# Mechanical Response and Functional Performance of Heat-Treated LPBF NiTi Shape Memory Alloys

## TL;DR

Heat treatment of 3D-printed NiTi alloys can control their mechanical behavior, enabling applications like actuators and energy dissipation.

## Contribution

The study reveals how solution treatment and aging alter deformation modes and phase transformations in LPBF NiTi.

## Key findings

- Solution treatment restores pseudoelasticity and reversible deformation in LPBF NiTi.
- Aging stabilizes martensite through Ni4Ti3 precipitation, leading to irreversible deformation.
- Processing enables a functional continuum from recoverable to dissipative behavior in NiTi alloys.

## Abstract

What are the main findings?
Solution treatment fully restores pseudoelasticity in LPBF NiTi.Aging stabilizes martensite via dense Ni4Ti3 precipitation.Deformation modes shift from reversible to irreversible with processing.

Solution treatment fully restores pseudoelasticity in LPBF NiTi.

Aging stabilizes martensite via dense Ni4Ti3 precipitation.

Deformation modes shift from reversible to irreversible with processing.

What are the implications of the main findings?
Post-processing allows precise tuning of NiTi functional behavior.ST enables actuator-type energy-storage applications.Aged states enhance energy dissipation and structural strengthening.

Post-processing allows precise tuning of NiTi functional behavior.

ST enables actuator-type energy-storage applications.

Aged states enhance energy dissipation and structural strengthening.

This study evaluates how solution treatment and aging influence the deformation mechanisms, phase transformations and functional performance of NiTi alloys produced by laser powder bed fusion (LPBF). Tensile tests performed at room temperature (RT) and −20 °C (LT) were combined with Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) analyses to correlate mechanical response with transformation thermodynamics and microstructural evolution. In the as-fabricated (AF) condition, deformation is governed by twinning and martensitic plasticity due to suppressed stress-induced martensite (SIM). Solution treatment (ST) restores reversible SIM at RT and preserves partial recoverability at LT as a result of microstructural homogenization and internal stress relief. Aging at 500 °C (A1h, A20h) promotes Ni4Ti3 precipitation, increasing transformation temperatures and stabilizing martensite, which leads to entirely irreversible deformation at both temperatures. These findings establish a clear functional continuum—ranging from recoverable (ST) to dissipative (AF) and fully irreversible (A20h) behavior—and provide a mechanistic framework for tailoring LPBF NiTi components for actuators, energy-storage and energy-dissipation applications.