Mechanical properties of Ti6Al4V fabricated by laser powder bed fusion: a review focused on the processing and microstructural parameters influence on the final properties

Ti6Al4V alloy is an ideal lightweight structural metal for a huge variety of engineering applications due to its distinguishing combination of high specific mechanical properties, excellent corrosion resistance and biocompatibility. In this review, the mechanical properties of selective laser-melted Ti6Al4V parts are addressed in detail, as well as the main processing and microstructural parameters that influence the final properties. Fundamental knowledge is provided by linking the microstructural features and the final mechanical properties of Ti6Al4V parts, including tensile strength, tensile strain, fatigue resistance, hardness and wear performance. A comparison between Laser Powder Bed Fusion and conventional processing routes is also addressed. The presence of defects in as-built Ti6Al4V parts and their influences on the mechanical performance are also critically discussed. The results available in the literature show that typical Laser Powder Bed–Fused Ti6Al4V tensile properties (>900 MPa yield strength and >1000 MPa tensile strength) are adequate when considering the minimum values of the standards for implants and for aerospace applications (e.g., ASTM F136–13; ASTM F1108–14; AMS4930; AMS6932).This work was supported by FCT national funds, under national support to an R&D units grant, through the reference projects UIDB/04436/2020 and UIDP/04436/2020 and also through the projects ADD2MECBIO (PTDC/EME-EME/1442/2020) and Additive_Manufacturing to Portuguese Industry_POCI-01-0247-FEDER-024533

The influence of laser power and scan speed on the dimensional accuracy of Ti6Al4V thin-walled parts manufactured by selective laser melting

Laser Powder Bed Fusion (LPBF) technologies such as Selective Laser Melting (SLM) are being increasingly considered as viable production routes. This paradigm change demands an in-depth understanding of the fabrication process and variables, as previous studies have shown that energy density calculation alone is insufficient, because parts fabricated using similar energy density, but using different combinations of parameters, can display significantly different properties and dimensions. Thin-walled parts are particularly influenced by processing parameters; in this sense, this study explores the influence of laser power and scan speed on the dimensions of Ti6Al4V thin-walled tubes. Predictive models for manufacturing Ti6Al4V thin-walled tubes were developed using Response Surface Methodology (RSM), and the most influential (single and combined) factors were determined using Analysis of Variance (ANOVA). Three models were obtained: for the wall melt zone thickness, the total wall thickness, and the hole width.FCT (Fundação para a Ciência e a Tecnologia) through the project PTDC/EME-EME/1442/2020 (Add2MechBio) and POCI-01-0247-FEDER-024533 (Add-Additive–Add additive manufacturing to Portuguese industry). Acknowledgments to the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020, and LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC)

MgO nanoparticles obtained by Pulsed Laser Ablation in Liquid: a study on fabrication versatility aiming different applications

Apresentação efetuada em "Junior Euromat 2022", em Coimbra, 2022Nano and micro-sized metal particles are used in diverse fields, from electronics to biomedical. Among them, Magnesia, also known as magnesium oxide (MgO), is one of the most interesting metal oxides due to its unique properties, such as a large electrochemically active surface area and chemical stability. Although chemical routes such as chemical reactions, thermal evaporation,sol-gel, chemical vapor deposition and hydrothermal treatments are mainly used to fabricate metal oxide nanoparticles, they require the use of toxic reagents and long processing times. Thus, developing a simple green synthetic process for preparing MgO nanoparticles remains a challenging topic of investigation. Pulsed laser ablation in liquid (PLAL) has emerged as a potential alternative to chemical methods because it does not require chemicals, generates no waste, and produces high-purity particles. By changing some parameters such as the laser wavelength, laser fluence, and liquid media the size and shape of the particles produced can be tailored. The obtained particles can be added to act as anti-biofilm agents on coatings. Both influence of the liquid medium and the laser energy on nanoparticle composition and morphology are investigated in this work, as well as the effects of laser energy and different liquid media on the properties and characteristics of these nanoparticles.Acknowledgements: This work was supported by Fundação para a Ciência e Tecnologia through the grant 2020.07257.BD, the projects UIDB/04436/2020 and UIDP/04436/2020. PTDC/EME-EME/1442/2020(Add2MechBio). Additionally, this work was developed within the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC)

