Setsuo Kajiwara

Stacking Fault Probabilities in Copper-Aluminum Martensite Transformed in Thin Foils

The martensite transformation of thin foils of Cu-Al alloy was studied to know the effect of specimen thickness on stacking fault probability in the martensite. Stacking fault probabilities were obtained from shifts of electron diffraction spots by applying the diffraction theory of crystal with stacking faults which has been developed by Kakinoki and Komura. Only one stacking fault parameter β was sufficient to describe stacking disorder in the present case. Obtained values of β cover almost all the range from 0 to 1, where β=1 corresponds to h.c.p. structure. Such large values of β including β=1 can not be obtained from the martensite transformation of bulk specimens. The effect of foil thickness on stacking fault probability was directly examined by making use of high transmissive power of 500 kV electron microscope, and it was found that the probability β increases with decreasing foil thickness. It is inferred that the martensite transformed in thin foils has a strong tendency to approach to h.c.p. s...

Stacking Disorder in Martensites of Cobalt and Its Alloys

Stacking disorder in the h.c.p. martensites of the pure Co, Co-10.2at%Be and Co-19.5at.%Ni alloys has been studied by electron diffraction, utilizing the selected-area diffraction technique of an electron microscope. The shifts of diffraction spots along [00.1] direction due to stacking faults are observed with these martensites. The shifts are analyzed by Kakinoki theory with Reichweites=2, and the corresponding stacking fault probabilities are found to be α=0.03~0.3. It is considered that these stacking faults are introduced due to the constraints imposed by the surrounding matrix crystal.

Stacking Disorder in Martensite of Cu-Zn Alloy

The faulting in stacking sequence of close-packed layers of the martensite in Cu–38.6 at. %Zn alloy has been studied by electron diffraction, utilizing the selected area diffraction technique of electron microscopy. Observed diffraction spots were shifted and diffused owing to the stacking faults. The shifts of sports were analyzed by the Kakinoki-Komura theory with Reichweite s =3, and the stacking fault probabilities α were found to be between 0.13 and 0.43, α being a fault parameter representing the cubic type stacking faults. The result is compared with the case of the Cu-Al martensite: the predominant type of stacking faults is cubic type for the Cu-Zn martensite while hexagonal type for the Cu-Al martensite. This difference is explained by the phenomenological theory of martensitic transformation.

Characterisation of Microstructure of Isothermally Transformed Martensite in Low Temperature in Powder and Bulk State of Fe–23Ni–3.6Mn (mass%) Alloy by Rietveld's Method

The present study concerns X-ray characterisation of the microstructures of the martensites of Fe–23Ni–3.6Mn alloy, transformed isothermally at low temperature. Along with the austenized powder and bulk forms of the alloy, coldworked powders have also been analysed. The methodology adopted is Rietvelds whole profile fitting technique which incorporates correction for preferred orientation of the crystallites. The results reveal important information on the crystallite (domain) sizes, residual microstrains, preferred orientation, stacking and compound fault probabilities, dislocation density etc., for both the austenite and martensite phases of the alloy. The martensite has smaller crystallite sizes and larger microstrain values, both of which are isotropic in nature for the transformed bulk and the austenized powders but anisotropic for the coldworked powders. The transformed matrix revealed high percentage of martensites in coldworked powder and bulk whereas annealed powder revealed about 8% volume fraction of martensites. The dislocation density values evaluated from the respective crystallite sizes and r.m.s. strain values are high (~1011 cm/cm3) in the martensitic phase by almost an order of magnitude compared to their respective austenite phase. The coldworked powder reveals high propensity of faulting. The hardness value of transformed bulk (191 kg/mm2) is more than double the value for the austenite bulk (95 kg/mm2). The results have been compared and correlated with those in two previous studies on the same alloy system having 3.3 and 3.8 mass% of Mn.

Lattice Imaging Study of Boundaries in Martensite in Shape Memory Alloys

The structure of boundaries in martensite in shape memory alloys has been studied using the lattice imaging technique of high resolution electron microscopy. Good coherence has been found between the close-packed planes at the boundaries. Such coherence makes the boundary quite mobile when an external stress is applied, and thereby a large shape change of the specimen is possible without any appreciable plastic deformation.