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Additive manufacturing was currently widely used to fabricate complex-shaped superalloy components for extreme environment applications. To replace the components prepared by the traditional approaches, it is crucial to ensure the reliability of AMed superalloys, especially in a thermal-stress environment. In this work, the high-temperature tensile properties of AMed GH4099 nickel-based superalloy are studied to establish the relationships among deformation temperatures, mechanisms, and failure responses. The results show that the deformation mechanisms at 600 °C are mainly cross-slip of the slip bands and arrays, which induced a ductile fracture. Increasing the tensile temperature will cause a shift of the dislocation movement from cross-slip to Orowan looping and stacking fault shearing to dislocation entangles-recovery-recrystallization, and the fracture mode transformed from pure ductile to mixed ductile-brittle. Additionally, the neighboring grain boundaries and the carbide-grain boundary bondings will also change with the temperature, which is further linked to the mediate-temperature brittleness and high-temperature abnormal plasticity of this superalloy. [ABSTRACT FROM AUTHOR]

Allvac 718Plus alloy is a promising Ni-based superalloy with excellent thermal stability and mechanical properties up to 704 °C. The γ′ coarsening, σ precipitation and the resulting degraded tensile properties at room and elevated (704 °C) temperatures during long-term thermal exposure at 704 and 760 °C are systematically investigated in this work. The results showed that a higher exposure temperature and a longer exposure time significantly accelerate the γ′ coarsening and σ precipitation. The σ particles were detrimental to the alloy by acting as the preferential nucleation sites for cracks, and the reduction in tensile strengths was mainly caused by the increasing size of γ′ precipitates during thermal exposure. Furthermore, there were significant differences between the deformation mechanisms of room-temperature and elevated-temperature (760 °C) tensile tests. Concerning the deformation mechanism of γ-matrix, planar slipping dominates during tensile testing at room temperature, while the formation of stacking faults and microtwinning are primary during tensile testing at elevated temperature (760 °C). The dominant precipitation strengthening mechanism depended on the γ′ characteristics of different thermal exposure conditions and the tensile temperature. The 704 °C/100 h exposure sample shows a dislocation shearing mechanism when tested at room or elevated (760 °C) temperature. Notably, the 760 °C/1000 h exposure sample exhibits a mixed precipitation strengthening mechanism of Orowan bypassing and superlattice stacking faults shearing when tensile tested at room temperature while showing a dislocation and superlattice stacking faults shearing mechanism when tensile tested at elevated (760 °C) temperature. • The Cr-rich σ particles nucleate at γ/η interfaces during long-term exposure in 718Plus alloy. • The σ formation is detrimental to room-temperature tensile ductility. • During tensile tests, planar slipping dominates at 25 °C while microtwinning and stacking faults dominate at 704 °C. • The dominant precipitation-strengthening mechanisms are predicted by calculating the critical γ′ size. [ABSTRACT FROM AUTHOR]

In this work, we creatively introduced MAX additives (Ti 2 AlC) into W alloy system to break the development bottleneck of ball milling technology: a large amount of oxygen impurities and large-sized second phase particles at grain boundaries (GBs). Unlike traditional oxides/carbides, Ti 2 AlC can undergo self-decomposition during high-temperature sintering stage (>1400 °C) on the basis of hydrogen sintering, and continue to adsorb a number of stubborn oxygen impurities to form various smaller, more dispersed, and stronger in-situ Ti x C y , TiO x , Al 2 O 3 , and Al x Ti y O z nanoparticles. Furthermore, these in-situ nanoparticles could maintain stable coherent interfaces with W, thereby more effectively refining, purifying, and strengthening matrix. Compared to traditional W-carbide/oxide alloys, MAX additives render our alloy with high hardness (521 ± 24 HV 0.2), a remarkable combination of high compressive strength (1262.9 ± 35.1 MPa) and large ductility (9.88%). This work provides a new perspective for the preparation of high-performance refractory metals and relevant engineering application. • The MAX phase (Ti 2 AlC) is innovatively added into W alloys. • The Ti 2 AlC phase decomposes at above >1400 °C and forms in-situ nanoparticles. • The Ti 2 AlC phase continues to adsorb stubborn oxygen impurities at sintering stage. • In-situ nanoparticles could maintain stable coherent interfaces with W. • The W-Ti 2 AlC alloy possess excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened (ODS) refractory metals, represented by tungsten and molybdenum alloy, possesses many excellent properties such as high-temperature strength, outstanding thermal microstructure stability and good resistances to oxidation and corrosion. However, in traditional preparation technologies, these ex-situ oxides usually form poor oxide/matrix interface relationships and keep coarse sizes at grain boundaries (GBs), which prominently limit the improvement of alloy mechanical properties until now. In this work, we skillfully employed novel phase interface engineering to successfully construct completely coherent oxide/matrix interfaces in ODS Mo alloys through the newly formed ternary phase oxide nanoparticles or diffusion layers. Furthermore, these ODS Mo alloys are characterized by ultrafine grains, ultrafine subgrains, small and dispersed intragranular and intergranular particles. An amount of oxygen impurities can also be depleted via phase interface engineering, thus purifying Mo matrix. The phase interface engineering endows ODS Mo alloys with ultrahigh strength, excellent ductility and excellent hot machinability, which illuminates a new research direction for those ex-situ oxide dispersion strengthened alloys with excellent mechanical properties. [ABSTRACT FROM AUTHOR]