Ti 6Al 4V Extra Low Interstitial Research Articles

Diamond machining of additively manufactured Ti6Al4V ELI: Newer mode of material removal challenging the current simulation tools

Single point diamond machining (SPDM) produces smooth machined surfaces that other production methods cannot match. While the mechanics of machining of cast alloys with SPDM is well-explored, the realm of SPDM for additively manufactured parts remains largely uncharted. This work reveals new insights into the surface generation process of an additively manufactured titanium alloy, specifically, a Ti6Al4V Extra Low Interstitials (ELI) alloy workpiece. Our examination of the chip morphology unveiled a distinct mode of chip removal, previously unrecorded in existing literature. During SPDM of additively made Ti6Al4V ELI workpiece, identification of numerous pores and discontinuities in the chips flowing on the tool rake face, indicating periodic intermittent cracking during the material's plastic flow was seen. To examine this phenomenon, a finite element analysis (FEA) model was developed. While the FEA model can well explain the machining mechanics and chip morphology of SPDM of cast Ti6Al4V ELI reported in the literature, it failed to describe the chip morphology that are obtained during machining of additively made workpiece in this work. This disparity underscores the need for innovative simulation approaches tailored for additively manufactured components. The experimental observations in this study highlight a unique form of chip formation in contrast to conventional Ti6Al4V alloy machining processes. At lower feeds, there was a presence of short, discontinuous chip formation with tearing at the outer periphery. Conversely, at higher feeds, a long, continuous ribbon-like chip formation was observed. In addition, some typical additive manufacturing defects appear on the machined surface and chips. Through optimisation of the SPDT parameters, a surface roughness (Ra) value of about 11.8 nm was achieved on additively manufactured Ti6Al4V ELI workpiece. This work provides a fresh perspective on the mechanics of SPDM for additively manufactured components, offering a stepping stone for subsequent studies.

Research on microstructure and mechanical properties of Ti–6Al–4V ELI fabricated by hybrid directed energy deposition with in-situ rolling and annealing

To achieve superior damage tolerance and fatigue properties, it is desirable for the microstructure of Ti-6Al-4V ELI (Extra Low Interstitial) titanium alloy to consist of equiaxed grains with a homogeneous lamellar structure. However, traditional forging and single additive manufacturing techniques require extreme processes such as quasi β heat treatment and hot isostatic pressing. In this paper, a hybrid directed energy deposition method that integrates in-situ rolling with simple annealing is proposed to simultaneously achieve these microstructures. The results indicate that the initial microstructures produced by hybrid directed energy deposition consist of fine equiaxed prior-β grains, inconspicuous interpass bright bands, randomly oriented lamellar structure and numerous small substructures at the TEM scale. Due to the plastic deformation caused by in-situ rolling, the primary β grains underwent significant refinement with a reduction in grain diameter from over 2000 μm to 113.8 μm. Besides, the unique microstructures and thickness of α laths are influenced by coarsening and dissolution mechanisms that are controlled by diffusion during phase transformation. Furthermore, a uniform microstructure without bright bands and excellent comprehensive properties can be achieved through heating at 880 °C for 2 h and natural cooling. These findings validate that hybrid directed energy deposition coupled with simple annealing present a novel and cost-effective approach for the direct manufacturing of uniform titanium alloy forgings.

Influence of heat treatment on the microstructure, wettability, and corrosion resistance of a Ti–30Nb–7Zr alloy used in biomedical applications

