Rotating Bend Fatigue
New independent testing has proven that Hardide-A coating improves the fatigue life of metal components by 4.5% compared with uncoated substrates. Hardide-A also eliminates the need for post-coating shot peening operations typically required when using traditional coating processes such as hard chrome plating (HCP) or thermal spray coatings such as HVOF.
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. Testing was carried out byWestmoreland Mechanical Testing and Research Ltd (WMTR), the independent aerospace qualified testing laboratory with bases in the UK and USA.
WMTR used theRotating 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.
The curve has been plotted for the coated samples vs uncoated and the S-N curve for the coated samples is clearly positioned above the uncoated control samples’ curve by ~40 MPa in the whole range of the N cycles to failure. The fatigue debit improvement of +4.5% after coating is an excellent result with the coated samples demonstrating better fatigue performance than the uncoated samples.
Improving fatigue resistance and eliminating costly secondary shot peening processes has been a priority for the industry for many years; these results are a significant advancement in materials optimisation for the aerospace industry.