Papers by Keyword: Phase Transformation

Abstract: The improvement of the mechanical behaviour of high performance steels brings about a renewed interest for the work hardening rate resulting from deformation-induced martensitic transformation or mechanical twinning. Even if these mechanisms are known for quite a long time, the deformation – transformation interactions that they induce is not yet fully characterised and understood. This study aims at characterising the microstructure evolution of a Fe-Mn steel grade during straining thanks to TEM and high resolution OIM. Particular patterns of austenite – e and a’ martensite are found.

Abstract: The ferrite to austenite phase transformation in microalloyed steel was studied, with a special focus on the orientation relationship between prior ferrite and subsequent austenite. Also the role of growth selection and preferred nucleation was investigated in this context. Their effects were examined at partial phase transformation.

Abstract: A series of hexacelsians with different compositions were synthesized by thermally induced transformation of a LTA zeolite. Various forms of hexacelsians have been characterized by XRPD, IR, Raman and 29Si MAS NMR method. The phase transformation a
b hexacelsian was investigated by DSC method. This phase transformation is sensitive to synthesis conditions, doping and thermal treatment. The peak maximum temperature, Tm, varies from 302 up to 353 oC. Heat of transformation changes from 0.42 to 1.77 kJ/mol.

Abstract: The elastic energy of a set of the twelve variants generated during the b ® a transformation of zirconium, with volume fractions fi, i=1..12, is derived with simplifying assumptions and the conditions on the fi to reach the energy minimum are established analytically. The minimum number of variants needed to reach this minimum is shown to be 6, and in this case, the variants have very specific volume fractions. Another result is that the maximum volume fraction of any variant is 1/3.

Abstract: Rutile TiO2 nanoparticles have been synthesized by direct hydrolysis method using TiCl3, TiCl4 as starting materials, yielding two different morphologies. The hydrolysis of TiCl3 resulted in needlelike rutile titania with the specific surface area of 74.5m2/g, while round particles about 200~400 nm with small acicular at edge, with specific area as high as 175m2/g, were obtained using TiCl4 as starting materials. The precipitates from TiCl4 hydrolysis could be changed into anatase phase without filtering and separation by varying pH of the system. The phenomenon was explained from the viewpoint of structure. The photocatalysed properties of rutile powders were compared with those of anatase of the same specific surface area. Rutile powders with initial crystalline size of 7 nm were found to have higher photocatalysed activity in the phenol degradation reaction than that which anatase has. The high activity of the as prepared lab-made rutile was attributed to the abundance of hydroxy groups in powders, which was proved by TG data, making the degradation reaction have more active sites. The agglomeration form of the rutile powder makes it easy for separation and reuse.

Abstract: The effect of hot deformation process on the structure within the temperature range corresponding to the g→a+P transformation was tested for commercial carbon steel containing of 0.158% C. Hot compression tests were performed at computer controlled constant cooling rate. Before testing CCT diagrams were carefully determined in order to fit hot deformation conditions to the g→a+P phase transformation range. The material microstructure was examined by means of optical and electron transmission microscopy. It was found that ferrite, pearlite or bainite were typical microstructural components observed at hot deformed samples. Localized distribution of pearlite or bainite that resulted from flow localization was observed rarely. Precipitation of carbides on ferrite grain boundaries is the most typical microstructural effect of the hot deformation/precipitation interaction that was noted for the most of hot deformed samples.

Abstract: Phase transformations during the heating of amorphous Fe-Si-B alloys were investigated. The differential thermomagnetic analysis and X-ray method are used for the studies. The intervals of phase transformations are revealed, and the magnetic properties of phases are determined. The method of calculation of magnetic effects during the phase transformations, registered by differential technique is suggested.