     

Microbial Corrosion Hazard in Fuel Storage Tanks in the Presence of Corrosion Inhibitors

Abstract

Tests were carried out in five light fuel oil storage tanks placed outdoors in the vicinity of Stockholm, Sweden, to study the effectiveness of some commercially available corrosion inhibitors in the presence of certain micro-organisms. Corrosion in the aqueous phase caused by Desulphovibrio desulphuricans, Thiobacillus ferro-oxidans and Cladosporium resinae was effectively stopped by the addition of a sodium nitrite-sodium tetraborate mixture, but was enhanced by each of three commercial oil-soluble inhibitors. In some cases the corrosion rate exceeded 3 mm/year. The results are of a preliminary nature, but give cause for alarm and suggest the need for further investigation.     

Engineering An Experimental Platform For High Throughput Reactivity Screening

The genomics revolution coupled to advances in computational power, informatics and robotics is driving drug discovery programs to produce drug candidates faster. This need has resulted in advances in high throughput methods for performing organic chemistry such as combinatorial and parallel synthesis. Yet there has not been a corollary advance in the ability to collect quantitative information on reactions that can be used to produce these drug candidates. This lack of an efficient and robust analytical method has resulted in a significant chemistry bottleneck. This work outlines a set of methods that helps address this chemistry bottleneck by using analytical constructs to detect and quantify reaction outcomes. To accomplish this, an integrated experimentalcheminformatics platform has been developed which couples an experimental design system, automated high throughput parallel and combinatorial synthesis methodology, sample processing, quantitative mass spectroscopy and automated data analysis. This platform is being used to optimize single reactions and the syntheses of whole libraries of compounds, and to generate large databases on specific reaction classes.     

Flexible and Scalable Automation Solutions For Scoring Single Nucleotide Polymorphisms Using Rolling Circle Amplification

A single nucleotide polymorphism (SNP) scoring assay that uses ligation-dependent Rolling Circle Amplification (RCA)† was transferred to a series of automated protocols addressing a range of throughput levels. The systems utilised various automation modules consisting of custom-made and offthe-shelf devices. Several system parameters were evaluated to ensure assay integrity and homogeneity. These included reagent carry over, liquid evaporation rates, thermal regulation of reactions and fluorescence reading capabilities.Data analysis software was developed in order to rapidly allocate SNP calls from data generated by the automated system. A modified fuzzy c -means clustering algorithm was employed to separate data points into groups associated with specific genotypes. Data were then presented graphically and within a summary table, which allowed easy and rapid organization and interpretation of data.     

Orientation relationship transition of nanometre sized interphase precipitated TiC carbides in Ti bearing steel

Abstract

The objective of the present study was to investigate the crystallography and morphology of TiC particles in a titanium containing high strength low alloy (HSLA) steel that form during isothermal transformation at a temperature in the (α + γ) phase field. The orientation relationships (ORs) were identified from selected area diffraction patterns (SADPs) and from moire fringes in high resolution transmission electron microscopy (HRTEM) lattice images. It was found that in the initial stages of the isothermal transformation, fine plate-like TiC particles develop and that these exhibit the Baker–Nutting (BN) OR with respect to the ferrite matrix. In the later stages of the transformation, however, coarser plate-like carbides are observed, and these adopt approximately the Nishiyama–Wassermann (NW) OR with respect to the ferrite matrix. The evidence indicates that OR transition is brought about simply by aging for a longer time at the transformation temperature, and also manifests a rotation of the precipitate during coarsening.     

Microstructure evolution and mechanical properties of nickel based honeycomb sandwich

Abstract

A nickel based superalloy honeycomb sandwich was manufactured by high temperature brazing. The microstructure evolution and the out of plate mechanical properties were investigated for honeycomb sandwiches aged at 1000&degC in the present paper. The maximum tensile stress was 28·5 MPa and the compressive yield strength was 29·6 MPa for the original specimens. These parameters decreased to 22·9 and 20·5 MPa for specimens aged for 2 h, to 18·2 and 12·2 MPa for specimens aged for 5 h and to 20·2 and 14·3 MPa for specimens aged for 10 h respectively. With increasing aging time the tensile elongation decreased, the intermetallic compounds and the eutectic structure in the brazing region disappeared, and the solid solution approaching the matrix gradually increased.     

Dwell time effect on fatigue crack growth of RR1000 superalloy

Abstract

The requirement for improved understanding of the behaviour of turbine disc alloys at elevated temperatures has led to an increased interest in the contribution of time dependant mechanisms to high temperature fatigue crack growth. A study has been conducted on a new powder alloy to investigate the contribution of such mechanisms when the applied waveform is varied in terms of hold periods and the influence of limited thermal exposure is included. Variable waveform tests performed in air at 725°C have indicated that the addition of a hold time at maximum load in a fatigue cycle tends to increase the crack growth rate per cycle in the as heat treated material. Crack growth in thermally exposed material is retarded by up to a 10 s hold time and then accelerated as the hold time increases further. Rapid near crack tip stress relaxation induced by γ′ coarsening is proposed to have a beneficial effect on the severity of this type of damage which causes the crack growth rate reduction for short hold times.     

Microstructure and properties of AlTiNiMnBx high entropy alloys

Abstract

AlTiNiMnB _x (x=0˙1, 0˙2, 0˙4 and 0˙5) high entropy alloys are prepared by an arc furnace. The results show that the alloys have a single bcc crystal structure. Boron additions lead to distortion of the crystal lattice and alloy strengthening. The highest hardness (779 HV) is achieved with 0˙5 at.-%B.     

Densification and microstructural evaluation during laser sintering of M2 high speed steel powder

Abstract

In the present work, the densification and microstructure of M2 high speed steel powder processed by direct laser sintering method was studied. Test specimens were produced using a 200 W continuous wave CO₂ laser beam at different scan rates ranging from 50 to 175 mm s^?1. The building process was performed under argon and nitrogen atmospheres in order to evaluate the role of sintering atmosphere. It was found that the sintered density strongly depends on the laser scan rate and thus on the duration time of the laser beam on the surface of the powder particles. Generally, with a decrease in the scan rate higher densification was obtained. However, formation of large cracks and delamination of the sintered layers is feasible at low scan rates. The results also demonstrated that sintering under argon atmosphere yields better densification compared to a nitrogen atmosphere, in particular at higher scan rates. The microstructure of laser sintered parts consisted of large and elongated pores parallel to the building direction. The metal matrix structure was found to be heterogeneous, i.e. carbon rich austenite was formed due to carbon segregation. This structure consisted of fine cellulars or dendrites of martensite and retained austenite. This article describes the influence of manufacturing parameters on the densification of laser sintered M2 high speed steel powder. The microstructural features of the processed parts are also addressed.