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Abstract: A new Al–3Ti–1B–0.2C master alloy with uniform microstructure was prepared using a melt reaction method in this study. In the master alloy, TiB2 particles exhibit hierarchical dendritic morphology, while TiC particles doped with a trace amount of B show a polyhedral morphology. The grain refining performance of the master alloy on A356 alloy has also been investigated. It is found that the addition of 0.2wt.% Al–3Ti–1B–0.2C master alloy can induce very effective grain refinement of the A356 alloy. The average grain size of α-Al is reduced to 167±8μm from about 1570μm and the grain refining efficiency does not fade obviously within 60min. Therefore, the mechanical properties of the A356 alloy have been improved obviously by the addition of the Al–3Ti–1B–0.2C master alloy, including the ultimate tensile strength, yield strength and elongation. [Copyright &y& Elsevier]

Abstract: In this study, the influence of Si and Ti contents on the microstructure, microhardness and morphology of TiAlSi intermetallics in ternary Al–Si–Ti alloys was investigated. The increase of Si addition in Al–xSi–2Ti alloys leads to an increase of Si content in TiAlSi phase as well as an increase of microhardness. A phase evolution from Ti(Al1−x Si x )3 to Ti7Al5Si12 at about 14wt.% Si was detected, while all the TiAlSi intermetallics exhibit flake-like. The increase of Ti content promotes the morphological transformation of TiAlSi from flake-like to block-like and primary Si particles are replaced by blocky TiAlSi particles in hypereutectic Al–Si alloy. The high-temperature strengthening effect of TiAlSi particles in a piston alloy was investigated and the strength is increased by 11.9% in this article, while the elongation and yield strength are increased by 17.6% and 10.1%, respectively. [Copyright &y& Elsevier]

Ta-10W alloy is an important high temperature structure material because of its high melting point and excellent high temperature performance. Laser powder bed fusion (LPBF) provide a new scheme to break limitation in producing Ta-10W complex structures. High-density Ta-10W samples manufactured by LPBF were first achieved in this work. The variation of molten pool morphology and interior defects with energy density was investigated, and excellent mechanical properties in room temperature were obtained. • LPEF is employed to manufacture the Ta-10W alloy for the first time. • Good sintering formability and high relative density are realized. • Excellent tensile properties at room temperature are obtained. [ABSTRACT FROM AUTHOR]

Abstract: A series of Al–Ti–C–B master alloys with different B/C ratios were prepared in the present study. It was found that with the increase of B/C ratio, the microstructure of Al–Ti–C–B was improved firstly and then became agglomerated at a very high B/C ratio. Furthermore, the grain refining performance of Al–Ti–C–B also varied with the increase of B/C ratio. The experimental results show that Al–Ti–C–B master alloy presents both a dispersive microstructure and a high grain refining efficiency at an optimum B/C ratio about 1/1. It is supposed that the improvement of Al–5Ti–0.25C–0.25B master alloy can be attributed to the high efficiency TiC x B y particles and a certain amount of TiB2 particles. [ABSTRACT FROM AUTHOR]

Electron beam layer solidification was used to prepare a nickel-based superalloy with refined microstructure and superior creep performance. It suggests that MC carbides could inherit from the solidification process, thus affect the performance of the alloy significantly. Microstructure analysis reveals that grain boundary microvoids and microcracks arised from slip and dislocation pile-ups are responsible for the creep fracture of the electron beam layer solidified alloy. The dislocation-precipitate interaction shows that cutting of a /2<110> partial dislocations and formation of APB are the decisive mechanisms for γ' phase, and for γ'' precipitates, shearing of a/ 2<110> doublets and a /6<211> partial dislocations act simultaneously. Electron beam layer solidification was used to prepare a nickel-based superalloy with refined microstructure and superior creep performance. The current findings suggest that MC carbides could inherit from the solidification process, thus affect the performance of the alloy significantly. Microstructure analysis reveals that grain boundary microvoids and microcracks arised from grain boundary slip and dislocation pile-ups are responsible for the creep fracture of the electron beam layer solidified alloy. Meanwhile, the dislocation-precipitate interaction works differently for γ'' and γ' during deformation. The cutting of a /2<110> partial dislocations and the formation of APB are the decisive mechanisms for γ' phase, and for γ'' precipitates, shearing of a /2<110> doublets and a /6<211> partial dislocations act simultaneously. The microstructures, creep behavior and deformation mechanisms of electron beam layer solidified Inconel 718 alloy. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Electron beam smelting layered solidification technology is applied to prepare a nickel-based superalloy for turbine disks with service temperature up to 850 ℃. The microstructures, segregation and homogenization behavior were investigated. The results show that there is a cellular crystal structure with a width of 1.5 mm between the layers, and the dendritic structure is observed within the layers. The average secondary dendrite arming spacing is 28.6 µm, which attributed to higher temperature of molten pool and faster cooling rate. After electron beam smelting layered solidification technology, the macrosegregation is eliminated, and the microsegregation is weakened. The average temperature on the molten pool surface during electron beam smelting is 1813 K according to evaporation rates of Ni. The effect of homogenization treatment on the microstructures and microsegregation evolution was discussed. Based two diffusion models, the diffusion coefficient of Nb and W at 1190 °C are calculated as 7.365 × 10−16 m2/s and 5.805 × 10−16 m2/s, respectively. • The microstructure of GH4975 prepared by EBS-LST are significantly reduced compared with alloy prepared by VIM plus VAR. • Electron beam smelting layered solidification technology can eliminate macrosegregation and reduce microsegregation. • The average temperature of the melt during smelting is calculated as 1813 K according to the evaporation rate of Ni. • The diffusion coefficients of Nb and W in GH4975 alloy are calculated base on two diffusion models at 1190 °C. [ABSTRACT FROM AUTHOR]

