Laser-based Additive Manufacturing of Bulk Metallic Glasses: Recent Advances and Future Perspectives for Biomedical Applications

Bulk metallic glasses (BMGs) are non-crystalline class of advanced materials and have found potential applications in the biomedical field. Although there are numerous conventional manufacturing approaches for processing BMGs, the most commonly used like copper-mould casting have some limitations. It is not easy to manage and control the critical cooling rate, especially when the fabrication of complex BMG geometries is involved. Other limitations of these techniques include the size constraints, non-flexibility, and the tooling and accessories are costly. The emergence of additive manufacturing (AM) has opened another promising manufacturing route for processing BMGs. AM processes, particularly laser powder-bed fusion (PBF-LB/M) builds parts layer-by-layer and successively fused the powder-melted feedstocks using prescribed computer-controlled laser scanner system, thereby forming a BMGs part upon sufficiently rapid cooling to ensure the glass forming-ability. PBF-LB/M overcomes the limitations of the pre-existing BMGs processing techniques by not only improving the part size, but also produces exceptionally complex structures and patient-specific implants. This review article aims to summarise and discuss the mechanism of BMGs formation through PBF-LB/M for biomedical applications and to highlight the current scientific and technological challenges as well as the future research perspectives towards overcoming the pore-mediated microcracks, partial crystallisation, brittleness and BMG size constraint

Bio-ceramic coatings adhesion and roughness of biomaterials through PM-EDM: a comprehensive review

Powder mixed-EDM is a newly emerging proposed manufacturing process which can simultaneously shape and coat the surface of conductive materials. Transformation of machined surface is occurred through melting and chemical reactions of the added powders, tools materials and dielectric fluid due to elevated temperature generation during the operation. Though the biomaterials such as titanium alloy, magnesium, 316 L SS and Co-Cr alloy attribute to higher mechanical strength, corrosion and wear resistance, and enough biocompatibility, these are limited to apply directly because of releasing the toxic elements and having inferior biological responses. Surfaces of bio-implants made from these biomaterials are therefore protected using bioactive and biocompatible coating. Hydroxyapatite is a bioceramic that possesses bone like element composition and excellent biocompatibility. The PM-EDM process with hydroxyapatite can enhance not only adhesion strength and roughness but also biocompatibility of the treated surface. It is proposed in this paper that carbide and oxide coating formation can improve the microhardness, bonding strength and roughness of surface of the substrates. This study comprehensively reports the current status of adhesion and surface coarseness of bio-ceramics based coating through PM-EDM process. A comparative critical analysis of employing bio-ceramic powder using various deposition techniques is presented in this review

Powder mixed-EDM for potential biomedical applications: A critical review

Powder mixed-electro discharge machining (PM-EDM) is a new emerging trend in research on electro-thermal process that can simultaneously shape and deposit a coating on the surface of the workpiece. PM-EDM is a hybridized form of EDM in which metallic powders are amalgamated in dielectric liquid to enhance both the machined surface condition and machining performance. Migration of materials on the cutting surface occurs by melting and chemical reactions during the operation from both the electrodes and metallic powders. 316L stainless steel, Ti-based alloys, Co-Mo-Cr-based alloys, magnesium and magnesium-based alloys are commonly utilized in manufacturing biomedical devices. These biomaterials, however, release toxic particles due to corrosion, wear, tear, and tiredness of the joint replacements through repeated loads and relative movements. Surfaces of bio-implants made from these biomaterials are therefore protected using bioactive and biocompatible coating. Several methods of deposition are used for coating purposes which have both advantage and drawback. This study proposes that the PM-EDM coating enhances the biomaterials’ mechanical characteristics, surface morphology, and topography. Through reflecting critical and analytical concerns, this review focuses extensively on the current progress of the PM-EDM process. Moreover, following various research initiatives, this paper outlines the critical challenges and future research scopes

Assessment of PM-EDM cycle factors influence on machining responses and surface properties of biomaterials: A comprehensive review

Powder mixed-electro discharge machining (PM-EDM) is recently evolving machining technique which can simultaneously remove and modify the machined surface through thermo-electrical process. It is a modified form of EDM in which the conductive powder elements are added in the dielectric liquid to enhance machined surface characteristics and machining responses. The commonly used biomaterials such as 316L stainless steel, Ti-based alloy, Ni–Ti, Mg alloy, and Co–Mo–Cr alloy have excellent mechanical characteristics while the biofunction of these materials are not in satisfactory level. Due to higher hardness, brittleness, and heat resistant natures of the biomaterials, it is very challenging to machine them with conventional machining. Both the system efficiency and modified surface properties depend on the associated electrical and non-electrical factors of PM-EDM cycle. This review focuses on the influence of process factors such as current, pulse duration, tool-polarity, duty cycle, potential voltage, types of liquid, and added powder concentration on performance outputs including material removal and tool wear rate, coating thickness, coarseness, microhardness, coating adhesion bonding, biocompatibility, and resistant to corrosion. This study also discusses influence of various powders on machining and modified surface characteristics of biomaterials. The future research scopes and challenges of PM-EDM process are included in this study thoroughly