Solid State Phenomena Vol. 231

Abstract: The microstructure of magnesium alloys containing 1% and 2.5% Mg, as well as the addition of 6% Zn and 0.6% Zr was examined in as-cast and as-extruded condition. After the casting process, the presence of Mg₂Ca and Ca₂Mg₆Zn₃ phases was determined by means of the scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The microstructure of MgCa0.8Zn6.1Zr0.6 and MgCa2.8Zn6.1Zr0.6 alloys after the extrusion process revealed an impact of Zr addition on grain refinement. The electron backscatter diffraction (EBSD) analysis showed that, among all the tested alloys, the smallest grain size was found in the MgCa2.8Zn6.1Zr0.6 alloy and the mean grain diameter amounted to about 4 mm. The analysis of texture has indicated that the lattice planes most often parallel to the cross-sections of the examined magnesium rods are the crystal lattice planes (1 0-1 0).

Abstract: The study presents the results of microstructure examinations and phase identification of precipitates in AlMn alloys containing zirconium after heat treatment and rolling. Chemical composition in microareas was determined by Energy Dispersive Spectrometry (EDS) microanalysis performed in Scanning Electron Microscope (SEM-EDS) and Scanning Transmission Electron Microscope (STEM-EDS) modes. Phase identification was carried out using Electron Backscatter Diffraction (EBSD) method. Studies have shown that Al₆Mn and α- Al₁₇(Fe_3.2Mn_0.8)Si₂ phases were formed in the melt. Microstructure examined by TEM showed the presence of finely dispersed spherical precipitates of zirconium. In the alloy with an addition of silicon and magnesium, numerous precipitates of an Mg₂Si phase were also found.

Abstract: The growth morphology and arrangement of tungsten and β-phase (Al (Fe, Cu)) in Al‑Cu‑Fe‑W alloy were analyzed. The composition of Al₆₅Cu₂₀Fe₁₄W₁ (at.%) was used for preparation of ingots containing the icosahedral quasicrystalline phase.The ingots were obtained in a two-stage process. At the first stage the induction melting of the elements and preliminary homogenization by mechanical mixing were carried out. The second stage was realized by vertical Bridgman technique of directional crystallization. The X-ray phase analysis, optical and scanning electron microscopy (SEM) observations and chemical analysis were performed. It was stated that the whiskers of tungsten were irregularly distributed in the volume of ingots. They often form a clump-like agglomerations. The whiskers have different diameters and length. Minimal diameter of the whiskers was about 10 – 100 nm and maximal – several dozen micrometers. The whiskers of tungsten formed a clump-like frames on which the membrane form of β-phase was stretched out or a non-planar oval forms.

Abstract: The microstructural characterization of butt friction stir welds of two different wrought aluminum alloys (work-hardened and heat treated) were studied. The detailed studies on the FSW process of dissimilar Al alloys are limited. In particular, the weld microstructure requires deeper characterization to better understand the phenomena occurring during mixing of dissimilar alloys.The characterization of friction stir welds was performed by scanning electron microscopy (an energy dispersive spectroscopy and an electron backscattered diffraction) and transmission electron microscopy. The dissimilar weld microstructure is complex, resembling a vortex-like structure. The microstructure of weld was highly asymmetrical with regard to the weld centerline. The research revealed a change in grain size in particular areas of the stirred zone. Recrystallization in the stirredzone occurred in particular areas in an irregular manner.

Abstract: 7CrMoVTiB10-10 (T24) steel is recommended for fabrication of boiler components such as water walls, water panels or headers without post weld heat treatment (PWHT). The chemical composition of this steel and cooling conditions after welding influence the susceptibility to cracking in weld metal during and after welding. TEM investigations showed that in the as-welded microstructure mixtures of bainite and martensite were dominating. This has an important implication for technological properties.

