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The orientation relationship between delta-phase plutonium and alpha-phase plutonium
326
Journal of Nuclear Materials 168 (1989) 326-327 North-Holland. Amsterdam
THE ORIENTATION
RELATIONSHIP
AND ALPHA-PHASE
PLUTONIUM
Clayton MST-13,
BETWEEN DELTA-PHASE
PLUTONIUM
*
E. OLSEN MS ESIl,
Los Alamos National Laboratory,
Los Alamos,
NM 87545, USA
Received 25 July 1988; accepted 9 June 1989
Microbeam X-ray diffraction on partiatly transformed Pu-2% Al alloys show the following relationship between the delta-phase matrix and the transformation alpha-prime phase product: (010) alpha /](111) cubic and (100) alpha ]j(llO) cubic + 5 O. The statistics of such a relationship are discussed.
1. Introduction Investigations [l] on Pu-2% Al alloys show these alloys to partially transform to the monoclinic alphaprime phase on cooling to liquid nitrogen temperatures. By controlling the rate and time of cooling it is possible to obtain delta-phase pluto~um grams having long needles of the alpha-phase transfo~ation product in them. The regular orientational relationships of the needles within each of the grains, strongly suggested an epitaxial relation between the delta-phase matrix and the alpha-phase transformation product.
2. Experimental techniques The samples were furnished to the writer in the form of metallurgically mounted, polished, and electrochemically etched samples with a 0.013 mm commercial household wrapping to prevent spread of contamination. These samples were examined in a Los Alamos designed oscillation X-ray system. This camera is used in conjunction with a fine focus X-ray generator [2]. The focal spot used is 100 microns by 1.4 mm line focus with a tube current of 3 mA at 36 kV. When this spot is viewed end on at the usual take off angle (6”) we view a spot 100 microns x 146 microns (current loading of 0.77 kW/mm*. For such finely focused X-ray spots the collimating system needs only to be a limiting diaphram * Work performed under the auspices of the US Department of Energy.
~22-3115/89/$03.50 (North-Holland
Physics
at the end of a metal tube (electron microscope diaphrams). The slit system is adjustable so that the X-ray beam can be centered on the axis of rotation of the oscillation camera. The sample in the metallurgical mount is placed in a brass holder which is mounted on the camera stage having x, y, and z translation. In addition to holding the metallur~c~ mount, the brass sample holder reduces the extranious gamma radiation from the sample. The polished surface of the sample is parallel to the oscillation axis of the camera. By rotation of the sample in the holder and use of the stage translations, it is possible to search the whole area of the polished sample to find suitable areas for examination and to position the selected area on the oscillation axis and in the X-ray beam. After positioning the sample, the microscope is translated away from the sample, and a cylindrical film hoider (57.3 mm diameter) is placed around the sample for the X-ray exposure. The design of the film holder does not require the removal of the slit system for its installation and the axis of the cylinder is coincedent with the oscillation axis. The radiation used in the diffraction study is white copper radiation. No difficulty is experienced with identification of the reflections coming from the alpha and beta radiation and the white radiation streaking helps with the location of strong reflections when the sphere of reflection for the alpha or beta radiation is not intersected. Excellent discussions of the geometries and interpretations of the diffraction patterns are given in two older refs. [3,4]. The sample is oscillated 15” in complimentary positions for 12 and 24 hours respectively.
0 Elsevier Science Publishers B.V. Publishing
Division)
C.E. Olsen / Orientation
relationship
3. Results The exposed and developed film is measured using zeta-epsilon and rho-phi Bemal charts. From the zeta-epsilon chart and the wavelength associated with a particular reflection, the interplanar d spacing can be calculated allowing identification of the source material and indexing of the reflection. From the rho-phi chart, the orientation of the source material with respect to the oscillation axis and the camera geometry can be made. Since illuminated area is within a single grain, the observed reflections and orientations can be assigned uniquely to the matrix or the transformation product and the orientations with respect to each other can be determined. Stereographic projections for standard axes in alphaand delta-phase plutonium were prepared using the face-centered cubic structure [6] as, space group Fm3m, u = 4.6371 A at 235 o C and the primitive monoclinic structure [7] as space group P2,/m, u = 6.183 A, b = 4.877 A, c = 10.963 A, and /3 = 101.79 ’ at 21’ C. Using the inter-reflection angles between the observed reflections in the delta-phase plutonium and the alpha-phase plutonium and the orientations between the phases, an unique solution was obtained when the b axis in the alpha-phase plutonium was parallel to a 111 axis in the delta phase pluto~um ((010) alpha~~(lll)) delta and the a axis in alpha phase plutonium is parallel +5” to
between 6- and a-phase Pu
32-l
one of the 110 directions in the delta-phase plutonium ((100) alpha]](llO) delta +5”). This relationship is of interest because of the pseudo-hexagonal arrangement in the ac plane of alpha plutonium. This relationship also explains why coarse grained delta-phase plutonium, on transformation, breaks up into fine grained alpha-phase plutonium. If one assumes a random axial selection within a grain of delta plutonium, there are four different (111) axes (not counting the senses of the axes) along which the b axis of the alpha phase can form. Around each (111) axis, there are three possible orientations for the u-c plane in alpha phase. If one allows for the positive and negative senses of the (111) axes, there are a total of 24 possible orientations for the alpha phase derived from the random axial nucleation in a single grain of deltaphase plutonium. One notes that the 24 possible orientations are not random but bear a definite relationship to the original delta-phase grain. The relationships are illustrated in fig. 1.
