Adam Kruk

TEM, HRTEM, electron holography and electron tomography studies of γ′ and γ″ nanoparticles in Inconel 718 superalloy

The aim of the study was the identification of γ′ and γ″ strengthening precipitates in a commercial nickel‐base superalloy Inconel 718 (Ni‐19Fe‐18Cr‐5Nb‐3Mo‐1Ti‐0.5Al‐0.04C, wt %) using TEM dark‐field, HRTEM, electron holography and electron tomography imaging. To identify γ′ and γ″ nanoparticles unambiguously, a systematic analysis of experimental and theoretical diffraction patterns were performed. Using HRTEM method it was possible to analyse small areas of precipitates appearance. Electron holography and electron tomography techniques show new possibilities of visualization of γ′ and γ″ nanoparticles. The analysis by means of different complementary TEM methods showed that γ″ particles exhibit a shape of thin plates, while γ′ phase precipitates are almost spherical.

The 3D Imaging and Metrology of CMSX-4 Superalloy Microstructure Using FIB-SEM Tomography Method

STEM-EDX and FIB-SEM tomography studies have been carried out to visualize three-dimensional morphology of the γ’ precipitates in different zones of ex-service turbine blade made of CMSX-4 single crystal superalloy. The results allowed the three dimensional analysis of the changes in microstructure of blade as resulting of operating conditions. Tomographic reconstructions provided quantitative data about γ and γ’ phase shape, size and volume fraction. It was shown that FIB-SEM tomography technique is suitable for 3D reconstruction of the objects of 100 nm in size or even smaller and thus enables the accurate quantitative microstructural analysis of this superalloy.

Pore shape and size dependence on cell growth into electrospun fiber scaffolds for tissue engineering: 2D and 3D analyses using SEM and FIB-SEM tomography

Electrospun nanofibers have ability to boost cell proliferation in tissue engineered scaffolds as their structure remind cells extra cellular matrix of the native tissue. The complex architecture and network of nanofibrous scaffolds requires advanced characterization methods to understand interrelationship between cells and nanofibers. In our study, we used complementary 2D and 3D analyses of electrospun polylactide-co-glycolide acid (PLGA) scaffolds in two configurations: aligned and randomly oriented nanofibers. Sizes of pores and fibers, pores shapes and porosity, before and after cell culture, were verified by imaging with scanning electron microscopy (SEM) and combination of focus ion beam (FIB) and SEM to obtain 3D reconstructions of samples. Using FIB-SEM tomography for 3D reconstructions and 2D analyses, a unique set of data allowing understanding cell proliferation mechanism into the electrospun scaffolds, was delivered. Critically, the proliferation of cells into nanofibers network depends mainly on the pore shape and pores interconnections, which allow deep integration between cells and nanofibers. The proliferation of cells inside the network of fibers is much limited for aligned fibers comparing to randomly oriented fibers. For random fibers cells have easier way to integrate inside the scaffold as the circularity of pores and their sizes are larger than for aligned scaffolds. The complex architecture of electrospun scaffolds requires appropriate, for tissue engineering needs, cell seeding and culture methods, to maximize tissue growth in vitro environment.

Characterization of the μ and P phase precipitates in the CMSX‐4 single crystal superalloy

A combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning‐transmission electron microscopy (STEM) using high‐angle annular‐dark‐field (HAADF) imaging, focussed ion beam‐ scanning electron microscopy (FIB‐SEM) tomography, selected area electron diffraction with beam precession (PED), as well as spatially resolved energy‐dispersive X‐ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), was used to investigate topologically close‐packed (TCP) phases, occurring in the CMSX‐4 superalloy subjected to high temperature annealing and creep deformation. Structural and chemical analyses were performed to identify the TCP phases and provide information concerning the compositional partitioning of elements between them. The results of SEM and FIB‐SEM tomography revealed the presence of merged TCP particles, which were identified by TEM and PED analysis as coprecipitates of the μ and P phases. Inside the TCP particles that were several micrometres in size, platelets of alternating μ and P phases of nanometric width were found. The combination of STEM‐HAADF imaging with spatially resolved EDS and EELS microanalysis allowed determination of the significant partitioning of the constituent elements between the μ and P phases.

Application of Analytical Electron Microscopy and Tomographic Techniques for Metrology and 3D Imaging of Microstructural Elements in Allvac® 718Plus™

The development of innovative materials for aeronautics requires use of modern research methods to characterize their structure on the level from micro- to nanoscale. Allvac® 718Plus™ (718Plus) is a relatively new nickel-based superalloy that has high strength, is corrosion resistant and has improved higher temperature performance compared to the 718, while retaining the excellent processing characteristics of this alloy. The aim of this study was the application of analytical electron microscopy and tomographic techniques to perform the qualitative and quantitative characterization of structural elements in the wrought and cast 718Plus. Determination of crystallographic structure of selected phases was performed using electron diffraction method supported by JEMS software. 3D imaging of microstructural elements and chemical compositions of selected phases were performed using STEM-EDX tomography technique using a probe Cs corrected Titan3 G2 60-300 with ChemiSTEM™ system. Tomographic reconstruction was performed using Simultaneous Iterative Reconstruction Technique (SIRT) method on a tilt series, which allowed visualizing the three-dimensional distribution of selected elements (Al, Cr) in the analysed volume. The shape and distribution of γ′ particles in the reconstructed volume, as well as complex particle composition of η-phase were analyzed using STEM-EDX and FIB-SEM tomography techniques. 3D imaging of precipitates in the interdendritic region (Laves and η phases) was performed using FIB-SEM tomography technique. The 3D visualization of reconstructed space was performed using ImageJ and Avizo Fire software. The study showed that advanced microscopic techniques and test methods in conjunction with tomography technique permits to obtain complementary information about the microstructure of 718Plus superalloy.

