K. Rodak

Phase Identification in Nickel-Based Superalloys Using EBSD/SEM and Electron Diffraction in STEM

Aero engine turbine blades made of nickel-based superalloys are critical components in flight safety. Therefore, it is very important to make sure that the chemical composition, phase composition and microstructure are suitable. However, due to their chemical compositions, superalloys are prone to many transformations and the formation of deleterious phases, which deteriorate the mechanical properties. Hence, investigations concerning the structural stability and phase identification—especially topologically close-packed phases (TCP)—are necessary. Because the volume fractions of these phases are generally small, phase identification should be performed by nanodiffraction techniques in a scanning transmission electron microscope (STEM) and electron backscatter diffraction in a scanning electron microscope (EBSD/SEM). These methods complement each other, but each of them is characterized by different difficulties and limitations. In this paper we present the possibilities and limitations of phase identification in single crystal CMSX-4 superalloy after long thermal exposure.

Microstructure and Mechanical Properties of Aluminum Processed by Multi-Axial Compression

. In this study, commercial Al was subjected to plastic deformation by multi-axial compression. The microstructure and mechanical properties in dependence on effective strain were studied. Aluminum was processed to effective strain f = 9.6. The misorientation distribution and subgrain/grain size were analyzed by using a scanning electron microscopy (SEM) equipment with electron back scattered diffraction (EBSD) facility. The dislocation microstructure was investigated by a scanning transmission electron microscope (STEM). The mechanical properties as: yield strength (YS), ultimate tensile strength (UTS), uniform and total elongation were performed on MTS QTest/10 machine equipped with digital image correlation method (DIC). Deformation of Al by the multi-axial compression leads to grain refinement to ultra-fine grains (UFGs) and improvement in strength properties. Material exhibits the following strength parameters: UTS: 129 MPa, YS: 124 MPa after deformation at f = 9.6. These values are about two times higher compared with initial state.

Effect of Compression with Oscillatory Torsion Processing on Structure and Properties of Cu

The results presented in this study were concerned with microstructures and mechanical properties of poly-crystalline Cu subjected to plastic deformation by a compression with oscillatory torsion process. Different deformation parameters of the compression with oscillatory torsion process were adopted to study their effects on the microstructure and mechanical properties. The deformed microstructure was characterized quantitatively by electron backscattered diffraction (EBSD) and scanning transmission electron microscopy (STEM). Mechanical properties were determined on an MTS QTest/10 machine equipped with digital image correlation. From the experimental results, processes performed at high compression speed and high torsion frequency are recommended for refining the grain size. The size of structure elements, such as average grain size (D) and subgrain size (d), reached 0.42 μm and 0.30 μm, respectively, and the fraction of high angle boundaries was 35% when the sample was deformed at a torsion frequency f = 1.6 Hz and compression rate v = 0.04 mm/s. These deformation parameters led to an improvement in the strength properties. The material exhibited an ultimate tensile strength (UTS) of 434 MPa and a yield strength (YS) of 418 MPa. These values were about two times greater than those of the initial state.

Microstructural studies of carbides in MAR-M247 nickel-based superalloy

Carbides play an important role in the strengthening of microstructures of nickel-based superalloys. Grain boundary carbides prevent or retard grain-boundary sliding and make the grain boundary stronger. Carbides can also tie up certain elements that would otherwise promote phase instability during service. Various types of carbides are possible in the microstructure of nickel-based superalloys, depending on the superalloy composition and processing. In this paper, scanning electron and scanning transmission electron microscopy studies of carbides occurring in the microstructure of polycrystalline MAR-M247 nickel-based superalloy were carried out. In the present work, MC and M23C6 carbides in the MAR-M247 microstructure were examined.

Study of Microstructure of the Al-Fe Alloys After Hot Rolling Deformation

The aim of the paper is a microstructure analysis of alloys from the Al-Fe system after hot rolling tests, conducted by using a scanning transmission electron microscopy STEM and scanning electron microscope equipped with EBSD detector. Hot rolling was carried out at Technical University of Ostrava, Faculty of Metallurgy and Material Engineering, Institute of Modelling and Control of Forming Processes. The samples were heated to a temperature of \(1200\,^{\circ }\)C. The EBSD and STEM techniques have been applied in order to determine the influence of chemical composition and deformation parameters on structural changes. The microstructure analysis has included parameters such us: grain/sub-grain size, area fraction of grains/subgrains, misorientation angles, grains/subgrains shape aspect ratio and dislocations structure. The research structure techniques in scanning-transmission electron microscopy revealed numerous FeAl28 alloy phase separations of secondary nucleating sites favoured energetically, which are the boundary of grains/subgrains and dislocations. These changes in the structure of the test results have been confirmed by EBSD, which revealed the presence of grains/subgrains misorientation angle boundaries above \(15^{\circ }\).

