Kinetics of tetrataenite disordering

• The first time–temperature data for tetrataenite disordering reaction is provided.
• Previous works does not give a complete picture of tetrataenite disordering.
• Apparent Curie temperature of tetrataenite should be referred to a time-scale.
• Tetrataenite can be used as a probe to detect thermal/shock events recorded in meteorites.

Tetrataenite is a chemically ordered L10-type Fe50Ni50 alloy detected for the first time in 1977 by 57Fe Mössbauer spectroscopy studies in iron meteorites. The thermal history of meteorites, in particular short thermal events like those associated to hypervelocity impacts, can be constrained by tracing the presence of tetrataenite or its disordering into taenite. The knowledge of the disordering kinetics of tetrataenite, that is associated with changes in its magnetic properties, is still very fragmentary so that the time–temperature history of these meteorites cannot be constrained in details. Furthermore, knowledge of disordering kinetics is important due to potential technological application of tetrataenite as a rare-earth free strong magnet. Thus, this work provides the first time–temperature data for disordering reaction of tetrataenite. We have shown that disordering is not an instantaneous process but is a kinetic limited reaction. It was shown that disordering may take place at any temperature above the order–disorder transition for L10 superstructure phase (~320 °C) when the appropriate time-scale is considered. This result means that the apparent Curie point for tetrataenite is not an absolute property in the sense that any estimate of this parameter should be referred to a given time-scale.