Superior Wear Resistance in EBM-Processed TC4 Alloy Compared with SLM and Forged Samples

Anisotropy in the Tensile Properties of a Selective Laser Melted Ti-5Al-5Mo-5V-1Cr-1Fe Alloy during Aging Treatment

In this work, the anisotropic microstructure and mechanical properties of selective laser melted (SLMed) Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy before and after aging treatment are investigated. Owing to the unique thermal gradient, the prior columnar β grains with {001} texture component grow in the building direction, and the mechanical properties of the as-fabricated Ti-55511 alloy exhibit slight anisotropy. Aging treatment creates uniform precipitation of the α phase at the boundaries as well as the interior of β grains. Due to the microstructure of the aged samples with a weak texture, the mechanical properties exhibit almost isotropic characteristics with an ultimate tensile strength of 1133 to 1166 MPa, yield strength of 1093 to 1123 MPa, and elongation from 13 to 16%, which meet the aerospace allowable specification very well. By XRD and EBSD analyses, the total dislocation density of the aged samples (~134.8 × 10¹³ m^-2) is significantly lower than that of the as-fabricated samples (~259.4 × 10¹³ m^-2); however, the aged samples exhibit a higher geometrically necessary dislocation (GND) density (~28.5 × 10¹³ m^-2) compared with the as-fabricated samples GND density (~2.9 × 10¹³ m^-2). Thus, a new approach to strengthening theory for estimating the anisotropic mechanical properties of AM alloys is proposed.

Preparation of Zirconium Hydrogen Phosphate Coatings on Sandblasted/Acid-Etched Titanium for Enhancing Its Osteoinductivity and Friction/Corrosion Resistance

Background

Sandblasted/acid-etched titanium (SLA-Ti) implants are widely used for dental implant restoration in edentulous patients. However, the poor osteoinductivity and the large amount of Ti particles/ions released due to friction or corrosion will affect its long-term success rate.

Purpose

Various zirconium hydrogen phosphate (ZrP) coatings were prepared on SLA-Ti surface to enhance its friction/corrosion resistance and osteoinduction.

Methods

The mixture of ZrCl₄ and H₃PO₄ was first coated on SLA-Ti and then calcined at 450°C for 5 min to form ZrP coatings. In addition to a series of physiochemical characterization such as morphology, roughness, wettability, and chemical composition, their capability of anti-friction and anti-corrosion were further evaluated by friction-wear test and by potential scanning. The viability and osteogenic differentiation of MC3T3-E1 cells on different substrates were investigated via MTT, mineralization and PCR assays.

Results

The characterization results showed that there were no significant changes in the morphology, roughness and wettability of ZrP-modified samples (SLA-ZrP0.5 and SLA-ZrP0.7) compared with SLA group. The results of electrochemical corrosion displayed that both SLA-ZrP0.5 and SLA-ZrP0.7 (especially the latter) had better corrosion resistance than SLA in normal saline and serum-containing medium. SLA-ZrP0.7 also exhibited the best friction resistance and great potential to enhance the spreading, proliferation and osteogenic differentiation of MC3T3-E1 cells.

Conclusion

We determined that SLA-ZrP0.7 had excellent comprehensive properties including anti-corrosion, anti-friction and osteoinduction, which made it have a promising clinical application in dental implant restoration.

Additive manufacturing of Ti6Al4V alloy via electron beam melting for the development of implants for the biomedical industry

Additive Manufacturing (AM) or rapid prototyping technologies are presented as one of the best options to produce customized prostheses and implants with high-level requirements in terms of complex geometries, mechanical properties, and short production times. The AM method that has been more investigated to obtain metallic implants for medical and biomedical use is Electron Beam Melting (EBM), which is based on the powder bed fusion technique. One of the most common metals employed to manufacture medical implants is titanium. Although discovered in 1790, titanium and its alloys only started to be used as engineering materials for biomedical prostheses after the 1950s. In the biomedical field, these materials have been mainly employed to facilitate bone adhesion and fixation, as well as for joint replacement surgeries, thanks to their good chemical, mechanical, and biocompatibility properties. Therefore, this study aims to collect relevant and up-to-date information from an exhaustive literature review on EBM and its applications in the medical and biomedical fields. This AM method has become increasingly popular in the manufacturing sector due to its great versatility and geometry control.

Selective Laser Melting of Aluminum and Its Alloys

The laser-based powder bed fusion (LBPF) process or commonly known as selective laser melting (SLM) has made significant progress since its inception. Initially, conventional materials like 316L, Ti6Al4V, and IN-718 were fabricated using the SLM process. However, it was inevitable to explore the possible fabrication of the second most popular structural material after Fe-based alloys/steel, the Al-based alloys by SLM. Al-based alloys exhibit some inherent difficulties due to the following factors: the presence of surface oxide layer, solidification cracking during melt cooling, high reflectivity from the surface, high thermal conductivity of the metal, poor flowability of the powder, low melting temperature, etc. Researchers have overcome these difficulties to successfully fabricate the different Al-based alloys by SLM. However, there exists no review dealing with the fabrication of different Al-based alloys by SLM, their fabrication issues, microstructure, and their correlation with properties in detail. Hence, the present review attempts to introduce the SLM process followed by a detailed discussion about the processing parameters that form the core of the alloy development process. This is followed by the current research status on the processing of Al-based alloys and microstructure evaluation (including defects, internal stresses, etc.), which are dealt with on the basis of individual Al-based series. The mechanical properties of these alloys are discussed in detail followed by the other important properties like tribological properties, fatigue properties, etc. Lastly, an outlook is given at the end of this review.

