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TEM investigations of ODS-materials
Micron and Microscopica Acta. Vol. 22. No. 1/2, pp. 179—180. 199!. Printed in Great Britain.
0739-6260/9! $3.(X) +0(10 Pergamon Press plc
TEM INVESTIGATIONS OF ODS-MATERIALS Oddvar Susegg*, Einar Hellum**, Arne Olsen*, Michael J. Luton# Department of Physics, University of Oslo, P.O. Box 1048, 0316 Oslo 3, Norway Raufoss A/S, Box 2, 2831 Raufoss, Norway # Exxon Research and Engineering, Annandale, NJ 08801, USA *
**
ODS-MATERIALS AND EXPERIMENTAL METHODS The present paper is a TEM study of ODS-materials. The starting material consists of 44 pm air atomized aluminium powder and 50 nm alumina powder. The ODS-material was produced in a ball mill in liquid nitrogen and subsequently hot isostatic pressed (HIP) and extruded at 400 - 500 °C. Specimens suitable for TEM were made by ion-thinning using Argon ions. The thin specimens were subsequently studied in a JEOL 200 CX and JEOL 2000 FX microscopes equipped with X-ray analyzers and electron energy loss spectrometer. The particle compositions have been analyzed and their phases identified. In addition the size distributions of the particles and dispersoids have been determined. RESULTS During material production some of the original aluminium oxide particles are preserved. In addition many small dispersoides are formed. They are important for the properties of the ODS-material. However, because commersial aluminium is used as starting material, particles with various Al-Fe and Al-Fe-Si phases (Skjerpe, 1989) are formed during the material production. They contribute also to the mechanical properties. In order to improve the ODS-materials it is important to know when the different phases are formed during the production process. Fig. Ia shows a typical particle of A1
3Fe. All the particles due to impurities of Fe and Si are rod-like. Particles of the A13Fe phase have frequently stacking faults and twins on (001) as demonstrated by the diffuse scattering shown in Fig. lb. Preliminary investigations show that the c-axis in Al3Fe is along the length of the extruded material. Fig. 2 shows another type of particle. Measurements of d-spacings show that they consist of the q1-Al-Fe-Si or the q2-Al-Fe-Si phase (Liu et a!., 1986, 1987). In addition to the large particles a lot of dispersoides were found. They have an average size of 15-20 nm (Fig. 3). They are formed on {1ll} planes in aluminium (Fig. 4a)). Fig. 4b is a microdiffraction pattern of the [1101 projection showing diffuse scattering consistent with small platelets in aluminium. Materials deformed at various conditions show a decrease in ductility with increasing temperature. This mechanical property has been correlated with the microstructure of the ODS-materials as found by TEM. REFERENCES Liu, P., Thorvalds son, T. and Dunlop, G . L., 1986 Formation of intermetallic compounds during solidification of dilute Al-Fe-Si alloys. Mater. Sci. Tech., 2: 1009 - 1018. Liu, P. and Dunlop, G.L., 1987 Determination of the crystal symmetry of two AlFe-Si phases by convergent-beam electron diffraction. J. Appl. Cryst., 20: 425 - 427. Skjerpe, P., 1989 Crystal Structure of Al-Fe-Si particles. Dr. thesis Oslo Univ. 179
180
0. Susegg et aL
— Fig. la BF of an Al
3Fe particle.
—~
~ôi’
S
Fig. lb Diffraction pattern showing diffuse streaks from stacking faults in Al3Fe.
— ~w.
.
I
Fig. 2 BF of an Al-Fe-Si particle.
Fig. 3 DF image of dispersoides.
Fig. 4a BF of ODS-material along the [1101 direction in the Al matrix,
Fig. 4b Diffraction pattern of ODS-rnaterial showing diffuse streaks along <111> aluminium directions. The orientation of the specimen is the same as in Fig. 4a.
0739-6260/9! $3.(X) +0(10 Pergamon Press plc
TEM INVESTIGATIONS OF ODS-MATERIALS Oddvar Susegg*, Einar Hellum**, Arne Olsen*, Michael J. Luton# Department of Physics, University of Oslo, P.O. Box 1048, 0316 Oslo 3, Norway Raufoss A/S, Box 2, 2831 Raufoss, Norway # Exxon Research and Engineering, Annandale, NJ 08801, USA *
**
ODS-MATERIALS AND EXPERIMENTAL METHODS The present paper is a TEM study of ODS-materials. The starting material consists of 44 pm air atomized aluminium powder and 50 nm alumina powder. The ODS-material was produced in a ball mill in liquid nitrogen and subsequently hot isostatic pressed (HIP) and extruded at 400 - 500 °C. Specimens suitable for TEM were made by ion-thinning using Argon ions. The thin specimens were subsequently studied in a JEOL 200 CX and JEOL 2000 FX microscopes equipped with X-ray analyzers and electron energy loss spectrometer. The particle compositions have been analyzed and their phases identified. In addition the size distributions of the particles and dispersoids have been determined. RESULTS During material production some of the original aluminium oxide particles are preserved. In addition many small dispersoides are formed. They are important for the properties of the ODS-material. However, because commersial aluminium is used as starting material, particles with various Al-Fe and Al-Fe-Si phases (Skjerpe, 1989) are formed during the material production. They contribute also to the mechanical properties. In order to improve the ODS-materials it is important to know when the different phases are formed during the production process. Fig. Ia shows a typical particle of A1
3Fe. All the particles due to impurities of Fe and Si are rod-like. Particles of the A13Fe phase have frequently stacking faults and twins on (001) as demonstrated by the diffuse scattering shown in Fig. lb. Preliminary investigations show that the c-axis in Al3Fe is along the length of the extruded material. Fig. 2 shows another type of particle. Measurements of d-spacings show that they consist of the q1-Al-Fe-Si or the q2-Al-Fe-Si phase (Liu et a!., 1986, 1987). In addition to the large particles a lot of dispersoides were found. They have an average size of 15-20 nm (Fig. 3). They are formed on {1ll} planes in aluminium (Fig. 4a)). Fig. 4b is a microdiffraction pattern of the [1101 projection showing diffuse scattering consistent with small platelets in aluminium. Materials deformed at various conditions show a decrease in ductility with increasing temperature. This mechanical property has been correlated with the microstructure of the ODS-materials as found by TEM. REFERENCES Liu, P., Thorvalds son, T. and Dunlop, G . L., 1986 Formation of intermetallic compounds during solidification of dilute Al-Fe-Si alloys. Mater. Sci. Tech., 2: 1009 - 1018. Liu, P. and Dunlop, G.L., 1987 Determination of the crystal symmetry of two AlFe-Si phases by convergent-beam electron diffraction. J. Appl. Cryst., 20: 425 - 427. Skjerpe, P., 1989 Crystal Structure of Al-Fe-Si particles. Dr. thesis Oslo Univ. 179
180
0. Susegg et aL
— Fig. la BF of an Al
3Fe particle.
—~
~ôi’
S
Fig. lb Diffraction pattern showing diffuse streaks from stacking faults in Al3Fe.
— ~w.
.
I
Fig. 2 BF of an Al-Fe-Si particle.
Fig. 3 DF image of dispersoides.
Fig. 4a BF of ODS-material along the [1101 direction in the Al matrix,
Fig. 4b Diffraction pattern of ODS-rnaterial showing diffuse streaks along <111> aluminium directions. The orientation of the specimen is the same as in Fig. 4a.