L. Swadzba

Structure and resistance to oxidation of an Al-Si diffusion coating deposited by Arc-PVD on a TiAlCrNb alloy

Abstract This article presents research results of isothermal and cyclic oxidation of TiAlNbCr intermetallic with and without an Al–Si coating. The coating was deposited by the arc-PVD method in two steps. Firstly, the AlSi layer was deposited then the samples were heated in a vacuum chamber to form a diffusion TiAlSi coating. After coating deposition the samples were heat-treated in vacuum at a temperature of 950 °C for a period of 2 h. Cyclic oxidation tests were carried out at 950 °C. The heating and cooling time was 5 min (3 °C/s). Mass changes of the specimen were recorded every 100 cycles. A total of 2400 cycles were performed. An analysis of the results obtained from cyclic oxidation was performed. The analysis of the Si effect on the structure of the layers and on the oxidation mechanism of the TiAlNbCr alloy was performed. Phase composition, morphology and the distribution of elements were defined by EDX, XRD and SEM in AlSi layers as well as in the scale. The results showed that Al–Si coatings (thickness approx. 40 μm) were effective in reducing the oxidation rate of γ-TiAl. The oxide formed on the surface of the Ti–48Al–2Cr–2Nb coating after oxidation is composed of a mixture of a large portion of Al 2 O 3 and a small portion of TiO 2 .

Overaluminising of NiCoCrAlY Coatings by Arc PVD on Ni-Base Superalloys

Investigations of depositing high temperature coatings on Ni base superalloys by the Arc-PVD method, using exothermic reaction processes between Ni and Al with NiAl intermetallic formation are presented in the article. By diffusion heating at 1323K, a NiAl high temperature diffusion coating containing 21 % at. Al and 50 pm thick was obtained. In the next stage coatings with more complex chemical compositionNiCoCrAlY were formed. The NiCoCrAlY coatings were made with two targets. Good consistence between the chemical composition of the targets and a uniform distribution of elements in the coatings was shown. Then the surface was also covered with aluminium by the Arc-PVD method. In the vacuum chamber of the equipment a synthesis reaction between NiCoCrAlY and Al with the formation of NiAl intermetallics of high Co, Cr, Y content was initiated. The final heat treatment of coatings was conducted in air and vacuum at 1323K. Strong segregation of yttrium into the oxide scale in the specimens heated in air was shown. It was possible to obtain NiAl intermetallics phase coatings modified by Co, Cr and Y by the Arc-PVD method. The coatings were formed on cast Ni base superalloy ZS6K and single crystal CMSX-4. An example of the application of this method for the aircraft engine turbine blades was presented. superalloys 2cQo Edited by T.M. Pollock, R.D. Kissinger, R.R. Bowman, K.A. Green, M. McLean. S. Olson, and J.J. Schim TMS (The Minerals, Metals &Materials Society), 2ooO