Dendritic liquation in the weld metal of welded joints in titanium alloys

Abstract

Dendritic liquation in the weld metal of welded joints in titanium alloys M A K H O R E VDendritic liquation is one of the consequences of non-equilibrium solidification formed as a result of diffusion in liquid and solid phases. It affects the nature of structure and phase changes taking place during heat treatment.When examining the process of formation of a welded joint in welding as a partial case of solidification, it is important to note three main factors affecting solidification and characterising its special features: short holding time of the metal in the liquid state resulting in suppression of separating diffusion in the liquid phase; high cooling rates causing high solidification rates and suppressing separating diffusion; solidification range of the alloy whose increase increases the susceptibility to dendritic liquation.I2 The first two factors are common to welding all alloys, the third is a characteristic of the alloy. Dendritic liquation in the weld metal of welded joints in titanium alloys is also studied in this work.One of the main tasks was to determine the parameters of dendritic liquation in relation to the type of welding and their changes in subsequent heat treatment of welded joints.Like dendritic liquation, zonal liquation also takes place in the cast structure of welded joints and is especially extensive when welding with a filler. This is determined by the conditions of introducing fillers and limited possibilities of stimng the pool due to short-term holding of the metal in the liquid state. A reduction of the extent of dilution of the parent metal by the filler is detected in the direction from the centre of the weld to the parent metal and from the top to the bottom of the weld.In addition to dendritic and zonal heterogeneity, there is phase chemical heterogeneity caused by the presence of two allotropic modifications of titanium and differences in the chemical composition of a-and P-phases. ' The process of phase recrystallisation in cooling the alloys is accompanied by extensive diffusion and redistribution of the alloying elements between a-and @phases which does not reach the equilibrium state. This causes extensive heterogeneity of the phase components as regards their chemical composition.'Failure of a structure through a welded joint is often caused by special features of the formation of the structure during welding. It is therefore important to examine the macro-and microstructure. the distribution of alloying elements and the phase composition in different zones of the weld metal to detect the most critical regions, for example, regions of preferential formation of the a,-phase, most acute stress raisers, etc. 663 1 Graph of distribution of aluminium in weld metal of VTZO pseudo-a-alloy: a) AA W; bl €6 W.In this work, an examination was made of the distribution of alloying elements in the weld metal of welded joints in VT20 pseudo-alloy, a + P-alloy of the VT23 type and aalloy of the VT19 type produced by automatic argon-arc welding (AAW) and electrom beam welding (EBW...

Complex alloying and heat treatment of titanium alloys

“…In this article, the results are presented of investigations with the evaluation of the mechanical and technological properties, the strength of the alloys, and also the economic aspects of the investigated tasks [3][4][5][6][7] .…”