Coating Production

A1 sample:

Bond coat: Al-35Si (RST, new development) Grain size 38-90 urn

Top coat: a) 25% MgO/ZrO- (Amperit) Grain size 10-53 um b) 8%Y203/Zr02 (Amperit) Grain size 10-70 um

Coatings were deposited using an Eutronic Plasma 80 kw unit. A mixture of argon + 12% hydrogen plasma bearing gas was used. We have sprayed sane samples with a cermet (ceramic/metallic mixture) layer (0.05 mm) in the ceramic coatings, approximately 0.5 mm apart in order to reduce the crack propagation in the coatings.

A second type of coating consists of a bond layer of Al-35Si (0.2 mm) with an intermediate layer 50%/50% Al-Si/stab. Zr02 (approximately 0.5 mm) or an intermediate where the metal concentration was lowered continuously to zero (pure Zrt^) over 0.5 mm. The ZrO^Y^O^ layer was 1.2 mm; respectively 16 mm.

Four samples sprayed with 8% Y20.j/Zr02 and 24% Mg0/Zr02 have shown that Y20, stabilized zirconia powders have better thermal shock properties compared to 25%Mg0/Zr02.

Coating Design No. 1: One coating design which was tested was a sandwich type coating of metal and stabilized zirconia coatings on silumin or cast iron. This is the same coating system as used at Battelle, Frankfurt, where the functional top layer is a laminate of ceramic and cermet (70% metal, 30% ceramic and 70% ceramic, 30% metal in the outer part). Fig. 10a illustrates the microstructure of the coating system. Battelle claimed that this type of coating can be adapted better to a given temperature load.

Our results have shown that this type of coating design easily develops cracks in the cermet layer which propagates to the ceramic/metal interphase causing defoliation of the ceramic layer (Fig. 10 b and c).

Coating Design No. 2: In the past, IKT has been intensively active in developing coating systems/materials for applying ceramic top coating on Al-alloy pistons. This has resulted in a new RST bond layer of IKT 201. The coating system consists of the following layers: A relatively thin bond layer on IKT 201 followed by an intermediate layer where the metal concentration drops continuously to zero over a range of 0.3 mm and a partially stabilized zirconia top coat up to 1.0-1.5 mm thick. The pore concentration in the ceramic is specified to be between 10 and 15% evenly distributed. An example of the microstructure in the as-sprayed condition is shewn in fig. 11.

in-80

Coated test samples with 1 mm thick top layer of partially stabilized zirconia have performed more than 2000 cycles without spalling (less than 10% of the surface).

BMW Automobile Test: Arrangements were made to coat the Al-Si pistons in a privately cwned BMW car which is used in European rally racing. These zirconia coated pistons with the RST bond coats were inspected periodically by borescope. No coating distress could be detected after 10,000 kilometers. Thermally insulating the piston cap increased the turbocharger output from 1.6 to 2.0 bar which produced additional horsepower.

Carbon-carbon composite for cylinder liner: The rapid progress made in recent years to bring the marine diesel engine to higher efficiencies has brought with it higher cylinder powers and lower fuel consumption. These excellent properties of the marine diesel engine have been achieved by raising cylinder working pressures and temperatures. This has caused higher mechanical and thermal load onto the combustion chamber components. At the same time bunker oils have declined in quality and the possibilities of corrosion and erosion have turned higher.

The new carbon-carbon composite with a good adherent plasma sprayed wear/erosion resistant layer on the inside. One example is shown in Fig. 12. This 10 mm wall thickness cylinder has been tested to 800 bars without noting any defect. This carbon-carbon composite should be a good candidate for a high temperature diesel engine liner with a major reduction in liner distortion from a true cylindrical shape.

REFERENCES:

1. R.H. Hoel and I. Kvernes, "The Microstructure of Thermal Barrier Coatings", National Thermal Spray Conference, Orlando Sept. 1987.

2. M. Ruhle et al. Advances in Ceramics 12, Science and Technology of Zirconia II 352-370 1983 Am. Cer. Soc.

3. T. Suga, I. Kvernes & G. Eisner, "Fracture Energy Measurements of

Ceramic Thermal Barrier Coatings",

Werkstofftechnik 15 (1984), p.

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