Additive manufacture of titanium structures allows the realisation of advanced design strategies not achievable through traditional manufacturing methods. This work analyses the performance of ...Ti-6Al-4V Kagome truss core structures produced by selective laser melting (SLM) for composite sandwich structures. These bio-inspired core structures can be manufactured for truss diameters larger than 0.6mm and internal truss angles of less than 60° without requiring additional support structures. Mechanical testing is conducted to determine the deformation and failure of the core structure in compression and shear. A finite element model validates the structural performance and can further optimise the unit cell design. Design charts show that the performance of the proposed titanium core in both compression and shear is superior (strength) or equal (stiffness) to honeycomb cores for aerospace applications.
The Achilles’ heel of additively manufactured Ti-6Al-4V by selective laser melting (SLM) is its inferior mechanical properties compared with its wrought (forged) counterparts. Acicular
α
′ martensite ...resulted from rapid cooling by SLM is primarily responsible for high strength but inadequate tensile ductility achieved in the as-fabricated state. This study presents a solution to eliminating the adverse effect of the nonequilibrium
α
′ martensite. This is achieved by enabling in situ martensite decomposition into a novel ultrafine (200–300 nm) lamellar (
α
+
β
) microstructure via the selection of an array of processing variables including the layer thickness, energy density, and focal offset distance. The resulting tensile elongation reached 11.4% while the yield strength was kept above 1100 MPa. These properties compare favorably with those of mill-annealed Ti-6Al-4V consisting of globular
α
and
β
. The fatigue life of SLM-fabricated Ti-6Al-4V with an ultrafine lamellar (
α
+
β
) structure has approached that of the mill-annealed counterparts and is much superior to that of SLM-fabricated Ti-6Al-4V with
α
′ martensite.
Deep-powder-bed additive manufacturing (AM) can lead to distinctive microstructural features. In this study, 300-mm long cylindrical rods (12-mm diameter) of Ti–6Al–4V were vertically built to the ...limit height of a commercial selective electron beam melting (SEBM) system for quantitative three-dimensional (3D) characterization of the defects by X-ray micro-computed tomography (μ-CT). Detailed μ-CT data from 18,337 consecutive slices revealed a strong dependence of defect characteristics on build height, including defect volume, population, sphericity, major axis length, depth and orientation angle. The first 100-mm build exhibited the worst presence of defects by each measurement, while the middle and last 100-mm builds contained much fewer defects, especially the last 100-mm build, which was free of lack-of-fusion defects (sphericity < 0.5). As a result, the first 100-mm build displayed 50% lower reduction of area and 20% lower strain-to-fracture than the last 100-mm build, while the tensile strengths varied within just ±3%. An outer 3-mm thick ring and a central 1.5-mm diameter region were found to contain substantially less defects along the 300-mm build height. The dependence of defect features on build height was attributed to the existence of an upward temperature gradient during SEBM. The 3D defect features revealed by μ-CT along the build height provide important implications for deep-powder-bed AM by SEBM.
•The energy per layer was found to be critical factor to print fully dense AlSi12 samples using SLM process.•The printing area along the build direction varies when a sample is built in different ...orientations.•The anisotropy of SLM-built samples corresponds to the variable energy per layer and printing area.•Fully dense SLM-built AlSi12 samples were printed by using energy per layer in an optimum range.
The anisotropy in the tensile properties of AlSi12 alloy fabricated using selective laser melting (SLM) additive manufacturing process was investigated. The tensile samples were printed in three different orientations, horizontal (H - 0°), inclined (I - 45°), and vertical (V - 90°), and found to exhibit yield strength between 225 MPa and 263 MPa, tensile strength between 260 MPa and 365 MPa, and ductility between 1 and 4%, showing distinct fracture patterns. It was established that the build orientation had insignificant effect on the microstructural characteristics of the SLM-printed samples, while XRD phase analysis showed variations in the Al (111) and Al (200) peak intensities. Consequently, the anisotropy in the mechanical properties of the SLM-printed AlSi12 samples was attributed to the differences in their relative density. Although the energy density was kept constant when printing the samples along different orientations, the “energy per layer” was found to be different owing to the variation in the printing area along the build direction. Further investigation on the effect of printing area, and correspondingly energy per layer, on the relative density was carried out. It was found that energy per layer in the range of 504–895 J yielded ≥99.8% relatively dense AlSi12 SLM-printed samples. This study puts forth a new idea that the density of the SLM-printed samples could be controlled using energy per layer as an input process parameter.
Sheet (0.41–4.80 mm thick) or thin plate structures commonly exist in additively manufactured Ti-6Al-4V components for load-bearing applications. A batch of 64 Ti-6Al-4V sheet samples with dimensions ...of 210/180 mm × 42 mm × 3 mm have been additively manufactured by selective electron beam melting (SEBM). A comprehensive assessment was then made of their density, surface flatness, microstructure, and mechanical properties in both as-built and hot isostatically pressed conditions, including the influence of the hot isostatic pressing (HIP) temperature. In particular, standard long tensile (156 mm long, 2 mm thick) and fatigue (206 mm long, 2 mm thick) test sheet samples were used for assessment. As-built SEBM Ti-6Al-4V sheet samples with machined surfaces fully satisfied the minimum tensile property requirements for mill-annealed TIMETAL Ti-6Al-4V sheet products, whereas HIP-processed samples (2 mm thick) with machined surfaces achieved a high cycle fatigue (HCF) strength of 625 MPa (R = 0.06, 10
7
cycles), similar to mill-annealed Ti-6Al-4V (500–700 MPa). The unflatness was limited to 0.2 mm in both the as-built and HIP-processed conditions. A range of other revealing observations was discussed for the additive manufacturing of the Ti-6Al-4V sheet structures.
