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Open access

A. Kruk, G. Cempura, S. Lech and A. Czyrska -Filemonowicz

Abstract

Allvac 718Plus (718Plus) is a high strength, corrosion resistant nickel- based superalloy used for application in power generation, aeronautics and aerospace industry. The 718Plus microstructure consists of a γ matrix with γ’-Ni3(Al,Ti) and some δ- Ni3Nb phases as well as lamellar particles (η-Ni3Ti, η*-Ni6AlNb or Ni6(Al,Ti)Nb) precipitated at the grain boundaries.

The primary strengthening mechanism for this alloy is a precipitation hardening, therefore size and distribution of precipitates are critical for the performance of the alloy. The aim of this study was to characterize precipitates in the 718Plus superalloy using Scanning Transmission Electron Microscope combined with Energy Dispersive X-ray Spectroscopy (STEM-EDX) and Focused Ion Beam Scanning Electron Microscope (FIB-SEM). The STEM-EDX and FIB-SEM tomography techniques were used for 3D imaging and metrology of the precipitates. Transmission electron microscopy and EDX spectroscopy were used to reveal details of the 718Plus microstructure and allow determine chemical composition of the phases. 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

Open access

M. Pawlyta, K. Labisz and K. Matus

Abstract

Aluminium recycling is cost-effective and beneficial for the environment. It is expected that this trend will continue in the future, and even will steadily increase. The consequence of the use of recycled materials is variable and difficult to predict chemical composition. This causes a significant reduction in the production process, since the properties of produced alloy are determined by the microstructure and the presence of precipitates of other phases. For this reason, the type and order of formation of precipitates were systematically investigated in recent decades. These studies involved, however, only the main systems (Al-Cu, Al-Mg-Si, Al-Cu-Mg, Al-Mg-Si-Cu), while more complex systems were not analysed. Even trace amounts of additional elements can significantly affect the alloy microstructure and composition of precipitates formed. This fact is particularly important in the case of new technologies such as laser surface treatment. As a result of extremely high temperature and temperature changes after the laser remelting large amount of precipitates are observed. Precipitates are nanometric in size and have different morphology and chemical composition. A full understanding of the processes that occur during the laser remelting requires their precise but also time effectively phase identification, which due to the diversity and nanometric size, is a major research challenge. This work presents the methodology of identification of nanometer phase precipitates in the alloy AlSi9Cu, based on the simultaneous TEM imaging and chemical composition analysis using the dispersion spectroscopy using the characteristic X-ray. Verification is performed by comparing the simulation unit cell of the identified phase with the experimental high-resolution image.

Open access

Y. Matsuoka, K. Watanabe, J. Nakamura, W. Lefebvre, S. Saikawa, S. Ikeno and K. Matsuda

Abstract

In this study, the early stage of aging in Mg-Gd-Y alloys has been observed by transmission electron microscopy (TEM), high angle annular dark field – scanning transmission electron microscopy (HAADF-STEM) and calculations of images and electron density and bond overlap population (BOP) by first principal to understand the origin of precipitation in this alloy. The small hexagon of 0.37 nm is the first precipitate in this alloy, and this is the evidence of short range ordering of D019 structure. This is referred as the pre β”-phase. In the peak aged condition, β’ phase with bco structure was mainly observed.

Open access

M. Rozmus-Górnikowska and M. Blicharski

The aim of this work was to investigate the microsegregation and precipitates formed due to segregation in Inconel 625 arc weld overlay coatings on boiler pipes. Examination of microsegregation and precipitates were carried out by means of a scanning electron microscope (SEM) equipped with an EDS detector as well as a transmission electron microscope (TEM) equipped with a HAADF (STEM) and an EDS detectors. The presence of precipitations in the weld overlay was also confirmed with X-ray diffraction analysis (XRD) of residue in the form of powder that remained after the electrolytic dissolution of weld overlay matrix.

The investigations showed that the interdendritic regions were considerably enriched during microsegregation with Nb, and less so with Mo. The distribution of Cr and Fe in the weld overlay is relatively uniform. The value of the partition coefficient k for Mo and Nb is lower than 1. Therefore, these elements segregate during solidification into the liquid and, once solidification is finished, the interdendritic regions are considerably enriched with these elements. The value of k for Cr, Ni and Fe are only slightly higher than 1. Though the Inconel 625 is a solid-solution strengthened alloy, precipitation of secondary phases occurs in weld overlays. Precipitations were identified as a Laves phase and carbonitrides (Nb, Ti)(C, N).

Open access

A. Urbańczyk-Gucwa, K. Radwański and K. Rodak

Abstract

The effect of second phase particles on grain refinement in CuFe2 alloy has been investigated by using rolling with the cyclic movement of rolls (RCMR) method. Two different population of second phase particles of Fe: coherent, about 10 nm in diameter and about 100 nm in size were obtained by applying aging treatment followed at 500°C for 2 h and at 700°C for 24 h respectively. In addition, solution treated samples were deformed by RCMR method at the same parameters. The microstructures of the CuFe2 alloy were analyzed using light microscope (LM), electron backscattered diffraction (EBSD) microscope technique and scanning transmission electron microscope (STEM). The presence of high-density of coherent Fe particles in the matrix inhibits recovery process and in the result obtained grain/subgrain boundaries have diffused character and are weakly visible. The largest particles which are not coherent with the matrix act as an effective barrier against the boundary motion.

