INFLUENCE OF EXTREME PLASTIC DEFORMATION ON THE MICROSTRUCTURE AND PROPERTIES OF METAL MATERIALS

V doktorski disertaciji je obravnavana problematika vpliva ekstremne plastične deformacije na mikrostrukturne spremembe disperzijsko utrjenega bakra, s ciljem, da se združi disperzijsko in deformacijsko utrjanje in ustvari nanostrukturni kompozit z izboljšanimi lastnostmi. V okviru doktorske disertacije je bila raziskana možnost doseganja velikih globin cone notranje oksidacije (CNO). Z modificiranim Rhinesovim paketom je bila dosežena zadostna globina cone notranje oksidacije za študij obnašanja disperzijsko utrjene zlitine med ECAP (Equal channel angular pressing) postopkom. Preučeno je bilo tečenje materiala na makro nivoju pri delno notranje oksidiranem preizkušancu in homogenem referenčnem vzorcu iz modelirne mase z namenom, da se ugotovi vpliv oksidnih delcev v CNO na tečenje materiala med ECAP postopkom in določi porazdelitev deformacije in stopnjo deformacijskega utrjanja po volumnu preizkušanca. Ugotovljeno je bilo, da na makroskopskem nivoju oksidni delci ne vplivajo na tečenje materiala, zato ni razlike v tečenju cone notranje oksidacije in trdne raztopine. S primerjavo razvoja mikrostrukture med ECAP postopkom v disperzijsko utrjenem materialu in trdni raztopini je bil ovrednoten vpliv oksidnih delcev na mehanizem plastične deformacije. Ugotovljeno je bilo, da oksidni delci povečajo fragmentacijo zrn med ekstremno plastično deformacijo, kar privede do nastanka nanometrskih enakoosnih zrn, ki so obdana z amorfnim mejnim področjem. Na osnovi rezultatov je bil postavljen model plastičnega tečenja nanostrukturnega kompozita v katerem se predpostavlja, da plastično tečenje poteka z drsenjem vzdolž mej zrn.This work deals with the influence of plastic deformation on microstructural evolution of dispersion strengthened copper with the aim of uniting the mechanism of dispersion and deformation strengthening to produce nanostructured composite with improved properties. Within the work the possibility of achieving greater depths of internal oxidation zone was studied. With the modified Rhines package a sufficient depth of internal oxidation zone was reached to study the behaviour of dispersion strengthened alloy during ECAP (Equal channel angular pressing) process. Material flow in a partly internally oxidized billet and in a homogenous reference sample made of modelling mass was also studied to analyse on the macro scale the influence of the internal oxidation zone on material flow behaviour during the ECAP process. The analysis was performed with the aim of revealing the uniformity of strain distribution and to get the information about deformation strengthening across the volume of the billet. It was found out, that on the macro scale the oxide particles do not affect the material flow, therefore there is no difference in flow of internal oxidation zone and solid solution. The influence of oxide particles on the mechanism of plastic deformation was evaluated by comparing the microstructural evolution during ECAP process of dispersion hardened material and solid solution. It was discovered, that the oxide particles increase the fragmentation of the grains during severe plastic deformation, which leads to the formation of nano-sized equiaxed grains with amorphous grain boundaries. Based on the results, the model of plastic flow for nanostructural composite was developed, in which it is assumed, that the plastic flow is carried out with sliding along amorphous grain boundaries