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Some applications of electron microscopy in the aircraft industry
Science Centre, Nijenborgh 18, AG Groningen, The Netherlands
9747
The superalloy Ma 6000 E is a Ni-base alloy developed for high creep resistance at intermediate as well as at high temperatures. The alloy has a complex composition being strengthened with several solid solution additions, y' precipitates for intermediate temperature strength and inert yttria for extreme elevated temperature creep resistance. The volume fraction of the y' (Ni3Al) precipitates is approximately 50% and their size about 0.2 pm in diameter. The yttriumoxide (Y2O3) volume fraction is 2.9% with an average particle size of 28 nm. Precipitates in an as received sample, deformed in tension to rupture at 760°C, are identified with an energydispersive X-ray system (EDS). Dislocation structures are studied using a 200 kV transmission electron microscope (JEM 200 cx). It is expected that dislocations bypass the yttriumoxide particles by looping, whereas y' precipitates can be bypassed either by loopinq or shearing. With increasing temperature dislocations will tend to climb rather than form coplanar Orowan loops around the particles. The experimental results are compared with predictions based on a model calculation for the critical particle diameter where cutting is taken over by looping.
THE INTERACTION BETWEEN DISLOCATIONS AND PRECIPITATES IN Al-Li ALLOYS STUDIED BY TEM A. J. Huis In 'T Veld, K. Hemmes, P. M. Bronsveld, G. Boom and J. Th. M. De Hosson Department of Applied Physics, University of Groningen, Materials Science Centre, Nijenborgh 18, 9747 AG Groningen, The Netherlands
In this paper, a transmission electron microscopic study of the mechanism of dislocation motion in Al-2.2 wt% Li is presented. TEM micrographs were taken using a JEM 200 CX operating between 120 and 160 keV. In order to obtain precipitates of different size, ageing times were varied from 1 hr to 115 hrs, and the ageing temperatures ranged between 200 and 245OC. Particle size distribution and volume fraction were determined using stereo-transmission electron microscopy. The increase in yield stress as a function of the experimentally determined particle size distribution and volume fraction can be predicted based on theoretical models.
FROM BLANK TO CAN-THE ORIGIN AND GROWTH OF THE MORPHOLOGY OF THE WALL OF A DWI CAN W. Van Koesveld and J. Schade Van Westrum Hoogovens groep bv, IJmuiden, Research and development, product technology
An extensive study of the morphology of the wall of the two-piece drawn and wall-ironed (dwi-) can has been made by both SEM and EPMA. Both the topography and the distribution of tin on the inner and outer sides of the wall could be logically explained as a product of the various stages in the forming process of the can. It is suggested that the mechanical properties of the steel base and those of the coating material have a strong influence on the resulting properties of the can wall.
SOME APPLICATIONS OF ELECTRON COPY IN THE AIRCRAFT INDUSTRY A. Kwakernaak
The basic strengthening mechanism of aluminium-lithium alloys is due to the formation of coherent 6' precipitates The addi(ordered Li2 phase A13Li). tion of Li to Al results in a reduction of density and an increased modulus of elasticity compared with conventional aluminium alloys. Consequently, the development of Al-Li alloys is highly desirable for structural applications, especially in aerospace industry.
and J. J. V. Konig
Technological
Schiphol,
MICROS-
The
Centre, Fokker Netherlands
b.v.,
Important applications of electron microscopy in the aircraft industry are the characterization of surfaces after chemical pretreatments and the study of fracture surfaces of aircraft parts. Transmission electron microscopy was used to study the structure of
Early work oxides on aluminium alloys. gave an indication of the importance of oxide morphology on adhesion. From parameter studies with variations in, e.g., electrolytes, solution temperatures and treatment times, correlations were found between oxide morphology and adhesion. Fractography plays an important role in the investigation of material behaviour under experimental and operational conditions. Determination of the modes and causes of fractures is important in order to detect shortcomings in the selection of materials, the design, the fabrication practice and the maintenance of aircraft parts.
FROM SHOWROOM TO SCRAP: XMA/AES INVESTIGATION OF CORROSION PROCESSES UNDER PAINT COATINGS W. J. Van Ooij
and T. H. Visser
Akzo Research, Corporate Department, Arnhem, The
Research Netherlands
In X-ray microanalysis the need for additional information on the surface composition of the material under investigation is often felt. Conversely, the surface analyst frequently wants to compare his data with bulk compositions. Both can be achieved by combining X-ray microanalysis and Auger electron spectroscopy in one instrument. In this study it is demonstrated that both techniques are almost ideally complementary and synergistic. As an example the corrosion reactions that take place in the interfacial zone between paint coatings and steel surfaces during artificial or natural weathering are discussed.
