J.P. Hirth et al. Acta Materialia 54(2006)1917-1925 have been described by Schwartz et al. [25]. Mitchell et al. discussions. This project was funded by the US Depart [2]. and Blobaum et al. [26], and are believed to corre- ment of Energy under Contract No. W-7405-ENG-36 spond to the cooperative reversion of many platelets to the 8 phase; they appear to be the result of an interplay References between the autocatalytically driven reversion of a cas cade of individual martensite units, and self-quenching [1] Hecker SS. Harbur DR, Zocco TG. Prog Mater Sci2004:49:429 caused by small changes of temperature and/or stress [2] Mitchell JN, Stan M, Schwartz DS, Boehlert C]. Metall Mater Trans accompanying each individual transformation burst. The 2004:35A:2267. large hysteresis is likely to be due to the high density of [3] Zachariasen WH, Ellinger F. Acta Cryst 1963: 16: 777 defects- interface dislocations. twins and lattice disloca 1] Hecker SS. Martensitic transformations in plutonium. Los Alamos tions-introduced during the 8 to transformation, as National Laboratory Report LA-UR-831715: 1983 J Crocker AG. J Nucl Mater 1965: 16: 306 well as residual stresses. These defects and locally high [6] Olsen CE. J Nucl Mater 1989: 168:326 stresses are likely to constrain the reverse motion of the [7] Zocco TG, Stevens MF, Adler PH, Sheldon rl, Olson GB. Acta a' platelets, causing their transformation back to the fcc Metall Mater 1991: 38: 2275 8 phase to be shifted to higher temperature [8] Choudry MA, Crocker AG. J Nucl Mater 1985: 127: 119 [9] Adler PH, Olson GB, Margolies DS. Acta Metall 1986: 34: 2053 l0] Wechsler MS, Lieberman DS, Read TA. Trans AIME 5. Conclusions 1953;197:1503 [ll] Bowles JS, Mackenzie JK. Acta Metall 1954; 2: 129 1. A defect-based topological model for the Pu-1.7 at [12] Pond RC, Hirth JP. Solid State Phys 1994: 47: 287 Ga martensite transformation of 8 to a gives a predic- [1]Hirth JP, Pond RC. Acta Mater 1996: 44: 4749 tion of the habit plane in good agreement with experi- [15] Pond RC, Celotto S, Hirth JP. Acta Mater 2003: 5 1:5385 mental results [16] Pond RC, Ma x, Hirth JP. In: Proceedings of ICOMAT conference 2. Experimentally observed twinning in a'is associated directly with the transformation strain and not with [17] Chen I-W, Chiao Y-H. Acta Metall 1985:33: 1827 the liD [18] Lawson AC, Roberts JA, Martinez B, Richardson Jr Jw. Philos Mag 3. LiD by slip is qualitatively consistent with the model [19] Zocco TG, Sheldon RI, Rizzo HEJ Nucl Mater1991:: 183:80 and with electron microscopy observations. 20] Hecker SS, Stevens MF. Los Alamos Sci 2000: 26: 336 4. Quantitative treatment of the LID cannot be performed [21] Pond RC, Sarrazat F Interf Sci 1996; 4: 99 without information on slip planes and directions as well [22] Bronisz SE, Tate RE. In: Kay Al, Waldron MB,editors.Proceedings as critical resolved shear stresses for slip on these Hal;1965.p.558 23]Liptai RG, Friddle RJ. In: Miner WN, editor. Proceedings of 4th international conference on plutonium and other actinides. Net York(NY): Metallurgical Society; 1970. p 406. Acknowledgements []Hirth JP, Lothe J. Theory of dislocations. Malabar (FL): Krieger; 225] Schwartz DS, Mitchell JN, Pete D, Ramos MR J Metal 2003: 55: 28 The authors thank Ramiro Pereyra and Darryl Lovato [26]Blobaum KJM, Krenn CR, Mitchell JN, Haslam JJ, Wall MA, for their superb metallography and T.G. Zocco for useful Massalski TB, et al. Metall Mater Trans A [in press].have been described by Schwartz et al. [25], Mitchell et al. [2], and Blobaum et al. [26], and are