Quantitative description of the microstructure–porosity of sialons and iron silicide inclusions

Sialon ceramics are a modern type of engineering ceramics with excellent mechanical, thermal and corrosion resistant properties. This paper describes the structure characterisation of porous sialon ceramics. It is possible to significantly improve the strength and crack resistance of sialon ceramics as a result of a reduction of the volume fraction of porosity.     

A new method for measurement of earth fault loop impedance

A novel method for accurate and quick measurement of earth fault loop impedance in a low-voltage system is presented. The theoretical principle of the method is based on sampling of the tested circuit voltage at properly chosen moments. The method makes possible the simultaneous measurement of impedance, resistance, and reactance. The digital display is calibrated such that quantities can be read directly     

Multifractal detection of overlaps based on a stereometric analysis of fracture surfaces: Application to fractures of sintered carbides

A methodology is presented of a multifractal image analysis which was applied to real stereometric files from profilographometric examinations of the fractures of WC-Co sintered carbides. The analysis was conducted based on the research scheme and theoretical basis discussed in [Stach S, Cybo J. Multifractal detection of overlaps based on a stereometric analysis of fracture surface: assumptions, Materials Characterization (in this issue).[1]]. The solution presented enables the detection of the locations of overlaps on a fracture surface and their graphic presentation.     

Effect of Zirconium on the Structure and Congruent Crystallization of a Supercooled Calcium Aluminosilicate Melt

The influence of zirconium as a nucleating agent on the congruent crystallization and relevant physical properties of a supercooled calcium aluminosilicate melt of a composition close to CaAl₂SiO₆ has been investigated up to 6 mol% ZrO₂. Zirconium marginally affects rheological and structural properties, decreasing the viscosity of the Zr‐free melt by no more than 0.25 log unit and, as observed by Raman spectroscopy, not changing significantly the polymerization state of the material. Whereas the Zr‐free melt crystallizes congruently and heterogeneously from the sample surface to yield yoshiokaite, a stuffed derivative of the nepheline structure, addition of zirconia promotes instead bulk crystallization of tetragonal ZrO₂ and then of yoshiokaite. The latter process takes place in two stages: dissolved Zr first promotes homogeneous precipitation of zirconia before yoshiokaite crystallizes congruently from a Zr‐depleted volume of melt around zirconia precipitates. This process makes zirconium, and probably other poorly soluble oxides, valuable to control congruent crystallization in silicate glass‐ceramics. From the recorded thermograms, an enthalpy of crystallization of 40 and 46 kJ/mol has been determined at 1060 and 1140 K, respectively, for CaAl₂SiO₆ yoshiokaite, a very low value that is likely due to the extensive atomic disorder of crystals precipitating at high degrees of supercooling.     

A complex procedure for describing porosity in precision cast elements of aircraft engines made of MAR-M 247 and MAR-M 509 superalloys

An analysis of the quality assurance systems applied in industry for an assessment of porosity in precision cast parts of aircraft engines has shown that they characterize with a lack of repeatability or reproducibility of the test results obtained. For this reason, a comprehensive procedure of porosity assessment has been developed. It has been shown in the research described here that the procedure guarantees obtaining an unambiguous, full characterization of porosity as well as accurate and repeatable test results.     

Methodology of quantitative evaluation of porosity,dendrite arm spacing and grain size in directionally solidified blades made of CMSX-6 nickel alloy

Modern nickel-based alloys are constructional materials used in the production of parts of aircraft engines. The paper presents the results of studies of nickel superalloy CMSX-6 used for the manufacture of blades for turbojet engines. The scope of the study encompasses a development of a quantitative evaluation methodology regarding the blade's porosity and primary structure, as well as an analysis of the influence of the location of material sampled for the study on the results of a quantitative evaluation of the structure. Parallel columnar crystals, characteristic for a correct solidification process during directional crystallization, were detected on the surface of the product. It has been found that porosity of the investigated blades does not exceed 0.145%, which is a sufficient value to fulfil the acceptance requirements for casts. The transitory region between the blade root and airfoil is an area of the highest porosity. In addition, an influence of the size of the blade's plane cross-section on the spacing of dendrite secondary arms in the cast has been evidenced.     

Thermal elongations in steam turbines with welded rotors made of advanced materials at supercritical steam parameters

This paper presents research results obtained for supercritical steam turbines. The analysis aims to develop data, knowledge bases and procedures to support the operational control of these turbines. The control involves thermal and strength states of the main components. The thermal states and axial elongation in turbine rotors and casings are modeled, and the results are analyzed. The components under investigation are made of more than one material.     

Metal magnetic memory testing of welded joints of ferritic and austenitic steels

The method of the metal magnetic memory testing is a passive method of non-destructive testing based on the residual magnetic field (RMF) of a component. It allows the localization of stress concentration zones in the objects under examination. The defects in welded joints are places of stress concentration. Also, due to the geometric notch effect and thermal deformations after welding, the welded joint is a stress concentrator. Therefore, not all indications obtained in the method of the MMM testing are defects in the common, standard meaning. Additionally, in the weld seams of austenitic steels, the non-uniformity of delta ferrite in the joint results in changes in the RMF distribution and gives rise to indications. The paper presents the ways of examination and assessment of welded joints by means of the method of the MMM testing. The presented research methodology is the outcome of a synthesis of own experience and the provisions of standards ISO 24497-1, 2, 3: 2007. The results obtained in the MMM testing were compared to the results of the radiographic testing (RT). It was found that the MMM testing allowed the detection of imperfections, including defects, in welded joints at the production stage. Knowing the potential of the method of the MMM testing it seems well justified that it should be used in the examination of welded joints at the operation stage. These joints, after non-destructive testing at the production stage, are not free from defects. The defects, together with imperfections at the micro-level, concentrate stresses from working loads. Wear processes and the development of micro- and macro-cracks proceed in them the fastest. By finding the stress concentration zones, the areas of potential cracks can be found. The development of reliable procedures of examination and assessment of welded joints with the use of the method of the metal magnetic memory testing still needs a lot of research.