Laser Powder Bed Fusion of GH4099 Superalloy: Parameter Optimization and Effect of Heat Treatment on Microstructure and Mechanical Properties

Abstract

Ni-Cr-Co-W superalloy (GH4099) can be used to manufacture high-temperature structural components of aero-engine combustion chambers for long-term service below 900°C. This study provides a comprehensive evaluation of the GH4099 superalloy fabricated using the laser powder bed fusion (LPBF) technique, focusing on the optimization of processing parameters and a systematic investigation of the microstructural evolution and mechanical properties of the as-deposited and heat-treated samples. An optimal parameter combination was established using the response surface method (RSM) design and the variance method. The as-deposited GH4099 alloy is primarily composed of columnar crystals grown epitaxially and M23C6 carbides without the generation of the γ′-phase. After solution treatment, recrystallization and grain growth occurred, with the alloy remaining as large, irregularly shaped polygonal columnar crystals. The aging process precipitated substantial γ′-phase, which internally existed as a mixture of equiaxed and columnar crystals. LPBF-GH4099 superalloy exhibited a maximum room-temperature tensile strength of 1137.80 MPa and a high-temperature tensile strength of 780 MPa at 800 ℃. Various strengthening mechanisms were observed in the as-deposited and heat-treated samples. The most significant grain boundary strengthening effect was observed in the deposit state, while solution strengthening was primarily due to the segregation of elements, such as Mo, W, and Cr, in the γ matrix. Precipitation strengthening, predominantly due to the γ′-phase, emerged as the main strengthening mechanism for the GH4099 superalloy post-aging treatment. This study presents significant insights into the LPBF-GH4099 alloy and provides a solid foundation for future studies and practical applications in this field.