Phase stability in ti/bcc multilayered thin films

Abstract

Materials structures with large surface area-to-volume ratios can exhibit size dependent physical and chemical properties that are different than their bulk form. These changes are often related to the material adopting a different crystallographic phase. Often these phase transformations are serendipitously observed with the criteria for their stability difficult to ascertain. This work elucidates the underpinnings of phase stability behavior in the nanoscale regime by providing a systematic study using Ti/bcc multilayered thin film architectures. The influences of lattice misfit, layer thickness, composition and chemical intermixing on the phase stability are determined. In situ thin film growth stresses of these materials are measured and correlated to the interfacial stress evolution to help rationalize the stability behavior. X-ray and electron diffraction have been employed to determine the phase with atom probe tomography used to characterize the chemical compositions within the materials and across the interfaces. This work will delineate how intrinsic film stress drives compositional intermixing across such interfaces which can thermodynamically promote phase transformations.