Effect of heat treatment on microstructure and mechanical properties of the hot-isostatic-pressed Inconel 718 powder compact

Significance Statement

    Powder metallurgy allows forming of complex-shaped components compared to wrought approach and ensures uniform microstructure and minimizes solidification defects compared to casting process, thus providing a unique processing route for component manufacturing using alloys such as Inconel 718. A key issue in the case of Inconel 718 is how to avoid the detrimental phases that cause low ductility and brittle fracture through post hot-isostatic-pressing heat treatment. We solved the problem by adopting a simpler, direct aging heat treatment scheme, and succeeded in improving grain boundary cohesion by removing the delta phase and reducing the amount of carbide precipitates. Compared to previous solution plus aging heat treatment, the new heat treatment saves both energy and time.    

Effect of heat treatment on microstructure and mechanical properties of the hot-isostatic-pressed Inconel 718 powder compact

Journal of Alloys and Compounds, Volume 590,  2014, Pages 227–232.

Litao Changa, b, Wenru Suna, Yuyou Cuia, Faqiang Zhangc, b, Rui Yanga.

 a Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, PR China and

b University of Chinese Academy of Sciences, Beijing 100049, PR China and

c Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, PR China.

Abstract

The present study deals with the optimization of the mechanical properties of the hot-isostatic-pressed Inconel 718 powder compact. Several heat treatments, including the solution plus aging with different solution temperature and the direct aging scheme, have been designed based on the phase relations of Inconel 718 and been employed for the optimization. The results indicate that the direct aging heat treatment is the best one, because it ensures a good balance of the strength and ductility of the powder compact. The tensile and stress rupture properties of the direct aged alloy have all met the specifications for Inconel 718. Solution process leads to a decrease of grain boundary strength and poor ductility because of the precipitation of carbide and {Delta} phase at the prior particle boundaries or formation of thermal induced porosities at the triple junctions, and is then not appropriate for the powder compact. Yield strength of the direct aged alloy is a little lower than the solution treated alloy because of over aging of the {Gamma}′′ precipitates.

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