Interface bonding behavior and failure mechanism of joining Tribaloy T-800/AISI 4140 via laser engineered net shaping

Abstract

As a potential material for surface coating and repair applications, Tribaloy T-800 was deposited on AISI 4140 alloy steel substrate through laser engineered net shaping (LENS) to investigate its compatibility with the substrate material with a focus on interface bonding behavior and failure mechanism. It was hypothesized that the interface bonding failure between these two dissimilar materials occurs under a high degree of lattice mismatch across the interface. The mismatch relates with the misfit dislocation caused by different crystal lattice parameters and crystalline structures. The hypothesis is proved experimentally and theoretically in this study and the following findings are obtained: Fe element diffuses from the substrate due to an increased diffusivity, resulting in a brittle intermetallic Wairauite α’-(CoFe) at the planar transition layer. A large lattice misfit (more than 20%) exists between the FCC α’-Co solid solution matrix and the BCC α’-(CoFe) Wairauite phase, indicating an incoherent interface with a large amount of dislocations at the interface. It implies that there is severe local stress occurs in this area where cracks could easily arise and then propagate along the interface.