Thermomechanical behavior of NiTi shape memory alloy tubes fabricated by laser powder bed fusion under compressive loading

Abstract This study investigates the thermomechanical performance of additively manufactured NiTi tubes as a foundational step toward designing and fabricating NiTi tubes for harnessing elastocaloric effect (eCE) using additive manufacturing (AM). By leveraging the design flexibility of AM, particularly producing thin-wall tubes and intricate structures, the eCE can be enhanced. The mechanical properties of these tubes must meet the necessary load bearing requirements for use in eC-based devices. To this end, NiTi tubes were fabricated using laser powder bed fusion process, and heat treatment was applied to ensure eCE requirements, mainly transformation temperatures. The thermomechanical performance of as-fabricated and heat-treated tubes under compressive load were evaluated. The results demonstrate that heat treatment significantly improves the material’s transformation temperature and stress hysteresis for practical eCE applications. differential scanning calorimetry analyses confirmed that the applied heat treatment effectively decreased the austenite finish temperature ( A f ) from 15.65 °C to 0.84 °C, enabling suitability for near-room-temperature cooling applications. Compression testing showed that heat-treated samples initiated martensitic transformation at ∼400 MPa and exhibited significantly reduced stress hysteresis compared to their as-built counterparts, which enhances energy efficiency in cyclic applications. To the authors’ best knowledge, this work is the first to report on the compressive behavior of laser powder bed fusion-fabricated Nitinol tubes, including their buckling performance. While full device demonstrations are beyond the present scope, our findings establish key design benchmarks and provide essential groundwork for integrating additively manufactured NiTi tubes into future elastocaloric cooling systems.