believed to corre￾spond to the cooperative reversion of many a0 platelets to the d phase; they appear to be the result of an interplay between the autocatalytically driven reversion of a cas￾cade of individual martensite units, and self-quenching caused by small changes of temperature and/or stress accompanying each individual transformation burst. The large hysteresis is likely to be due to the high density of defects – interface dislocations, twins, and lattice disloca￾tions – introduced during the d to a0 transformation, as well as residual stresses. These defects and locally high stresses are likely to constrain the reverse motion of the a0 platelets, causing their transformation back to the fcc d phase to be shifted to higher temperature. 5. Conclusions 1. A defect-based topological model for the Pu–1.7 at.% Ga martensite transformation of d to a0 gives a predic￾tion of the habit plane in good agreement with experi￾mental results. 2. Experimentally observed twinning in a0 is associated directly with the transformation strain and not with the LID. 3. LID by slip is qualitatively consistent with the model and with electron microscopy observations. 4. Quantitative treatment of the LID cannot be performed without information on slip planes and directions as well as critical resolved shear stresses for slip on these systems. Acknowledgements The authors thank Ramiro Pereyra and Darryl Lovato for their superb metallography and T.G. Zocco for useful discussions. This project was funded by the US Depart￾ment of Energy under Contract No. W-7405-ENG-36. References [1] Hecker SS, Harbur DR, Zocco TG. Prog Mater Sci 2004;49:429. [2] Mitchell JN, Stan M, Schwartz DS, Boehlert CJ. Metall Mater Trans 2004;35A:2267. [3] Zachariasen WH, Ellinger F. Acta Cryst 1963;16:777. [4] Hecker SS. Martensitic transformations in plutonium. Los Alamos National Laboratory Report LA-UR-83-1715; 1983. [5] Crocker AG. J Nucl Mater 1965;16:306. [6] Olsen CE. J Nucl Mater 1989;168:326. [7] Zocco TG, Stevens MF, Adler PH, Sheldon RI, Olson GB. Acta Metall Mater 1991;38:2275. [8] Choudry MA, Crocker AG. J Nucl Mater 1985;127:119. [9] Adler PH, Olson GB, Margolies DS. Acta Metall 1986;34:2053. [10] Wechsler MS, Lieberman DS, Read TA. Trans AIME 1953;197:1503. [11] Bowles JS, Mackenzie JK. Acta Metall 1954;2:129. [12] Pond RC, Hirth JP. Solid State Phys 1994;47:287. [13] Hirth JP, Pond RC. Acta Mater 1996;44:4749. [14] Hirth JP. J Phys Chem Solids 1994;55:985. [15] Pond RC, Celotto S, Hirth JP. Acta Mater 2003;51:5385. [16] Pond RC, Ma X, Hirth JP. In: Proceedings of ICOMAT conference [in press]. [17] Chen I-W, Chiao Y-H. Acta Metall 1985;33:1827. [18] Lawson AC, Roberts JA, Martinez B, Richardson Jr JW. Philos Mag 2002;B82:1837. [19] Zocco TG, Sheldon RI, Rizzo HF. J Nucl Mater 1991;183:80. [20] Hecker SS, Stevens MF. Los Alamos Sci 2000;26:336. [21] Pond RC, Sarrazat F. Interf Sci 1996;4:99. [22] Bronisz SE, Tate RE. In: Kay AI, Waldron MB, editors. Proceedings of 3rd international conference on plutonium. London: Chapman & Hall; 1965. p. 558. [23] Liptai RG, Friddle RJ. In: Miner WN, editor. Proceedings of 4th international conference on plutonium and other actinides. New York (NY): Metallurgical Society; 1970. p. 406. [24] Hirth JP, Lothe J. Theory of dislocations. Malabar (FL): Krieger; 1992. [25] Schwartz DS, Mitchell JN, Pete DV, Ramos MR. J Metal 2003;55:28. [26] Blobaum KJM, Krenn CR, Mitchell JN, Haslam JJ, Wall MA, Massalski TB, et al. Metall Mater Trans A [in press]. J.P. Hirth et al. / Acta Materialia 54 (2006) 1917–1925 1925