Understanding of Heat Treatment on the Durability of Cobalt Alloy Thin Film Coated on Mild Steel

Mild steel is used extensively in infrastructure and industry due to its excellent mechanical quality. However, this type of steel is susceptible to fatigue failure, such as low-high cycle fatigue, thermal fatigue, and contact fatigue, which reduces the life span of components. The objective of the study is to investigate the effect of heat treatments on the CoNiFe coated mild steel on hardness, surface roughness, and fatigue life. The mild steel substrate was electrodeposited using CoNiFe nanoparticles, followed by heat treatment processes such as annealing and quenching. The highest coating mass recorded by 45 min coating without Heat Treatment (HT) was 1.02 g, while the lowest coating mass recorded by 15 min coating without HT was 0.35 g. The highest improvement of microhardness was observed on a 45 min coating without HT, which was 315.82 HV as compared to the uncoated substrate, which was 132.40 HV. The lowest surface roughness was obtained by the 15 min samples without HT (0.20 µm), while the highest recorded surface roughness was obtained on the uncoated substrate (0.42 µm). The fatigue performance of 30 min coating with HT (quenching) was the highest, with a cycle life of 1,000,000 cycles and 80% Ultimate Tensile Strength (UTS) loading, respectively. The lowest fatigue performance was recorded from the uncoated substrate with cycle life and yield stress percentages of 1,450 cycles and 80% of UTS loading, respectively. Coated substrates show significant improvement on fatigue life, indicating the synergy of coating with post heat treatments to enhance the materials durability under cyclic hence showing high potential of improving mild steel's performance for a wide range of applications.