Abstract: Due to aggressive gases produced during combustion process of biomass, some elements of the power boiler should be covered with a material that possesses very high corrosion resistance (e.g. Inconel 625). This paper presents results of microstructural studies of Inconel 625 padding weld on waterwall elements (made of 13CrMo4-5 steel) for steam boiler designed for biomass combustion. The microstructural studies were carried out using Scanning- as well as Transmission Electron Microscopy methods. The padded weld layer exhibited dendritic structure. In the weld layer γ phase with an increased dislocation density and stacking faults was observed. In the base material (13CrMo4-5 steel) titanium nitrides, complex carbides and Laves phase enriched in niobium were observed.

Abstract: The investigation was focused on the microstructure characterization as well as changes in chemical composition and hardness of water wall tubing weld overlaid with Inconel 625. The analysis comprised studies in a light and electron microscopy scale that included the evaluation of weld overlays microstructure and microsegregation of alloying elements across the overlay and base metal interface. The particular attention was turned to the distribution of the main element content (Fe, Ni, Mo, Nb, Cr) in the base metal fusion zone as well as in the weld overlay itself. It was shown that the solidification process resulted in significant segregation in alloying elements giving rise to the substantial differences in chemical composition between dendrite cores and interdendritic spaces. It is believed that the microsegregation together with precipitation of secondary phases may contribute to the deterioration of corrosion resistance and overall mechanical properties of weld overlay including ductility and fracture toughness.

Abstract: Ni-base alloys, like Inconel 625, exhibit a high temperature corrosion and oxidation resistance. For this reason, these alloys are typically used as a one of the most important coating material and can be applied in a different environments and elements of devices having various applications. In this work, Inconel 625 was deposited onto a carbon steel P235GH by Cold Metal Transfer method. Due to the segregation of Ni, Cr, Nb and Mo elements the Inconel 625 weld overlays cladded on boiler pipes P235GH obtained the dendritic structure, with the formation of a second phases at the end of solidification. The presence of γ (with high dislocation density), the Laves and (Nb,Ti)C phases was revealed by means of TEM examinations. The multipoint EDS analysis confirmed the presence of low Fe concentration in the Inconel 625 alloy coatings. The concentration profiles of Ni, Cr, Mo and Nb performed across the dendritic structure showed segregation of these elements.

Abstract: The results of a microstructure, energy dispersive X-ray spectroscopy (EDS) analysis and hardness investigations of the hypoeutectoid steels with 1% Ni, imitating by its chemical composition toughening steels, are presented in the paper. According to PN-EN 10027 standard this steel should have a symbol 37NiMo4-3.The kinetic of phase transformation of undercooled austenite of investigated steel was presented on CCT diagram (continuous cooling transformation). The CCT diagram of tested steel is characterized in that the curves of beginning of the diffusion transitions form a letter "C" and are not separated from bainitic transformation by the stability range of the undercooled austenite.The EDS analysis performed for the selected cooling rates did not reveal any changes in the distribution of alloying elements of hypoeutectoid 37NiMo4-3 steel. However, these studies, from the point of view of the effect of alloying elements (acting jointly) are only the preliminary assessment analysis (beginning) of the impact of the chemical composition gradient in micro-scale in iron-based alloys.

Abstract: The turbine wheel is the most affected element in passenger car turbochargers. In order to meet the requirements for the high temperature corrosion, vibrations and the mechanical resistance in the oxidizing environment of the exhaust gases, the turbine wheel is produced from polycrystalline nickel based superalloys, Inconel 713C in the as-cast condition. In this work the methods and results of turbine wheel failure analysis are presented. For this type of research, correlative microscopy, light microscope Axio Imager Z2m (LM), scanning electron microscope Zeiss Ultra Plus with field emission (FESEM) equipped with EDX detector and stereoscopic microscope were used. The results of this work suggest that the Inconel 713C turbine wheel was damaged by two factors: fatigue cracking at low frequencies and grain boundaries oxidation.