Mechanical Response and Superelastic Properties of Cu-11.85Al-3.2Mn-0.1Ti TPMS Structures Printed by Laser Powder Bed Fusion

Abstract

Triply periodic minimal surfaces (TPMS) are structures with smooth surfaces and excellent energy absorption properties. Combining new functional materials, such as shape memory alloys, with TPMS structures provides a novel and promising research field. In this study, three TPMS structures (Gyroid, Diamond, and Primitive) of Cu-11.85Al-3.2Mn-0.1Ti alloy were printed by laser powder bed fusion, which is favorable for the fabrication of complex structures. The manufacturing fidelity, mechanical response, and superelastic properties of the three structures were investigated. Stress distributions in the three structures during compression were analyzed by finite element (FE) simulation. The three structures were equipped with high-quality, glossy surfaces and uniform pores. However, due to powder adhesion and forming steps, there were volumetric errors and dimensional deviations between the samples and the CAD models. The errors were within 1.6% for the Gyroid and Diamond structures. The dimensional deviations at the nodes in the three structures were less than 0.09 mm. The microstructures of all structures were β1´ martensite, consistent with the cubic sample. Experimental results of compression showed that the structures underwent a layer-by-layer compression failure mode, and the Primitive structures exhibited a more pronounced oscillatory process. The Diamond structures showed the highest first fracture stress and strain of 164.67 MPa and 13.89%, respectively. It also possessed the lowest yield strength (61.97 MPa) and the best energy absorption properties (7.6 MJ/m3). Through the deformation analysis, the Gyroid and Diamond structures were found to fracture at a 45° direction, while the Primitive structures fractured horizontally. These findings were consistent with the results obtained from the FE simulation, which showed equivalent stress distributions. After applying various pre-strains, the Diamond structures displayed the highest superelastic strain of up to 3.53%. The superelastic recovery of all samples ranged from 63.5% to 71.5%.

1. Introduction

Triply periodic minimal surfaces (TPMSs) as a new type of lattice structures show excellent performance [1–3], such as high strength-to-weight ratio, adequate strength, excellent energy absorption properties [4–6], excellent thermal [7, 8], and acoustic insulation properties [9]. Moreover, they have surface characteristics such as smooth surface and uniform radius of curvature [3, 10]. TPMSs have been used in areas like heat changers [7], energy absorption instruments [11], bone implants [12], etc. Laser powder bed fusion (LPBF) as an advanced manufacturing method allows the preparation of parts with complex geometries [13, 14]. This allows TPMS structures with complex surfaces to be printed. Due to self-supporting properties, TPMS structures are suitable for LPBF [6, 15].

At present, various TPMS structures have been printed by LPBF. The properties of TPMS structures are related to unit cell parameters [16, 17], volume fractions [18], geometric topologies [14, 19–21], and materials [22, 23]. Yan et al. found that 316L Gyroid structures with different properties can be designed and fabricated by controlling size parameters and volume fractions [24]. Wei et al. demonstrated that the mechanical properties and energy absorption ability of 316L Diamond structures were positively correlated with volume fractions [18]. Zhang et al. compared the mechanical properties of three 316L TPMS sheet structures (Gyroid, Diamond, and Primitive) printed by LPBF [25]. The structures showed excellent stiffnesses, plateau stresses, and energy absorption capabilities, and Diamond structures possessed the best performance. Similarly, taking the Gyroid, Diamond, and Primitive structures as the subjects of study, Sun et al. investigated the properties of LPBF-printed AlSi10Mg TPMS structures [22]. The Diam