Selective laser melting of Ti6Al4V sub-millimetric cellular structures: prediction of dimensional deviations and mechanical performance

Ti6Al4V sub-millimetric cellular structures arise as promising solutions concerning the progress of conventional orthopedic implants due to its ability to address a combination of mechanical, physical and topological properties. Such ability can improve the interaction between implant materials and surrounding bone leading to longterm successful orthopedic implants. Selective Laser Melting (SLM) capability to produce high quality Ti6Al4V porous implants is in great demand towards orthopedic biomaterials. In this study, Ti6Al4V cellular structures were designed, modeled, SLM produced and characterized targeting orthopedic implants. For that purpose, a set of tools is proposed to overcome SLM limited accuracy to produce porous biomaterials with desired dimensions and mechanical properties. Morphological analyses were performed to evaluate the dimensional deviations noticed between the model CAD and the SLM produced structures. Tensile tests were carried out to estimate the elastic modulus of the Ti6Al4V cellular structures. The present work proposes a design methodology showing the linear correlations found for the dimensions, the porosity and the elastic modulus when comparing the model CAD designs with Ti6Al4V structures by SLM.This work was supported by FCT through the grant SFRH/BD/ 128657/2017 and the projects PTDC/EMS-TEC/5422/2014_ADAPT PROSTHESIS, NORTE-01-0145-FEDER-000018 – HAMaBICo and UID/ EEA/04436/2019

Improving the interface between orthopaedic implants and bone - a comparison between different surface treatments

Apresentação efetuada em "Junior Euromat 2022", em Coimbra, 2022Orthopedic implants for load-bearing applications are usually composed of titanium-based materials. However, insufficient bioactivity of metallic materials impairs the bonding with bone, compromising osseointegration at an early stage. The implant-bone interface may be improved by regulating some surface properties of the biomaterials, including surface chemical composition, surface energy, roughness and topography, which influence the behavior of bone cells. In the present study, commercially pure titanium and Ti6Al4V alloy were used to investigate the effect of three surface treatments, after performing two different chemical pre-treatments, on the characteristics of the obtained oxide films. Regarding the pre-treatments, no major differences were observed between performing alcohol cleaning or acidic pre-treatment, considering the surface crystallinity, roughness and wettability. However, the TiO2 layer formed upon anodic oxidation, hydrothermal treatment and anodic oxidation followed by hydrothermal treatment presented different characteristics regarding its crystallinity, roughness, thickness and wettability. This study compared specific surface treatments and the hydrothermal treatment is proposed as a simple treatment capable of improving the characteristics of the implant surface, thereby promoting osteoconductivity. In fact, the culture of human Mesenchymal Stem Cells on Ti-based materials subjected to hydrothermal treatment and consequent induction of osteogenic differentiation confirm the improved surface characteristics.This work was supported by FCT (Fundação para a Ciência e a Tecnologia) through the grant SFRH/BD/141056/2018 and the projects PTDC/EME-EME/1442/2020, POCI-01-0145-FEDER-030498, UIDB/04436/2019 and UIDP/04436/2020. In addition, this work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC)

Corrosion and tribocorrosion behaviour of Ti6Al4V produced by selective laser melting and hot pressing in comparison with the commercial alloy

The corrosion and tribocorrosion behaviour of SLM-produced Ti6Al4V alloy was studied in comparison with its HP and commercial counterparts in 9 g/L NaClsolution at body temperature. Results showed that SLM processing route influenced the electrochemical response of the SLM-produced alloy by leading to a relatively lower quality for the passive film due to decreased beta phase and the formation of alpha' phase. However, after tribocorrosion, neither the total volume loss nor the volume loss under the influence of mechanical wear and wear accelerated corrosion showed any statistically significant difference between the processing routes.This study was supported by FCT with the reference project UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020 - Program Operacional Competitividade e Internacionalizacao (POCI) with the reference project POCI-01-0145-FEDER-006941, together with projects NORTE-01-0145-FEDER-000018-HAMaBICo and PTDC/EMS-TEC/5422/2014. The authors would also like to acknowledge Prof. Grata Minas for the provision of the profilometry

Desenvolvimento de compósitos de alumínio obtidos por um processo de sinterização assistida por pressão