ANALYSIS NITRIDED
OF SURFACE STEEL
D. Schalkoord
LAYERS
ON
and E. J. Mittemeijer
Laboratory of University of Rotterdamseweq The Netherlands
Metallurgy, Technology, 137, 2628
Delft AL
Delft,
Nitriding of steels is applied to improve the fatigue resistance and/or the tribological and anti-corrosion properties. For an understanding of the property changes induced by nitriding a descrip-
tion of the nitrided structure is recharacterization quired: morphological is frequently performed using the light the lattice distortions can microscope, be analyzed by X-ray diffraction methods, and the nitrogen concentration profiles can be determined by X-ray The latter analysis is microanalysis. performed using a specially prepared -r'-FedN specimen as a nitrogen standard; for quantification of the measured nitrogen K, k-ratios several correction procedures are compared. By the combination of light-microscopical techniques and X-ray microanalysis the constitution of the (dominant) two-phase outer layer built during the nitriding process can be revealed. In the diffusion zone adjacent to the outer layer relatively large nitrogen contents are measured which are ascribed to lattice strain provoked by the misfit between precipitates and The association between atoms matrix. of the alloying elements (e.g. chromium, originally present in carbides) and nitrogen atoms leads to carbide precipitation at grain boundaries in the diffusion zone and to a carbon-rich zone ahead of the diffusion zone.
TEM STUDIES OF ELECTRO-CERAMIC INTEGRATED CIRCUIT MATERIALS
AND
M. P. A. Viegers Philips 5600 JA
Research Eindhoven,
Laboratories, The Netherlands
Some recent studies of ceramic capacitors and integrated circuits are presented. The particular examples dealt with concern: --SrTi03 boundary layer capacitor material: It is prepared by the addition of Bi203 to prefired SrTi03 matrix material. In this way one obtains semiconductive grains, separated by an insulating layer. Since the actual capacitance is located at the grain boundaries, the nature of the grain boundary area is of great importance. TEM studies have shown that individual grains indeed were separated by a very thin, generally amorphous, second phase. In addition, each grain appeared to contain a grain-shell region, in which Bi had been incorporated in the SrTi03 crystal lattice. It is shown that the microstructural features of the grain shell fit in with a dissolution/epitaxial-growth model.
9747
The superalloy Ma 6000 E is a Ni-base alloy developed for high creep resistance at intermediate as well as at high temperatures. The alloy has a complex composition being strengthened with several solid solution additions, y' precipitates for intermediate temperature strength and inert yttria for extreme elevated temperature creep resistance. The volume fraction of the y' (Ni3Al) precipitates is approximately 50% and their size about 0.2 pm in diameter. The yttriumoxide (Y2O3) volume fraction is 2.9% with an average particle size of 28 nm. Precipitates in an as received sample, deformed in tension to rupture at 760°C, are identified with an energydispersive X-ray system (EDS). Dislocation structures are studied using a 200 kV transmission electron microscope (JEM 200 cx). It is expected that dislocations bypass the yttriumoxide particles by looping, whereas y' precipitates can be bypassed either by loopinq or shearing. With increasing temperature dislocations will tend to climb rather than form coplanar Orowan loops around the particles. The experimental results are compared with predictions based on a model calculation for the critical particle diameter where cutting is taken over by looping.
THE INTERACTION BETWEEN DISLOCATIONS AND PRECIPITATES IN Al-Li ALLOYS STUDIED BY TEM A. J. Huis In 'T Veld, K. Hemmes, P. M. Bronsveld, G. Boom and J. Th. M. De Hosson Department of Applied Physics, University of Groningen, Materials Science Centre, Nijenborgh 18, 9747 AG Groningen, The Netherlands
In this paper, a transmission electron microscopic study of the mechanism of dislocation motion in Al-2.2 wt% Li is presented. TEM micrographs were taken using a JEM 200 CX operating between 120 and 160 keV. In order to obtain precipitates of different size, ageing times were varied from 1 hr to 115 hrs, and the ageing temperatures ranged between 200 and 245OC. Particle size distribution and volume fraction were determined using stereo-transmission electron microscopy. The increase in yield stress as a function of the experimentally determined particle size distribution and volume fraction can be predicted based on theoretical models.
