Cracking mechanisms and prevention of Stellite 6# surface layer built by laser cladding during thermal cyclic process

This study analyzed the mechanism of the development and propagation of crack of Stellite 6 coating fabricated by laser cladding during thermal cyclic process and adopted the buffer layer between Stellite 6 coating and substrate to prevent the crack from generating. An obvious crack initiating from the layer surface was observed at 104 times of thermal cyclic treatment. The macrotensile stress, Laves phase, and nanocarbides along stacking faults detected by TEM (transmission electron microscopy), XRD (X-ray diffraction), and SEM (scanning electron microscopy) measurements were closely related to the initiation and propagation of the crack. SAED (Selected area electron diffraction) and HRTEM (high-resolution transmission electron microscopy) results demonstrated specific orientations between γ-Co, ε-Co, and nanocarbides formed in the thermal cyclic process, and details were depicted by 3D modeling. The adoption of the Inconel 625 buffer exerted a positive effect on cracking resistance, and no cracking phenomenon occurred at 300 times of thermal cyclic process resulting from the compressive residual stress during the fatigue test. Lastly, the microhardness of the coating with and without the buffer layer in different cycling times was measured. The coating without the buffer layer and the zone of the buffer layer coating far from the interface acquired enhancement in hardness performance. The hardness of the buffer layer coating near the interface first increased and then decreased.