Femtosecond laser micromachining of Ni–Mn–Ga magnetic shape memory alloy

Abstract

Ni–Mn–Ga magnetic shape memory alloys (MSMAs) exhibit large magnetic-field-induced strain (MFIS) of ~6–12%, which is significantly higher than that of commonly used actuation materials such as piezoelectric and magnetostrictive materials. This high strain makes Ni–Mn–Ga MSMAs promising candidates for microscale actuation devices. However, the inherent brittleness of Ni–Mn–Ga MSMAs poses a challenge for fabrication using conventional machining techniques due to their susceptibility to crack formation under mechanical and thermal stresses. Ultrashort pulse width laser processing has emerged as an effective approach for the precise micromachining of brittle and difficult to-machine materials. Femtosecond pulse width laser (FPWL) employs ultrashort laser pulses rather than continuous irradiation, thereby enabling precise material removal with minimal thermal damage.

In this work, FPWL is used to machine Ni–Mn–Ga MSMAs. Processing parameters were systematically varied to identify optimal conditions for micromachining Ni–Mn–Ga MSMA. A single crystal Ni–Mn–Ga gripper structure was fabricated using optimized parameters, showing ~6.5% MFIS, close to the theoretical maximum. This result demonstrates that the functional behavior of the material is not affected by FPWL machining. Subsequently, three-dimensional micromachining was systematically investigated, leading to an improved understanding of process–geometry relationships. Based on these findings, micropillars were fabricated, confirming the capability of FPWL to produce functional MSMA structures at the microscale.

In addition, periodic surface structures formed during machining were systematically studied. These laser-induced periodic surface structures, combined with microscale features, facilitated the development of surfaces with tunable wettability. Overall, these results demonstrate that FPWL micromachining supports the fabrication of functional MSMA structures, advancing the development of multifunctional MSMA-based devices.