Design And Optimization For Light Absorbing Coatings For Laser Heat Treatment

At room temperature laser reflectivity of metal materials is very high, especially for CO2laser rise up to more than90%. Therefore, the pretreatment of metal surface is usually used to increase the absorptance of laser before laser heat treatment Phosphate and black absorption coating method are widely used as pretreatment method, but the former easy to cause the failure of phosphate solution, and the latter easy to be ablated under high temperature, resulting in lower absorption rate. However, usually the melting point of metal oxides is above2200℃, with characteristics of peak absorption and high absorption rate for CO2laser, so it will not be ablated in the laser treatment, which greatly increased the absorption rate of CO2laser, and will not cause environmental pollution. Therefore, on the basis of the problems above, a kind of absorb light coating based on metal oxide for aggregate is developed, which have high absorbency and well process performance.Different metal oxides have different absorption performance for CO2laser. Therefore this study investigated the absorption capacity of6kinds of metal oxides (TiO2, ZrO2, ZnO, A12O3, MgO and Cr2O3) for the CO2laser by metallographic and other methods, and discussed the relationship between the absorb ability and energy level structure. The results show that metal oxides have different absorption rates under different laser power density. For TiO2coating with power density less than3539W/cm2, its absorption rate is higher than other metal oxides and lower than the graphite coating. When the power density higher than3539W/cm2, it owns the highest absorption rate. For power density of4953W/cm2, the order of absorption rate of metal oxides for CO2laser from highest to the lowest is TiO2, Z1O2, Al2O3, MgO, ZnO, graphite coating and Cr2O3. Analysis shows that the impurity energy level in forbidden band make TiO2absorb CO2laser photons energy through free charge carriers which are in conduction band. With the increase of laser power density, the absorption rate of T1O2coating increase quickly. So in high power processing, TiO2is a better aggregate of absorb light coaling.On the basis of the above studies, a conparative study of different particle sizes of T1O2on CO2laser absorption was processed, and the optimum size is definited under laboratory condition. Studies show that among the TiO2with average size of45μm,13μm,6.5μm and1.6μm, the absorption rate of TiO2with1.6μm is highest. With the decrease of TiO2particle size, the absorption rate increases. Analysis shows that, specific surface area of TiO? is increased along with particle size decreasing, thus increasing the absorptance of laser, and also increasing the coating density and the adhesion of coating and matrix, so1.6μm is the best TiO2particle size under laboratory condition among the TiO2particles of four types we used.From the above research results can be seen, the absorption rate of average particle sizel.6μm TiO2is highest, so it can be as the aggregate to develop absorb light coating. It is discussed that the influence of thickness and formula of the binder, solvents and aggregate for laser absorbing rate by the orthogonal experimental method. After verification test optimization results show:when the thickness of absorb light coating is about0.1mm, and the aggregate content is30%, and binder content is15%, laser hardening area of the corresponding sample is the largest, and absorption rate is the highest, so this formula can be used to develop the absorb light coating which have high laser absorption rate and well process performance.