Dissertation for candidate of science degree in specialty 05.16.01 – metal science and heat treatment of metals. – National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute", Kyiv, 2019.
The dissertation is devoted to the establishment of the laws of diffusion phase formation during thermal and ionic processing of nanoscale layered film compositions of BCC (V, Fe, Cr), HCC (Ag, Pt, Ni, Cu) and HCT (FePt) lattices, among which systems are complete components (V-Ag); with a wide range of solid solutions (V-O) and ordering effects (Fe-Pt); and varying degrees of mutual solubility (Ni-Cu-Cr); with significantly different thermodynamic and crystal-chemical properties of the interacting components V-Ag, Fe-Au, Ni-Cu, Ni-Cr).
At the systematic level, the laws of diffusion phase formation and formation of structures that are an atypical for a massive state are investigated, as well as the influence of an additional (intermediate) layer, nanoscale factor, annealing atmosphere, and ionic surface treatment. For this purpose, a complex of experimental research methods was used: mass spectrometry of secondary neutral particles and secondary ions, X-ray diffractometry with grazing incidence beam geometry, structural and phase analysis by GIWAXS method, transmission electron microscopy, atomic force microscopy, in-situ electron diffraction, four-probe resistometry, SQUID magnetometry. New methodological approaches to the structural analysis of nanoscale materials using synchrotron radiation (with a photon flux density of up to 12 orders of magnitude and an exposure duration 150 times shorter than traditional X-ray diffraction methods) have allowed us to establish a number of new effects. These studies were performed at the SPring-8 Synchrotron Center of the National Institute of Physico-Chemical Research RIKEN, Japan.
For the first time on the investigated compositions it is shown that under the influence of the nanoscale factor at thermal (in the temperature range 623-923 K) and ionic (with doses of irradiation 1016-1017 ion/cm2), atypical for a massive state structures of different type are formed: solid solutions of substitution and supersaturated solids of impurity penetration (oxygen in BCC-vanadium), structural constituents of mutually insoluble elements (V-Ag, Cu-Cr), three-component phases VхAgуОz, FeхPtуAuz, NiхCuуCrz, fine-dispersed structures, Fe grain boundaries saturated with Ag, A in, Cu, Cr. The selected heat and ion treatment modes are typical for industrial technologies.
An annealing atmosphere (oxygen-, hydrogen-containing, neutral or ultra-high vacuum) as well as the creation of special layers of metal layers or substrates between metallic layers or on the substrate, have a regulatory influence on the development of thermally-activated processes of structures formation atypical for the massive state in the investigated nanoscale film compositions. Substantially other crystal-chemical, physical and magnetic characteristics (type of crystal lattice, degree of affinity for oxygen, electrical conductivity, magnetic susceptibility); the combination of annealing atmosphere and additional layers allows to:
– block diffusion processes in V, V/Ag film materials when annealing in high vacuum 10-7 Pa compared to annealing in oxygen-containing atmospheres;
– slow down the diffusion processes in the oxygen-containing annealing atmosphere by adding a HCC-Ag layer (low affinity to oxygen) to the BCC-V film (high affinity to oxygen);
– accelerate the diffusion processes and phase formation (formation of the ordered L10-FePt phase intensifies when adding a paramagnetic FCC-Au metal layer to the FCT-FePt ferromagnetic alloy); in a hydrogen-containing atmosphere, the diffusion of Au into the L10 phase intensifies;
– stabilize the desired phase with promising properties and surface roughness by adding hydrogen to the neutral atmosphere (argon) of the FePt/Au/FePt thermal treatment by blocking the diffusion-induced grain boundaries migration of the L10-FePt phase.
A multistage diffusion model as a set of diffusion mass transfer processes is confirmed, which includes different dominant diffusion phase formation mechanisms distributed over time. At the same time for the first time on the studied compositions the following set of dominant mechanisms is established:
– diffusion by grain boundaries (Ag – in layer V; Au – in layer L10-FePt; Cu, Cr – in layer Ni);
– output of the atoms of the components of the inner layers to the outer surface with the formation of the diffusing components phases (VхAgуОz, FeхPtуAuz, NiхCuуCrz);
– saturation of grain boundaries of V, FePt, Ni layers by diffusing Ag, Au, Cu and Cr elements;
– bulk diffusion from boundaries to volume of grains;
– diffusion-induced grain boundaries migration with the formation of bulk structures atypical for the massive state.
