| Thermal fatigue damage is one of the major reasons which lead to the failure ofhot-work dies. There is consumption of hot-work die about10billion RMB in Chinadue to low using life of domestic dies. Therefore, improvement in thermal failureproperty and reduction in fabricating cost of hot-work die possesses economicsignificance. In previous studies, thermal fatigue property of3Cr2W8V steel, which isthe common material for hot-work die in China, has been improved effectively by laserbiomimetic coupling (LBC) technique which imitates the coupling effect of flora andfauna surfaces. However, for the investigation of thermal fatigue properties of hot-workdies treated by LBC technique, there are many coupling elements and characteristicparameters which can influence the thermal fatigue properties. Moreover, the responsesof thermal fatigue properties of different hot-work dies materials treated by LBCtechnique are different. On the other hand, the thermal cycles temperatures are alsoimportant for the thermal fatigue properties of materials treated by LBC technique.Thus, the influence mechanisms of these factors on the thermal fatigue properties needto be further explored and revealed.Therefore, the effects of morphologies of shapes coupling elements on the thermalfatigue properties of LBC samples were studied. During different thermal cyclestemperatures, the responses of thermal fatigue properties of different hot-work diessteels treated by LBC technique were investigated. Moreover, variations ofmicrostructures and microhardnesses for parent metal and units were researched afterthermal fatigue cycles. In addition, the influence of materials coupling elementsstrengthening treatment on the thermal fatigue property of LBC samples was studies.The stress field of untreated sample after cooling during thermal fatigue cycles wassimulated, and combined with the tensile property of LBC samples and untreated samples before and after thermal fatigue cycles to analyze the mechanism forimproving the thermal fatigue property of LBC sample. The main results indicate that:1. According to the contours and dimensions of morphologies of shapes couplingelements, three kinds of units morphologies were defined, i.e.―prolate‖morphology unit which the ratio of width and depth of unit was greater than4times and―U‖morphology unit which unit contour was similar to parabola, aswell as―V‖morphology unit which contour was similar to triangle. Theinfluence of morphologies of shapes coupling elements on the thermal fatigueproperties of LBC samples were revealed, i.e.―U‖morphology unit had the bestthermal fatigue property, followed by―V‖morphology unit and―prolate‖morphology unit.2. During different thermal cycles temperatures, the responses of thermal fatigueproperties of different hot-work dies steels treated by LBC technique weredifferent. Three kinds of hot-work die steels treated by LBC technique hadbetter thermal fatigue property than untreated samples during different thermalfatigue cycles temperatures. During the thermal cycles temperature at600℃, thethermal fatigue properties of LBC samples sorted HD＞HHD＞H13. During thethermal cycles temperatures at650℃,700℃and750℃, the thermal fatigueproperties of LBC samples sorted HHD＞H13＞HD. During different thermalcycles temperatures, the thermal fatigue behavior of LBC sample with griddingshape is the best, followed by striation shape and spot shape among the shapescoupling elements.3. During different thermal cycles temperatures, different responses of thermalfatigue properties of different hot-work dies steels treated by LBC techniquewere revealed. During the thermal cycles temperature at600℃, after thermalfatigue testing, the hardness of HD steel and unit of HD steel were still thehighest, moreover the microstructure of different kinds of hot-work dies steelsand units had no significant change. Therefore, during the thermal cyclestemperature at600℃, HD steel LBC sample had the best thermal fatigue property. During the thermal cycles temperatures at at650℃,700℃and750℃,after thermal fatigue testing, thermal cycling softening resistance andmicrostructure thermal stability of HHD steel and unit of HHD steel were thebest. Thus, during the thermal cycles temperatures at650℃,700℃and750℃,HHD steel LBC sample had the best thermal fatigue property.4. The influences of materials coupling elements strengthening treatment on thethermal fatigue property of biomimetic coupling samples were revealed.a) The microstructures of units of tempered or annealed H13steel were refinedby electropulsing. Cryptocrystalline martensite were obtained when H13steel was treated by electropulsing. The thermal fatigue property of LBCsample was improved further due to better overall performance after treatedby electropulsing.b) Comparing with laser melting (LM), the microstructures and chemicalcompositions of units were changed by laser cladding (LC). Microstructurethermal stability and thermal cycling softening resistance of LC unit werebetter than that of LM unit. LC biomimetic coupling sample was moreeffective to improve thermal fatigue behavior than LM biomimetic couplingsample.5. The influence mechanisms of improved thermal fatigue property of materialstreated by LBC technique were revealed.a) The materials treated by LBC technique had finer microstructures and bettercomprehensive properties than that of untreated materials. On the basis ofindividual strengthening of the units and double-phases compoundstrengthening, the thermal fatigue cracks initiation resistance was improved.On the other hand, shapes coupling elements had different effect on thethermal fatigue cracks propagation resistance which decrease thepropagation speed of thermal fatigue cracks and improve the thermal fatiguecracks propagation resistance.b) Owing to the thermal fatigue cracks initiate and propagate within a certaindepth of materials surface, as well as the depth of thermal fatigue cracks increases with the increasing thermal fatigue cycles, different unitsmorphologies had different degrees of improvement in thermal fatigueproperty.―Prolate‖morphology unit had the smallest area and lowest depthwhich lead to the worse thermal fatigue property among differentmorphologies units. The area of―U‖morphology unit was bigger than thatof―prolate‖morphology unit, and―V‖morphology unit is narrower than the―U‖morphology unit indepthdirection, therefore,―U‖morphology unit hadthe best thermal fatigue property. |
