Post-Processing and Surface Characterization of Additively Manufactured Stainless Steel 316L Lattice: Implications for BioMedical Use

Effect of Different Sandblasting Parameters on the Properties of Additively Manufactured and Machined Titanium Surfaces

BACKGROUND/AIM

In dentistry, the surfaces of titanium implants are often sandblasted and acid-etched in order to support successful osseointegration. The aim of this study was to investigate the impact of various sandblasting parameters on the surface roughness, contact angle and surface energy of additively manufactured (TiAl6V4) and machined commercially pure titanium (cpTi) surfaces.

MATERIALS AND METHODS

A total of 56 disc-shaped samples were produced using either laser powder bed fusion (TiAl6V4) or using precision cutting (cpTi). The samples were then sandblasted with different angles, distances, and pressures using an automated sandblasting machine. Afterwards, surface roughness and contact angle for water and diiodomethane were measured, and scanning electron microscopy images were taken.

RESULTS

The results showed that the initially rough TiAl6V4 samples became smoother after sandblasting, while the smooth cpTi surfaces became rougher. Sandblasting pressure had the most significant influence on surface roughness. The surface energy of sandblasted TiAl6V4 samples showed no significant change compared to the as-built state (26.6±1.3 to 26.3±1.8 mJ/m2). In contrast, cpTi samples showed a reduction in surface energy after sandblasting (32.3±1.6 to 26.8±1.2 mJ/m2). Scanning electron microscopy revealed irregular surfaces with grooves and ridges for both types of samples. The roughness of TiAl6V4 decreased at higher sandblasting pressures, whereas cpTi surfaces became rougher.

CONCLUSION

Surface roughness after sandblasting is strongly influenced by the initial surface, which differs in additively manufactured TiAl6V4 samples compared to machined cpTi surfaces.

Surface Enhancement of Additively Manufactured Bone Plate Through Hybrid-Electrochemical Magnetorheological Finishing Process

Additive manufacturing or 3D printing provides the benefits of individualizing the implant per patient requirements. However, the poor surface quality of additively manufactured biomaterial is a major limitation. Hence, hybrid-electrochemical magnetorheological (H-ECMR) polishing is developed to improve the surface quality of fabricated parts. H-ECMR finishing is an advanced surface polishing operation that avails the synergic action of mechanical abrasion and the electrochemical reaction to enhance the surface quality of the workpiece without hampering its surface topography. Furthermore, the developed H-ECMR finishing process reduces the finishing time and produces a uniform surface quality compared with the conventional magnetorheological (MR) finishing process. However, the surface finishing of the parts having a hole-of-pocket feature through the H-ECMR finishing process is a major challenge as MR fluid gets trapped inside those holes or pockets. A feature-based hybrid H-ECMR finishing process is developed to resolve the issue. In this case, paraffin wax is applied to the holes and pockets before the H-ECMR process occurs. In the present work, bone plates are fabricated through selective laser melting, and their surface quality is further enhanced through the H-ECMR finishing process. Bone plates are necessary to provide mechanical stability during bone fracture healing by adapting to the chemical environment. The final Ra value of 21.37 nm is attained from 9.36 μm through H-ECMR finishing. Pin-on-disk study is carried out on the biomaterial to analyze its wear resistance. The surface topography of the workpiece is analyzed through scanning electron microscopy before and after finishing, and it was observed that a uniform surface is achieved after polishing. Apart from the average surface roughness (Ra ), other roughness parameters such as skewness (R sk) and kurtosis (R ku) are analyzed to study the attribute of the surface irregularities.

An Experimental Parametric Optimisation for Laser Engraving and Texturing to Integrate Zirconia Ceramic Blocks into Stainless Steel Cutlery: A State-of-the-Art Aesthetically Improved Perspective

Cutlery and flatware designs are an everchanging phenomenon of the manufacturing industry. Worldwide hospitality businesses demand perpetual evolution in terms of aesthetics, designs, patterns, colours, and materials due to customers' demands, modernisation, and fierce competition. To thrive in this competitive market, modern fabrication techniques must be flexible, adoptive, fast, and cost effective. For decades, static designs and trademark patterns were achieved through moulds, limiting production to a single cutlery type per mould. However, with the advent of laser engraving and design systems, the whole business of cutlery production has been revolutionised. This study explores the possibility of creating diverse designs for stainless steel 304 flatware sets without changing the entire production process. The research analyses three key laser process parameters, power, scanning speed, and number of passes, and their impacts on the resulting geometry, depth of cut, surface roughness, and material removed. These parameters are comprehensively studied and analysed for steel and zirconia ceramic. The study details the effects of power, scanning speed, number of passages, and fluence on engraved geometry. Fluence (power*number of passages/scanning speed) positively influences outputs and presents a positive trend. Medium power settings and higher scanning speeds with the maximum number of passages produce high-quality, low-roughness optimised cavities with the ideal geometric accuracy for both materials.