Electron beam smelting (EBS) has been used to fabricate the Inconel 740 superalloy. Microstructures, hardness, and deformation characteristics of the alloy are studied. It is observed that carbides and fine secondary phase nuclei are distributed in the hot worked EBS 740 superalloy. The Ostwald ripening occurs during solution treatment and leads to aggregation of the γ′ precipitates, the size of γ′ precipitates varies from several nanometers to more than one hundred nanometers as a result. The average size of the secondary phase is < 30 nm after aging treatment and the average Vickers hardness is measured to be about 370. The critical shear stress is calculated to be 0.627 GPa with governing mechanism of shearing, causing a stronger strengthening effect than the traditionally prepared Inconel 740 superalloy. The compression behavior indicates that the EBS 740 superalloy shows higher flow stress than 740H at low Zener-Hollomon parameter, which may arise from the undissolved γ′ precipitates and higher activation energy Q . The tensile results show that the fracture surface exhibits a ductile fracture pattern, in contrast to no obvious plastic deformation on the macroscopic fracture. Crack propagation proceeds in a transgranular fracture mode with facets and voids presented on the fracture surface. [ABSTRACT FROM AUTHOR]

• SLM is employed to manufacture the GH4099 alloy for the first time. • Inhibit the precipitation of γ-γ' phase in the as-deposited state. • Excellent tensile properties at room and high temperature are obtained. The brittle γ–γ' eutectic phase in the inter-dendritic region is the major cause of cracking of GH4099 alloys prepared by laser additive manufacturing technology. In this study, selective laser melting (SLM) was employed to prepare GH4099 alloy with refined microstructures. The alloy showed excellent mechanical properties, while the alloy cracking was retarded effectively. Fine γ′ precipitates were formed after aging treatment, which contributed greatly to the high strength of GH4099 alloy. The tensile strength of the alloy at room temperature and high temperature were 1217.8 and 955.0 MPa, respectively. [ABSTRACT FROM AUTHOR]

Electron beam smelting (EBS) was used to prepare the Inconel 740 superalloy. The microstructure and hardness of Inconel 740 were investigated both under hot working condition and followed by solution heat treatment under high temperature ranging from 1120 to 1210 °C for 30 min. The results show that fine γ′ nucleus and primary MC carbides exist in the hot working superalloy. With increasing temperature of solution treatment, TiNiSi phase is gradually solutionized into the matrix, whose volume fraction decreases exponentially. γ′ precipitates coarsening occurs at 1150 °C, while higher temperature solution treatment leads to the solution of γ′ precipitates. γ″ phase has been found keeping a stringent coherent relationship with Nb 0.03 Ni 3 Ti 0.97 phase at 1180 °C, and utterly transformed into Nb 0.03 Ni 3 Ti 0.97 phase at 1210 °C. The hardness of the solution-treated superalloy is lower than that of hot working, the value decreases at first and then increases with increasing of solution temperature, which is attributed to dislocations interaction and localized shear stress caused by γ′ precipitates and local stress fields. [ABSTRACT FROM AUTHOR]

Abstract: A new kind of Al–5Ti–0.3C master alloy with a uniform microstructure was prepared by using Al–5C alloy as a carbon source in this study. In the master alloy, TiC particles exhibit hexagonal platelet and macroporous morphologies, distributing homogeneously in the aluminum matrix. It is supposed that TiC particles are synthesized by the reaction between dissolved Ti and Al4C3. The grain refining performance of the master alloy on commercial pure aluminum was investigated. The average grain size of α-Al can be reduced from 3300μm to 178μm with the addition of 0.2wt.% of the prepared Al–5Ti–0.3C master alloy. Besides, the grain refining efficiency is stable and does not fade within 30min. [Copyright &y& Elsevier]

A new electron beam smelting technology was employed to prepare the Inconel 718 alloy, and the microstructure evolution and nucleation and coarsening mechanisms of γ', γ″ and δ phase of this alloy was investigated. The microstructures can be refined by means of electron beam smelting, and good microstructure stability is observed at 700 °C, which is at least 20 °C beyond the limiting temperature that Inconel 718 alloy can sustain for prolonged periods. The γ' and γ″ precipitates could be formed in less than 1 h when aged at 700 °C and 800 °C, in which the coarsening of γ' follows the conventional Lifshitz-Wagner theory, while the γ″ follows the Lifshitz-Slyozov encounter Modified theory. When thermal aged at 900 °C, both γ' and γ″ precipitates are absent. The nucleation of δ phase is arised from the stacking faults in γ″ precipitates induced by formation of a /6 〈211〉 Shockley partial dislocations or the lattice distortion when thermal aged at lower temperature. While at higher temperature, the arrangement of a /2 〈110〉 matrix dislocations is responsible for the nucleation of δ phase. The coarsening of δ phase is discontinuous during prolonged exposure. The growth rate of the δ lath is controlled by the coarsening in lengthwise direction at first, and then by the intermittent growth in both length and width direction at lower temperature. While for the δ phase nucleated from the matrix, the growth of δ lath is determined by its thickening firstly, and then the coherent growth occurs along the length direction with aging proceeding • A new electron beam smelting technology was used to prepare the Inconel 718 alloy. • The EBS 718 alloy shows good microstructure stability at 700 °C. • The precipitation behavior of γ' and γ″ differs from some Inconel 718 alloys. • The coarsening of δ phase is discontinuous during prolonged exposure. [ABSTRACT FROM AUTHOR]