Traditional coating processes such as hard chrome plating (HCP) or thermal spray coatings such as HVOF typically require post-coating shot peening operations, whereas Hardide-A eliminates the need for this entirely. Historically, fatigue debit after coating can be as much as 40-60% and only following shot peening of the coated surface can this be reduced to around a 20% debit. The Hardide-A coating recorded a fatigue life increase of +4.5% after coating while also eliminating the need for shot peening.
Fatigue debit of surface coated metals has been a long-standing problem for the aerospace industry, particularly on components that have been coated with HCP and HVOF. Fatigue testing was carried out by Westmoreland Mechanical Testing and Research Ltd (WMTR), the independent aerospace qualified testing laboratory with bases in the UK and USA.
WMTR used the Rotating Bend Fatigue test method complying to BS ISO 1143:2010. This test is considered to be the most sensitive to the effects of surface treatment on fatigue properties.
S99 steel samples were coated with 63-70 microns and ~950 Hv of Hardide-A which are mid-value thickness and hardness properties for this coating type.
The results were achieved due to the enhanced toughness, compressive residual stresses and homogeneous pore-free structure of Hardide-A, which prevent the initiation and propagation of cracks under high-cycle fatigue conditions.