Commercially pure titanium (cp Ti ASTM F67) and the Ti–6Al–4V ELI (Extra Low Interstitial) alloy (ASTM F136) are commonly used as biomaterials due to their biocompatibility, mechanical strength, and corrosion resistance. The low mechanical resistance of cp Ti reduces its applications. The F136 alloy may release toxic ions (Al and V). Moreover, the fact that the elastic modulus of the F136 is larger than the bone leads to stress shielding and induces bone loss. These factors drive research towards the development of new biomedical metal alloys with more suitable mechanical properties. β titanium and β-metastable alloys have special attention as potential alternatives to the F136 alloy applications. This work aimed to analyze the microstructure, wettability, and corrosion resistance of the β Ti–30Nb–7Zr alloy before and after heat treatment, and compare the results with those for the F136 alloy. The β Ti–30Nb–7Zr is an alloy based on non-toxic elements and with a smaller elastic module than F136. The techniques of open circuit potential, potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy were used. The results of this work showed that the Ti–30Nb–7Zr alloy in the as-received condition had a β matrix with precipitates, and after recrystallization heat treatments, the precipitates were eliminated. The Ti–30Nb–7Zr alloy heat treated at 500 °C for 30 min had α phase precipitates, which increased the surface energy and decreased the corrosion resistance. The best corrosion resistance was observed in Ti–30Nb–7Zr after heat treatment at 900 °C for 1 h. The conclusion is that after adequate heat treatment, the Ti–30Nb–7Zr alloy is an alternative to Ti–6Al–4V for biomedical applications.

Surface Characteristics and Residual Stress Variation in Semi-Deep Hole Machining of Ti6Al4V ELI with Low-Frequency Vibration-Assisted Drilling

This study examined the impact of vibration-assisted drilling (VAD) on hole quality and residual stress in Ti-6Al-4V ELI (Extra Low Interstitials) material. Ti-6Al-4V ELI possesses excellent mechanical properties but presents challenges in machining, including chip evacuation, burr formation, and elevated cutting temperatures. VAD, particularly low-frequency vibration-assisted drilling (LF-VAD), has been explored as a potential solution to address these issues. The research compares LF-VAD with conventional drilling (CD) under various cutting and cooling conditions. LF-VAD exhibits higher maximum thrust forces under specific conditions, which result in accelerated tool wear. However, it also demonstrates lower RMS (root mean square) forces compared to CD, offering better control over chip formation, reduced burr formation, and improved surface roughness within the hole. Furthermore, LF-VAD generates greater compressive residual stresses on the hole’s inner surface compared to CD, suggesting enhanced fatigue performance. These findings indicate that LF-VAD holds promise for improving the hole’s surface characteristics, fatigue life, and overall component durability in Ti-6Al-4V machining applications.

Performance of additively manufactured Ti6Al4V ELI finger joints: biomechanical testing and evaluation for arthritis management

Abstract Approximately 24 out of every 100 adults in the United States, or 58.5 million people, have arthritis, which refers to a condition that causes pain and inflammation in a joint according to US National Center for Chronic Disease Prevention and Health Promotion. Osteoarthritis is the most common type of arthritis, and it may damage almost any joint but mainly occur in hands, hips and knees. While there are several joint replacement options for hips and knees, there are only limited options for finger joints. In this paper, we report on several aspects of testing of novel finger joints: testing apparatus design, cadaveric performance test and material testing results of titanium joints using 3D-printed Ti6Al4V extra low interstitial (ELI). Soft cadaveric hands with finger joints were surgically replaced by additively manufactured titanium joints following the exact same anatomy of the cadavers. These small joints were engineered to mimic the biological and natural movements of fingers. The apparatus, methodology and results of biomechanical tests were deployed to evaluate and validate the joints particularly those of titanium joints manufactured via laser powder bed fusion methods (PBF-L/M).

