Study of metal structure welded on the titanium malleable alloy

Abstract

The weldability of titanium and its alloys depends on their physical and chemical properties. The most important of them are: high activity of titanium at elevated temperatures, significant tendency of grain growth at heating and the possibility of brittle phases forming during cooling of the welded joint. Nitrogen, oxygen and especially hydrogen in wide range of concentrations with titanium form interstitial solid solutions. These gases sharply decrease plasticity and considerably increase hardness and strength of the metal. Interstitial impurities (gases) cause brittle failure of seams, increase their tendency towards cold cracking and delayed fracture. The metallographic examinations of the seams obtained by mechanized welding on the titanium malleable alloy ВТ 3-1 GOST 19807 (Ti-6Al-2Cr-2,5Mo-Zr by CR ISO 15608) by the wire ВТ 1-0 GOST 19807 in the medium of argon was carried out by us.It is established that abrupt changes in the structure and, correspondingly, properties occur in the dilution zone. The size of this zone depends on the following basic factors: method and welding conditions, chemical composition of the alloy, thickness of the sheets to be welded, conditions for welding. Dilution zone appears to be determining for the estimation of weldability of titanium alloys and operation capacity of welded joints.