Application of analytical electron microscopy and FIB-SEM tomographic technique for phase analysis in as-cast Allvac 718Plus superalloy

Abstract The superalloys are usually used as structural material in jet engines due to their high-temperature stability and good endurance. Many components found in the hot-part of jet engines are of complex shape, therefore casting is utilized for to their production. One of the problems associated with the casting process of highly alloyed alloys, such as superalloys, is partitioning of alloying elements upon solidification. This segregation might lead to the formation of low melting temperature eutectics. Their presence in the material microstructure will have a negative effect on the weldability. Negative impact on weldability is one of the reasons why secondary phases should be avoided as microstructural elements in the welded materials. To eliminate such hazardous phases, the material should be subjected to a heat treatment with the aim of homogenizing the microstructure and chemical composition, which should enhance the weldability. The aim of this work was the application of analytical electron microscopy in combination with energy dispersive X-ray spectroscopy as well as tomographic techniques for qualitative and quantitative characterization of structural elements in as-cast Allvac 718Plus Ni-based superalloy subjected to later heat treatment. Alloy 718Plus is a newly developed superalloy in which the secondary Laves phase forms as a low-melting eutectic upon casting. The development of innovative materials for aeronautics and clean energy systems requires the use of modern research methods for structure characterization on the level from micro- to the nanoscale. The performed analysis, allowed identification of phases (Laves and η) occurring in interdendritic regions of as-cast Allvac 718Plus superalloy and analyzing their microstructure down to the atomic scale, which revealed their complex nature. The experiments and investigation show that advanced microscopic techniques and test methods in conjunction with tomographic techniques enable complementary information about solidified structures of the alloy to be obtained that can be useful for the understanding process of casting and welding of the Allvac 718Plus.

Microstructure of an oxide scale formed on ATI 718Plus superalloy during oxidation at 850 °C characterised using analytical electron microscopy

Abstract The microstructure of a scale formed on the ATI 718Plus superalloy during oxidation at 850 °C for up to 1 000 h in air was characterised using various electron microscopy techniques taking advantage of recent development and capabilities of energy dispersive X-ray spectrometry. The study shows that a protective multilayered Cr2O3 scale was formed on this alloy; the outer Cr2O3 layer was coarse-grained, while the inner one was fine-grained. Underneath, a thin layer composed of TiNbO4 as well as an internal oxidation zone that was a dozen or so micrometres thick and consisted of individual Al2O3 precipitates had formed. The growth of the Cr2O3 layer caused the appearance of a chromium depletion zone, in which the γ′ particles were not observed.

The 3D Imaging and Metrology of Microstructural Elements in Innovative Materials for Clean Energy Systems and Aeronautics

The aim of this study was presentation the results of new tomographic techniques application to characterize structural elements in nickel-based superalloys for disc and blades using in aircraft engines and gas turbines in energy systems. Visualization of phases presented in as-service high chromium creep resistant steel for modern power plant applications was also performed using STEM-EDX and FIB-SEM electron tomography. Electron tomography (STEM-EDX) and FIB-SEM tomography were used for 3D imaging and metrology of the precipitates. Transmission electron microscopy and TEM-EDX spectroscopy were used to reveal details of the superalloys and steel microstructures and phases’ chemical compositions. The study showed that electron tomography techniques permit to obtain complementary information about microstructural features (precipitates size, shape and their 3D distribution) in the reconstructed volume with comparison to conventional particle analysis methods, e.g. quantitative TEM and SEM metallography.

Characterization of microstructure and mechanical properties of electron beam welded Allvac 718Plus butt welded joint

Allvac 718Plus (718Plus) is a high strength, corrosion resistant commercial polycrystalline nickel-based superalloy developed by ATI ALLVAC over 10 years ago. 718Plus has been designed to fuse the most desired properties of Inconel 718 and Waspaloy, producing advantages of good mechanical properties, higher working temperature than Inconel 718, good fabricability and reasonable cost of production. 718Plus is strengthened by γʹ phase and other precipitates which are located mainly at grains boundaries. Compared to Inconel 718, 718Plus has increased concentration of Al, Ti and Co and decreased amount of Fe. Weldability of 718Plus is comparable to Inconel 718, thus there is a risk of intergranular microcracking in heat affected zone (HAZ). The test joint have been welded autogenously using electron beam at 120 kV accelerating voltage, 10 mA current and 78 cm/min welding speed. The microstructure of casted base material, heat affected zone (HAZ) and weld metal of electron beam welded 718Plus were investigated by means of light (LM) and scanning electron microscopy (SEM). SEM observations of welded joint microstructure were performed using secondary electrons (SEM–SE). SEM/EDS analysis were carried out. Both MC type carbides and Laves phase were observed in interdendritic regions of base material. The microstructure of heat affected zone was composed of γ matrix, γʹ phase and MC-type carbides, Laves phase and Laves/γ eutectic. In weld metal zone no γʹ precipitates were observed. The microhardness measurements have shown a decrease in weld metal and HAZ. It can be caused by an influence of the welding process thermal cycle.

Pad Welding of Inconel 625 Layer on Structural Steel Used in the Power Industry

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.