VT20 titanium alloy properties estimation after removing of operational carbonaceous impurities by chemical means

Аuthors

Nochovnaya N. A., Nikitin Y. Y.^*, Gudkov S. V., Savushkin A. N.

All-Russian Scientific Research Institute of Aviation Materials. State Research Center of the Russian Federation, 17, Radio str., Moscow, 105005, Russia

*e-mail: nikitinyj@viam.ru

Abstract

The lack of information in domestic and foreign sources on the effect of carbonaceous impurities purification technology on titanium alloys' properties complicates for technologists selection of the most effective and safe methods of purification of a gas turbine engine compressor air-gas channel parts and units.

The purpose of this work consists in evaluating the property change of VT20 titanium alloy while removing carbonaceous impurities by chemical means.

The studies were performed with laboratory samples manufactured from a VT20 alloy sheet-billet. Caronaceous impurities, imitating operational ones, were applied on a number of samples according to the developed technology.

Eight foreign made and domestic chemical technologies (compositions) were studied as purification means.

The authors established that the most effective removal of the carbonaceous impurities from the surface of the heat-proof VT20 titanium alloy was ensured by domestic purifying solution No 1, a two-stage purification technology in alkaline and acid solutions (“loosening + etching”), and foreign made solution HDL 202. However, while purifying carbonaceous impurities with HDL 202 solution a general etching of the surface and its microstructure change might occur.

The surface roughness values of the VT20 titanium alloy do not change significantly after the removal of impurities. The relief and profiles of the purified surfaces have a shape similar to those of the original samples.

A slight increase in the microhardness of the purified samples (up to 5%) can occur due to gas saturation of thin surface layers, due to both formation of carbonaceous impurities and the processes of chemical surface purifying.

When purifying the surface from carbonaceous impurities, the activity of the surface decreases, regardless of the type of the solution used. The least decrease in activity is ensured by cleaning solution No 1.

There is no deterioration of moistening characteristics by the VPr16 solder of the surface purified from the carbonaceous impurities by purifying solution No 1 or two-stage “loosening + etching” technology and HDL 202 solution.

Purification of carbonaceous impurities by all studied solutions does not lead to VT20 alloy strength and plastic characteristics degradation, and to a change in the character of its destruction under conditions of static loading.

Keywords:

carbonaceous impurities, roughness, surface activity, microhardness, strength, ductility, soldering, heat-proof titanium alloy

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