Simulation-based investigation on ultra-precision machining of additively manufactured Ti-6Al-4V ELI alloy and the associated experimental study

Additive Manufacturing (AM) has shown excellent research potential for biomedical implants, complex aerofoil structures, military applications, high-pressure cryogenic vessels, and automobile components. The mechanical properties exhibited by the additively manufactured Ti6Al4V ELI alloy components are significantly different from traditionally manufactured Ti6Al4V alloy due to the material anisotropy, orientation of the microstructure, and variation in heat treatments. Among AM techniques, SLM (Selective laser melting) offers unparalleled design flexibility with minimum impurities and high reproducibility. However, post-processing of additive manufactured components is essential due to their poor surface finish and lack of dimensional accuracy. Ti6Al4V ELI (Extra Low Interstitials) alloy is a difficult-to-cut material in Ultra-Precision Machining (UPM) due to its excessive tool wear, hardness, and chemical reactivity. Optimizing machining parameters for better surface finish by UPM is time-consuming and often not economical. Modeling and simulation provide a low-cost approach for the investigation of machining. In this work, a series of cutting experiments have been carried out on additively manufactured Ti6Al4V ELI alloy to study the cutting mechanism during UPM. In addition, Finite Element Model (FEM) is employed to understand the chip formation and cutting forces in UPM with a built-in Johnson-Cook (JC) model and a Johnson-Cook-TANH (JC-TANH) vectorized user-defined material subroutine (VUMAT) model. Cutting forces corresponding to the JC model and JC-TANH are examined with the experimental forces in literature, and the results are found to be fairly close.

Peptide grafting on intraosseous transcutaneous amputation prostheses to promote sealing with skin cells: Potential to limit infections.

The long-term success of intraosseous transcutaneous amputation prostheses (ITAPs) mainly relies on dermal attachment of skin cells to the implant. Otherwise, bacteria can easily penetrate through the interface between the implant and the skin. Therefore, infection at this implant/skin interface remains a significant complication in orthopedic surgeries in which these prostheses are required. Two main strategies were investigated to prevent these potential infection problems which consist in either establishing a strong sealing at the skin/implant interface or on eradicating infections by killing bacteria. In this work, two adhesion peptides, either KRGDS or KYIGSR and one antimicrobial peptide, Magainin 2 (Mag 2), were covalently grafted via phosphonate anchor arms to the surface of the Ti6Al4V ELI (extra low interstitials) material, commonly used to manufacture ITAPs. X-ray photoelectron spectroscopy, contact angle, and confocal microscopy analyses enabled to validate the covalent and stable grafting of these three peptides. Dermal fibroblasts cultures on bare Ti6Al4V ELI surfaces and functionalized ones displayed a good cell adhesion and proliferation on all samples. However, cell spreading and viability appeared to be improved on grafted surfaces, especially for those conjugated with KRGDS and Mag 2. Moreover, the dermal sheet attachment, was significantly higher on surfaces functionalized with Mag 2 as compared to the other surfaces. Therefore, the surface functionalization with the antimicrobial peptide Mag 2 seems to be the best approach for the targeted application, as it could play a dual role, inducing a strong skin adhesion while limiting infections on Ti6Al4V ELI materials.

Carbon emissions, techno-economic and machinability assessments to achieve sustainability in drilling Ti6Al4V ELI for medical industry applications

In the last decade, cryogenic machining has made a significant impact as a sustainable machining technique, demonstrating machinability improvements in terms of tool life, surface quality of machine parts, low environmental effects and reduced cost of overall machining operation. A near-to-dry machining technique, Electrostatic Minimum Quantity Lubrication (EMQL) has also emerged as a sustainable machining technique, which is an environmentally-friendly alternative to the flood machining process. Although these coolant/lubrication strategies have been studied extensively, there is no direct comparison of both these machining techniques in the aspects of ecology, economy and machining performances. In this novel study, cryogenic liquid carbon dioxide (LCO2) and EMQL techniques are used for high-speed drilling of Ti6Al4V ELI (extra low interstitial) grade, and the sustainability and machinability assessment of these techniques are evaluated which can help medical implant manufacturing industries to implement these techniques as an economic and sustainable replacement of the conventional cooling/lubrication techniques. Ti6Al4V ELI is widely used in the medical industry for Hip and Knee joint endoprosthesis, bone screws, collar bone and dental implants. The sustainability aspects were evaluated in terms of carbon emission and cost analysis of the processes. It was found that the EMQL cutting condition exhibited 27.69% higher carbon emission and 67.60% higher cost of machining operation compared to cryogenic LCO2 cutting condition. Moreover, the tool life experienced when machining using cryogenic LCO2 cutting condition was at least 4 times higher than tool life found when using the EMQL cutting condition. The surface roughness of the workpiece material was higher (56.40%) when using the EMQL coolant. These results were attributed to adhesion wear and chip clogging phenomena which were found to be the main factors for reduced tool life and higher surface roughness in EMQL cutting condition. Therefore, from this study, it can be concluded that cryogenic LCO2 coolant performs significantly better compared to EMQL coolant, providing improved machinability of the titanium workpiece and superior sustainability of the cutting operation.

