Abstract
It was determined that in an electrolyte containing 1.75 g/L KOH+1 g/L Na2SiO3+2 g/L NaAlO2, with an increase in current density from 15 A/dm2 to 50 A/dm2, the phase composition of the coating changes. In the three-phase state (aluminum titanate, rutile, and amorphous-like phase), with increasing j, instead of an amorphous-like phase, a crystalline mullite phase appears. The hardness of the coating increases from 5400 MPa to 12500 MPa. It was found that, in combination with aluminum titanate, mullite is the basis for achieving high hardness in the coating. The formation of a ceramic micro-arc oxide coating on the surface of the VT3-1 titanium alloy makes it possible to reduce the dry friction coefficient by more than 5 times to f=0.09.The effect of electrolysis conditions during micro-arc oxidation of the VT3-1 alloy (titanium-based) on the growth kinetics, surface morphology, phase-structural state, and physical and mechanical characteristics (hardness, coefficient of friction) of oxide coatings was studied. It was found that the process in the mode of micro-arc discharges is stably implemented on the VT3-1 alloy in an alkaline (KOH) electrolyte with additions of sodium aluminate (NaAlO2) and liquid glass (Na2SiO3). This makes it possible to obtain coatings up to 250 μm thick. In this case, a linear dependence of the coating thickness on the time of the MAO process is observed. The growth rate of the coating increases with increasing current density. The highest growth rate was 1.13 μm/min. It was revealed that in an electrolyte containing 1 g/L KOH+14 g/L NaAlO2 with an increase in the duration of oxidation from 60 to 180 minutes, the relative content of the high-temperature phase, rutile, increases. In the coatings obtained in the electrolyte 1.75 g/L KOH+1 g/L Na2SiO3+2 g/L NaAlO2, with an increase in the duration of the MAO process, the relative content of the amorphous-like phase decreases and the content of the crystalline phase of mullite (3Al2O3·2SiO2) increases
Highlights
Plasma processes have recently become the basis of modern surface hardening technologies [1, 2]
As shown by the studies given in [35, 36], coatings obtained as a result of micro-arc oxidation of titanium alloys can significantly increase the elastic modulus and wear resistance of the base material
There is no doubt that with a change in the growth kinetics of a coating on a titanium alloy, there is a change in the structure and phase composition of such a coating, which determine its basic properties
Summary
Plasma processes have recently become the basis of modern surface hardening technologies [1, 2]. Due to the strong disequilibrium of such processes, it is difficult to simulate them [3, 4], to predict the properties obtained as a result of plasma technologies of materials, the method of structural engineering began to be used [5, 6] This is especially important for engineering materials, where surface properties in most cases determine their functional characteristics. To obtain the required composition of the coating, it is necessary to change the technological conditions in the process of micro-arc oxidation In this regard, the development of the method of structural engineering for the MAO process is of great importance. The generalization of structural data for various types of materials is the basis for working out the MAO technology in order to optimize it
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