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Displacive transformations in niobium-ruthenium
viii
ABSTRACTS OF ARTICLES TO APPEAR IN A C T A M E T
decreases following the relation d ~ ~ -p/N where p and N are creep parameters about equal to 3.2 and 7.4 respectively. These values of p and N are in close agreement with those obtained from stress reduction tests in creep experiments. Attention is drawn to the need for new creep models which identify the. lmportance of subgrain boundaries to the creep process. .
The strain energy of a spheroidal inclusion was evaluated exactly using the Eshelby theory. Numerical results for an oblate spheroid are presented in a parametric form in terms of the transformation strain tensor. Using atomistlc transformation mechanisms, the transformation strain was determined for bcc-hcp martensitic transformation in Ti and its alloys. The lattice correspondence satisfied the Burgers relationship and the c/a-ratio in the product phase was taken as 1.586. The habit plane was predicted on the basis of the strain energy minimization principle. Results of the calculatlon indicate that the strain energy is minimized when the morphology of hcp Ti martensite is a thin disc-shaped inclusion lying on a plane close to (i I X)B, where X is equal to 1.2 to 1.3. This habit plane is in excellent agreement with experimental observations.
ORDERED STRUCTURES IN RANDOM GRAIN BOUNDARIES
D. H. Warrington* & M. Boon + *Department of Metallurgy Sheffield University England +University of Nijmegen Netherlands Received
November 5, 1974
Calculations are presented on the probability that the rotation across a grain boundary in a random polycrystalllne aggregate will lie within specified deviations of rotations leading to a CSL (coincidence site lattice) or a CAD (coincident axial direction). It is shown that in the case of cubic crystals only a small proportion of rotations lie within acceptable directions of low order C.S.L.'s but that the majority of boundary rotations will lie close to low order C.A.D. rotations. Some implications of these results are discussed.
.
Vol. 9, No. 3
The present approach is discussed in detail and compared with the crystallographic theory based on the invarlant p l a n e strain hypothesis. .
DISPLACIVE TRANSFORMATIONS IN NIOBIUM-RUTHENIUM BiJoy K. Das & David S. Lieberman Department of Metallurgy & Mining Engineering & Materials Research Laboratory University of Illinois Urbana, Illinois Received April II, 1972 Revised November 20, 1974
THE BCC-HCP MARTENSITIC TRANSFORMATION M. Shibata & KanJi Ono Materials Department School of Engineering & Applied Science University of California Los Angeles, California Received September i0, 1974 Revised November 20, 1974
viii
Displacive phase transformations in near-equiatomlc Nb-Ru alloys have been studied using electrical resistivity measurements, optical metallograph and X-ray diffraction. Alloys containing between 41 and 45 at.~ Ru undergo a CsCl (B) to tetragonal (B') transformation on cooling from 1500°C to room temperature. Alloys containing more than 46 at.% Ru exhibit a two step CsCI (B) to tetragonal (B') to orthorhombic (~")
Vol. 9, No. 3
ABSTRACTS OF ARTICLES TO APPEAR IN A C T A M E T
.
transformation on cooling to room temperature. Although the product of each successive transformation consists of stacks of twins (in ~ ' ~ ", twins within twins), the transformations do not proceed by the advance of sharp planar interfaces as in many of the first order martensitic transformations resulting in morphologically similar products. Rather, the interphase region consists of a small volume of the crystal over which the parent phase is gradually distorted into the product phase.
6.
ix
FRAGMENTED TWINS IN Mo-35 at.% Re ALLOY S. Mahajan Bell Laboratories Murray Hill, New Jersey Received August 28, 1974 Revised November 12, 1974
CREEP FRACTURE IN URANIUM • DIOXIDE G. L. Reynolds, B. Burton & M. V. Speight Central Electricity Generating Board Berkeley Nuclear Laboratories Berkeley, Gloucestershire Received November ii, 1974
Creep fracture processes have been studied in UO2. At high rates of strain fracture occurs by the propogation of the triple point cracks which extend large distances along grain boundaries. At lower rates of strain the fracture mode involves the growth of rounded cavities on boundaries parallel to the compressive stress axis. The growth of these cavities is attributed to a vacancy condensation mechanism driven by internally generated tensile components of stress. The magnitude of this tensile stress is calculated and the conditions for growth are estimated.
The crystallographic features of fragmented twins and associated substructures have been correlated by transmission electron microscopy. In three out of the four cases examined, fragmented segments exhibit no lateral displacements with respect to each other, whereas in one situation offset is observed in the absence of glide dislocations whose Burgers vector is not parallel to the twinning vector. In the majority of the cases, fragmentations are envisaged to be obstacle-induced, whereas the latter case is consistent with slip-lnduced fragmentation hypothesis. Further, in a few cases it has been possible to identify the obstacles; the origin of these obstacles is also considered.
.
STORED ENERGY IN DEFORMED COPPER CRYSTALS G. Gottstein, + J. Bewerunge ++ H. Mecking + & H. Wollenberger ++ + Institut f. Allgemelne Metallkunde und Metallphysik der RWTH Aachen, W. Germany d-~ Van de Graaff-Labor der KFA Julich, W. Germany Received November 22, 1974
Copper single crystals (99.999% purity) of six different orientations and polycrystals (mean grain diameter d-0.35mm) were deformed in tension at 78K. The energy release from 40°C up to 400°C was measured by means of an annealing calorimeter (electron beam calorimeter) All specimens were observed to release energy only during recrystalllzation. The measured values of
It is shown that non-stoichiometric and large grained material is more susceptible to creep damage. This increased susceptibility is attributed to the increased magnitude in grain boundary sliding offsets in the large grained material and to increased ease of sliding in the non-stoichiometric material.
ix
ABSTRACTS OF ARTICLES TO APPEAR IN A C T A M E T
decreases following the relation d ~ ~ -p/N where p and N are creep parameters about equal to 3.2 and 7.4 respectively. These values of p and N are in close agreement with those obtained from stress reduction tests in creep experiments. Attention is drawn to the need for new creep models which identify the. lmportance of subgrain boundaries to the creep process. .
