V.K. Shatalov – Dr.Sc. (Eng.), Professor, Bauman Moscow State Technical University, Kaluga Branch. E-mail: firstname.lastname@example.org
A.A. Blatov – Engineer, Bauman Moscow State Technical University, Kaluga Branch. E-mail: email@example.com
The results of experimental production of hard surfacing wire with application of a micro-arc oxidation technique are discussed. The advantages of the suggested method are shown.
The chemical-heat treatment and anodizing methods are considered advanced methods of improving the antifriction properties and wear resistance of parts made of titanium alloys working under contact loads. A process of thermal oxidation results in development of a layer of titanium oxides with high mechanical strength and high wear resistance. Anodizing allows obtaining oxide films with isolated anti-friction components in their composition.
Welding deposition of a high hardness metal layer is an efficient technique for enhancing the life time of titanium alloy parts working in a marine or in other aggressive environment under repeated static loads and abrasion.
Surfacing wire surface coating with stable oxides is a widely used method of saturation of titanium alloys with oxygen.
Such alloys as 2B, VT6sv and PT 7M enriched with oxygen during thermal oxidation are widely used as surfacing wire materials.
Thermal oxidation is carried out by exposing the surfacing wire to 950°C in air for 3 to 4 hours. The surface of the wire gets covered with scale. The technique is power-, time- and labor consuming. It includes more than 10 process operations. Cleaned of scale, wire subjected to vacuum annealing to remove hydrogen.
We use micro-arc oxidation (MAO), which is a relatively simple process. It is flexible in energy and temporal characteristics management and optimization. The MAO method is based on anodic oxidation in an electrolyte solution at high potential. The high potential causes microplasma breakdowns (mikro-arcs) at the anode surface.
Titanium alloy oxide coating thickness (10 microns in the present work) is mainly determined by current density and by duration of the process. The surface coating obtained by MAO must be uniform and must have a color from light gray to dark gray, with various shades.
Experiments confirmed the benefits of the method. Metal deposited by argon arc welding using a non-consumable electrode with MAO treated filler wire satisfies the composition, quality and hardness requirements.
In contrast to thermal oxidation, MAO does not increase concentration of hydrogen in the wire, eliminating the vacuum degassing, quenching in water and subsequent mechanical after-treatment. MAO allows achieving a considerably higher production rate in comparison with thermal oxidation.