Grain refinement mechanism of gas tungsten arc welded joint of tantalum thin walled tube

In order to get a nice welded joint of tantalum and control the size of grain,the temperature range of grain growth was obtained,and the tantalum sheet butt welding and tantalum tube welding tests were carried through using the gas tungsten arc welding for TA1 with the thickness of 0.56 mm.Furthermore,the influence of pressure on the weld solidification for pure tantalum was discussed.With the optic microscope and SEM,the microstructure of welded joint was investigated.The results show that the temperature range of grain growth of tantalum is 1 150-1 300℃.Under the condition of roller forming of thin tantalum tube,the grain refinement is obvious,and the maximal size of grain is about half compared with butt welding of sheet.Under the pressure of roller during welding,the number of the grain and velocity of the nucleation formation of weld are increased for the thin tantalum tube;a large number of is formed in the metal and the surface energy of grain boundary is decreased because of proliferating and interaction of dislocations.Simaltaneonsly,the grain in growth is broken,thus the grains of weld and heat-affected zone are refined.