The strain energy of a spheroidal inclusion was evaluated exactly using the Eshelby theory. Numerical results for an oblate spheroid are presented in a parametric form in terms of the transformation strain tensor. Using atomistlc transformation mechanisms, the transformation strain was determined for bcc-hcp martensitic transformation in Ti and its alloys. The lattice correspondence satisfied the Burgers relationship and the c/a-ratio in the product phase was taken as 1.586. The habit plane was predicted on the basis of the strain energy minimization principle. Results of the calculatlon indicate that the strain energy is minimized when the morphology of hcp Ti martensite is a thin disc-shaped inclusion lying on a plane close to (i I X)B, where X is equal to 1.2 to 1.3. This habit plane is in excellent agreement with experimental observations.
ORDERED STRUCTURES IN RANDOM GRAIN BOUNDARIES
D. H. Warrington* & M. Boon + *Department of Metallurgy Sheffield University England +University of Nijmegen Netherlands Received
November 5, 1974
Calculations are presented on the probability that the rotation across a grain boundary in a random polycrystalllne aggregate will lie within specified deviations of rotations leading to a CSL (coincidence site lattice) or a CAD (coincident axial direction). It is shown that in the case of cubic crystals only a small proportion of rotations lie within acceptable directions of low order C.S.L.'s but that the majority of boundary rotations will lie close to low order C.A.D. rotations. Some implications of these results are discussed.
.
Vol. 9, No. 3
The present approach is discussed in detail and compared with the crystallographic theory based on the invarlant p l a n e strain hypothesis. .
DISPLACIVE TRANSFORMATIONS IN NIOBIUM-RUTHENIUM BiJoy K. Das & David S. Lieberman Department of Metallurgy & Mining Engineering & Materials Research Laboratory University of Illinois Urbana, Illinois Received April II, 1972 Revised November 20, 1974
THE BCC-HCP MARTENSITIC TRANSFORMATION M. Shibata & KanJi Ono Materials Department School of Engineering & Applied Science University of California Los Angeles, California Received September i0, 1974 Revised November 20, 1974
viii
Displacive phase transformations in near-equiatomlc Nb-Ru alloys have been studied using electrical resistivity measurements, optical metallograph and X-ray diffraction. Alloys containing between 41 and 45 at.~ Ru undergo a CsCl (B) to tetragonal (B') transformation on cooling from 1500°C to room temperature. Alloys containing more than 46 at.% Ru exhibit a two step CsCI (B) to tetragonal (B') to orthorhombic (~")
Vol. 9, No. 3
ABSTRACTS OF ARTICLES TO APPEAR IN A C T A M E T
.
transformation on cooling to room temperature. Although the product of each successive transformation consists of stacks of twins (in ~ ' ~ ", twins within twins), the transformations do not proceed by the advance of sharp planar interfaces as in many of the first order martensitic transformations resulting in morphologically similar products. Rather, the interphase region consists of a small volume of the crystal over which the parent phase is gradually distorted into the product phase.
6.
ix
FRAGMENTED TWINS IN Mo-35 at.% Re ALLOY S. Mahajan Bell Laboratories Murray Hill, New Jersey Received August 28, 1974 Revised November 12, 1974
CREEP FRACTURE IN URANIUM • DIOXIDE G. L. Reynolds, B. Burton & M. V. Speight Central Electricity Generating Board Berkeley Nuclear Laboratories Berkeley, Gloucestershire Received November ii, 1974
Creep fracture processes have been studied in UO2. At high rates of strain fracture occurs by the propogation of the triple point cracks which extend large distances along grain boundaries. At lower rates of strain the fracture mode involves the growth of rounded cavities on boundaries parallel to the compressive stress axis. The growth of these cavities is attributed to a vacancy condensation mechanism driven by internally generated tensile components of stress. The magnitude of this tensile stress is calculated and the conditions for growth are estimated.
The crystallographic features of fragmented twins and associated substructures have been correlated by transmission electron microscopy. In three out of the four cases examined, fragmented segments exhibit no lateral displacements with respect to each other, whereas in one situation offset is observed in the absence of glide dislocations whose Burgers vector is not parallel to the twinning vector. In the majority of the cases, fragmentations are envisaged to be obstacle-induced, whereas the latter case is consistent with slip-lnduced fragmentation hypothesis. Further, in a few cases it has been possible to identify the obstacles; the origin of these obstacles is also considered.
.
STORED ENERGY IN DEFORMED COPPER CRYSTALS G. Gottstein, + J. Bewerunge ++ H. Mecking + & H. Wollenberger ++ + Institut f. Allgemelne Metallkunde und Metallphysik der RWTH Aachen, W. Germany d-~ Van de Graaff-Labor der KFA Julich, W. Germany Received November 22, 1974
Copper single crystals (99.999% purity) of six different orientations and polycrystals (mean grain diameter d-0.35mm) were deformed in tension at 78K. The energy release from 40°C up to 400°C was measured by means of an annealing calorimeter (electron beam calorimeter) All specimens were observed to release energy only during recrystalllzation. The measured values of
It is shown that non-stoichiometric and large grained material is more susceptible to creep damage. This increased susceptibility is attributed to the increased magnitude in grain boundary sliding offsets in the large grained material and to increased ease of sliding in the non-stoichiometric material.
ix