Vat Photopolymerization of Sepiolite Fiber and 316L Stainless Steel-Reinforced Alumina with Functionally Graded Structures

Abstract

Alumina (Al₂O₃) ceramics are widely used in electronics, machinery, healthcare, and other fields due to their excellent hardness and high temperature stability. However, their high brittleness limits further applications, such as artificial ceramic implants and highly flexible protective gear. To address the limitations of single-phase toughening in Al₂O₃ ceramics, some researchers have introduced a second phase to enhance these ceramics. However, introducing a single phase still limits the range of performance improvement. Therefore, this study explores the printing of Al₂O₃ ceramics by adding two different phases. Additionally, a new gradient printing technique is proposed to overcome the limitations of single material homogeneity, such as uniform performance and the presence of large residual stresses. Unlike traditional vat photopolymerization printing technology, this study stands out by generating green bodies with varying second-phase particle ratios across different layers. This study investigated the effects of different contents of sepiolite fiber (SF) and 316L stainless steel (SS) on various aspects of microstructure, phase composition, physical properties, and mechanical properties of gradient-printed Al₂O₃. The experimental results demonstrate that compared to Al₂O₃ parts without added SF and 316L SS, the inclusion of these materials can significantly reduce porosity and water absorption, resulting in a denser structure. In addition, the substantial improvements, with an increase of 394.4% in flexural strength and an increase of 316.7% in toughness, of the Al₂O₃ components enhanced by incorporating SF and 316L SS have been obtained.

Keywords: functionally graded structures; mechanical properties; microstructure characterizations; physical properties; vat photopolymerization.

Figure 1

(a) A picture and (b) an SEM image of SFs; (c) a picture and (d) an SEM image of 316L SS. Macroscopically, the SFs are white powders, while microscopically they are in forms of bundles and laths. The length of SFs ranges from 20 to 60 µm.

Figure 2

A diagram showing a schematic of the Al₂O₃ slurry preparation.

Figure 3

(a) Gradient printing process flow diagram, (b) Al₂O₃ green body printing diagram, and (c) printed physical image.

Figure 4

Diagrams showing schematics and objects of (a) VPP printing of Al₂O₃ green bodies, (b) post-curing of Al₂O₃ green bodies in a UV curing box, (c) drying of Al₂O₃ green bodies in a vacuum drying oven, and (d) degreasing and sintering processes. (a₁–d₁) The images of the corresponding equipment.

Figure 5

Thermal analysis tests. (a) Debinding temperature curve. (b) Sintering.

Figure 6

Effects of SF and 316L SS content on XRD.

Figure 7

The EDS elemental distribution maps of (a) Al element, (b) Si element, and (c) Ni element. Of an Al₂O₃ sample with 6 wt.% SF and 316L SS content. (d) An EDS energy spectrum diagram.

Figure 8

SEM images of sintered samples with the addition of (a) 0 wt.%, (b,c) 2 wt.%, (d,e) 4 wt.%, (f,g) 6 wt.%, and (h,i) 8 wt.% SF and 316L SS addition for S1 and S2.

Figure 9

SEM images of sintered samples with the addition of (a) 0 wt.%, and (b,c) 2 wt.%, (d,e) 4 wt.%, (f,g) 6 wt.%, and (h,i) 8 wt.% SF and 316L SS addition for S3 and S4.

Figure 10

SEM images of sintered samples with the addition of (a) 0 wt.% and 6 wt.% SF and 316L SS addition for (b) S1, (c) S2, (d) S3, and (e) S4.

Figure 11

The line scanning images of the Al₂O₃ gradient sample: (a) microstructure, (b) Al elements, (c) Ni elements, (d) Mg elements, and (e) Si elements.

Figure 12

Effects of SF and 316L SS content on (a) XPS full spectrum, (b) XPS fine spectrum of Al 2p.

Figure 13

Effects of SF and 316L SS contents on (a) shrinkage rates along X, Y, and Z directions, (b) bulk density, and (c) apparent porosity and water absorption rates of Al₂O₃ samples.

Figure 14

Mechanical properties of Al₂O₃ samples with different SF and 316L SS contents: (a) Stress–strain curves, (b) flexural strength, and (c) toughness.