Recent topics in microstructure control by magnetic field in Ni2MnGa and CoPt and new transformation behavior in Ti-Ni-Fe alloys

Tomoyuki Kakeshita ,  Takashi Fukuda 

Department of Materials Science and Engineering, Graduate School of Engineering,Osaka University, Suita, Osaka, Japan, Suita 565-0871, Japan

Abstract

Three topics related to solid-solid phase transformations will be presented. The first topic is related to ferromagnetic Ni2MnGa. The condition for rearrangement of martensite variants by magnetic field in this alloy will be discussed quantitatively. In addition, we will show that a new phase (X-phase) appears in Ni2MnGa prior to the formation of the intermediate phase on cooling. The parent to X-phase transformation is close to second order while the X to intermediate phase transformation is obvious first order. The second topic is related to microstructure control using magnetic field. In the topic, we will show that single variant state of ordered CoPt (tetragonal L10-type structure) can be obtained by an ordering heat-treatment under magnetic field. We also show that magnetic field is especially effective at the early stage of ordering for obtaining single variant state. The third topic is related to the so-called precursor phenomena in Ti-Ni-Fe shape memory alloys. In the topic we will show the existence of a commensulate phase, which inherits the microstructure of the incommensulate phase and is probably different from the R-phase. Furthermore, we will discuss how the anomalies observed in Ti-Ni alloys are related to the instability of the B2-phase.

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Presentation: Invited at E-MRS Fall Meeting 2007, Symposium E, by Takashi Fukuda
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-15 06:57
Revised:   2009-06-07 00:44
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