Papers by Keyword: Nanocrystalline Coating

Abstract: Combined treatment including vacuum arc deposition a hard nanocrystalline TiCuN coating followed by electron-beam treatment has been carried out in the present work. The structure and phase composition of surface layer have been studied by scanning and diffraction transmission electron microscopy. The modes of treatment leading to a dramatic improvement of microhardness and wear-resistance of modified material have been determined. It has been established that the combined treatment results in microscopic delamination of the silumin by elements and an interlayer of thickness ~20 nm dominated by silicon atoms is formed along the coating substrate interface.

Abstract: The rehealing ability of the oxide scales on sputter-deposited Ni-based K52 nanocrystalline coatings after pitting corrosion had been studied by polarization curves in 3.5% NaCl solution. The results indicated that the oxide scales formed on the nano-coatings exhibited excellent rehealing ability after pitting corrosion, and the rehealing oxide scales still had high corrosion resistance. The rehealing ability was declined with longer immersion time in the chloride solution. EDX analyses revealed that the oxide scales within the pits were composed of mixed-oxides. The mixed-oxides were made up of two layers: the external oxide layer was composed of Cr₂O₃ and TiO₂ and the internal oxide layer was Al₂O₃.

Abstract: The electrochemical behaviour of the rehealing oxide scales on the K52 nanocrystalline coatings had been studied by polarization curves. The results indicated that the oxide scales formed on the nano-coating exhibited rehealing ability after pitting corrosion, and the coating still had excellent corrosion resistance. The rehealing ability was enhanced with prolonged re-oxidation time. EDX analyses revealed that the oxide scales within the pits were composed of mixed-oxides (Cr2O3, Al2O3 and TiO2). The mixed-oxides were made up of two layers: the external oxide layer was composed of Cr2O3 and TiO2 and the internal oxide layer was Al2O3.

Abstract: K38 nanocrystalline coatings with various amounts of yttrium addition were deposited by magnetron sputtering. Cyclic oxidation tests were conducted at 800-1000oC in air in order to reveal the effect of reactive elements on the oxidation behavior of nanocrystalline material. The results indicated that the influence of yttrium was not observable at 800oC. At 900 and 1000oC, addition of 0.1 wt.% Y decreased the growth rate of scale, while 0.5 wt.% Y addition significantly increased the oxidation rate of nanocrystalline coating.

Abstract: The isothermal and cyclic oxidation behaviors of a Ni-based superalloy with singlecrystalline (SC), polycrystalline and nanocrystalline (NC) structures were studied at 1000°C. Results indicated that a uniform oxides scale consisted of external Cr2O3 with little TiO2 and internal continuous Al2O3 formed on SC alloy. A non-uniform external oxide of which some locations were nodule-like scale was formed on surface of cast alloy. The nodule-like parts consisted of TiO2, Cr2O3 and serious internal oxidation of Al, and rest flat surface was a Cr2O3 and Al2O3 layer. A continuous Al2O3 layer formed on the sputtered NC coating. The micro-structure influenced the oxidation mechanism and resulted in different oxide scale formed on three materials, which greatly influenced materials’ oxidation and cyclic-oxidation resistance.

Abstract: Development of advanced ternary nitride coatings such as titanium aluminium nitride and titanium vanadium nitride has attracted significant industrial interest in recent years. Titanium vanadium nitride is considered one of the advanced ternary nitride coatings of great commercial potential. It is believed with the additional element, the oxidation resistance of the coatings can be greatly improved at elevated temperatures. Furthermore, the type of elements selected can produce unique coating properties that can be beneficial to machining of different materials. This paper is to report a study on the structural stability of nanostructured titanium vanadium nitride coatings in high temperature annealing. Nanostructured titanium vanadium nitride coatings were produced by reactive magnetron co-sputtering on AISI H13 tool steel substrates at 240oC. Heat treatment was applied to the coatings at temperatures up to 1000oC. It was found that an unexpected grain refinement of the coatings occurred in the heat treatment process. Grain size of the coatings was found to decrease from ~200-300 nm to ~150 nm after the heat treatments. A strong TiN/TiVN (200) component was found to exist at temperatures up to 700oC but was depleted at higher annealing temperatures. With a finer and densified grain structure, the hardness of the coatings substantially increased from ~800 HV to ~1700 HV.

Abstract: γ-titanium aluminide a promising structural material for automotive and aircraft applications at high temperatures suffers from poor gas corrosion resistance. It has been proved in this work by means of microthermogravimetry and SEM, EDS, EBSD and X-Ray diffraction carried out and under isothermal conditions and thermal cycling that a great improvement of the oxidation resistance of this material can be achieved due to magnetron sputtered coatings of γ-TiAl with vatious additions (Ag, Cr, Mo, Nb, Si or Ta) or their combinations. The oxidation rate of some of these coatings is four orders of magnitude smaller than that of the bare γ-TiAl substrate.

Abstract: Ternary chromium aluminium nitride (Cr,Al)N coatings were produced by reactive magnetron co-sputtering technique at different nitrogen deposition pressures. Densified nanostructured coatings with grain size below 100 nm were obtained under critically controlled deposition conditions at low nitrogen partial pressures. The nanostructured coatings were generally of improved surface roughness and properties. Microhardness measurements showed that the coatings had much higher hardness than those of coarser grain sizes. It is believed that the refinement of the coating structure at low nitrogen pressures is associated with a larger number of atoms/molecules depositing on the substrate with higher energies, thus enhancing the adatom mobility and nucleated cluster formation in the coatings. The relationship between the grain size reduction and the deposition rate of the coatings was analysed.