Effect of the thickness of Ti intermediate layer on the microstructure and mechanical properties of the W/Ta multilayer composites

Abstract

Mechanical properties of tungsten (W) multilayer composites can be modified by the toughening layers and interfacial microstructure between W layer and toughening layer. The W/Ta multilayer composite usually shows low tensile strength and toughness because of the low strength of Ta layers and large bonding strength between W layer and Ta layer. In order to improve the strength and toughness of the W/Ta multilayer composite, Ti intermediate layers with different thickness ranging from 30 µm to 100 µm have been added between W layer and Ta layer to get a kind of W/Ti/Ta/Ti multilayer composites. It can be found that the thickness of the Ti layer has a large effect on the microstructure and mechanical properties of the W/Ta multilayer composites. The solid solution with pure β-Ti and β-Ta are formed in the Ti layer when the thickness of Ti layer is lower than 50 µm. Ti layer composed of β-Ti, β-Ta and α precipitates is developed when the thickness of Ti layer is larger than 80 µm. The comprehensive mechanical properties of the W/Ta multilayer composites increase as the thickness of Ti intermediate layer increases. The tensile strength of the W/Ti/Ta/Ti multilayer composites is up to 642 MPa, which is much higher than that of the W/Ta multilayer composites (274 MPa). The tensile strength of these multilayer composites can be evaluated by a modified mix model considering the interfacial stress concentration factor. As the fracture mechanism of the W/Ta multilayer composites is also modified by addition of the Ti layer, the toughness of the W/Ti/Ta/Ti multilayer composites is improved because of the delamination along with the W/Ti interface and plastic deformation of the Ti/Ta/Ti layer in plane stress condition.