Investigation of the properties and microstructure titanium alloy BT 6 welded connections

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. Special features of breaking of the seams obtained by mechanized welding on the malleable alloy BT 6 GOST 19807 (Ti-6Al-V4) by CR ISO 15608 by the wire BT 1-0 GOST 19807 in the medium of argon was carried out. It is established that breaking the welded connection begins simultaneously in several places. Usually initiation of fracture (crack formation) is observed in the dilution zone with the multilayer welding. Also on the weld face and zone near the weld are formed numerous small cracks. In the zone of maximum stresses appear usually several main cracks, which lead to the structural failure. The formation of many cracks requires high expenditure of energy; therefore this destruction slow and can be noticed. This prevents emergency structural failure.