Influence of heat treatment and loading direction on compressive deformation behaviour of Ti–6Al–4V ELI fabricated by powder bed fusion additive manufacturing

In this study, we have investigated the effects of heat treatment and loading direction on anisotropic compressive behaviour of additively manufactured (AM) Ti–6Al–4V ELI (extra low interstitials). AM samples were fabricated by powder bed fusion (PBF) processing, heat-treated between 800 °C and 950 °C, and compressed along two directions (i.e. parallel and perpendicular to the building direction) with a strain rate of 10−3 s−1 at room temperature. The heat treatment effectively leads to increasing ductility of as-built by decomposing the α′ phase to α and β phases. The heat-treated samples show a significantly lower yield strength than the as-built sample, which has a higher pre-existing dislocation density. As the annealing temperature increases, the yield strength decreased with a broadening of α lath thickness. Furthermore, perpendicular loaded samples have significantly higher strain hardening rate and ductility than parallel loaded samples. However, most of these anisotropic responses disappeared with indistinct morphologies. Anisotropic properties can be ascribed to the directional features of the microstructure resulting from the additive manufacturing process.

Mechanical properties and in vitro cytocompatibility of dense and porous Ti–6Al–4V ELI manufactured by selective laser melting technology for biomedical applications

The Ti–6Al–4V alloy is the most common biomaterial used for bone replacements and reconstructions. Despite its advantages, the Ti–6Al–4V has a high stiffness that can cause stress-shielding. In this work, we demonstrated that the selective laser melting (SLM) technology could be used to fabricate porosity in Ti–6Al–4V extra low interstitial (ELI) to reduce its stiffness while improving cell adhesion and proliferation. With a porosity of 14.04%, the elastic modulus of the porous Ti–6Al–4V ELI was reduced to 80 GPa. The compressive stress and the 3-point-bending flexural tests revealed that the porous Ti–6Al–4V ELI possessed a brittle characteristic. The additional pores within the beams of the lattice structures of porous Ti–6Al–4V ELI increased its surface arithmetic average roughness, Ra = 3.94 μm. The in vitro cytocompatibility test showed that the SLM printing process and the post-processes did not cause any toxicity in the MC3T3-E1 cells. The in vitro cell proliferation test also showed that the porous Ti–6Al–4V ELI increased the proliferation rate of osteogenic induced MC3T3-E1 cells on Day 7. The findings from this study would provide engineers and researchers with both the mechanical information and biological understanding of SLM printed porous Ti–6Al–4V ELI, and SLM printed dense Ti–6Al–4V ELI towards biomedical applications.

Acoustic behaviour of 3D printed titanium perforated panels

Titanium alloys such as Ti6Al4V is amongst the most widely studied metallic materials in the broad context of metal 3D printing. Although the mechanical performances are well understood, the acoustic performance of 3D printed Ti6Al4V, and Ti6Al4V ELI (Extra Low Interstitial) has received limited attention in the literature. As such, this study investigates the normal incidence sound absorption coefficient (α) and Sound Transmission Loss (STL) of both Ti6Al4V and Ti6Al4V ELI samples manufactured using Selective Laser Melting (SLM). The influence of material thickness on acoustic responses and the potential of developing Ti6Al4V micro-perforated panels (MPP) at 400–1600 Hz is also explored. The sound absorption of three aesthetic perforations printed using Ti6Al4V and the influence of a porous back layer was also investigated. The experimental measurements were carried out using an impedance tube following ISO10534-2. The result of the study establishes that 3D printed non-circular perforations featuring porous back-layer can exhibit improved sound absorption coefficient.

