Damage behavior of Ni-B and Ni-B-TiO2 coatings on AISI P20 steel under indentation and bending

This study examines the influence of TiO2 nanoparticles on the structure, mechanical properties, and fracture behavior of Ni-B coatings applied to heat-treated AISI P20 steel. Mechanical performance was assessed through indentation and step-by-step three-point bending tests on both coated and uncoated substrates. Vickers and Brinell indentation tests revealed that both Ni-B and Ni-B-TiO2 coatings reduce the substrate's plasticity by approximately 50%. Uncoated AISI P20 steel exhibited only plastic deformation even under high stress applied by the Brinell indenter, whereas coated samples displayed distinct cracking modes, significantly affecting the damage behavior. The incorporation of TiO2 nanoparticles led to coating spallation under Brinell indentation. However, during bending, the Ni-B-TiO2 coating demonstrated greater resistance to cracking than the Ni-B coating. Furthermore, two-sided coatings showed significantly higher crack resistance than one-sided coatings, irrespective of their composition. The maximum normal stress at crack initiation was approximately 1.6 to1.7 times higher for the two-sided coatings.