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

•High-entropy alloys (HEAs) presented extraordinary thermo-physical properties.•Various in-situ monitoring techniques have been applied to traditional metallic materials.•The adaptability of in-situ techniques to additive manufacturing (AM) of HEAs has neither been reviewed nor established.•HEAs are composed of various elements, presenting a complex thermal gradient during AM printing.•This article critically analyzes the current in-situ monitoring techniques and their implication for HEAs printing.