Characterization of the diffusion bonding behavior of pure Ti and Ni with different surface roughness during hot pressing

Pure Ti and pure Ni thin plate with different surface roughness (the surfaces are proceeded with 280#, 1000# silicon carbide and polished with 0.05 mu m silicon latex particles) are joined through diffusion bonding during hot pressing at 1073 K for 30 min. A quantitative analysis of scanning electron microscope (SEM)/atomic force microscopy (AFM) images is carried out to determine the morphologies of the long ridges of triangular section in the ground surfaces. It is found that the typical microstructure shows a alpha-Ti/beta-Ti/Ti2Ni/TiNi/TiNi3/solution phase (Ni)/Ni multilayer structure in the joint interface of the specimens. The thickness of the Ti2Ni and TiNi3 layers increases with the decreasing of the surface roughness, while the beta-Ti and TiNi do not appear in the joint interface because of the insufficient diffusion when the surface are ground with P280 or P1000 grit SiC. There are some microvoids generated in the diffusion bonded interfaces, which should greatly influence the mechanical properties of the joints, but the microvoids were getting fewer and smaller with the decreasing of surface roughness. Meanwhile, the shear tests are conducted at room temperature and the shear strength of the joint interface are 0.95 MPa, 2.705 MPa and 23.82 MPa with three different surface roughness. From the observation of the fracture surfaces of the samples which are ground with 280# silicon carbide, it can be found that the fractures happen mainly along the original Ti/Ni interface as lots of microvoids appear in the Ti/Ni interface, and furthermore, the cracks are also mainly generated between the TiNi3 and Ni matrix duo to the high elastic modulus of solution phase (Ni) when the surfaces are polished with 0.05 mu m silicon latex particles. (C) 2014 Published by Elsevier Ltd.