Source: https://mfint.imp.kiev.ua/en/abstract/v40/i11/1521.html
Timestamp: 2019-04-25 12:38:15+00:00

Document:
A modification of the surface layer of a Ti6Al4V titanium alloy is carried out using ultrasonic impact treatment (UIT) with addition of the Al$_2$O$_3$ and Cr$_2$O$_3$ powders to the deformation zone. As shown by means of x-ray diffraction phase analysis, optical and scanning electron microscopies, the surface layers of composite are formed during the UIT induced severe plastic deformation. The microhardness of the composite layers is 2 times higher than that of the matrix alloy. The high-temperature oxidation of composite layers containing Cr$_2$O$_3$ particles and the Cr$_2$O$_3$ + Al$_2$O$_3$ mixture leads to strengthening the underlying layers due to the formation of a solid solution of oxygen in the $\alpha$-phase, which is not observed in the case of a layer/coating formed with addition of Al$_2$O$_3$. According to the gravimetric analysis of samples during the cyclic high-temperature oxidation in air (20 cycles for 5 hours at a temperature of 550°C), it is concluded that the composite layer/coating saturated with Al$_2$O$_3$ particles have the highest heat resistance. This is due to the close values of the thermal expansion coefficients of Al$_2$O$_3$ coating and Ti6Al4V alloy, as opposed to the behaviour of the rough alloy and other composite layers, which are destroyed during the cyclic heating–cooling process.
Key words: ultrasonic impact treatment (UIT), composite layers, oxide powders, coating, microhardness, heat resistance.
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