Page 79 - MSAM-2-4

Materials Science in Additive Manufacturing Laser DED-produced Ti-6Mn-4Mo alloy

are often used as knee and hip replacements. However, as forging, casting, hot rolling, and machining. However,
those materials exhibit certain weaknesses when implanted additive manufacturing methods offer an alternative
in the human body. For instance, despite its corrosion method for producing biocompatible parts . Industry
[13]
resistance, SUS316L steel has been reported to suffer from can benefit from additive manufacturing technology due to
localized corrosion. Furthermore, austenitic stainless steels its distinctive advantages, such as customized small batch
contain a significant amount of Ni known to cause allergic production, simplification of the manufacturing process,
problems. Implants made of Co-Cr alloys may release ions capability of handling complex geometries, as well as waste
of Co, Cr, and Mo, which increase the risk of inflammatory and cost reduction. As a result, many biomedical products
reactions and other complications . Ti alloys, on the other can benefit from implementing additive manufacturing
[2]
hand, have better suitability due to their lower toxicity and technology to obtain products of novel and complex
balanced properties. Commercially, pure titanium (CP-Ti) shapes and with functionally graded compositions. Various
and Ti-6Al-4V were originally designed to be used as additive manufacturing technologies are available for
structural materials and now are among the most used obtaining metal components. The predominant processes
Ti-based biomaterials . However, the mechanical strength are powder bed fusion (PBF) such as selective laser melting
[3]
of CP-Ti is relatively low compared to other alloys such as (SLM), and directed energy deposition (DED) techniques
Co-Cr alloys, thus limiting its applications where intensive such as powder-blowing laser DED [14,15] . The majority of
wear use or high strength is expected . Ti-6Al-4V has additive manufacturing studies on biocompatible Ti alloys
[4]
much better mechanical performance than CP-Ti, but it are based on PBF processes. Such processes are usually
is known to release cytotoxic elements such as V and Al better controlled and thus more accurate. However, DED
which may cause health issues [5,6] . Some new Ti alloys with processes are more efficient and often less costly compared
good biocompatibility and no toxic elements, as well as with PBF processes. More importantly, DED processes
improved performance, have been investigated , but these are more potent in terms of material synthesis capability
[7]
alloys often contain expensive elements, such as Nb and Ta. based on the in situ alloying mechanism . This is because
[16]
Ti-based alloys exist in two allotropic forms. Below many DED systems are able to dynamically adjust the alloy
882.3°C, hexagonal-close-packed (HCP) α phase is stable; composition through multi-channel powder feed control,
above this allotropic transformation temperature, body- while the alloy composition is generally fixed in PBF
centered-cubic (BCC) β phase is formed. The temperature processes.
at which either α or β phase is stable can be modified In recent years, numerous studies have employed
by addition of interstitial and substitutional elements. PBF processes to obtain Ti-6Al-4V materials to address
Therefore, phase composition and thus mechanical various research issues. A major goal of those studies
properties of Ti alloys can be controlled by the addition has been on how to control the elastic modulus and cell
of alloying elements. The β phase Ti alloys generally have adhesion of printed parts by induced porosities [17-19] . For
higher strength and lower elastic modulus compared to instance, Tseng et al. used a PBF method to produce
[20]
the Ti alloys with α or α + β alloys. For that reason, the Ti-6Al-4V lattice structures suitable for the growth of
research in Ti-based biocompatible alloys has paid close bone cells. Furthermore, the corrosion behaviors of
attention to β-stabilizing elements, such as Nb, Ta, Mo, Ti-6Al-4V produced by PBF as well as the effects
[21]
[4]
and Mg . Another strong β-stabilizer is Mn which is also of PBF process parameters on corrosion resistance of
not expensive and has low toxicity compared to other the resultant Ti-6Al-4V [17,22] were investigated. Other
β-stabilizers [8,9] . Ti-Mn alloys with Mn concentrations biocompatible Ti-based alloys produced by PBF methods
between 8% and 13% were found to possess not only have been widely investigated. For instance, binary alloys
mechanical properties similar to Ti-6Al-4V but also such as Ti-Nb synthesized by laser PBF were studied for
cytotoxicity and cell viability close to CP-Ti . The addition mechanical properties [23,24] , and the effects of pore size on
[10]
of a third element with weaker β-stabilizing effect can mechanical and shape memory properties were studied on
simplify the control of Mn addition . For this reason, the porous NiTi scaffolds . Furthermore, next-generation
[25]
[11]
previous studies investigated the effect of Mo addition to biomaterials such as Ti-Nb-Ta [26-28] and Ti-Nb-Zr were
[29]
Ti-Mn alloy [9,12] . Mo is a trace element found in the human evaluated for biocompatibility, printability, and possibility
body and less cytotoxic than V, Fe, and Co. The addition to tailor elastic modulus by build orientation .
[30]
of Mo to Ti-Mn system may also activate twinning, thus Researchers have also employed DED methods to
improving balance between strength and ductility. study the biocompatible Ti-based alloys. For Ti-6Al-4V,
Until recently, biocompatible metallic alloys have investigations in recent years were focused on the
been fabricated by traditional fabrication methods, such mechanical properties [31,32] , the influence of thermal cycling

Volume 2 Issue 4 (2023) 2 https://doi.org/10.36922/msam.2180