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Special Section: Bioprinting of 3D Functional Tissue Constructs

Regular Section

Original research article

by Sachini Wickramasinghe, Truong Do, Phuong Tran
Additive manufacturing has allowed producing various complex structures inspired by natural materials. In this research, the bio-inspired suture structure was 3D printed using the fused deposition modeling printing technique to study its bending response behavior. Suture is one of the most commonly found structures in biological bodies. The primary purpose of this structure in nature is to improve flexibility by absorbing energy without causing permeant damage to the biological structure. An interesting discovery of the suture joint in diabolical ironclad beetle has given a great opportunity to further study the behavior of these natural suture designs. Inspired by the elliptical shape and the interlocking features of this suture, specimens were designed and 3D printed using polylactic acid thermoplastic polymer. A three-point bending test was then conducted to analyze the flexural behavior of each suture design, while digital image correlation and numerical simulation were performed to capture the insights of deformation process.

Original research article

by Jingjia Sun, Meng Guo, Keyu Shi, Dongdong Gu
In this work, mesoscopic simulation and experimental studies were applied to investigate the influence of powder morphology and characteristics on laser absorption behavior and printability of nanoparticle-coated 90W-Ni-Fe powder during laser powder bed fusion (LPBF). The mechanism of laser-material interaction and the thermal behavior of molten fluid during LPBF were revealed, thereby optimizing the powder preparation parameters. It showed that when the powder preparation parameters were optimized (i.e., ball-to-powder weight ratio of 1:2, milling speed of 250 rpm, and milling time of 6 h), the Ni and Fe nanoparticles were uniformly dispersed on W particles and, meanwhile, the sufficiently high sphericity of the W matrix particles was maintained. The nanoparticle-coated 90W-Ni-Fe powder had a sound laser absorption behavior with laser absorptivity of 93.51%, leading to the high LPBF printing quality with a smooth surface free of balling phenomenon and microcracks. Specimen fabricated using optimally prepared powder has a high density of 98% and a low surface roughness of 7.91 μm. The LPBF-processed 90W-Ni-Fe alloys had a uniform hardness distribution with an average value of 439.47 HV1 and significantly enhanced compression properties with compressive strength of 1255.35 MPa and an elongation of 24.74%. The results in this work provided a physical understanding of complex and interdependent laser-powder interaction and melt pool formation mechanisms during LPBF of W-based alloys that are governed by powder characteristics.

Original research article

by Guo Liang Goh, Haining Zhang, Guo Dong Goh, Wai Yee Yeong, Tzyy Haur Chong

The sintering of printed nanoparticle films is a necessary processing step for most nanoparticle inks to make the printed film functional. The sintering of nanoparticle is usually performed through thermal sintering, photonic sintering, induction sintering, etc. Intense pulsed light (IPL) sintering method is one of the most popular sintering methods for nanoparticle inks due to the fast and effective process, but it may yield mediocre performance if improper sintering parameters are used. In this work, we investigate the correlation between the two factors which are the print passes of aerosol jet printing and the sintering distance of the samples on the effect of the surface morphology and sheet resistance. A contradictory correlation between the two factors was observed and a multi-objective optimization was carried out using machine learning method to identify the most optimum conditions for both factors. We found that multi-objective optimization approach is effective in reducing the conflicting responses, thus the sintered thin film can have low sheet resistance and low surface roughness. This work provides an essential guide for achieving conductive films with electrical conductivity and low surface roughness using IPL sintering process for fast fabrication of multi-layered electronics such as electrochemical electrodes.

Review article

by Vineeth Menon, Clodualdo Aranas Jr., Gobinda Saha
The cold gas dynamic spray process is a manufacturing process strategically designed for coatings. The conditions for the deposition of materials to form coatings have evolved over several decades. Copper and copper-based cold spray coatings are an interesting field for investigation, as it has substantial commercial demand and acceptance. Several important works have already been performed in this regard that shows the immense popularity of its applications in power industries. Cold gas dynamic spray, being an economic process, can produce coatings with superior quality and low oxidation. In this paper, a particular focus has been given to copper-based cold spray coatings along with their deposition parameters. The various mechanical, electrical, corrosion, and tribological properties of these copper-based cold spray coatings are commendable and economically lucrative. A good amount of experimental data has also been included in this review article to provide comprehensive information and future scope of research about copper-based cold spray coatings.

Review article

by Yao Ting Ang, Swee Leong Sing, Joel Choon Wee Lim

In addition to laser powder bed fusion, directed energy deposition (DED) is also gaining interest as an effective metal additive manufacturing technique. Due to its system configuration, it is more efficient and flexible for materials development. Therefore, it can be used for processing of metal matrix composites (MMCs) through the use of powder mixture as feedstock. 316L stainless steel has high corrosion resistance, biocompatibility, and ductility. Several studies have shown the feasibility of using DED to process 316L stainless steel. The material properties of 316L stainless steel can be improved using reinforcement particles such as TiB2 to form MMCs. In this study, the effects of process parameters on microstructure and mechanical properties of 316L stainless steel reinforced with TiB2 (316L/TiB2) MMC were studied. The process parameters, including laser power, scanning speed, and hopper speed, were varied and analyzed using Taguchi L9 array. It was found that the process parameters have insignificant effect on the bulk density of the samples produced. Through this study, it is also found that tumble mixing was not suitable for the powder feedstock preparation for MMCs to be processed by DED. The microstructure of DED 316L/TiB2 MMC samples consists of columnar and equiaxed grains. Columnar grains were located within the layers while equiaxed grains were located at the interlayer zones. Fine sub-grains were also observed within these grains and their boundaries were enriched with molybdenum and chromium segregations. Precipitates containing titanium were also observed to segregate at the sub-grain boundaries. Finally, the Vickers microhardness of the DED 316L/TiB2 MMC was found to be similar to pure 316L stainless steel produced by DED.