Open access

A. Kukuła-Kurzyniec, J. Dutkiewicz, P. Ochin, L. Perrière, P. Dłuzewski and A. Góral

In the present paper glass forming ability and structure of Al-Si-Ni based alloys were investigated. Three alloys starting from the ternary Al78Si12Ni10 [alloy 1], Al75Si12Ni8Zr5 [alloy 2] and Al73Si5Ni7Cu8Zr7 [alloy 3] were subjected to melt spinning process. The mean thickness of the obtained ribbons amounted between 25 and 40 μm. XRD and DSC studies showed predominantly amorphous structure of the ribbons. STEM and HRTEM methods confirmed participation of crystalline phase identified mainly as Al solid solution with the grain size near 10 nm. The mean microhardness [0.1N] of the ribbons was measured for alloys 1 - 3 respectively: 457 HV, 369 HV and 536 HV. The high value of hardness can be related to the presence of α-Al dispersoids in the amorphous matrix.

Open access

M. Rozmus-Górnikowska and M. Blicharski

Abstract

The aim of this work was to investigate the microstructure and chemical composition of the transition zone between 16Mo3 steel and Inconel 625 weld overlay coating produced by the Cold Metal Transfer (CMT) method. Investigations were primarily carried out through transmission electron microscopy (TEM) on thin foils prepared by FIB (Focus Ion Beam).

The chemical analysis demonstrated that the amount of certain elements (Fe, Ni, Cr, Mo, Nb) in the transition zone between the base material and the weld overlay changes quickly, from the composition of the steel to the composition of the composite zone. STEM and TEM investigations revealed that two areas are clearly visible in the transition zone. In the narrow band close to the fusion boundary where plates are clearly visible and the M s temperature is higher than room temperature, electron diffraction analyses show reflections of martensite and austenite. Moreover, the crystallographic relations between martensite and austenite can be described by the Kurdjumov-Sachs (K-S) relationship {110}α{111}γ<11¯1>α<11¯0>γ ). The microstructure of the part of the transition zone with an M s temperature lower than room temperature as well as that of the composite zone is austenite. The investigations proved that the width of the martensitic area can be significantly limited by using the CMT technique for weld overlaying.

Open access

K. Matus, M. Pawlyta, G. Matula and K. Gołombek

Abstract

The aim of this article of this paper is to present issues related to characterization of nanometric-sized carbides, nitrides and/or carbonitrides formed during tempering of carbide-steel cermets. Closer examination of those materials is important because of hardness growth of carbide-steel cermet after tempering. The results obtained during research show that the upswing of hardness is significantly higher than for high-speed steels. Another interesting fact is the displacement of secondary hardness effect observed for this material to a higher tempering temperature range. Determined influence of the atmosphere in the sintering process on precipitations formed during tempering of carbide-steel cermets. So far examination of carbidesteel cermet produced by powder injection moulding was carried out mainly in the scanning electron microscope. A proper description of nanosized particles is both important and difficult as achievements of nanoscience and nanotechnology confirm the significant influence of nanocrystalline particles on material properties even if its mass fraction is undetectable by standard methods. The following research studies have been carried out using transmission electron microscopy, mainly selected area electron diffraction and energy dispersive spectroscopy. The obtained results and computer simulations comparison were made.

Open access

A. Kruk and A. Czyrska-Filemonowicz

The development of innovative materials for clean energy systems and aeronautics requires use of modern research methods to characterize the structure on the level from micro- to nanoscale. Modern two-dimensional imaging techniques recently available in electron microscopes allow use of tomographic methods to characterize the structure of materials. Application of modern three dimensional imaging techniques such as electron tomography allows accurate qualitative and quantitative measurement of the structure elements in the micro- and nanoscale. The electron tomography studies have been carried out for three-dimensional visualization and metrology of different materials for clean energy systems and aeronautics. Electron tomography results provided quantitative data about shape, size and distribution of the particles, complementary to those obtained by means of quantitative TEM metallography.

Open access

M. Zygmunt-Kiper, L. Blaz and M. Sugamata

Abstract

Mechanical alloying of high-purity aluminum and 10 wt.% NiO powders combined with powder vacuum compression and following hot extrusion method was used to produce an Al-NiO composite. Mechanical properties of as-extruded materials as well as the samples annealed at 823 K /6 h, were tested by compression at 293 K - 770 K. High mechanical properties of the material were attributed to the highly refined structure of the samples. It was found that the structure morphology was practically not changed during hot-compression tests. Therefore, the effect of deformation temperature on the hardness of as-deformed samples was very limited. The annealing of samples at 823 K/6 h induced a chemical reaction between NiO-particles and surrounding aluminum matrix. As a result, the development of very fine aluminum oxide and Al3Ni grains was observed.