Alleviating the adverse influence of nitride coating on the fatigue performance of Ti6Al4V by Ni alloying

Abstract

In this paper, we propose an effective way to alleviate the adverse influence of nitride coating on the fatigue performance of Ti6Al4V. The effect of different Ni alloying concentrations (0 at.%, 10.4 at.%, and 25.8 at.%) on the surface morphology, microstructure, mechanical responses, fracture toughness of representative CrN coating, and its influence on the fatigue behavior of Ti6Al4V was studied. With the rise of Ni alloying concentration, CrN coating surface roughness decreases. The columnar width of CrN decreased from 31.8 nm to 23.5 nm at around 10.4 at.% Ni alloying content. Moreover, the introduction of soft Ni resulted in decreased elastic modulus and hardness of CrN. However, with 10.4 at.% Ni alloying in CrN, the fracture toughness was enhanced, rising from 2.92 MPa m1/2 to 3.22 MPa m1/2. The rotating bending fatigue property of Ti6Al4V was reduced due to the lower crack resistance of the CrNiN coating. After 1 × 106 cycles, the fatigue limits of Ti6Al4V with CrN and CrNiN (10.4 at.% Ni) coating were 452 MPa and 505 MPa. Adding Ni to CrN coating reduced surface roughness and lowered stress concentration during cyclic loading. Furthermore, Ni alloying improved the coating toughness, which decreased the fatigue crack length in Ti6Al4V induced by fracture of CrN. Thus, the negative influence of CrN on Ti6Al4V fatigue performance was mitigated.

Keywords

• CrNiN coating
• Microstructure evolution
• Fracture toughness
• Mechanical property
• Fatigue performance