On the Effect of Electron Beam Melted Ti6Al4V Part Orientations during Milling

The machining of the electron beam melting (EBM) produced parts is a challenging task because, upon machining, different part orientations (EBM layers’ orientations) produce different surface quality even when the same machining parameters are employed. In this paper, the EBM fabricated parts are machined in three possible orientations with regard to the tool feed direction, where the three orientations are “tool movement in a layer plane” (TILP), “tool movement perpendicular to layer planes” (TLP), and “tool movement parallel to layers planes” (TPLP). The influence of the feed rate, radial depth of cut, and cutting speed is studied on surface roughness, cutting force, micro-hardness, microstructure, chip morphology, and surface morphology of Ti6Al4V, while considering the EBM part orientations. It was found that different orientations have different effects on the machined surface during milling. The results show that the EBM parts can achieve good surface quality and surface integrity when milled along the TLP orientation. For instance, surface roughness (Sa) can be improved up to 29% when the milling tool is fed along the TLP orientation compared to the other orientations (TILP and TPLP). Furthermore, surface morphology significantly improves with lower micro-pits, redeposited chips, and feed marks in case of the TLP orientation.

A Review of Heat Treatments on Improving the Quality and Residual Stresses of the Ti–6Al–4V Parts Produced by Additive Manufacturing

Additive manufacturing (AM) can be seen as a disruptive process that builds complex components layer upon layer. Two of its distinct technologies are Selective Laser Melting (SLM) and Electron Beam Melting (EBM), which are powder bed fusion processes that create metallic parts with the aid of a beam source. One of the most studied and manufactured superalloys in metal AM is the Ti–6Al–4V, which can be applied in the aerospace field due to its low density and high melting point, and in the biomedical area owing to its high corrosion resistance and excellent biocompatibility when in contact with tissues or bones of the human body. The research novelty of this work is the aggregation of all kinds of data from the last 20 years of investigation about Ti–6Al–4V parts manufactured via SLM and EBM, namely information related to residual stresses (RS), as well as the influence played by different heat treatments in reducing porosity and increasing mechanical properties. Throughout the report, it can be seen that the expected microstructure of the Ti–6Al–4V alloy is different in both manufacturing processes, mainly due to the distinct cooling rates. However, heat treatments can modify the microstructure, reduce RS, and increase the ductility, fatigue life, and hardness of the components. Furthermore, distinct post-treatments can induce compressive RS on the part’s surface, consequently enhancing the fatigue life.

A comparative study on the nanoindentation behavior, wear resistance and in vitro biocompatibility of SLM manufactured CP-Ti and EBM manufactured Ti64 gyroid scaffolds

The present study investigates the nanoindentation behavior, wear resistance and in vitro biocompatibility of SLM manufactured CP-Ti and EBM manufactured Ti64 gyroid scaffolds and the results were compared to those of casting CP-Ti. Both the SLM- and EBM manufactured scaffolds exhibited anisotropic properties with higher reduced modulus (up to 10%) and nanohardness (up to 30%) in the transverse direction than those in building direction. The wear resistance of scaffolds in transverse direction was higher than those of in building direction by up to ∼25% and ∼82% for SLM manufactured CP-Ti and EBM manufactured Ti64 scaffolds, respectively. The SLM manufactured CP-Ti scaffolds displayed significant enhancement in wear resistance over cast dense CP-Ti with 75% lower mean worn height during a nanowear test. The coefficient of friction was varied between 0.11 and 0.24 and exhibited a steady mean value of 0.15-0.18 for CP-Ti and Ti64 scaffolds, respectively. During in vitro cell culture study, CP-Ti scaffolds showed higher cell viability and cell adhesion density in comparison to Ti64 scaffolds for all unit cell sizes. Moreover, cell adhesion density of scaffolds with smaller unit cell sizes (G2) are lower than those of larger unit cells (G3). SEM observations confirmed that both the inner space and surfaces of gyroid scaffolds provided a suitable environment for cell migration, attachment and proliferation after cell culture for 7 d. STATEMENT OF SIGNIFICANCE: It is essential to evaluate the properties of EBM/SLM manufactured scaffolds and to determine whether they can meet the tough performance requirements of the biomedical industry. In this study, nanoindentation and nanowear properties of SLM manufactured CP-Ti and EBM manufactured Ti64 gyroid scaffolds with different unit cell sizes and sample orientations were evaluated and compared to cast dense CP-Ti samples. Moreover, the in vitro biocompatibility of the scaffolds was assessed and compared to each other. To our best of knowledge, this type of study on EBM/SLM manufactured CP-Ti and Ti64 scaffolds have not been reported, to date.

Mechanical Behavior of Ti6Al4V Scaffolds Filled with CaSiO3 for Implant Applications

Triply periodic minimal surfaces (TPMS) are becoming increasingly attractive due to their biomedical applications and ease of production using additive manufacturing techniques. In the present paper, the architecture of porous scaffolds was utilized to seek for the optimized cellular structure subjected to compression loading. The deformation and stress distribution of five lightweight scaffolds, namely: Rectangular, primitive, lattice, gyroid and honeycomb Ti6Al4V structures were studied. Comparison of finite element simulations and experimental compressive test results was performed to illustrate the failure mechanism of these scaffolds. The experimental compressive results corroborate reasonably with the finite element analyses. Results of this study can be used for bone implants, biomaterial scaffolds and antibacterial applications, produced from the Ti6Al4V scaffold built by a selective laser melting (SLM) method. In addition, Ti6Al4V manufactured metallic lattice was filled by wollastonite (CaSiO3) through spark plasma sintering (SPS) to illustrate the method for the production of a metallic-ceramic composite suitable for bone tissue engineering.