Powder Metallurgy HIP Process Study and Mechanical Property Evaluations for IN740H

The effects of hot isostatic pressing (HIP) parameters and powder size distribution (PSD) on the resulting microstructure and properties of powder metallurgy (P/M) IN740H have been investigated. Properties can be substantially tailored through the appropriate management of these parameters. Applying a thermal presoak to the input powder prior to the sintering stage of HIP can significantly increase average grain size and coarse grain fraction, enabling a trade for improved creep resistance at the expense of tensile strength. Powder thermal presoak was found to have a larger impact on microstructure and properties than the use of a coarser PSD alone. Additionally, substantial grain growth and grain boundary migration is observed in P/M IN740H at HIP temperatures above 1260 degrees C. Given its inherently finer grain size, P/M HIP IN740H typically outperforms its cast and wrought counterparts in tensile response. Creep life at 700-800 degrees C was inferior to wrought due to PPBs coincident with grain boundaries which served as cavity nucleation sites, leading to lower creep ductility. The ability to adjust the microstructure toward a more balanced creep and tensile behavior allows P/M HIP IN740H to be considered for high-temperature applications in advanced ultra-supercritical steam and supercritical carbon dioxide power cycles.

Automated summary

The effects of hot isostatic pressing (HIP) parameters and powder size distribution (PSD) on the microstructure and properties of powder metallurgy (P/M) IN740H were investigated. Managing these parameters appropriately can significantly tailor the properties of the material. Applying a thermal presoak to the input powder prior to sintering in HIP can increase grain size and coarse grain fraction, resulting in improved creep resistance but decreased tensile strength. The impact of powder thermal presoak on microstructure and properties is greater than that of a coarser powder size distribution alone. Furthermore, significant grain growth and grain boundary migration were observed in P/M IN740H at temperatures above 1260 degrees C in HIP. Compared to cast and wrought counterparts, P/M HIP IN740H with finer grain size typically has better tensile response. However, its creep life at 700-800 degrees C is inferior to wrought materials due to cavity nucleation sites at grain boundaries, leading to lower creep ductility. The ability to adjust the microstructure for a balanced creep and tensile behavior makes P/M HIP IN740H suitable for high-temperature applications.