Reproducibility of Replicated Trabecular Bone Structures from Ti6Al4V Extralow Interstitials Powder by Selective Laser Melting

Reproducibility of Replicated Trabecular Bone Structures from Ti6Al4V Extralow Interstitials Powder by Selective Laser Melting

Evaluation of mechanical properties, in vitro corrosion resistance and biocompatibility of Gum Metal in the context of implant applications

In recent decades, several novel Ti alloys have been developed in order to produce improved alternatives to the conventional alloys used in the biomedical industry such as commercially pure titanium or dual phase (alpha and beta) Ti alloys. Gum Metal with the non-toxic composition Ti–36Nb–2Ta–3Zr–0.3O (wt. %) is a relatively new alloy which belongs to the group of metastable beta Ti alloys. In this work, Gum Metal has been assessed in terms of its mechanical properties, corrosion resistance and cell culture response. The performance of Gum Metal was contrasted with that of Ti–6Al–4V ELI (extra-low interstitial) which is commonly used as a material for implants. The advantageous mechanical characteristics of Gum Metal, e.g. a relatively low Young's modulus (below 70 GPa), high strength (over 1000 MPa) and a large range of reversible deformation, that are important in the context of potential implant applications, were confirmed. Moreover, the results of short- and long-term electrochemical characterization of Gum Metal showed high corrosion resistance in Ringer's solution with varied pH. The corrosion resistance of Gum Metal was best in a weak acid environment. Potentiodynamic polarization studies revealed that Gum Metal is significantly less susceptible to pitting corrosion compared to Ti–6Al–4V ELI. The oxide layer on the Gum Metal surface was stable up to 8.5 V. Prior to cell culture, the surface conditions of the samples, such as nanohardness, roughness and chemical composition, were analyzed. Evaluation of the in vitro biocompatibility of the alloys was performed by cell attachment and spreading analysis after incubation for 48 h. Increased in vitro MC3T3-E1 osteoblast viability and proliferation on the Gum Metal samples was observed. Gum Metal presented excellent properties making it a suitable candidate for biomedical applications.

Short-Term Heat Treatment of Ti6Al4V ELI as Implant Material.

Due to its mechanical properties and good biocompatibility, Ti6Al4V ELI (extra low interstitials) is widely used in medical technology, especially as material for implants. The specific microstructures that are approved for this purpose are listed in the standard ISO 20160:2006. Inductive short-term heat treatment is suitable for the adjustment of near-surface component properties such as residual stress conditions. A systematic evaluation of the Ti6Al4V microstructures resulting from short-term heat treatment is presently missing. In order to assess the parameter field that leads to suitable microstructures for load-bearing implants, dilatometer experiments have been conducted. For this purpose, dilatometer experiments with heating rates up to 1000 °C/s, holding times between 0.5 and 30 s and cooling rates of 100 and 1000 °C/s were systematically examined in the present study. Temperatures up to 950 °C and a holding time of 0.5 s led to microstructures, which are approved for medical applications according to the standard ISO 20160:2006. Below 950 °C, longer holding times can also be selected.

