• Miranda, R. M.
• Silva, Rui J. C.

Abstract

Laser beam technology has been largely investigated for welding and joining for micro and more recently nano components. When the scale goes down to few micron or even nanometers melting has to be controlled in the range of a few nanometers The ultra fast pulsed lasers and femtosecond (fs) lasers are innovative tools in nanoscopic processing [1] for microelectronics, optoelectronics and medical industry. Femtosecond laser irradiation can result in an ultra fast and non thermal melting of materials with promising results for joining dissimilar materials in the micro or nano scale ranges [2]. Femtosecond laser can also synthesis nanoparticles by ablation. Therefore, it is possible to synthesis and joining nanoparticles at the same time: ablate the material or melt the outer surface depositing this on the substrate surface assisted by the beam jet pressure. Shape memory alloys as NiTi have remarkable properties as biocompatibility, good strength and ductility and research is required to fully exploit their potential in innovative applications [3]. The aim of the present study is to use femtosecond lasers to process NiTi is both machining, joining and deposition, assessing the effects of laser irradiation of this material. Three applications are reported. Deposition assisted by fs laser of NiTi onto a glass substrate was studied identifying the track geometry, the characteristics of the deposited particles both morphological and its chemical composition. A femtosecond laser from Coherent, Elite Duo USP 1K was set to impinge on the glass lamellae side was used. It was found that glass surfaces can be micro engineered controlling the femtosecond laser process for depositing NiTi particles in a pattern controlled by the laser beam intensity, proving NiTi can be bonded to glass. The laser beam produces micrometric droplets of molten metallic NiTi projected onto the surface by a shockwave produced in two directions, along and perpendicular to the laser traveling direction. A second application was machining of NiTi aiming to preserve both the chemical and the mechanical properties. Fentosecond laser was tested to analyze their potential for machining NiTi as it allows non thermal processing of materials by ablation. Since the fluence of a femtosecond laser is much higher than in pulsed Nd- YAG and it was shown that the surface preserves its properties. Finally, laser brazing of equiatomic NiTi and Ti6Al4V was performed with silver based filler material in nanopaste and membrane shapes. Insipient fusion of the silver brazing alloy was observed that is insufficient to promote the joining. The microstructural analysis of the fracture surface revealed insipient melting of the filler, with insufficient adherence to the substrates with no surface diffusion promoting joining.The results point out that a proper strategy for brazing would require a higher melting and applied compressive force.

Topics

• nanoparticle
• Deposition
• impedance spectroscopy
• surface
• silver
• melt
• glass
• glass
• strength
• chemical composition
• ductility
• joining
• biocompatibility
• lamellae