Ta clustering and microstructural evolution in the A1 to L1Fe52PtX(Ta1−X) phase transformation

Abstract

A series of Fe52Pt48,Fe52.3Pt46.3Ta1.4 and Fe52Pt40.7Ta7.3 thin films were sputter deposited and subsequently annealed at 550 and 750 °C for 30 min. The as-deposited films, which adopted the A1 phase, had a change from a predominate (111) fiber texture to (200) with the Ta additions. This has been explained in terms of the competition between the surface energy and strain energy. Annealing at 550 °C facilitated the L10 order in Fe52Pt48 and Fe52.3Pt46.3Ta1.4. Upon annealing at 750 °C, all three composition films phase transformed into L10. Atom probe tomography revealed nanoscale clustering in the annealed Ta containing films. The formation of these clusters appeared to be a necessary initial step to allow the L10 ordering reaction to occur but clustering in of itself is not sufficient for order. For the Fe52Pt40.7Ta7.3 film, the Ta must be depleted within the matrix to a sufficient level to allow the binary Fe–Pt to order. For the Fe52.3Pt46.3Ta1.4 film, these clusters were qualitatively observed within the grains at 550 °C and in the grain boundaries at 750 °C. The Fe52Pt40.7Ta7.3 film had clusters within and near grain boundaries. The clustering in the grain boundaries deterred grain growth through a Zener-based pinning mechanism.

Application of Atom Probe Tomography in Understanding Thin Film Chemical Ordering and Stress Behavior

“…Note the presence of clusters near the grain boundaries which helped to reduce grain growth. These images were taken from reference [2].…”

“…The next example involves the A1 to L1 0 chemical ordering reaction in Fe 52 Pt 1-x Ta x thin films, where x = 1.4 or 7.3 at.% [2]. There have been conflicting reports in the literature if Ta additions either lower or raise the ordering temperature.…”