Tese de doutoramento em Engenharia MecânicaInnovation in engineering was numerous times achieved through innovative combinations of materials. Aluminum matrix composites (AMCs) are one of these innovations that allow combining light weight alloys with chosen reinforcements in order to obtain improved materials when compared to unreinforced aluminum alloys, with optimized mechanical, wear and physical properties. Powder Metallurgy processes advantages like higher control over the reinforcement/matrix reactivity and also their versatility, allowing for any type of aluminum alloy to be combined with any reinforcements, make these processes and especially pressure-assisted sintering extremely appealing for the production of AMCs. This work is concerned with the development, production and characterization of several aluminum based composites, manufactured by a hot pressing process, with the purpose of improving mechanical and/or wear performance of an Aluminum-Silicon (AlSi) alloy. NiTi short-fiber-AlSi; Ni particulate-AlSi; Ti particulate-AlSi; SiC particulate-AlSi and hybrid AlSi-(Ti-SiC) composites were produced and studied. For each of these composites, the bond established between reinforcement and matrix was studied in order to assess their properties, correlating them with the composite properties and also the underlying reinforcing mechanisms. NiTi short-fiber reinforced AlSi composites exhibited a strength increase comparatively to AlSi alloy. This increase was predominantly related with the reinforcement effect and the induced compressive stresses due to the shape memory effect. These composites revealed an effective load transfer between matrix and fibers, indicating the development of an advantageous interface between fiber and matrix. Additionally, this study showed that over extended sintering times can be detrimental, leading to a decrease in shear strength. Nickel particulate reinforced AlSi composites exhibited an expressive reactivity with the formation of a continuous and uniform interface composed by Al3Ni intermetallic. These composites revealed an effective load transfer from matrix to reinforcement, with improvement in strength and hardness, when compared with AlSi alloy, although displaying a ductility reduction. These composites exhibited a wear behavior improvement when compared to AlSi alloy. Titanium particulate reinforced AlSi composites and Silicon Carbide particulate reinforced AlSi composites revealed higher strength but lower ductility than the AlSi alloy. Hybrid AlSi composites, reinforced with Titanium and Silicon Carbide particulates were proven to be an effective solution to achieve beneficial compromises between strength and ductility, unachievable by using a single reinforcement. These composites displayed significant wear behavior improvement when compared to AlSi alloy.A inovação em engenharia tem sido inúmeras vezes alcançada através de combinações inovadoras de materiais. Os compósitos com matriz de ligas de alumínio são uma dessas inovações, permitindo combinar ligas de baixa densidade com reforços selecionados de modo a obter materiais com propriedades físicas, mecânicas e ao desgaste otimizadas e superiores às das ligas de alumínio. Um maior controlo sobre a reatividade entre reforço e matriz e a possibilidade de combinar qualquer liga de alumínio com qualquer reforço, fazem dos processos de metalurgia dos pós, e particularmente a sinterização assistida por pressão, ideais para a produção de compósitos de alumínio. Este trabalho foca-se no desenvolvimento, produção e caracterização de vários compósitos produzidos por um processo de sinterização assistida por pressão, com o objetivo de melhorar o comportamento mecânico e ao desgaste de uma liga de alumínio-silício (AlSi). Foram produzidos compósitos de AlSi reforçados com: fibras curtas de NiTi; partículas de Ni; partículas de Ti; partículas de SiC e ainda compósitos híbridos reforçados com SiC e Ti. Para cada um destes compósitos, a ligação entre reforço e matriz foi caracterizada e as suas propriedades correlacionadas com os mecanismos de reforço e com as propriedades do compósito. Os compósitos de AlSi reforçados com fibras curtas de NiTi demonstraram um aumento de resistência mecânica comparativamente à liga de AlSi. Este aumento foi devido maioritariamente ao efeito do reforço e às tensões residuais de compressão, introduzidas pelo efeito de memória de forma. Estes compósitos revelaram uma efetiva transferência de carga entre matriz e reforço, indicando a presença de uma eficiente interface entre reforço e matriz. Este estudo demonstrou ainda que prolongar o tempo de sinterização pode ser prejudicial, levando a uma redução da tensão de rotura ao corte. Os compósitos de AlSi reforçados com partículas de Ni evidenciaram uma substancial reatividade entre reforço e matriz, com a formação de uma interface contínua e uniforme composta pelo intermetálico Al3Ni. Estes compósitos revelaram transferência de carga entre matriz e reforço, com aumento da tensão de rotura e dureza, embora com redução de ductilidade, quando comparados com a liga não reforçada. Estes compósitos apresentaram uma melhoria no comportamento ao desgaste, relativamente à liga de AlSi. Os compósitos de AlSi reforçados com partículas de Ti, bem como os reforçados com partículas de SiC apresentaram maior resistência mecânica comparativamente com a liga não reforçada, tendo no entanto menor ductilidade. Os compósitos híbridos reforçados com partículas de Ti e de SiC demonstraram ser uma solução eficaz para obter um compromisso vantajoso entre resistência e ductilidade, inatingível quando utilizado um único reforço. Estes compósitos demonstraram uma significativa melhoria no comportamento ao desgaste, relativamente à liga de AlSi.Fundação para a Ciência e a Tecnologia - Bolsa de Doutoramento SFRH/BD/65754/2009

