No description available.

No description available.

A study has been made of super-elasticity and the strain-memory effect in Cu-Al-Ni alloys in the composition range 14 wt. % Al and 2 to 6 wt. % Ni. These alloys have a bcc structure on quenching and show a low temperature transformation to a body-centered orthorhombic martensitic structure. It is this transformation that is responsible for the super-elastic and strain-memory effects. Tests on both single and polycrystalline specimens showed that the maximum super-elasticity occurred close to As. At higher temperatures the effect gradually decreased, whilst at lower temperatures it decreased very quickly. The magnitude of the effect was large in single crystal specimens (> 6%), but small in polycrystal specimens (< 1.5%). The super-elastic effect was caused by stress-induced martensite (SIM). Two types of SIM were observed: thin plates of thermoelastic martensite which was always reversible, and wide plates of burst-type martensite. This burst-type martensite was responsible for the major portion of SIM, and whether it was reversible or not on removal of the stress controlled the amount of super-elasticity observed. The strain-memory effect occurred on deformation either in the martensitic state (temperature <Mf) or in the temperature range where the martensite once formed was stable (temperatures close to Ms). Deformation caused reorientation of the martensite plates and when the specimen was heated, the martensite disappeared and the specimen reverted back to its original shape. This effect was explained on the basis of development of martensite plates of favorable orientation on stressing. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Reproduction de : Thèse de doctorat : Sciences de l'ingénieur. Mécanique des matériaux : Metz : 2000.

No description available.

Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The morphology and crystallography of the martensite transformation in pure iron and low alloy Fe-C, Fe-Mn, Fe-Mn-Si, Fe-Ni steels which contain no retained austenite was studied. Single surface trace analyses by transmission electron microscopy on directions parallel and normal to the martensite substructure were found to be consistent with the martensite crystals having the form of plates rather than needles. The directions normal to the martensite substructure plates were consistent with a {145}M habit plane. Optical studies of the martensite surface shears within prior austenite grains revealed that 4 shear variants generally occur. However grains containing 5 or more shear variants could be found which appears to suggest an austenite habit plan close to but different from {111}A. A single surface trace analysis of the martensite surface shears using the austenite annealing twin vestiges to orient the grain was consistent with an austenite habit plant ~ 7° from {111}A. Two inhomogeneous shear systems were found to predict the experimental results when applied to the Wecheler, Lieberman, Read theory of martensite transformations. They are (100)A[010]A and (111)A[112]A. The (111)A[112]A system is to be generally preferred as its predicted habit planes ( 7.12° from {111}A and 5.03° from {145}M are more consistent with the trace analyses. Preliminary work included an investigation of the maraging properties of the Fe-Mn-Si system. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

A study has been made of the martensitic transformations occurring in β-phase silver-cadmium and silver-zinc alloys. In silver-cadmium alloys the M(s) temperature was found to change from -44°C to -137°C as the cadmium content changed from 44.2 at. % Cd to 47.0 at. % Cd. Alloys of silver-zinc did not show any martensitic transformation; even on cooling to liquid helium temperature. The thermal martensite in Ag-45 at. % Cd alloy was found to have an orthorhombic structure of the 2H type. This was confirmed by X-ray diffraction and electron microscopy. A spontaneous martensite with a face centred cubic structure was found to occur along the thin edges of perforated specimens used for electron microscopy, because of the relaxation of volume constraints during thinning. In both Ag-45 at. % Cd and Ag-41 at.% Zn alloys a <111> slip direction was found. Also it was shown that Ag-45 at. % Cd alloy was elastically anisotropic, a characteristic very common to β-phase alloys. In both Ag-Cd and Ag-Zn alloys a face centred tetragonal structure could be formed on deforming the specimens by rolling or by tensile deformation. The structure changed to close-packed on severe deformation e.g. by filing. At lower Cd and Zn contents this close-packed structure was face centred cubic, whilst at higher alloy concentrations, this structure was close-packed hexagonal. Pseudo-elasticity was found to occur by stress-induced martensitic transformation. Maximum pseudo-elasticity occurred at temperatures just above A(f) and the actual amount of pseudo-elasticity was found to be dependent on the orientation of the tensile axis. The strain memory effect was studied by deforming specimens below A(f) and then heating. At temperatures below M(f), deformation of the martensite takes place and it is suggested that there is a change in the martensite structure, involving a change from thermal martensite to stress-induced martensite. The experimentally determined habit planes for thermal, stress-induced and deformation martensites were found to agree well with the values obtained using phenomenological theory assuming a {110}<11Ī0> microscopic shear. The 'elastic' elongations accompanying the transformation could be accounted for using the theory. A mechanism suggesting the course of the transformation was developed. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

There is considerable potential for the use of thin film shape memory alloys in the field of microtechnology due to their high power to volume ratio. The main obstacles for fabrication arise mainly due to the narrow regime over which shape memory behaviour is observed and the paucity of process techniques. Shape memory transition in brass only occurs in the alloy composition range 38.5 - 41.6 wt %% zinc. This study used a pyrophosphate electrolyte containing Cu2P2O7, Zn2P2O7 salts and an excess of K4P207 and KNO3, for brass deposition as a replacement for cyanide electrolytes because it is non-toxic and noncorrosive. A rotating disc electrode was employed to systematically examine polarisation data and a rotating cylinder electrode was employed to produce thin brass films and deduce the current efficiencies of copper, zinc and brass deposition with respect to deposition potential. Thin films were plated between 5- 301im, they all displayed a smooth, uniform homogenous deposit with no precipitates or oxide inclusions. The current efficiencies were found to be < 45% for copper, < 15% for zinc and between 10 - 30% for brass. The microstructural characterisation of the Cu-Zn thin alloys was undertaken by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray fluorescence (EDAX), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). XRD showed all the electrodeposited Cu-Zn alloys to have same phase composition as those predicted by the equilibrium phase diagram for Cu-Zn. This confirmed the existence of the parent p-phase within the shape memory composition range, which undergoes the martensitic transformation. TEM showed these foils to be composed of a matrix of a, p and martensite nano sized grains (< 40nm) co-existing with a sparse distribution of larger grains (200-300nm). The larger grains were always martensite in nature, recognisable by their twinning planes. Differential scanning calorimetry analysis shows evidence of a martensitic transformation change for the thin brass films.

Th. doct.--Métall.--Paris Sud, 1991. / Résumé en anglais. Bibliogr. p. 111-114.