Analysis of Ultrasonic Vibration-Assisted Ball Burnishing Process on the Tribological Behavior of AISI 316L Cylindrical Specimens

In this study, we analyzed the effects of vibration assistance, combined with a ball burnishing process, in terms of topology, residual stresses, and tribological properties on 316L shafts. The burnishing variables consisted of the variation of the input force, the number of passes, and the activation of the vibration assistance, which is based on a 40 kHz frequency and 8 μm of vibration amplitude, derived in a screening design of three factors. The results show that the medium-high level of burnishing force, high level of the number of passes, and the activation of the vibration assistance are the best options in order to improve the average roughness, the microstructure, the increase in the compressive residual stresses, and the wear enhancement, besides all variables being significant in the p-value analysis through ANOVA. Statistically, the vibration-assisted ball burnishing improved the average roughness by 2.9%, enlarged the von Mises stress on the surface by 11.5% and enhanced the wear resistance of a 316L shaft and WC-Co ball contact up to 7.3%.

Progress in partially degradable titanium-magnesium composites used as biomedical implants

Titanium-magnesium composites have gained increasing attention as a partially degradable biomaterial recently. The titanium-magnesium composite combines the bioactivity of magnesium and the good mechanical properties of titanium. Here, we discuss the limitations of conventional mechanically alloyed titanium-magnesium alloys for bioimplants, in addition we summarize three suitable methods for the preparation of titanium-magnesium composites for bioimplants by melt: infiltration casting, powder metallurgy and hot rotary swaging, with a description of the advantages and disadvantages of all three methods. The titanium-magnesium composites were comprehensively evaluated in terms of mechanical properties and degradation behavior. The feasibility of titanium-magnesium composites as bio-implants was reviewed. In addition, the possible future development of titanium-magnesium composites was discussed. Thus, this review aims to build a conceptual and practical toolkit for the design of titanium-magnesium composites capable of local biodegradation.

Additive Manufacturing of Biomaterials-Design Principles and Their Implementation

Additive manufacturing (AM, also known as 3D printing) is an advanced manufacturing technique that has enabled progress in the design and fabrication of customised or patient-specific (meta-)biomaterials and biomedical devices (e.g., implants, prosthetics, and orthotics) with complex internal microstructures and tuneable properties. In the past few decades, several design guidelines have been proposed for creating porous lattice structures, particularly for biomedical applications. Meanwhile, the capabilities of AM to fabricate a wide range of biomaterials, including metals and their alloys, polymers, and ceramics, have been exploited, offering unprecedented benefits to medical professionals and patients alike. In this review article, we provide an overview of the design principles that have been developed and used for the AM of biomaterials as well as those dealing with three major categories of biomaterials, i.e., metals (and their alloys), polymers, and ceramics. The design strategies can be categorised as: library-based design, topology optimisation, bio-inspired design, and meta-biomaterials. Recent developments related to the biomedical applications and fabrication methods of AM aimed at enhancing the quality of final 3D-printed biomaterials and improving their physical, mechanical, and biological characteristics are also highlighted. Finally, examples of 3D-printed biomaterials with tuned properties and functionalities are presented.

Biomedical Alloys and Physical Surface Modifications: A Mini-Review

Biomedical alloys are essential parts of modern biomedical applications. However, they cannot satisfy the increasing requirements for large-scale production owing to the degradation of metals. Physical surface modification could be an effective way to enhance their biofunctionality. The main goal of this review is to emphasize the importance of the physical surface modification of biomedical alloys. In this review, we compare the properties of several common biomedical alloys, including stainless steel, Co-Cr, and Ti alloys. Then, we introduce the principle and applications of some popular physical surface modifications, such as thermal spraying, glow discharge plasma, ion implantation, ultrasonic nanocrystal surface modification, and physical vapor deposition. The importance of physical surface modifications in improving the biofunctionality of biomedical alloys is revealed. Future studies could focus on the development of novel coating materials and the integration of various approaches.

Progressing towards Sustainable Machining of Steels: A Detailed Review

Machining operations are very common for the production of auto parts, i.e., connecting rods, crankshafts, etc. In machining, the use of cutting oil is very necessary, but it leads to higher machining costs and environmental problems. About 17% of the cost of any product is associated with cutting fluid, and about 80% of skin diseases are due to mist and fumes generated by cutting oils. Environmental legislation and operators’ safety demand the minimal use of cutting fluid and proper disposal of used cutting oil. The disposal cost is huge, about two times higher than the machining cost. To improve occupational health and safety and the reduction of product costs, companies are moving towards sustainable manufacturing. Therefore, this review article emphasizes the sustainable machining aspects of steel by employing techniques that require the minimal use of cutting oils, i.e., minimum quantity lubrication, and other efficient techniques like cryogenic cooling, dry cutting, solid lubricants, air/vapor/gas cooling, and cryogenic treatment. Cryogenic treatment on tools and the use of vegetable oils or biodegradable oils instead of mineral oils are used as primary techniques to enhance the overall part quality, which leads to longer tool life with no negative impacts on the environment. To further help the manufacturing community in progressing towards industry 4.0 and obtaining net-zero emissions, in this paper, we present a comprehensive review of the recent, state of the art sustainable techniques used for machining steel materials/components by which the industry can massively improve their product quality and production.