Effect of a laser pre-quenched steel substrate surface on the crack driving force in a coating–steel substrate system

Abstract

A mechanical model of a coating/laser pre-quenched steel substrate specimen with a crack oriented perpendicular to the interface between the coating and the hardened layer is developed to quantify the effects of the residual stress and hardness gradient on the crack driving force in terms of the J-integral. It is assumed that the crack tip is in the middle of the hardened layer of the pre-quenched steel substrate. Using a composite double cantilever beam model, analytical solutions can be derived, and these can be used to quantify the effects of the residual stress and the hardness gradient resulting from the pre-quenched steel substrate surface on the crack driving force. A numerical example is presented to investigate how the residual compressive stress, the coefficient linking microhardness and yield strength and the Young's modulus ratio of the hardened layer to the coating influence the crack driving force for a given crack length.

On the cyclic bending behaviour of a hard coating on a ductile substrate with periodic surface hardened regions

“…This is because the residual compressive stresses within the substrate always retard the penetration of the vertical coating crack into it, while the residual tensile stresses induce such penetration. Thus, the theoretical prediction by Yang et al (2007) is partly verified, in which it is reported that the as-quenched layer shall retard the penetrating of a vertical crack into the substrate. These results also indicate that a continuous surface quenched layer may induce severe interface fractures when the specimen is subjected to cyclic bending.…”

“…In fact, such a residual stress state would lead to great increase in the resistance of the vertical crack extending into the as-quenched regions and increasing the driving force extending into the origin substrate. This has also been argued by Yang et al (2007). Thus, in effect, above the as-quenched regions, the driving force for the vertical crack deflecting into the interface shall be strengthened.…”

“…Later on, Wu et al (2007) revealed experimentally that the controllable cracking of the coating can also be developed when the specimen is subjected to in-plane tension, which is considered to be largely due to the unique pattern of the yielding stresses and residual stresses in the structure. Thereafter, Yang et al (2007) investigated analytically the effect of the yielding stresses and residual stresses on the extension of the vertical crack into the as-quenched substrate by a meso-scale mechanical model, of which the prediction has been partly verified experimentally by this work.…”

A mechanical model for the quantification of the effect of laser quenching on CTOD in steels

“…Apart from the wear and erosion experiments, it should be emphasized that most of the experiments in the studies mentioned above were restricted to the fatigue property research under dynamic loads. Recently, a mechanical model was developed to quantify the effect of laser quenching on crack driving force in terms of J-integral, and it could be obtained that the dominant factor influencing the crack driving force was the residual stress (Yang et al, 2006(Yang et al, , 2007. However, the residual stress is approximated as a mean value over the crack length, and the residual stress gradient effect was not considered in (Yang et al, 2006(Yang et al, , 2007.…”

Research on the Micro-Crack Density of a Chromium Coating/Steel Substrate with and without Laser Pre-Quenching Treatment

“…[7,8]. Some mechanisms responsible for the improvement have been reported, such as the hardness improvement of the steel substrate surface [8], the finer microstructure of the interface as well as the coating itself [7] and the decrease of the crack driving force in the hardened layer by residual compressive stress and yield strength improvement by the technology [9][10][11]. In this work, a comparative investigation on the initial micro-crack density of the Cr coating on the laser pre-quenched steel substrate surface and original steel substrate surface is investigated.…”