Enhanced Laser Micro-Machining of Tubular Ni-Ti Alloys: Unraveling Reactive Gas Effects on Cut Rate and Thermal Damage

University Of Alabama Tuscaloosa, Tuscaloosa AL

Investigators

Abstract

Nitinol is a remarkable binary alloy composed of nearly equal parts of nickel and titanium, with unique properties, such as superelasticity and shape memory. The alloy's distinct characteristics make it invaluable in various fields, including biomedical devices, aerospace engineering, and consumer electronics. However, micromachining Nitinol presents challenges due to its high strength, rapid work hardening, and susceptibility to thermal damage, which can alter mechanical performance. This research aims to challenge the status quo that Nitinol laser cutting is a relatively slow process by seeking to formulate a data-driven quantification of the mechanics behind fluid flow dynamics and microstructural alterations during processing. With laser micromachining, the photon beam interacts with the material, inducing significant heat accumulation, material melting, and subsequent fluid flow, which significantly influences the quality and integrity of the final product. This research looks to unravel the dynamics of melt flow, heat generation, and temperature distribution in real time during Nitinol laser cutting, all of which are crucial aspects of realizing the microstructure-process-property relationship. Additionally, this research will be complemented by the following educational outreach activities, providing learning opportunities for students: “Introduction to Engineering for High Schoolers” and “Engineer for a Week”. In summary, the results provided by this research aim to reduce the cost of life-saving medical device treatments using Nitinol worldwide. This research targets the underlying fundamental science surrounding the relationship between laser cutting melt flow dynamics and the resultant microstructural evolution to answer the following research questions: (i) Is there a difference in the melt ejection velocity between a reactive assist gas and an inert assist gas that can demonstrate variances in melt flow dynamics, (ii) Will increased ejection velocities reduce thermal gradients, subsequently reducing microstructural alterations, (iii) With reduced microstructural alterations, is mechanical performance preserved? Overall, it is hypothesized that when a melt-dominant laser cutting process is combined with an exothermic reactive oxygen assist gas, the oxygen combustion reaction will aid in expelling the melt pool away from the proximity of the laser cut region, resulting in higher cutting rates and lower thermal gradients, reducing conditions conducive to microstructural alterations. As a result, the integrity of the grain structure will be preserved, enabling enhanced material quality, improved performance, and eliminating the need for additional post-processing, all while achieving faster cut rates. The overarching focus of this research will be in-situ analysis of thermal gradients during cutting, high-speed imaging of melt flow behavior, and advanced microstructural characterization post-cutting. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.