Crossed-Wire Laser Microwelding of Pt-10 Pct Ir to 316 Low-Carbon Vacuum Melted Stainless Steel: Part I. Mechanism of Joint Formation

Abstract

The excellent biocompatibility and corrosion properties of Pt alloys and 316 low-carbon vacuum melted (LVM) stainless steel (SS) make them attractive for biomedical applications. With the increasing complexity of medical devices and in order to lower costs, the challenge of joining dissimilar materials arises. In this study, laser microwelding (LMW) of crossed Pt-10 pct Ir to 316 LVM SS wires was performed and the weldability of these materials was determined. The joint geometry, joining mechanism, joint breaking force (JBF), and fracture modes were investigated using optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and microtensile testing. It was shown that the mechanisms of joint formation transitioned from (1) brazing, (2) a combination of brazing and fusion welding, and (3) fusion welding with increasing pulsed laser energy. The joints demonstrated various tensile failure modes including (1) interfacial failure below a peak power of 0.24 kW, (2) partial interfacial failure that propagated into the Pt-Ir wire, (3) failure in the Pt-Ir wire, and (4) failure in the SS wire due to porosity and severe undercutting caused by overwelding. During this study, the optimal laser peak power range was identified to produce joints with good joint geometry and 90 pct of the tensile strength of the Pt-10 pct Ir wire.

Crossed-Wire Laser Microwelding of Pt-10 Pct Ir to 316 LVM Stainless Steel: Part II. Effect of Orientation on Joining Mechanism

“…Complexities due to the number of alloying elements in the SS wire have made identifying a single low melting point composition, as was done in Reference 11, difficult. There are several differences in the joint formation when the Pt-Ir wire was subject to the incident beam compared to what was found in Part I [14] of this study when the SS wire was subject to the incident beam. When the Pt-Ir wire was on top initially, the SS wire below melted due to conduction of heat through the unmolten Pt-Ir wire rather than from the laser energy itself.…”

“…As was performed in Part I of this study, [14] fully annealed 0.38-mm-diameter Pt-10 pct Ir and springtempered 316 LVM SS wires were joined by laser spot microwelding. However, in this study, the Pt-10 pct Ir wire was subject to the incident laser beam rather than the 316 LVM SS wire.…”

“…On the contrary, when the SS wire was subject to the incident laser beam, it was melted directly by the laser energy and wet the Pt-Ir wire below, creating a brazed joint. [14] In this case, only a small portion of the Pt-Ir wire became molten until the power was increased above 0.39 kW, where full penetration was achieved. The amount of Pt and Ir mixed in the molten SS material was minimal, and porosity was not observed until full penetration occurred.…”

“…This was not the case when the SS wire material was subject to the incident laser beam. [14] When considering the thermal gradient, the MZ does not occur predominately at the weld surface, the highest temperature region, where vaporization is most likely to occur when the SS wire is subject to the incident beam. [14] As a result, the temperature in the MZ may not reach a degree high enough to cause vaporization.…”

“…The current study will address the difference in joint morphology and joint breaking force (JBF) with increasing laser power. A comparison is made between the joints in this work, where the Pt-10 pct Ir wire was subject to the incident laser beam to joints made in a sister article, [14] where 316 LVM SS wire was subject to the incident laser beam. Furthermore, the porosity defect that arises when Pt-10 pct Ir wire was subject to the incident laser beam will be addressed providing significant scientific findings that are essential for dissimilar materials joining.…”