Effect of heat treatment on grain boundary character and strength-ductility synergy in additive-manufactured Hastelloy X
Description
Nickel-based superalloys fabricated by selective laser melting often suffer from a strength-ductility trade-off due to non-equilibrium microstructures. Here, we demonstrate that this limitation can be overcome by grain boundary engineering through multi-stage heat treatments. In Hastelloy X, solution treatment at 1175°C followed by furnace cooling triggers complete recrystallization, producing an optimal microstructure with a high fraction of Σ3 annealing twins (22.1%) and high-angle grain boundaries (64.6%). This unique configuration, along with uniformly distributed grain boundary carbides, promotes strain-accommodating boundary sliding and alleviates dislocation pile-up. Consequently, the material achieves an exceptional strength-ductility synergy (ultimate tensile strength: 663.5 MPa; ductility: 43.7%), representing a 30.4% enhancement in ductility over conventional forged material. We reveal that the enhanced performance stems from a transition in the dominant strengthening mechanism, where solid solution strengthening effectively compensates for the reduced contribution from grain boundaries. This work provides a microstructural design strategy to unlock the full potential of additive manufacturing for high-performance alloys.
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Steps to reproduce
After powder drying (150°C/8h), selective laser melting experiments are carried out using a German EOS M290. The 316L substrate is preheated to 180°C for printing under the protection of argon atmosphere, the process parameters are: laser power of 260W, laser scanning speed of 1400mm/s, scanning spacing of 70μm, single-layer laying of powder with a thickness of 0.04mm, and a scanning strategy of 67°scanning and printing with a strip rotation, the strips printing strategy can minimize the thermal stress and the overlap of the laser scanning path6. Cubic specimens (10× 10×10mm³) and standard dog-bone tensile coupons are fabricated via electrical discharge machining (EDM) from as-built blocks, with all sampling orientations aligned parallel to the building direction. Solution treatment temperatures are selected as 1125°C (SF1), 1175°C (SF2), and 1200°C (SF3) with furnace cooling. All heat treatments are conducted in a muffle furnace (SXL-1700C) under argon shielding.
Institutions
- Sichuan University