Agnieszka Twardowska

Low temperature Ti-Si-C thin film deposition by ion beam assisted methods

Thin, multiphase Ti-Si-C coatings were formed by IBSD or by IBAD methods on AISI 316L steel substrates in room temperature, using single Ti3SiC2 target. In those methods the TiXSiCY coatings were formed from the flux of energetic atoms and ions obtained by ion sputtering of the Ti3SiC2 compound sample. As sputtering beam the beam of Ar+ ions at energy of 15keV was applied. In the IBAD method the dynamically formed coatings were additionally bombarded by beam of Ar+ ions at energy of 15keV. The ion beams parameters were obtained by using Monte Carlo computer simulations. The morphology (SEM, TEM), chemical (EDS/EDX) and phase composition (XRD) examinations of formed coatings were provided as well as confocal Raman microspectroscopy. Analyzed coatings were relatively thin (150nm-1μm), flat and dense. XRD analysis indicated in amorphous TiSi, the traces of Ti5Si3 and other phases from Ti-Si-C system (TiSi, TiSi2,Ti3SiC2). For chemical bonds investigation, the laser beam with length of 532nm was used. Those analyses were performed in the low (LR) or in high (HR) resolution modes in room temperature and in 4000C. In the HR mode the spectral resolution was close to 2 cm−1. In Raman spectra peaks at: 152cm−1, 216cm−1, 278cm−1, 311 cm−1, 608cm−1, 691cm−1 were recorded. Nanoindentation tests were done on coated and uncoated substrates with diamond, Berkovich-type indenter. Vickers hardness HIT and reduced elastic modulus EIT were calculated using Olivier& Pharr method. HIT for coated substrates was in the range 2.7 to 5.3 GPa, EIT was 160 GPa.

Influence of carbon dopants on the structure, elasticity and lattice dynamics of Ti5Si3C x Nowotny phases

Density functional theory studies on the Ti5Si3C x systems with various concentrations of carbon impurities () are reported. The effects of interstitial carbon atoms on crystal and electronic structures, and on the elastic and vibrational properties of the Ti5Si3C x compound are analysed and discussed. The results of the present investigations indicate not only strong bonding between carbon atoms and their neighbouring titanium atoms, but also the effects of carbon impurities on the atomic bonds beyond the immediate proximity of the dopants. These determine to a great extent the electron densities of states, and the structural and elastic properties of the Ti5Si3C x Nowotny phases. Although carbon atoms tend to stabilise Ti5Si3C x phases, they also have a negative effect on their ductile properties. The strong impact of carbon impurities on the lattice dynamics of Ti5Si3C x compounds is revealed by the phonon and Raman spectra, which remain sensitive to changes in the interatomic distances. In C-doped systems the phonon bands originating from the vibrations of carbon impurities appear at high frequencies and remain well-separated from the lower lying phonon bands dominated by the vibrations of Ti and Si sublattices. The lower frequency phonon bands also experience changes due to the incorporated dopants. Impurities occupying the interstitials of the Ti5Si3 lattice are responsible for the appearance of new infrared active and optically inactive modes of A 2u , E 1u and E 2u symmetries, leaving the number of Raman active modes unchanged. Modifications to the dynamical properties of ternary Ti5Si3C x phases manifest themselves via shifts and the suppression of phonon peaks as well as the emergence of new phonon peaks which are absent in the binary Ti5Si3 system. The observed effects become enhanced with an increased concentration of carbon impurities.

On the wear of TiBx/TiSiyCz coatings deposited on 316L steel

Abstract Bilayer TiBx/TiSiyCz coatings were formed on AISI 316L steel substrates by dual beam ion beam assisted deposition from TiBx and TiSiyCz targets. Coated and uncoated substrates were subjected to nanoindentation, scratch and friction-wear tests. Scratch and ball-on-disc tests were conducted in non-lubricated sliding, using a diamond pin and 100Cr6 steel ball, respectively. Scanning electron microscopy and atomic force microscopy were used to examine the surfaces of coated samples, before and after tests. To investigate wear mechanisms in the coating–substrate systems, thin foils were prepared from worn areas for transmission electron microscopy observations. TiBx/TiSiyCz coatings proved to be well adherent to steel substrates. The main wear mechanism was of abrasive type. Intensive plastic deformation of steel substrate under critical loads was revealed.

Vibrational Spectroscopy of Binary Titanium Borides: First-Principles and Experimental Studies

Vibrational dynamics of binary titanium borides is studied from first-principles. Polarized and unpolarized Raman spectra of TiB, TiB2, and Ti3B4 are reported along with the experimental spectra of commercial powder and bulk TiB2 containing less than 1 wt.% of impurity phases. The X-ray diffraction spectroscopy, applied for phase composition examination of both bulk and powder materials, identifies only the TiB2 phase. The simulated Raman spectra together with literature data support interpretation and refinement of experimental spectra which reveal components arising from titanium dioxide (TiO2) and amorphous boron carbide (B4C) impurity phases as well as graphitic carbon. These contaminations are the by-products of synthesis, consolidation, and sintering aids employed to fabricate powder and bulk titanium diboride.

Ti–Si–C Films Formed by Dual Beam Ion Assisted Deposition

Ti–Si–C coatings were formed at room temperature on AISI 316L steel substrates by dual beam ion assisted deposition technique from single compound Ti3SiC2 target. Scanning and transmission electron microcopy method were used to examine as-deposited coatings. Their morphology was smooth and dense and their thickness were in the range from 100 nm to 1μm. Raman spectra of coated substrates were collected up with five peaks at the same positions as for Ti3SiC2 compound target. TEM and HRTEM examinations, accompanied by SAED analyses revealed that deposited films were amorphous. Nanoindentation tests were provided on coated and uncoated substrates and hardness HIT and reduced elastic modulus EIT were calculated using the Oliver & Pharr method.