Enhancing the adhesive bonding strength of NiTi shape memory alloys by laser gas nitriding and selective etching

Laser gas nitriding process (LGN) was applied on NiTi shape memory alloy to obtain an alloyed surface consisting of TiN dendrites in NiTi matrix. By applying subsequent selective etching process, the matrix material in the alloyed layer can be selectively removed and a three-dimensional network of TiN dendrites is left on the surface protruding from the metal substrate. The 3D dendritic network provides extra surface area and locking mechanism for the adhesion joint. The microstructures of such textured surface were examined. The adhesion jointing characteristics of the surfaces were studied. A 150% increase in the lap-joint strength was achieved in the laser gas nitrided and etched specimen as compared with the sandblasted and etched ones.