Aira Matsugaki

In recent years, high-entropy alloys (HEAs) have attracted significant attention owing to their remarkable physical properties such as high strength. It has also been reported that HEAs have a high potential as biomaterials. Bcc-type bio-HEAs possess high strength and biocompatibility equivalent to those of pure titanium. Bio-metallic materials require a low Young's modulus, similar to that of natural bone, but the Young's modulus of bio-high entropy alloys has not yet been clarified. Therefore, this study elucidates the relationship between microstructure control and Young's modulus in titanium-based bio-HEAs. The TiNbTaZrMo-based bio-HEAs were composed of two bcc phases. These two phases correspond to dendrite and interdendrite structures, respectively. In this study, it was found that by varying the volume fractions of these two phases, it is possible to control the Young's modulus.

Biomedical materials used for reconstructing bone function lost due to trauma or disease include artificial joints, bone fixation materials, and bone replacement materials, which are indispensable medical devices in the treatment of orthopedic-related diseases. Their roles are not limited to physically replacing a defective site and acting as a scaffold for bone regeneration. In recent years, medical devices that work on the molecular and cellular level to realize functional repair of tissues and organs through integration with the living body have been developed. The design of biocompatible and biofunctional surfaces requires a spatial and temporal hierarchy of interface phenomena between non-living materials and living organisms. The control of the properties of these artificial materials through their design, processing methods, and surface treatment techniques is closely related to local cell adhesion, tissue regeneration, and systemic metabolic reactions. Bone engineering research, including the creation of such materials, is indispensable in supporting bone medicine, as it affects from molecular adsorption at the bio/material interface to the control of cell adhesion, bacterial adhesion, and immune response, from biochemical reactions occurring in milliseconds to bone connectivity over a period of years. In addition, advances in technologies, including additive manufacturing, can establish surface property control targeting selective activation of biomolecules, from advanced nanoscale structural control to single-molecule chemical modification. In particular, additive manufacturing is a promising technology that can achieve high spatial resolution for micrometer-order cell control and high corrosion resistance that leads to a reconstruction of tissues and organs through controlling the bio/materials interfacial reactions. The control of bio functions through the molding of external and internal shapes and the control of their crystallographic organization is expected to make a significant contribution to the realization of bone quality-targeted medicine, which has been difficult to achieve with conventional materials technology alone. Furthermore, it is expected to play a significant role in the future development of ultraearly disease prediction and digital medical technology. The elucidation of atomic-scale phenomena at the interface between non-living organisms and living organisms will make it possible to realize bone treatment tailored to the pathology and skeletal structure of each patient by accumulating fundamental knowledge and understanding it from a multilevel perspective.

Chromium (Cr) metal has garnered significant attention in alloy systems owing to its exceptional properties, such as a high melting point, low density, and superior oxidation and corrosion resistance. However, its processing capabilities are hindered by its high ductile–brittle transition temperature (DBTT). Recently, powder bed fusion-laser beam for metals (PBF-LB/M) has emerged as a promising technique, offering the fabrication of net shapes and precise control over crystallographic texture. Nevertheless, research investigating the mechanism underlying crystallographic texture development in pure Cr via PBF-LB/M still needs to be conducted. This study explored the impact of scan speed on relative density and crystallographic texture. At the optimal scan speed, an increase in grain size attributed to epitaxial growth was observed, resulting in the formation of a cubic texture. Consequently, a reduction in high-angle grain boundaries (HAGB) was achieved, suppressing defects such as cracks and enhancing relative density up to 98.1%. Furthermore, with increasing densification, Vickers hardness also exhibited a corresponding increase. These findings underscore the efficacy of PBF-LB/M for processing metals with high DBTT properties.

Chromium (Cr) metal has garnered significant attention in alloy systems owing to its exceptional properties, such as high melting point, low density, and superior oxidation and corrosion resistance. However, its processing capabilities are hindered by the high Ductile-Brittle Transition Temperature (DBTT). Recently, powder bed fusion-laser beam for metals (PBF-LB/M) has emerged as a promising technique, offering the fabrication of net shapes and precise control over crystallographic texture. Nevertheless, research investigating the mechanism underlying crystallographic texture development in pure Cr via PBF-LB/M still needs to be conducted. This study explores the impact of scan speed on relative density and crystallographic texture. At the optimal scan speed, an increase in grain size attributed to epitaxial growth was observed, resulting in the formation of cubic texture. Consequently, a reduction in High Angle Grain Boundaries (HAGB) was achieved, suppressing defects such as cracks and enhancing relative density up to 98.1%. Furthermore, with increasing densification, Vickers hardness also exhibited a corresponding increase. These findings underscore the efficacy of PBF-LB/M for processing metals with high DBTT properties.