Improving the High-Temperature Mechanical Properties of L-PBF CM247LC Through HIPing and Aging Treatments

Abstract CM247LC was fabricated using L-PBF with optimized build parameters to minimize cracking. This paper explores the potential for using HIPing, followed directly by aging heat treatments, to optimize tensile and creep properties while reducing the number of heat treatments and the cost of processing. Samples were HIPed at 1250 °C and 100 MPa followed by aging treatments chosen to replicate those given to the DS alloy after solutioning. Heat treatments at 1250 °C, both the furnace only and HIP, have similar effects on grain structure, but change γ ′ morphology. The slow cool following HIPing results in large (~2 µ m) octo-dendritic primary γ ′, and the subsequent anneals have radically different effects on the microstructure. The best tensile performance at 900 °C is produced by minimizing the volume fraction of primary γ′ during the anneal at 1080 °C and peak-aging the secondary γ ′, formed during the cool from 1080 °C, and aging at 870 °C. Creep tests at 982 °C and 179 MPa show that the HIP treatment is essential to prevent early failure. It is remarkable that the optimum tensile microstructure performs well in creep despite large primary γ ′. Omitting a separate solution treatment gives a radically different microstructure but tensile properties that match those from the cast alloy, without compromising the creep performance at low strain.