On the laser additive manufacturing of high-entropy alloys: A critical assessment of in-situ monitoring techniques and their suitability

Abstract

High-entropy alloys (HEAs) have gained increasing attention from the industrial and scientific communities due to their extraordinary thermo-physical properties. Introducing the laser additive manufacturing (LAM) technique as a viable fabrication process of HEAs provides many advantages over traditional methods. One of the main challenges facing widespread industrial utilization of LAM is the limited ability to monitor and predict various types of defects during the printing process. Several operando (in-situ) monitoring techniques have been developed to detect failure when printing commonly used LAM alloys, such as stainless steel, titanium, and nickel alloys. The adaptability and effectiveness of these techniques to LAM of HEAs have neither been reviewed nor established. In this work, we highlight the unique properties of HEAs, discuss current traditional fabrication methods of HEAs, and present recent advances in LAM of HEAs and the advantages over traditional techniques. In addition, we present a comprehensive review of the current in-situ monitoring techniques applied in LAM for commonly used alloys, followed by a critical assessment of the adaptability of these techniques to the LAM of HEAs. Since HEAs are composed of multiple constituents in varying proportions with a variable size distribution, morphology, and melting temperature, the heat distribution at the laser-material regime fluctuates, resulting in a complex thermal gradient with a non-uniform melt pool morphology and the generation of corresponding defects. Existing in-situ techniques are not explicitly designed to handle such a complex thermal distribution, and their effectiveness can be compromised. Therefore, conducting this critical review and assessment is urgently needed. Besides, a novel in-situ monitoring technique design has been proposed based on the difficulties identified during literature analysis.