Abstract
The bond strength and microstructure of a Cu (copper)/W (tungsten) joint friction-welded with an intermediate layer of Nb (niobium) foil 7-25 μm thick have been investigated in order to find proper thickness of the intermediate layer for obtaining a joint with high performances and slight microstructural changes in the weld. The tensile strength of the joint was increased more rapidly with the friction time, as the thickness of the intermediate layer was decreased. For all the joint obtained in this investigation, a number of Nb particles were incorporated into the Cu adjacent to the weld interface, forming a mixed region of Cu and Nb. The width of this mixed region and the number density of the involved Nb particle were decreased, as the intermediate layer thickness was decreased. In this mixed region and at the weld interface, significant amounts of porosities and uncontacted areas were observed at friction times shorter than 2 s, when the intermediate layer thickness was more than 15 μm. From these results, it can be concluded that in the Nb foil employed in this investigation thinner one is more favorable as an intermediate layer for the friction welding of copper to tungsten. The effect of the intermediate layer on the bond strength is also discussed considering the interaction of the Nb particle with W and O during the friction welding.
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