Effect of structural heterogeneity on the corrosion resistance of welded joints in titanium alloys

The effect of structural heterogeneity on the corrosion rate, stress corrosion and electrochemical properties of welded joints in commercial Ti of VT1-0 grade of PT3V, VT5-1 and OT4 alloys was determined. Mechanised welding of 8 mm thick sheets of these alloys was carried out by Ar TIG welding with no edge preparation and without filler wire. To equalise the grain structure in the weld, heat affected zone (HAZ) and parent metal, the welded joints were subjected to annealing in vacuum and air for 1 h at temperatures 15 plus/minus 5 deg C higher than the temperature of polymorphous transformation for each alloy. Subsequently, specimens were prepared from the Ti alloys, with the weld positioned in the transverse direction, and were used to determine the corrosion rate and susceptibility to stress corrosion cracking. Tests of continuous corrosion were carried out in 5% HCl, in concentrated solutions of formic and acetic acids, and in a solution which contained H sub 2 SO sub 4 with and without the addition of Cu exp 2+ ions. The susceptibility to corrosion cracking was examined in nitric acid at its boiling point and in CH sub 3 OH + 0.4% HCl solution at room temperature. The electrochemical properties of various sections of the welded joint in the condition after welding and after annealing in air and vacuum were determined. Visual and metallographic determinations were also made. (Original in Russian). Graphs, Photomicrographs. 4 ref.--A.R.