Micro-Crack Formation in Laser Structuring of Titanium Alloys for Orthopedic Applications

Abstract

Abstract Titanium alloys have been widely employed as essential raw materials for manufacturing implants in orthopedics due to their excellent biocompatibility, corrosion resistance, and mechanical properties similar to human bones. In order to form effective bonding between the titanium alloy implant and the human bone at an appropriate time, micro-structures are required to create on titanium alloy surfaces through surface modification, so that the bone cells can propagate and grow. Laser-induced micro/nano hierarchical structures on titanium alloy implants are capable of improving the adhesion, arrangement and proliferation of osteoblasts. However, significant micro-crack appears on the metal surfaces after the nanosecond laser treatment, which will do harm to mechanical and corrosion resistance performances of the implants and may even in turn damage patients’ health. This work aims at investigating the formation mechanism and influencing factors of micro-cracks to achieve laser-structured titanium alloy implants with reduced or even no micro-crack for orthopedic applications. Laser ablation experiments were conducted on titanium alloy surfaces to produce micro-grooves/protrusions. Specifically, three key laser process parameters such as the laser scanning speed (v), laser frequency (f), and scan repetition (n) were considered in terms of their influences on the crack morphology. The smaller the laser scanning speed, the large the micro-crack number and the more chaotic of their distribution. The speed of nanosecond laser processing should be increased to reduce the generation of micro-cracks. It can be inferred that micro-cracks on laser-structured titanium alloy surfaces are mainly ascribe to the generated thermal stress during laser processing.