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Inverse-Heusler Mn2FeSi alloy prepared by powder metallurgy route
Životský, O. ; Skotnicová, K. ; Čegan, T. ; Juřica, J. ; Gembalová, L. ; Zažímal, František ; Jirásková, Yvonna ; Szurman, I.
The Mn2FeSi inverse-Heusler alloy was prepared by solid-state reactions using ball milling for 168 h in n hexane. Two milling procedures varying in the ball-to-powder ratio, namely 4:1 and 10:1, were used to follow \ntheir influence on alloy formation and its physical properties. In both cases no Heusler structure was obtained \ndirectly and therefore the subsequent annealing at 1223 K for 1.5 h in pure Ar was applied. The energy dispersive X-ray analysis resulted in the chemical composition about 49.0-49.9 at% Mn, 25.3-25.6 at% Fe, and \n24.8-25.4 at% Si, in a good agreement with nominal one. X-ray diffraction of both powders confirmed inverse Heusler XA structure of lattice parameters 0.5675 nm (4:1) and 0.5677 nm (10:1), only slightly higher as \ntheoretically obtained 0.560 nm. The presence of minor oxidation phases was also observed in the particle \nstructure of powders. Magnetic properties were analysed at low and room temperatures. Both alloys exhibit \nparamagnetic behaviour at room temperature confirmed by transmission Mössbauer spectroscopy \nmeasurements. Different magnetic behaviour of alloys is observed below 65 K.
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AGEING OF BINARY Ti-Ni ALLOY AND ITS INFLUENCE ON TRANSFORMATION CHARACTERISTICS
Szurman, I. ; Kursa, M. ; Petlák, D. ; Dlouhý, Antonín
Transformation temperatures of binary alloys from Ti-Ni system are highly sensitive to chemical composition of the alloy. This sensitivity, however, causes rather considerable complications already during process of preparation. Transformation temperatures of bays rich in Ni can be successfully modified. The key to modification of transformation temperatures lies in use of precipitation reaction of quenched over-saturated solution for influencing of composition of TiNi matrix and thus to precise control of transformation temperatures. Principle of this method consists in metastable balance between intermetallic phase TiNi and coherent precipitates Ti3Ni4. Although the precipitate Ti3Ni4 is considered to be metastable in comparison with TiNi3, it is highly stable at temperatures below 600 degrees C. During precipitation reaction Ti3Ni4 is formed and this phenomenon is connected with decrease of Ni content in TiNi matrix, which leads to increased temperatures of phase transformations TR (temperature of formation of R-phase) and Ms (temperature 'martensite start'). It is important that transformation temperature after long-term ageing is independent on chemical composition of the alloy, and it depends only on temperature of ageing as a consequence of equilibrium between these phases. This phenomenon should not occur at ageing at higher temperatures, formation of precipitate Ti3Ni4 should occur only during cooling of the sample from the temperature of ageing. The alloy Ni50.6-Ti (at. %), prepared in high-frequency induction vacuum furnace, was chosen as experimental material. Samples of the alloy were sealed into evacuated quartz glass tube and aged at constant temperature with various durations of dwell. Afterwards transformation characteristics of the samples were determined by DSC method.
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