Effect of synthesis temperature on the phase formation of NiTiAlFeCr compositionally complex alloy thin films

A Marshal, P Singh, D Music, S Wolff-Goodrich… - Journal of Alloys and …, 2021 - Elsevier
Journal of Alloys and Compounds, 2021Elsevier
The synthesis temperature dependent phase formation of Ni 10 Ti 10 Al 25 Fe 35 Cr 20 thin
films is compared to a bulk processed sample of identical composition. The as-cast alloy
exhibits a dual-phase microstructure which is composed of a disordered BCC phase and
AlNiTi-based B2-and/or L2 1-ordered phase (s). Formation of the BCC phase as well as an
ordered AlNi-based B2 phase is observed for a thin film synthesised at 500° C (ratio of
synthesis temperature of thin film to melting temperature of bulk alloy: T/T m= 0.49), which is …
Abstract
The synthesis temperature dependent phase formation of Ni10Ti10Al25Fe35Cr20 thin films is compared to a bulk processed sample of identical composition. The as-cast alloy exhibits a dual-phase microstructure which is composed of a disordered BCC phase and AlNiTi-based B2- and/or L21-ordered phase(s). Formation of the BCC phase as well as an ordered AlNi-based B2 phase is observed for a thin film synthesised at 500 °C (ratio of synthesis temperature of thin film to melting temperature of bulk alloy: T/Tm = 0.49), which is attributed to both surface and bulk diffusion mediated growth. Post deposition annealing at 900 °C (T/Tm = 0.75) of a thin film deposited without intentional heating results in the formation of NiAlTi-based B2 and/or L21-phase(s) similar to the bulk sample, which is attributed to bulk diffusion. Depositions conducted at room temperature without intentional substrate heating (T/Tm = 0.20) resulted in the formation of an X-ray amorphous phase, while a substrate temperature increase to 175 °C (T/Tm = 0.28) causes the formation of a BCC phase. Atom probe tomography of the thin films deposited without intentional substrate heating and at 175 °C indicates the formation of ∼5 nm and ∼10 nm FeAl-rich domains, respectively. This can be rationalized based on the activation energy for surface diffusion, as Ti and Ni exhibt 2.5 to 4 times larger activation energy barriers than Al, Fe and Cr. It is evident from the homologous temperature that the phase formation observed at 500 °C (T/Tm = 0.49) is a result of both surface and bulk diffusion. As the temperature is reduced, the formation of FeAl-rich domains can be understood based on the differences in activation energy for surface diffusion and is consistent with kinetically limited thin film growth.
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