High pressure torsion deformation of nanocarbon-reinforced metal matrix composites

Andreas Katzensteiner

Research output: ThesisDoctoral Thesis

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Abstract

In this work, severe plastic deformation (SPD) was used to produce ultrafine-grained (ufg) and nanocrystalline (nc) metal-matrix composites (MMC) with various carbon-derived reinforcement phases. Nickel/Carbon nanotube (Ni/CNT), silver/nanodiamond (Ag/ND), gold/nanodiamond (Au/ND) and nickel/nanodiamond (Ni/ND) composites were produced from powder, either through colloidal mixing, sintering and subsequent high-pressure torsion (HPT) deformation or through ball milling and HPT-consolidation and -deformation. The microstructural evolution of the HPT-deformed composites was investigated with scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). It could be shown, that the amount of HPT-deformation has a strong influence on the grain size of the matrix material and the size and distribution of the second phase particles. Other similar important influencing factors were the amount of reinforcement particles, the HPT-deformation temperature and for the ball milled composites the milling time and milling velocity. With the right combination of production parameters, it was possible to create MMCs with grain sizes and second phase particle sizes smaller than 100 nm and a homogeneous distribution of the second phase materials. The mechanical properties of the MMCs were investigated with microhardness measurements, tensile tests and compression tests. The microhardness was measured to increase in concordance with a decrease in the grain size, an increase in the amount of second phase particles as well as with the improvement of the second phase distribution. Along with the microhardness increase, the tensile and compression strength also increase while the ductility of the MMCs decreases. Compression tests showed a certain mechanical anisotropy in the MMCs which depends mostly on the shape of the second phase particles and their size in relation to the grain size.
Translated title of the contributionHochdrucktosions-Verformung von Nanokohlenstoff-verstärkten Metall-Matrix-Kompositen
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Clemens, Helmut, Assessor B (internal)
  • Bachmaier, Andrea, Co-Supervisor (internal)
  • Pippan, Reinhard, Assessor A (internal)
Publication statusPublished - 2019

Bibliographical note

embargoed until null

Keywords

  • High pressure torsion
  • metal matrix composites
  • carbon nanotubes
  • nanodiamonds

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