Evaluation of toughness of hard coatings

Abstract

Repeated impact has been introduced to evaluate different properties of hard coatings, such as impact wear resistance, bonding strength, fatigue, etc. The load and impact number relationships are similar to that of fatigue curves, and close to some real applications of coated parts. Cr-Cu-N coatings were performed on a hardened steel substrate and the repeated impact tests were conducted on the coating substrate system. At a low impact load, the intrinsic strength of the coating layer and the bonding strength between the coating and substrate are in competition. Coating layer cracking or delamination might occur and the strength plays an important role like that of high cycle fatigue. When the load is increased and towards the low cycle fatigue regime, toughness of the coating layer turns out to be predominant. The cohesive failure in high load regime preferentially depends on the toughness of the coating layer, and the failure cycles can be employed as a toughness criterion.

Micro-scale impact testing - A new approach to studying fatigue resistance in hard carbon coatings

“…At the macro-scale coating impact resistance is commonly evaluated in non-depth sensing tests with indenters of WC-Co, hardened steel [29] or silicon nitride [30], typically with radii of 2.5 or 3 mm [30][31][32][33][34] although smaller radii (e.g. around 1 mm) have also been used [35][36][37][38][39][40].…”

Fatigue-like failure of thermally oxidised titanium in reciprocating pin-on-plate wear tests

“…Arai et al however determined that rolling/sliding tests were more suitable for assessing coating durability than impact ("hammering") tests as the latter showed a number of coating failure mechanisms in addition to adhesive failure (flaking) [22]. Similarly, Bao et al determined that cohesive failure frequently dominated the coating response in impact tests and instead suggested that repeated impact tests be used to assess coating toughness [29]. Recently, instrumented micro/nano scale impact testing has been developed as a potential adhesion test [30].…”

The repeated spherical indentation test: an efficient way to evaluate the adhesion of hard coatings

“…14 Only adhesive failure is associated with the adhesion of the coating, but the impact test always involves cohesive failure, which is related to coating toughness. 15,16 Although the adhesion measured for a hard coating under a load is close to that under service conditions, it is still difficult to detach the coating from the substrate along the interface.…”