Acknowledgements
The author wishes to thank E.G. Zukas and R.A. Pereyra of MST-5 for preparing and providing the samples.
References
Fig. 1. The axial relationship between delta-phase plutonium and alpha-phase plutonium.
[l] S.S. Hecker, E.G. Zukas, J.R. Morgan and R.A. Pereyra, Proc. Int. Conf. on Solid-Solid Phase Transformations, Eds. H.I. Aaronson, D.E. Laughlin, R.F. Sekerka and CM. Wayman (American Institute of Mining, Metallurgical and Petroleum Engineers, New York, 1982) pp. 1339-1343. (21 W. Ehrenberg and W.E. Spear, Proc. Phys. Sot. London B64 (1951) 67. (31 M.J. Buerger, X-Ray C~stallo~aphy (Wiley, New York, 1942) Chpt. 1, pp. 188-213. [4] N.F. McHenry, H. Lipson and W.A. Wooster, The Interpretation of X-Ray Diffraction Photographs (D. Van Nostrand Company, Inc., New York, 1953) Chpt. 5, pp, 48-70. [5] 0. Johari and G. Thomas, The Stereographic Projection and Its Applications, Techniques of Metals Research, Vol. IIA, Ed. R.F. Bunshah (Wiley, New York, 1969). [6] F.H. Ellinger, AIME Trans. 206 (1956) 1256. [7] W.H. Zachariasen and F.H. Ellinger, Acta Crystall. 16 (1963) 717.
Journal of Nuclear Materials 168 (1989) 326-327 North-Holland. Amsterdam
THE ORIENTATION
RELATIONSHIP
AND ALPHA-PHASE
PLUTONIUM
Clayton MST-13,
BETWEEN DELTA-PHASE
PLUTONIUM
*
E. OLSEN MS ESIl,
Los Alamos National Laboratory,
Los Alamos,
NM 87545, USA
Received 25 July 1988; accepted 9 June 1989
Microbeam X-ray diffraction on partiatly transformed Pu-2% Al alloys show the following relationship between the delta-phase matrix and the transformation alpha-prime phase product: (010) alpha /](111) cubic and (100) alpha ]j(llO) cubic + 5 O. The statistics of such a relationship are discussed.
1. Introduction Investigations [l] on Pu-2% Al alloys show these alloys to partially transform to the monoclinic alphaprime phase on cooling to liquid nitrogen temperatures. By controlling the rate and time of cooling it is possible to obtain delta-phase pluto~um grams having long needles of the alpha-phase transfo~ation product in them. The regular orientational relationships of the needles within each of the grains, strongly suggested an epitaxial relation between the delta-phase matrix and the alpha-phase transformation product.
2. Experimental techniques The samples were furnished to the writer in the form of metallurgically mounted, polished, and electrochemically etched samples with a 0.013 mm commercial household wrapping to prevent spread of contamination. These samples were examined in a Los Alamos designed oscillation X-ray system. This camera is used in conjunction with a fine focus X-ray generator [2]. The focal spot used is 100 microns by 1.4 mm line focus with a tube current of 3 mA at 36 kV. When this spot is viewed end on at the usual take off angle (6”) we view a spot 100 microns x 146 microns (current loading of 0.77 kW/mm*. For such finely focused X-ray spots the collimating system needs only to be a limiting diaphram * Work performed under the auspices of the US Department of Energy.