FROM BLANK TO CAN-THE ORIGIN AND GROWTH OF THE MORPHOLOGY OF THE WALL OF A DWI CAN W. Van Koesveld and J. Schade Van Westrum Hoogovens groep bv, IJmuiden, Research and development, product technology
An extensive study of the morphology of the wall of the two-piece drawn and wall-ironed (dwi-) can has been made by both SEM and EPMA. Both the topography and the distribution of tin on the inner and outer sides of the wall could be logically explained as a product of the various stages in the forming process of the can. It is suggested that the mechanical properties of the steel base and those of the coating material have a strong influence on the resulting properties of the can wall.
SOME APPLICATIONS OF ELECTRON COPY IN THE AIRCRAFT INDUSTRY A. Kwakernaak
The basic strengthening mechanism of aluminium-lithium alloys is due to the formation of coherent 6' precipitates The addi(ordered Li2 phase A13Li). tion of Li to Al results in a reduction of density and an increased modulus of elasticity compared with conventional aluminium alloys. Consequently, the development of Al-Li alloys is highly desirable for structural applications, especially in aerospace industry.
and J. J. V. Konig
Technological
Schiphol,
MICROS-
The
Centre, Fokker Netherlands
b.v.,
Important applications of electron microscopy in the aircraft industry are the characterization of surfaces after chemical pretreatments and the study of fracture surfaces of aircraft parts. Transmission electron microscopy was used to study the structure of
Early work oxides on aluminium alloys. gave an indication of the importance of oxide morphology on adhesion. From parameter studies with variations in, e.g., electrolytes, solution temperatures and treatment times, correlations were found between oxide morphology and adhesion. Fractography plays an important role in the investigation of material behaviour under experimental and operational conditions. Determination of the modes and causes of fractures is important in order to detect shortcomings in the selection of materials, the design, the fabrication practice and the maintenance of aircraft parts.
FROM SHOWROOM TO SCRAP: XMA/AES INVESTIGATION OF CORROSION PROCESSES UNDER PAINT COATINGS W. J. Van Ooij
and T. H. Visser
Akzo Research, Corporate Department, Arnhem, The
Research Netherlands
In X-ray microanalysis the need for additional information on the surface composition of the material under investigation is often felt. Conversely, the surface analyst frequently wants to compare his data with bulk compositions. Both can be achieved by combining X-ray microanalysis and Auger electron spectroscopy in one instrument. In this study it is demonstrated that both techniques are almost ideally complementary and synergistic. As an example the corrosion reactions that take place in the interfacial zone between paint coatings and steel surfaces during artificial or natural weathering are discussed.
ANALYSIS NITRIDED
OF SURFACE STEEL
D. Schalkoord
LAYERS
ON
and E. J. Mittemeijer
Laboratory of University of Rotterdamseweq The Netherlands
Metallurgy, Technology, 137, 2628
Delft AL
Delft,
Nitriding of steels is applied to improve the fatigue resistance and/or the tribological and anti-corrosion properties. For an understanding of the property changes induced by nitriding a descrip-
tion of the nitrided structure is recharacterization quired: morphological is frequently performed using the light the lattice distortions can microscope, be analyzed by X-ray diffraction methods, and the nitrogen concentration profiles can be determined by X-ray The latter analysis is microanalysis. performed using a specially prepared -r'-FedN specimen as a nitrogen standard; for quantification of the measured nitrogen K, k-ratios several correction procedures are compared. By the combination of light-microscopical techniques and X-ray microanalysis the constitution of the (dominant) two-phase outer layer built during the nitriding process can be revealed. In the diffusion zone adjacent to the outer layer relatively large nitrogen contents are measured which are ascribed to lattice strain provoked by the misfit between precipitates and The association between atoms matrix. of the alloying elements (e.g. chromium, originally present in carbides) and nitrogen atoms leads to carbide precipitation at grain boundaries in the diffusion zone and to a carbon-rich zone ahead of the diffusion zone.
TEM STUDIES OF ELECTRO-CERAMIC INTEGRATED CIRCUIT MATERIALS
AND
M. P. A. Viegers Philips 5600 JA
Research Eindhoven,
Laboratories, The Netherlands
Some recent studies of ceramic capacitors and integrated circuits are presented. The particular examples dealt with concern: --SrTi03 boundary layer capacitor material: It is prepared by the addition of Bi203 to prefired SrTi03 matrix material. In this way one obtains semiconductive grains, separated by an insulating layer. Since the actual capacitance is located at the grain boundaries, the nature of the grain boundary area is of great importance. TEM studies have shown that individual grains indeed were separated by a very thin, generally amorphous, second phase. In addition, each grain appeared to contain a grain-shell region, in which Bi had been incorporated in the SrTi03 crystal lattice. It is shown that the microstructural features of the grain shell fit in with a dissolution/epitaxial-growth model.