The Effect of the Toughness on the Wear Resistance of ALUMINA – TITANIA Coatings Obtained by APS

Al₂O₃ coatings can be used to improve the wear resistance of materials exposed to triblogical conditions, however some times, the conditions to which they are exposed produce cracks formation and particles detachment thus decreasing the coating protection capacity. In order to improve Al₂O₃ coating resistance, their toughness have to be increased which can be achieved by adding TiO₂ into them.

 In this work the effect on the toughness and wear resistance of coatings, two factors were studied: the ratio TiO₂ in Al₂O₃ matrix (respectively 13 and 40 % weight of TiO₂) and the size distribution of the sprayed particles (5 – 30 μm and 15 - 45 μm).

 Coatings were obtained by atmospheric plasma spraying on steel disks. The flow rate of Ar/H₂ plasma forming gas was 45/15 L/min, the current intensity varied between 400 and 600 A, the stand off distance was 100 mm and the preheating temperature of substrate surface was 300°C. The anode nozzle internal diameter was 6 mm.

 Toughness of coatings was measured using the indentation test with the Lawns– Evans–Marshall equation while the wear resistance was determined by measuring the wear track made by an alumina ball (6 mm in diameter) on the coated disk (ball on disk test).

 For the triblogical tests, the linear speed between the coated disk and the ball was 0,1 m/s, the normal load was 5 N and the tests were carried out during 20 000 cycles in dry condition with and without N₂ jet blowing off the debris.

 Results demonstrate the drastic influence of the toughness on the tribological behavior of the coating.