Innovative 3D-printed osteogenic-stimulating structures for orthopaedic implants

9th International Conference on Mechanics of Biomaterials and Tissues, 16-20 December 2023 in Waikoloa, Hawaii[Excerpt] According to The Lancet, "Total hip arthroplasty is the surgery of the century". In the upcoming decades, approximately 10 million total hip and knee arthroplasties (THA and TKA) are expected annually, aiming to restore complete joint functionality and enable pain-free mobility. However, more than 20% of the existing implant solutions induce severe bone resorption, ultimately requiring revision surgery 15-25 years after the initial THA and TKA procedures can result to 70% revision surgeries increase in the future. These surgeries require a substantial financial commitment, encompassing billions of dollars allocated towards medical facilities, equipment, specialized medical personnel, and intensive care units. Consequently, this represents one of the federal governments’ most substantial annual healthcare expenditures. [...]This work was supported by FCT (Fundação para a Ciência e a Tecnologia) by the project PTDC/EME-EME/1442/2020 (Add2MechBio)

MSC morphofunctional programming for improved orthopaedic implantation outcomes

Orthopaedic interventions have risen over the last two decades and are expected to increase due to aging population. Despite advances in orthopaedic implant research, prosthetic failure is often observed, leading to implant replacement. Impaired implant fixation is mainly due to an improper mechanical stimulation at the interface between natural bone and the implant, often composed of Ti6Al4V. At the cellular level, bone remodelling is correlated to the osteoblastic differentiation dynamics of bone-marrow derived mesenchymal stem cells (MSC) in response to changes in their environment. Although the importance of the cytoskeleton as a major mechanotransducer in MSC is widely accepted, it remains elusive how mechanochemical signals regulate MSC differentiation in their interaction with bone and implants.This work was supported by FCT (Fundação para a Ciência e a Tecnologia) through the grants SFRH/BD/141056/2018, COVID/BD/152996/2022 and UMINHO/BID/2023/04 and the projects PTDC/EME-EME/1442/2020, POCI-01-0145-FEDER-030498, UIDB/04436/2020 and UIDP/04436/2020. In addition, this work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MCTES (PIDDAC)

High density HAp and β-TCP blocks for biomedical applications - fabrication strategy and resulting properties

Calcium phosphate compounds, such as HAp and β-TCP, are attractive biomaterials for implants due to a direct bonding to hard tissue owed to their chemical similarity to the inorganic components of human bone. In this study, hot pressing technique was used to produce fully dense HAp and β-TCP using two different approaches: a single holding time versus two holding times, aiming to compare their microstructure, porosity, and mechanical properties. Results showed that by using two holding times the densification was enhanced, which improved the flexural strength of both β-TCP and HAp.This work was supported by FCT (Fundação para a Ciência e a Tecnologia) through the project PTDC/EME-EME/1442/2020 (Add2MechBio). This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC). Also, this work was supported by FCT national funds, under the national support to R&D units grant, through the reference project UIDB/04436/2020 and UIDP/04436/2020. Also, H. Pereira acknowledges FCT for her PhD scholarship (2020.07257.BD)