Estudo da soldabilidade e características termomecânicas de juntas NiTi-TiMo para fabricação de grampos ortopédicos.

Abstract

Shape memory alloys (SMAs), such as NiTi, are renowned for their exceptional mechanical strength, remarkable corrosion resistance, and inherent ability to recover their original shape after deformation. TiMo alloys have also garnered considerable attention due to their promising properties. Ongoing research and development efforts in these materials aim to optimize their characteristics for various applications, particularly in biomedical devices. However, the complexity involved in manufacturing structures with intricate geometries using these alloys often necessitates the creation of permanent joints through welding. The welding of dissimilar alloys, such as NiTi and TiMo, offers a pathway for developing complex structures and custom devices in orthopedic applications, including clamps. This study examines the gas tungsten arc spot welding (GTAW) process, using micro-pulses on dissimilar superelastic NiTi and TiMo wires, each with a diameter of 0.9 mm, to produce prototypes of orthopedic clamps. The research initially focused on identifying the optimal welding parameters to achieve joints with superior mechanical strength. Multiple combinations of power settings and welding durations were tested in double pulse sequences using a micro-welding apparatus. Tensile tests to fracture and metallographic analyses of the welded joints, conducted through optical microscopy (OM), provided critical data needed to select the two most favorable welding conditions. These selected conditions were then applied to the fabrication of orthopedic clamp prototypes, using overlapped wires and four angular welding pulses. The welded joints were validated through tensile and bending tests to fracture, conducted at a controlled temperature of 37°C. Additionally, the clamps were subjected to mechanical cycling tests, simulating repeated openings and closings up to a 90° angle over 50 cycles, at the same temperature, to evaluate their resistance to mechanical stress, representative of human body conditions. The welded clamp prototypes demonstrated the ability to withstand loads exceeding 7 N while maintaining their superelastic properties. It can be inferred that the production of welded orthopedic clamps from dissimilar NiTi-TiMo wires is feasible.