Evolution mechanism of the interfacial reaction layers in the joints of diffusion bonded Mo and Al foils

Mo foil (10-20 μm in thickness) and Al foil (20-60 μm in thickness) were vacuum diffusion bonded at 600-640°C under 20 MPa for 54 min-6 h. The joints were examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to study the evolution mechanism of the reaction layers. The results show that Al atoms diffuse into Mo grain boundaries and form reaction products as Mo₃Al₈, MoAl₄, MoAl₅ and MoAl₁₂. The surface oxide film is eroded by the growths of the reaction products that plow into the lamellar texture of Mo grain boundaries. Mo₃Al₈ layer grows by 'taking root' downwards and transforms into MoAl₄ and MoAl₅ phases upwards by absorbing Al atoms. MoAl₁₂ layer grows up from MoAl₅ layer in the same way. When the supplement of Al atoms ceases, MoAl₁₂ transforms reversely into MoAl₅ and MoAl₅ into MoAl₄ via the loss of Al atoms. However, MoAl₄ continues to precipitate from Mo₃Al₈ layer. At last, there are MoAl₄ and Mo₃Al₈ remained on the joint interface.