Electro Discharge Machining – A Suitable Fabrication Process for High‐Pressure/High‐Temperature Equipment

• Published in: Chemical engineering & technology Vol. 41; no. 5; pp. 994 - 1002
• Main Authors: Hertweck, Benjamin, Kimmel, Anna-Carina L., Steigerwald, Thomas G., Alt, Nicolas S. A., Schlücker, Eberhard
• Format: Journal Article
• Language: English
• Published: Frankfurt Wiley Subscription Services, Inc 01-05-2018
• Subjects: Ammonothermal crystal growth; Electric discharge machining; Electro discharge machining; High temperature; High‐pressure equipment; High‐temperature corrosion; Honing; Nickel base alloys; Nickel‐based alloys; Pressure vessels; Superalloys; Surface stability
• ISSN: 0930-7516; 1521-4125
• DOI: 10.1002/ceat.201700680

Electro discharge machining (EDM) is an important manufacturing process for hard‐to‐cut materials like nickel‐based alloys, e.g., alloy 718. Its high yield strength at high temperature make it a suitable material for vessels for high‐pressure/high‐temperature applications, in particular for ammonothermal pressure vessels. This report first summarizes the relationship between microstructure and properties of alloy 718 for practitioners. Second, it focuses on the metallographic description of alloy 718 surfaces proceeded by EDM and its behavior during use as equipment for ammonoacidic systems. Furthermore, the finding of suitable post‐processing, namely honing, to achieve high stability of the surface at high‐pressure atmosphere is included.
Ammonothermal reactors are mainly made of nickel‐based alloys which are classified as hard‐to‐cut materials. Therefore, advanced manufacturing processes like electro discharge machining became more important for efficient fabrication processes. Regarding its suitability, this powerful manufacturing tool was evaluated successfully for high‐pressure, high‐temperature, and high‐purity processes.