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Materials Science in Additive Manufacturing NiTi lattice: Performance optimization
alloys can safely prevent excessive swaying of the piers, as structure is less conducive to additive manufacturing. In
demonstrated by Fang et al. who introduced NiTi washer contrast, an emerging bionic structure, that is, the TPMS
springs into seismic bridge design. To explore its use in structure, not only reduces the stress concentration at
4
orthopedic applications, Xie et al. treated the surface of the node but also changes the geometric characteristics
NiTi alloy to improve surface hardness and antibacterial of the lattice structure, making its surface smoother
properties. 5 and the stress distribution more uniform. 21-23 In this
study, the body-centered cubic (BCC) lattice structure
The NiTi porous structure features high specific
strength and stiffness, as well as remarkable mechanical and the I-graph-wrapped package (I-WP) lattice structure
generated through minimal surface optimization were
properties in low-density structures. The internal structure investigated. 24,25 The I-WP curved surface, commonly
of conventionally made NiTi porous structure is composed referred to as I-WP, is a kind of TPMSs. The “I” denotes
of randomly distributed pores with different shapes, giving the BCC lattice. The “WP” is the abbreviation for “wrapped
a random microstructure that leads to local performance package,” named for the resemblance of finite portions
differences and affects the structure’s applications. of the I-WP surface to string arrangement on a simply
However, the development of additive manufacturing wrapped package. 26
technology has enabled the precise fabrication of NiTi
porous structures with regular shapes inside. Laser Therefore, BCC and I-WP structures were selected for
6,7
powder bed fusion (LPBF) technology is an emerging experiments to study the forming quality and properties of
polymer and metal additive manufacturing technology NiTi lattice structures prepared by LPBF. The applicability
that uses a laser or electron beam as the energy source of the TPMS optimization design method in the field of
to melt or sinter powder materials in a layer-by-layer metal materials prepared by the LPBF process was also
fashion. 8-11 Hussain et al. utilized LPBF to prepare a NiTi investigated in this study.
triply periodic minimal surface (TPMS) lattice, revealing 2. Methods
the effects of process parameters and structural topology
on microstructure characteristics. 12 2.1. Design and manufacture of lattice structures
The service life of NiTi materials is extremely critical 2.1.1. Design of BCC and I-WP
in applications such as cardiovascular stents and As shown in Figure 1, the volume fraction of the sample is
13
14
helical springs. Over the past few decades, many cyclic 10%. The unit cell is a cube with a side length of 5 mm. The
compression experiments have been conducted on NiTi whole sample is composed of unit cells and is a cube with a
alloys. Kan et al. studied the functional degradation side length of 20 mm.
15
of superelastic NiTi rods in cyclic tension-unloading
and compression-unloading experiments, while Safdel The BCC lattice structure was designed by the 3D
16
et al. investigated the tensile-compression asymmetric geometric modeling software Creo (Pro/E), whereas the
behavior of NiTi alloys by laser powder bed melting. I-WP lattice structure was parameterized using MATLAB,
17
However, studies on the fatigue properties of NiTi alloys and their implicit function control equations are as follows:
remain scarce. The experiments of Zhang et al. showed
18
that rock-like splitting and chipping through nucleation Fx yz t(, ,, ) = 2 ( cos 2π x cos 2π y
and slow, stable growth of compression-parallel cracks L L
driven by very small stress intensity are the major factors y z z z x
driving fatigue failure of the material. Zhao and Kang + cos 2π L cos 2π L + cos 2π L cos 2π L ) t − (I)
19
showed that the fatigue life of NiTi alloy microtubules
would be affected by the loading path and stress level Where L denotes the unit cell size, which was 5 mm
under uniaxial cyclic loading. Most of the previous in this study, and t denotes the control volume fraction,
20
studies focused on the fatigue performance of the alloy which was 10%.
or the structure itself. However, there was no comparison
between structural optimization design and fatigue 2.1.2. Materials and equipment
performance. NiTi alloy powder with an elemental ratio of 1:1 was
For the most commonly used strut-based lattice prepared by electrode induction melting gas atomization
structure, the sharp pillar at the node can lead to and purchased from Avimetal Powder Metallurgy
higher stress concentration, which adversely affects Technology Co., Ltd. The density of the powder was
3
the mechanical properties and fatigue properties of the 6.45 g/cm . The BLT-S210 (Xi’an Bright Laser Technologies,
sample. Furthermore, the cantilever of strut-based lattice Ltd., China) was utilized to conduct the LPBF process.
Volume 3 Issue 2 (2024) 2 doi: 10.36922/msam.3380
