Influence of multilayer nanoarchitecture on phase transformations in the Ti-Cr-Zr system

Abstract

Nanocrystalline thin films find extensive applications due to their high mechanical strength and wear resistance. However, the challenge is to prevent unwanted grain growth during operation, especially at high temperatures, due to the increased grain boundary volume, which elevates the system's overall energy. Addressing this issue necessitates identifying optimal heat treatment conditions and selecting appropriate chemistry to stabilize grain boundaries. This study investigates the grain growth and phase evolution within Ti-Cr-Zr magnetron sputtered nano multilayers with 5 and 10 nm individual layer thickness, subjected to vacuum heat treatment at 1100 °C for 5 and 10 min. Characterization involved X-ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). During deposition, evidence of diffusion was observed as the multilayers formed Cr4TiZr, TiCr2, and Cr2Zr, phases. The Ti-Cr-Zr nanoscale system multilayers with 10 nm individual layer thickness also exhibited the emergence of Ti0.3Zr0.7 phase. During heat treatment grain growth occurred, after 10 min an average grain size of 173.7 nm and 119.1 nm was noted for the Ti-Cr-Zr nanoscale system multilayer with 5 nm and 10 nm individual layer thickness, respectively. The different growth rates are attributed to their distinct interfacial volumes, influencing the reaction velocity due to the variations in nano-layer thickness. No new phases were formed after heat treatment for the case of 10 nm individual layer thickness coating. However, 5 nm individual layer coatings showed the emergence of Ti0.3Zr0.7 phase, not present after deposition. In conclusion, this research achieved the desired nano grain stabilization of the Ti-Cr-Zr system nanoscale multilayers after heat treatment at 1100 °C for 10 min. This process led to the complete decomposition of the multilayer structure, resulting in the formation of grains smaller than 200 nm, marking a significant step toward the effective control of grain growth in nanocrystalline materials.