In situ TEM tensile testing on high-entropy alloy coating by laser surface alloying

A unique technique, in situ TEM tensile testing, was used to investigate the fracture process of Ni-Cr-Co-Ti-V-Al high-entropy alloy coating with complex phases. The results of in situ TEM observation indicated that during the fracture process, dislocations get together in the interface between BCC HEA phase and (Co, Ni)Ti2 compounds and crack propagation happens along the phase interface, leading to the final rupture, which proves that the phase interface may be the probable failure place. Also, the fracture strength and Young's modulus were calculated according to the stress-strain curve from the in situ TEM tensile testing. The stress-strain curve shows a good linearity, confirming the brittle failure. The fracture strength is calculated to be ∼3.3 GPa and the fracture strain is measured to be ∼3.1%. The Young's modulus of the tensile sample is calculated to be ∼102 GPa, quite close to that of bulk titanium alloy.