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Title: Grain Boundary Engineering of Inconel 625 using Iterative Thermomechanical Processing
Authors: Ali Bader Alshemali 
Supervisor: Prof. Khaled Al-Fadhalah
Degree Awarded: M. Sc Degree in: Mechanical Engineering
Keywords: Grain Boundary Engineering , Iterative Thermomechanical Processing
Issue Date: 2019
Publisher:  Kuwait university - college of graduate studies
Abstract: Grain boundary engineering (GBE) is relatively a new method for microstructural modification of metallic materials via altering characteristics and distribution of grain boundaries. GBE involves the use of thermomechanical processing (TMP) to improve the properties of FCC metals of low stacking energy. TMP is typically applied via iterative cycles of cold working and subsequent annealing of the metal. In such a case, annealing results in massive formation of twins leading to an increase in the fraction of special grain boundaries, such as Σ3 boundaries, and thus breaking the network of random grain boundaries. Inconel alloys have been the subject of recent studies for the aim of microstructural enhancement via GBE. This type of superalloys is known to have high-temperature strength, excellent formability, and outstanding corrosion resistance. In particular, Inconel 625 is characterized by high content of molybdenum making the alloy resistant to oxidization and corrosion. Yet, grain boundaries are susceptible to intergranular attack, particularly when sensitization occurs during welding. There are few studies for Inconel 625 and GBE can offer great benefit to improve its microstructure and mechanical properties. Therefore, the current study has focused on manipulating the grain boundary structure of Inconel 625 via GBE. This has been achieved by applying a TMP scheme of four iterations. Each iteration consists of cold rolling Inconel samples by 25% thickness reduction and subsequent annealing at 1000 °C for 15 min. The effectiveness of TMP was evaluated by looking into the formation of special boundaries, with increasing number of iterations, and its effect on the properties of Inconel 625. To do that, microstructure examination of GBE samples has been conducted using SEM and EBSD.
Appears in Programs:0630 Mechanical Engineering

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