Plasma enhanced paste aluminizing of Ti–45Al–2Nb–2Mn–1B with Al–Si alloy

Ti–45Al–2Nb–2Mn–1B was plasma enhanced paste aluminized at 800 °C for 30 min with Al–Si alloys, to investigate the effect of silicon on the structure of coatings and oxidation compounds. Optical and electron microscopy revealed fine and coarse particles of blocky and plate like or needle type particles of Ti5Si3 and TiSi2 phases in aluminum or TiAl3 matrix of the coating layers.

X-ray diffraction (XRD) and Energy Dispersive X-ray (EDX) studies demonstrated the dissolution of Si in the TiAl3 and TiAl2 phases and dissolution of aluminum in Ti–Si structures. The thickness of the layers was approximately 300 μm. Cracks were observed in the coatings with low amount of silicon after preparation operations, whereas coatings with high silicon were not cracked after treatments and other operations.

The hardness of the aluminized samples with low silicon was about 500 HV0.5 and that of the samples with highest silicon was around 248–435 HV0.5. Oxidation of the coatings was carried out at 900 °C in atmospheric air pressure. Oxidation of silicon modified layers showed fine and dispersed Ti5Si3 and TiSi2 particles in the TiAl3 matrices.

Oxidation resulted in the production of Al2O3 oxide phase in the top layers that appeared among the Ti(Al,Si)3 grains of the matrix. The coatings with highest silicon showed less diffusion of oxygen into the top layers. Vickers microhardness of these layers increased up to 800 HV0.5 without cracking of the layers.

This paper is published in journal of Surface and Coating Technology.

Request for PDF