The Microstructure of AlSi7Mg Alloy in as Cast Condition

The complex microstructure of as-cast AlSi7Mg alloy has been investigated. Microstructure observations were done using light microscopy, scanning electron microscopy and transmission electron microscopy. Chemical composition of the microstructure constituents was investigated by means of energy dispersive spectrometry, conducted both during SEM and STEM investigations. Selected area diffraction was used to identify the phases in the alloy. Microstructure of the alloy in the as-cast condition consists of Al-Si eutectic and intermetallic phases in the interdendritic regions. These are: Mg2Si, α-AlFeMnS, β-AlFeSi and π-AlFeSiMg phases. What is more, number of fine precipitates were found within the α-Al dendrites. Only the occurrence of U1 (MgAl2Si2) phase has been confirmed.

Refinement of the Cu Structure by Oscillatory Compression Test

Polycrystalline Cu has been deformed at room temperature by oscillatory compression method to true reduction εh = 0.6 and 1. Microstructure by using transmission electron microscopy (TEM) and texture evolution after deformations was investigated. Oscillatory compressed microareas contains two distinctive regions: fine grains inside banded microstructure with large misorientation and surrounding matrix with submicrometer subgrains with a fraction of both low and high angle boundaries. Moreover nucleation of new grains under recrystallization takes place at the local-regions. The study of the crystal orientation distribution during applied deformation showed that the pole figure registered for the sample after compression shows ring of pole density, which concentrates around projection of <011>. Oscillatory compression causes formation of two axial texture components: <001> and <011>.

The microstructural characteristics of Al processed using severe plastic deformation procedures

The structure of Al is subjected to Severe Plastic Deformation (SPD) by means of compression with oscillatory torsion and by combined method: compression and next compression with oscillatory torsion (combined method I) and compression followed by annealing at 250?C/1 min with next compression with oscillatory torsion (combined method II). Al samples were deformed at torsion frequency (f), changed from 0 Hz (compression) to 1.6 Hz under a constant torsion angle (α) ≈6° and compression speed (v) = 0.1 mm/s. For combined methods, the samples were compressed for strain e = 0.7 and next deformed at mentioned parameters of compression with oscillatory torsion. The structural analysis shows that the processing by compression with oscillatory torsion ensures obtaining a structure (at selected parameters) with a mean grain size ≈1.6 µm. Combined methods of deformation lead to grain refinement to about ≈0.9 µm. Moreover, material with uniform Ultra-Fine Grained (UFG) microstructure was obtained. The microstructures contain high angle grain boundaries. Texture measurements reveal a weak texture after processing. [Received 11 April 2007; Accepted 26 July 2007]

Heat Treatment of CuFe2 and CuCr0.6 Alloys and the Effect of Precipitates on the Grain Refinement

The results of microstructure and hardness investigations of the CuFe2 and CuCr0.6 alloys after solution and ageing treatment are presented in this paper. The variants of heat treatment as: solution at 1000 ◦C per 3 h and ageing treatment at 500 ◦C for 2 h and at 700 ◦C for 24 h were chosen for severe plastic deformation process realized by rolling with the cyclic movement of rolls method. The structure of CuFe2 and CuCr0.6 alloys was analysed using scanning transmission electron microscopy, and the quantitative studies of the substructure was performed with MET-ILO software, on the basis of images acquired on scanning transmission electron microscope.

Strength–Energy and Structural Effects of Dynamic Deformation of Aluminum Alloy

This paper presents the results of dynamic deformation tests performed on aluminum alloy PA4. The studiem was carried out by using rotary hammer, in the range of high rate of deformation: 400 – 2000 s-1. The test were carried using a rotary hammer of RSO type owned by Silesian Technical University in Institute of Technology Metals. Before the dynamic deformation, the heating treatment was carried out allowed for eliminating structural effects resulting from the previous technological treatments and for obtaining the homogenous grain structure. The tests were carried out with linear velocity in the range of 5 – 30 m/s. After deformation the following mechanical characteristics were determined: deformation limit εg, strain rate , tensile strength UTS, impact strength U. Independently of the dynamic deformation tests were carried out tensile test under static conditions. Moreover bending test were performed on Charpy type hammer with initial impact energy equal 300 J. The analysis of the microstructure was carried out using scanning electron microscopy Hitachi S–3400 N.