INFLUENCE OF LARGE ARTIFICIAL POROSITY ON BENDING BEHAVIOUR OF TI6AL4V ELI ADDITIVELY MANUFACTURED SPECIMENS SUBJECTED TO TYPICAL LOADS DURING MASTICATION

Effective quality control of implants made using additive manufacturing is an important task for suppliers to comply fully with existing regulations and certifications. To study the influence of porosity on the mechanical behaviour of mandibular implants produced by additive manufacturing, preliminary tests with longitudinal flat samples were performed with 3D point bending tests. Ti6Al4V Extra Low Interstitial (ELI) specimens with artificial porosity were designed and subjected to typical loads during mastication. In this work, a finite element simulation was constructed to investigate the bending behaviour of samples, which was consistent with the experimental results. The work shows that even large artificial cavities (designed up to 0.42 mm) do not significantly affect the strength of additively manufactured 2.5 mm-thick Ti6Al4V ELI specimens under typical static loads of mandibular implants, in the considered loading conditions, and for samples subjected to appropriate surface finishing and annealing heat treatment.

Comprehensive Biological Evaluation of Biomaterials Used in Spinal and Orthopedic Surgery.

Biological acceptance is one of the most important aspects of a biomaterial and forms the basis for its clinical use. The aim of this study was a comprehensive biological evaluation (cytotoxicity test, bacterial colonization test, blood platelets adhesion test and transcriptome and proteome analysis of Saos-2 cells after contact with surface of the biomaterial) of biomaterials used in spinal and orthopedic surgery, namely, Ti6Al4V ELI (Extra Low Interstitials), its modified version obtained as a result of melting by electron beam technology (Ti6Al4V ELI-EBT), polyether ether ketone (PEEK) and polished medical steel American Iron and Steel Institute (AISI) 316L (the reference material). Biological tests were carried out using the osteoblasts-like cells (Saos-2, ATCC HTB-85) and bacteria Escherichia coli (DH5α). Results showed lack of cytotoxicity of all materials and the surfaces of both Ti6Al4V ELI and PEEK exhibit a significantly higher resistance to colonization with E. coli cells, while the more porous surface of the same titanium alloy produced by electron beam technology (EBT) is more susceptible to microbial colonization than the control surface of polished medical steel. None of the tested materials showed high toxicity in relation to E. coli cells. Susceptibility to platelet adhesion was very high for polished medical steel AISI 316L, whilst much lower for the other biomaterials and can be ranked from the lowest to the highest as follows: PEEK < Ti6Al4V ELI < Ti6Al4V ELI-EBT. The number of expressed genes in Saos-2 cells exposed to contact with the examined biomaterials reached 9463 genes in total (ranging from 8455 genes expressed in cells exposed to ELI to 9160 genes in cells exposed to PEEK). Whereas the number of differentially expressed proteins detected on two-dimensional electrophoresis gels in Saos-2 cells after contact with the examined biomaterials was 141 for PEEK, 223 for Ti6Al4V ELI and 133 for Ti6Al4V ELI-EBT. Finally, 14 proteins with altered expression were identified by mass spectrometry. In conclusion, none of the tested biomaterials showed unsatisfactory levels of cytotoxicity. The gene and protein expression analysis, that represents a completely new approach towards characterization of these biomaterials, showed that the polymer PEEK causes much more intense changes in gene and protein expression and thus influences cell metabolism.

Design Aspects of Hip Implant Made of Ti-6Al-4V Extra Low Interstitials Alloy

The main concerns in design of hip implants are fracture and fatigue related issues. In this paper, reverse engineering is used to re-design a hip implant produced by precision casting, using Ti6Al4V Extra Low Interstitials (ELI) alloy. As the most critical part, hip neck has been in the focus of this analysis, keeping in mind that the lower the thickness is, the higher the movement of joint may be, but affecting its structural integrity at the same time. Thus, 5 different models are created with different neck thickness and analyzed by using the Finite Element Method (FEM) for stress-strain calculation and extended FEM (XFEM) for fatigue crack growth.

