Effects of crystal orientation on weldability and microstructural evolution occurring during linear friction joining of single crystal nickel-base superalloy to polycrystalline nickel-base superalloy were studied. Electron microscopy was used to characterize deformation and microstructural development. Changes in friction coefficient with changes in crystal orientation were observed and correlated to the metallurgical adhesion. These changes were explained by taking into consideration the single crystal deformation mechanisms. It was concluded that the orientation of the single crystal with reference to the principal axes of the pressure force is of utmost importance during linear friction welding (LFW) due to changes in orientation of the primary slip system in the fcc-based single crystal lattice. © 2008 Elsevier B.V. All rights reserved.