~22-3115/89/$03.50 (North-Holland
Physics
at the end of a metal tube (electron microscope diaphrams). The slit system is adjustable so that the X-ray beam can be centered on the axis of rotation of the oscillation camera. The sample in the metallurgical mount is placed in a brass holder which is mounted on the camera stage having x, y, and z translation. In addition to holding the metallur~c~ mount, the brass sample holder reduces the extranious gamma radiation from the sample. The polished surface of the sample is parallel to the oscillation axis of the camera. By rotation of the sample in the holder and use of the stage translations, it is possible to search the whole area of the polished sample to find suitable areas for examination and to position the selected area on the oscillation axis and in the X-ray beam. After positioning the sample, the microscope is translated away from the sample, and a cylindrical film hoider (57.3 mm diameter) is placed around the sample for the X-ray exposure. The design of the film holder does not require the removal of the slit system for its installation and the axis of the cylinder is coincedent with the oscillation axis. The radiation used in the diffraction study is white copper radiation. No difficulty is experienced with identification of the reflections coming from the alpha and beta radiation and the white radiation streaking helps with the location of strong reflections when the sphere of reflection for the alpha or beta radiation is not intersected. Excellent discussions of the geometries and interpretations of the diffraction patterns are given in two older refs. [3,4]. The sample is oscillated 15” in complimentary positions for 12 and 24 hours respectively.
0 Elsevier Science Publishers B.V. Publishing
Division)
C.E. Olsen / Orientation
relationship
3. Results The exposed and developed film is measured using zeta-epsilon and rho-phi Bemal charts. From the zeta-epsilon chart and the wavelength associated with a particular reflection, the interplanar d spacing can be calculated allowing identification of the source material and indexing of the reflection. From the rho-phi chart, the orientation of the source material with respect to the oscillation axis and the camera geometry can be made. Since illuminated area is within a single grain, the observed reflections and orientations can be assigned uniquely to the matrix or the transformation product and the orientations with respect to each other can be determined. Stereographic projections for standard axes in alphaand delta-phase plutonium were prepared using the face-centered cubic structure [6] as, space group Fm3m, u = 4.6371 A at 235 o C and the primitive monoclinic structure [7] as space group P2,/m, u = 6.183 A, b = 4.877 A, c = 10.963 A, and /3 = 101.79 ’ at 21’ C. Using the inter-reflection angles between the observed reflections in the delta-phase plutonium and the alpha-phase plutonium and the orientations between the phases, an unique solution was obtained when the b axis in the alpha-phase plutonium was parallel to a 111 axis in the delta phase pluto~um ((010) alpha~~(lll)) delta and the a axis in alpha phase plutonium is parallel +5” to
between 6- and a-phase Pu
32-l
one of the 110 directions in the delta-phase plutonium ((100) alpha]](llO) delta +5”). This relationship is of interest because of the pseudo-hexagonal arrangement in the ac plane of alpha plutonium. This relationship also explains why coarse grained delta-phase plutonium, on transformation, breaks up into fine grained alpha-phase plutonium. If one assumes a random axial selection within a grain of delta plutonium, there are four different (111) axes (not counting the senses of the axes) along which the b axis of the alpha phase can form. Around each (111) axis, there are three possible orientations for the u-c plane in alpha phase. If one allows for the positive and negative senses of the (111) axes, there are a total of 24 possible orientations for the alpha phase derived from the random axial nucleation in a single grain of deltaphase plutonium. One notes that the 24 possible orientations are not random but bear a definite relationship to the original delta-phase grain. The relationships are illustrated in fig. 1.
Acknowledgements
The author wishes to thank E.G. Zukas and R.A. Pereyra of MST-5 for preparing and providing the samples.
References
Fig. 1. The axial relationship between delta-phase plutonium and alpha-phase plutonium.
[l] S.S. Hecker, E.G. Zukas, J.R. Morgan and R.A. Pereyra, Proc. Int. Conf. on Solid-Solid Phase Transformations, Eds. H.I. Aaronson, D.E. Laughlin, R.F. Sekerka and CM. Wayman (American Institute of Mining, Metallurgical and Petroleum Engineers, New York, 1982) pp. 1339-1343. (21 W. Ehrenberg and W.E. Spear, Proc. Phys. Sot. London B64 (1951) 67. (31 M.J. Buerger, X-Ray C~stallo~aphy (Wiley, New York, 1942) Chpt. 1, pp. 188-213. [4] N.F. McHenry, H. Lipson and W.A. Wooster, The Interpretation of X-Ray Diffraction Photographs (D. Van Nostrand Company, Inc., New York, 1953) Chpt. 5, pp, 48-70. [5] 0. Johari and G. Thomas, The Stereographic Projection and Its Applications, Techniques of Metals Research, Vol. IIA, Ed. R.F. Bunshah (Wiley, New York, 1969). [6] F.H. Ellinger, AIME Trans. 206 (1956) 1256. [7] W.H. Zachariasen and F.H. Ellinger, Acta Crystall. 16 (1963) 717.