The Advanced Materials and Manufacturing Technologies (AMMT) program is aiming at the accelerated incorporation of new materials and manufacturing technologies into nuclear-related systems. Complex Ni-based components fabricated by laser powder bed fusion (LPBF) could enable operating temperatures at T > 700°C in aggressive environments such as molten salts or liquid metals. However, available mechanical properties data relevant to material qualification remains limited, in particular for Ni-based alloys routinely fabricated by LPBF such as IN718 (Ni- 19Cr-18Fe-5Nb-3Mo) and Haynes 282 (Ni-20Cr-10Co-8.5Mo-2.1Ti-1.5Al). Creep testing was conducted on LPBF 718 at 600°C and 650°C and on LPBF 282 at 750°C. finding that the creep strength of the two alloys was close to that of wrought counterparts. with lower ductility at rupture. Heat treatments were tailored to the LPBF-specific microstructure to achieve grain recrystallization and form strengthening γ' precipitates for LPBF 282 and γ' and γ" precipitates for LPBF 718. In-situ data generated during printing and ex-situ X-ray computed tomography (XCT) scans were used to correlate the creep properties of LPBF 282 to the material flaw distribution. In- situ data revealed that spatter particles are the potential causes for flaws formation in LPBF 282. with significant variation between rods based on their location on the build plate. XCT scans revealed the formation of a larger number of creep flaws after testing in the specimens with a higher initial flaw density. which led to a lower ductility for the specimen.

The Haynes 282 Ni-based superalloy (57Ni-20Cr-10Co-8.5Mo-2.1Ti-1.5Al) is a very promising candidate for the fabrication by additive manufacturing of gas turbine components of complex geometries. Alloy 282 was fabricated by electron beam melting (EBM) and exposed to two different heat treatments, (a) solution anneal (SA) at 1135°C followed by the standard 2-step aging treatment (2h at 1010°C plus 8h at 788°C) and (b) SA followed by 4h 800°C. Large elongated grains were observed for the as-fabricated and annealed EBM 282 materials, with a γ′ (Ni 3 (Al,Ti)) average size of ~100 nm and 20 nm, respectively. The as-fabricated EBM 282 alloy exhibited good ductility at 20-900°C and tensile strength slightly lower than the tensile strength of wrought 282. Annealing the alloy resulted in a moderate increase of the alloy strength at 800 and 900°C but a decrease of the alloy ductility. The creep lifetime at 800°C, 200MPa of the as-fabricated and annealed EBM 282 specimens machined along the build direction was 2 times and 1.5 times superior to the expected lifetime for wrought 282, respectively. For creep specimens machined perpendicular to the build direction, the lifetimes were ~25% lower compared to the wrought alloy. These creep results are directly related to the strong grain texture of the EBM 282 alloy and the limited impact of the initial γ′ (Ni 3 (Al,Ti)) size on alloy 282 creep properties.

The harsh operating conditions of Advanced Ultra-Supercritical (A-USC) power plants, i.e., steam operation conditions up to 760°C (1400°F)/35 MPa (5000 psi), require the use of Ni-based alloys with high temperature performance. Currently, the U.S. Department of Energy Fossil Energy program together with Electric Power Research Institute (EPRI) and Energy Industries of Ohio (EIO) is pursuing a Component Test (Comets) project to address material- and manufacturing-related issues for A-USC applications. Oak Ridge National Laboratory (ORNL) is supporting this project in the areas of mechanical and microstructure characterization, weld evaluation, environmental effect studies, etc. In this work, we present results from these activities on two promising Ni-based alloys and their weldments for A-USC applications, i.e., Haynes 282 and Inconel 740H. Detailed results include microhardness, tensile, air and environmental creep, low cycle fatigue, creep-fatigue, environmental high cycle fatigue, and supporting microstructural characterization.