Additive Manufacturing of Ti-Based Intermetallic Alloys: A Review and Conceptualization of a Next-Generation Machine

TiAl-based intermetallic alloys have come to the fore as the preferred alloys for high-temperature applications. Conventional methods (casting, forging, sheet forming, extrusion, etc.) have been applied to produce TiAl intermetallic alloys. However, the inherent limitations of conventional methods do not permit the production of the TiAl alloys with intricate geometries. Additive manufacturing technologies such as electron beam melting (EBM) and laser powder bed fusion (LPBF), were used to produce TiAl alloys with complex geometries. EBM technology can produce crack-free TiAl components but lacks geometrical accuracy. LPBF technology has great geometrical precision that could be used to produce TiAl alloys with tailored complex geometries, but cannot produce crack-free TiAl components. To satisfy the current industrial requirement of producing crack-free TiAl alloys with tailored geometries, the paper proposes a new heating model for the LPBF manufacturing process. The model could maintain even temperature between the solidified and subsequent layers, reducing temperature gradients (residual stress), which could eliminate crack formation. The new conceptualized model also opens a window for in situ heat treatment of the built samples to obtain the desired TiAl (γ-phase) and Ti3Al (α2-phase) intermetallic phases for high-temperature operations. In situ heat treatment would also improve the homogeneity of the microstructure of LPBF manufactured samples.

Effect of Post Processing Heat Treatment Routes on Microstructure and Mechanical Property Evolution of Haynes 282 Ni-Based Superalloy Fabricated with Selective Laser Melting (SLM)

Selective laser melting (SLM) is one of the most widely used additive manufacturing technologies. Fabricating nickel-based superalloys with SLM has garnered significant interest from the industry and the research community alike due to the excellent high temperature properties and thermal stability exhibited by the alloys. Haynes-282 alloy, a γ′-phase strengthened Ni-based superalloy, has shown good high temperature mechanical properties comparable to alloys like R-41, Waspaloy, and 263 alloy but with better fabricability. A study and comparison of the effect of different heat-treatment routes on microstructure and mechanical property evolution of Haynes-282 fabricated with SLM is lacking in the literature. Hence, in this manuscript, a thorough investigation of microstructure and mechanical properties after a three-step heat treatment and hot isostatic pressing (HIP) has been conducted. In-situ heat-treatment experiments were conducted in a transmission electron microscopy (TEM) to study γ′ precipitate evolution. γ′ precipitation was found to start at 950 °C during in-situ heat-treatment. Insights from the in-situ heat-treatment were used to decide the aging heat-treatment for the alloy. The three-step heat-treatment was found to increase yield strength (YS) and ultimate tensile strength (UTS). HIP process enabled γ′ precipitation and recrystallization of grains of the as-printed samples in one single step.

The Effect of Post Annealing on Physical Properties of NiTe2 Thin Film Fabricated by Magnetron Sputtering

In this study, the effect of post annealing time on the physical properties of NiTe₂ thin films with 2D structure deposited by co-sputtering was investigated. After heat treatment for 10 min, nickel ditelluride thin films with a composition of Ni : Te = 1 : 2 exhibited transmittance of 46% and a resistivity of 40 μΩ • cm. When using both Ni and Te targets, the formation of NiTe₂ with 2D structure was found to depend on the co-sputtering and heat treatment conditions. Thin films with the composition of NiTe₂ were deposited on glass substrates by co-sputtering (Radio Frequency : Te, Direct Current : Ni). The Ni : Te = 1: 2 composition was confirmed by X-ray Photo Electron Spectroscopy (XPS) after in situ heat treatment in the sputter chamber (10 min, 20 min, 40 min, 80 min). In this study, we confirmed that the NiTe₂ thin film with the ratio of Ni : Te = 1 : 2 can be obtained by co-sputtering, followed by in situ heat treatment. We believe that the NiTe₂ thin film is a potential candidate for transparent electrodes because of its high electrical conductivity and 2D structure. It should be possible to reduce the thickness of the NiTe₂ films with 2D structure by exfoliation, thus increasing their optical transparency.

Effect of in-situ heat treatment and process parameters on the laser-deposited IN718 microstructure and mechanical properties

ABSTRACTThe direct laser-deposited Inconel 718 (IN718) specimens were produced using 1073 nm, high power continuous wave (CW), IPG Ytterbium fibre laser and in-situ heat treatment. The laser power and in-situ heat treatment temperature were fixed while varying the laser scanning speed from 0.83 to 2.50 cm/s. The microstructure and micro-hardness of the IN718 specimens were characterized using an optical microscope (OM), scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS or EDX) and Vickers system. The microstructure of the specimens consists of γ-matrix as the primary phase, Nb-rich particles, constitutional liquation cave, liquation cracking and ductility-dip cracks. It was found that the micro-hardness profile of the IN718 specimens was gradually increased with the increase of the distance from the surface.

Enhanced mechanical properties of plasticized polylactic acid filament for fused deposition modelling: Effect of in situ heat treatment

The objective of this study is to characterize the effect of in situ heat treatment on polylactic acid (PLA) and plasticized PLA during fused deposition modelling (FDM) with the motivation to improve their mechanical, thermal and physical properties. The in situ heat treatment was formed during the FDM by adjusting the bed temperature to 70°C, 90°C and 120°C. The performance of 3D, the printed samples, was compared with the compression moulded samples treated at the same temperature using a vacuum oven. PLA was plasticized with poly (ethylene glycol) (PEG) at different compositions of 0, 5 and 10 wt% of PEG. The properties of PLA, plasticized PLA and FDM-printed sample were analysed using Instron, differential scanning calorimeter (DSC) and X-ray diffraction (XRD). It was found that the addition of PEG into PLA decreased the tensile strength, elongation at break and tensile modulus of the materials. However, after heat treatment in the vacuum oven and FDM, the properties were generally higher at 90°C and this was believed to be primarily due to the effect of crystallization. This can be proved by formation of double melting peak, correspond to melt-crystallization mechanism, observed in DSC. The formation of different crystal was supported by XRD analysis where the amorphous peak had transformed into sharp peak at 16.9° and 19.3°, which indicates an improved crystallinity. Comparison between the compression moulded sample and FDM demonstrated that the in situ heat treatment in FDM had the most significant impact on tensile modulus.