Page 73 - MSAM-3-3

Materials Science in Additive Manufacturing Gradient porous material design criteria

1. Introduction of understanding of how to achieve deformation-induced
densification through design, making it difficult to
In previous research, porous structures play an important predict their mechanical properties, including the energy
role in the construction of lightweight parts and biomedical absorption. 27
implants. Metal foam is one of the conventional porous
materials. However, porosity and pore size are hard to In previous studies, various designs of gradient
control during the process and thus the performance is porosity materials have been investigated to improve
difficult to predict. Therefore, porous structural materials mechanical properties. Moreover, deformation-induced
1,2
using additive manufacturing technology have been densification phenomena have been reported and are
widely studied. Regarding the additive manufacturing thought to contribute to high energy absorption. However,
2-7
process, three-dimensional materials are stacked layer by systematic research is lacking to explore the design criteria
layer according to the slicing data of the design model. to achieve deformation-induced densification, and it
8,9
Among these additive manufacturing technologies, two would be beneficial for further applications if empirical
types of methods are widely used to melt metal powder rules for estimating energy absorption could be developed.
together on the powder bed: selective laser melting and Two types of porous structures/bionic structures, Schon-
electron beam melting, which are also called laser powder Gyroid and Schwarz-Diamond, were investigated in this
bed fusion (LPBF) and electron beam powder bed fusion, study to explore the design criteria for deformation-
respectively. By controlling microscale structural design, induced densification of gradient porosity materials.
4,10
porous structures with complex geometries can be easily The porous structure materials were fabricated by LPBF
formed, leading to an orderly porous structure without using Ti-6Al-4V due to its good mechanical properties
redundant design. and high specific strength. Moreover, after exploring
28
Many structures, such as orthogonal structures, the relationship between the structure design and the
rhombus structures, and helical structures, have been deformation-induced densification phenomenon, the
studied by other researchers. 11-17 In the present study, relevant mechanical properties of the gradient porosity
different porosity structures have been used in measuring materials can therefore be predicted. As a result, the
different kinds of mechanical properties. For example, empirical rule for estimating the energy absorption of
different unit cells are designed to improve the mechanical gradient porosity materials can be developed.
properties, 18-20 such as fatigue, impact resistance, and
21
22
energy absorption. Furthermore, recently, triply periodic 2. Experimental procedures
23
minimal surface (TPMS) has emerged as an ideal tool In this study, the spherical Ti-6Al-4V alloy powder
to generate porous structures. Mathematical functions was provided by Chung Yo Materials Co., Ltd, Taiwan.
are used to construct the porous TPMS structure and The powder size ranges mainly from 15 to 45 µm. All
thus build the database of their physical and mechanical the samples of Ti-6Al-4V alloy were printed using the
properties. 9 SolidMEN AM 300 system with LPBF technology under
3
Schon-Gyroid and Schwarz-Diamond models usually an argon atmosphere of 1 × 10 mbar. The power, scanning
exhibit good performance in terms of mechanical speed, beam diameter, hatch distance, and layer thickness
properties. 24,25 Recently, gradient porosity materials have were 100 W, 1087.5 mm/s, 50 µm, 0.081 mm, and 30 µm,
presented the application potential due to their excellent respectively.
energy absorption capacity. During the deformation, All the compressive samples were designed as
the struts first fracture in the region with the highest rectangular columns with a width and length of 15 mm
porosity, come into contact, get stuck with other struts, and a height of 30 mm. The samples were divided into
and then deform again as a lower-porosity material. Such six layers; each layer could accommodate a unit cell with
a deformation-induced densification process leads the a height of 5 mm. To examine the deformation-induced
gradient porosity materials to deform without catastrophic densification phenomenon of the gradient porosity
fracture, thus presenting a higher ductility and higher materials and develop the empirical rule for estimating the
energy absorption capacity than that of single porosity energy absorption, Schon-Gyroid, and Schwarz-Diamond
materials. 26-28 Moreover, it also shows that the yield lattice structures were introduced to design the porous
strength and Young’s modulus will gradually increase with
the continuous porosity change. 26,27 However, although materials. The commonly used topological structures
gradient porosity materials have been expected to exhibit included Schon-Gyroid and Schwarz-Diamond lattices,
29,30
and mathematical functions such as Equations 1 and 2
good energy absorption capacities, it is difficult to optimize
the design of the gradient porosity materials due to a lack φ = sin X cos Y + sin Y cos z + sin z cos X = C (1)
G
Volume 3 Issue 3 (2024) 2 doi: 10.36922/msam.4234