Today additive manufacturing is shaping the future of global manufacturing and is influencing the design and manufacturability of tomorrows products. With selective laser melting (SLM), parts can be ...built directly from computer models or from measurements of existing components to be re-engineered, and therefore bypass traditional manufacturing processes such as cutting, milling and grinding. Benefits include: 1) new designs not possible using conventional subtractive technology, 2) dramatic savings in time, materials, wastage, energy and other costs in producing new components, 3) significant reductions in environmental impact, and 4) faster time to market. SLM builds up finished components from raw material powders layer by layer through laser melting. SLM removes many of the shape restrictions that limit design with traditional manufacturing methods, thereby allowing computationally optimised, high performance structures to be utilised. Functional engineering prototypes and actual components can then be built in their final shape with minimal material wastage. Samples and small product runs can be produced quickly at comparatively low cost to test and build market acceptance without major investment. In this chapter we present and discuss some of the concepts and findings involved in the design, manufacture and examination of high-value aerospace components from Ti-6Al-4V alloy produced at the RMITs Advanced Manufacturing Precinct.
The present study reports on additive manufacturing of a Ti-30Ta (at.%) high-temperature shape memory alloy (HT-SMA) using electron beam powder bed fusion (PBF-EB/M) technique. Detailed ...microstructure analysis was conducted to reveal the microstructural evolution along the entire process chain, i.e. from gas-atomised powder to post-processed material. PBF-EB/M processed structures with near full density and an isotropic, β-phase stabilised microstructure, i.e. equiaxed β-grains of around 20 µm in diameter with no preferred crystallographic orientation, are reported. As revealed by differential scanning calorimetry, post-process heat-treated Ti-Ta demonstrates a reversible martensitic phase transformation well above 100°C. Although partly unmolten Ta-particles after both gas atomisation and PBF-EB/M remain a challenge towards robust processing, PBF-EB/M appears to show significant potential for fabrication of Ti-Ta HT-SMAs, especially when functional metal parts and components with complex shapes are required, which are difficult to fabricate conventionally.
► Interfacial fracture toughness was evaluated using circumferentially notched tensile specimens (CNT). ► Interfacial fracture toughness of coated materials was evaluated as a function of mode ...mixity. ► A well defined pre-crack was introduced at the interface of a coating–substrate system. ► The results showed an increase in the interfacial fracture toughness with an increase in phase angle. ► CNT specimens are shown to be capable of producing reputable results of interfacial fracture toughness.
The evaluation of interfacial strength is a challenging task due to the complexity of loading, the thickness of coating and the material conditions of interface cracking and coating spallation. In this study, a new method using circumferentially notched tensile (CNT) specimens is proposed for evaluating the interfacial fracture toughness of coated materials. The 0°, 15°, 30° and 45° notch angled mild steel cylindrical substrates with electroplated nickel were tensile tested. A well defined precrack was introduced at the interface for quantitative evaluation of adhesion. In situ acoustic signals were acquired to obtain the crack initiation or the critical load. The crack initiation and propagation were analysed using scanning electron microscope. Finite element analyses were used to evaluate the critical interface energy release rate as a function of mode mixity from the obtained critical load. The results showed an increase in the interfacial fracture toughness values with an increase in the phase angle. Based on the findings, it has been concluded that this proposed method is an easier testing method to evaluate the adhesive properties of coatings on metallic substrates compared to traditional methods.
► Interfacial fracture toughness was evaluated using circumferentially notched tensile specimens (CNT). ► Interfacial fracture toughness of coated materials was evaluated as a function of mode ...mixity. ► A well defined pre-crack was introduced at the interface of a coating-substrate system. ► The results showed an increase in the interfacial fracture toughness with an increase in phase angle. ► CNT specimens are shown to be capable of producing repeatable values of interfacial fracture toughness.
This paper introduces an effective interfacial fracture toughness test based on interface fracture mechanics theory. This testing method uses a circumferentially notched tensile (CNT) specimen, which is ideally suited for determining the interfacial fracture resistance of coatings. Unlike other interfacial fracture tests, this test is simple to prepare, requires minimum test setup and is easy to model. An interfacial pre-crack was generated between a nickel coating and mild steel cylindrical substrate to evaluate adhesion strength. In situ acoustic and SEM analyses were used to determine the crack initiation or the critical load of failure. The critical energy release rate, critical stress intensity factors and phase angle were determined using the
J integral which was determined by applying the critical load to the finite element model. A detailed finite element analysis was carried out to study the effect of different interface pre-crack positions and mode mixity on energy release rate for different notch angles and elastic modulus ratios. The cracking resistance of the interface was characterised by the notch angle of CNT specimens. The analysis showed an increase in interfacial fracture toughness as phase angle increases and was significant when the phase angle was large. The combined results of computational and experimental analysis showed that any defect or stress concentration at the interface could significantly weaken the adhesion of coating.
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