Effect of local ?over-growth? on fracture behaviors of coated titanium fiber fabricated by plasma electrolytic oxidation

The local 'over-growth' behavior of plasma electric oxidation (PEO) coating plays a vital role in the fracture of alloy. In this work, the effect of the 'over-growth' on the fracture behavior of PEO coating on the titanium fiber substrate was investigated by the tensile and bending. The 'over-dissolution' on the surface of fiber occurred by concentrated plasma discharge during the discharge stage, which lead to the 'over-growth' behavior and formed a 'zigzag' region in the interface between fiber and coating. The 'over-growth' behavior induces the concentration of residual stress generated by PEO, which provides a driving force for the crack initiation and propagation. The cracks propagate from the 'zigzag' interface to the fiber substrate resulting in the reduction of the tensile strength for the coated fiber by 45%, compared with the original fiber. Besides, the cracks propagate from the 'zigzag' interface to the coating surface, which causes coating cracking and peeling off. This work provides a potential application in surface treatment on fibers and the theoretical basis for optimizing ceramic coating.