Effects of harmonic structure on the electrochemical behavior of biomedical Ti6Al4V

Metallic implants with Harmonic Structure has been reported to perform better mechanical properties compared to traditional microstructure on several biomedical alloys. Researchers have shown mechanic improvement when obtaining this microstructure but, there is a literature gap about the electrochemical behavior of these alloys related to harmonic microstructure obtainment. Thus, in this paper, the HS Ti6Al4V was obtained by Spark Plasma Sintering in order to be compared on its electrochemical behavior to commercial α + β Ti6Al4V ELI (Extra Low Interstitial), which is one of the most studied alloys for implants due to its biocompatibility and because of its good relation of the mechanical and electrochemical properties. Optical microscopy was conducted to verify the morphology and microstructure of the alloys, X-ray diffraction analyses to crystalline phase determination. For the electrochemical stability analysis, Open Circuit Potential curves were obtained in chloride media followed by voltammetry profile analysis on simulated blood solution, finally, the electrical parameters of the corrosion process were obtained using Electrochemical Impedance Spectroscopy. The results indicated that the materials presented a very similar electrochemical behavior with high polarization resistance, with almost no difference in the values of the curves, indicating there is no inference on the electrochemical behavior or corrosion resistance from the Ti6Al4V alloy with the harmonic structure.

Extra low interstitial titanium based fully porous morphological bone scaffolds manufactured using selective laser melting

Lattice structure based morphologically matched scaffolds is rapidly growing facilitated by developments in Additive Manufacturing. These porous structures are particularly promising due to their potential in reducing stress shielding and maladapted stress concentration. Accordingly, this study presents Extra Low Interstitial (ELI) Titanium alloy based morphological scaffolds featuring three different porous architecture. All scaffolds were additively manufactured using Selective Laser Melting from Ti6Al4V ELI with porosities of 73.85, 60.53 and 55.26% with the global geometry dictated through X-Ray Computed Tomography. The elastic and plastic performance of both the scaffold prototypes and the bone section being replaced were evaluated through uniaxial compression testing. Comparing the data, the suitability of the Maxwell criterion in evaluating the stiffness behaviour of fully porous morphological scaffolds are carried out. The outcomes show that the best performing scaffolds presented in this study have high strength (169 MPa) and low stiffness (5.09 GPa) suitable to minimise stress shielding. The matching morphology in addition to high porosity allow adequate space for flow circulation and has the potential to reduce maladapted stress concentration. Finally, the Electron Diffraction X-ray analysis revealed a small difference in the composition of aluminium between the particle and the bonding material at the scaffold surface.

An interlaboratory comparison of X-ray computed tomography measurement for texture and dimensional characterisation of additively manufactured parts

This paper presents the results of the CT-STARR (CT-Surface Texture for Additive Round Robin) Stage 1 interlaboratory comparison. The study compared the results obtained for the extraction of areal surface texture data per ISO 25178-2 from five X-ray computed tomography (CT) volume measurements from each of four laboratories. Two Ti6Al4V ELI (extra-low interstitial) components were included in each of the CT acquisitions. The first component was an additively manufactured (AM) cube manufactured using an Arcam Q10 electron beam melting (EBM) machine. Surface texture data was extracted from CT scans of this part. The values of selected parameters per ISO 25178-2 are reported, including Sa, the arithmetic mean height, for which the values from the Nikon MCT 225 metrology CT measurements were all within 0.5% of the mean reference focus variation measurement. CT resolution requirements are discussed. The second component was a machined dimensional test artefact designed to facilitate independent analysis of CT global voxel scaling errors and surface determination errors. The results of mathematical global scaling and surface determination correction of the dimensional artefact data is reported. The dimensional test artefact errors for the XT H 225 commercial CT for length, outside diameter and inside diameter reduced from -0.27%, -0.83% and -0.54% respectively to less than 0.02% after performing mathematical correction. This work will assist the development of surface texture correction protocols, help define surface-from-CT measurement envelope limits and provide valuable information for an expanded Stage 2 interlaboratory comparison, which will include a more diverse range of CT systems and technologies, further expanding the surface-from-CT knowledge base.