Laser Cladding Of Si-Hf Anti-Oxidation Coating On The Carbon Substrate

Carbon materials are good aerospace materials,which have high melting point,low density,high temperature and low thermal expansion coefficient.However,it is easy to be oxidized at higher temperature,which limits the development space of carbon materials.The traditional coating preparation technology has some disadvantages such as low bonding strength and long processing time.Laser cladding technology has the advantages of short processing time and controllable processing range.In this paper,laser cladding method was used to fabricate Si-MoSi₂-HfB₂,Si-MoSi₂-SiC-HfB₂and Si-MoSi₂-ZrO₂/Si-MoSi₂-HfB₂coating.Its ablation performance was evaluated by laser surface ablation.The antioxidant properties were evaluated by 1773K high temperature oxidation.The ablation peeling strength?change of phase composition,combination between coating and substrate and structure transformation were studied by coating weight change,scratching failure load,XRD and SEM,which were used to evaluated ablation properties.The mechanism of laser ablation of coating was discussed.The oxidation resistance of coating was studied by weight change,XRD and SEM.The ablation properties and oxidation resistance were compared.In the Si-MoSi₂-HfB₂1500?oxide coating experiment,the components of coating quality has a certain degree of rise,the surface is relatively compact,but there are a certain number of holes and cracks,among them the slowest S10M15 coating weight,showed the strongest antioxidant activity,the coating in the laser cladding process the weight change ratio is the lowest(0.15±0.01%),average scratch coating binding load is 10.6N(84.4Mpa).However,the average scratch adhesion of S5M25coating is the highest(101.12Mpa),and the weight loss rate is only 0.16±0.01%.There is a thin layer of oxide on the surface of the coating,and the coating is compact and has few defects.The thickness of the coating reaches 50?m,and the cross section is uniformly distributed granular structure without obvious holes and penetrating cracks,which can better protect the carbon matrix.In addition,in the process of laser line ablation,with the increase of ablation times,the scratch strength gradually decreases.After five times of ablation,the S5M25 coating has the lowest ablation rate(1.54mg/min)and the highest scratch adhesion(56.53Mpa),and its surface and cross-section are still dense,without obvious cracks and holes,showing excellent laser ablation resistance.Compared with Si-MoSi₂-SiC-HfB₂coating,the weight loss rate and scratch strength of laser cladding Si-MoSi₂-SiC-HfB₂coating increase;C30H50 has the lowest weight loss rate(0.34%)and the highest scratch strength(99.53Mpa).Compared with S5M15 coating,the weight loss rate of C30H50 coating increases with the addition of SiC,but the coating cracks decrease significantly,the coating morphology is improved after cladding,and the scratch strength increases by 46%;meanwhile,SiC is distributed between white granular structures,the number of microcracks and holes on the surface of the coating decreases significantly after laser line ablation,there is no obvious penetrating crack on the cross section,and the thickness of the oxide layer also increases.Compared with S5M15 coating,the ablation rate of C30H50 coating is reduced by 15%,the scratch strength is increased by 10%,and the laser ablation resistance of the coating is improved.When sintered at1500?for 80 min,C30H50 powder is denser,with the weakest oxidation degree and the best oxidation resistance.When proper amount of SiC is added,the surface cracks and pores are reduced,and the density of the coating is increased,which is beneficial to enhance the oxidation resistance.Suffering the influence of ZrO₂spatter,the weight loss rate of double-layer S10M20Z70 coating is higher than that of S20M15 coating,but the scratch strength is increased by 130%;the density of the coating is improved,the inner and outer coatings are well bonded,there is no obvious interface,and the coating cross section has no penetrating cracks and large holes,so the outer coating has better anti-oxidation protection ability for the inner coating.After ablation,the weight loss of the coating is greatly reduced and the coating tends to be stable.S10M20Z70showed the lowest ablation rate(2.34 mg/min)and the highest scratch strength(117.04Mpa),which was 85.99Mpa(277%)higher than that of S20M15 coating;in addition,the oxidation weight gain of S10M20Z70 at 1500?was the smallest(only1.55 mg/cm²at 80 min).There are different phase structures in the coating,such as acicular,small granular and massive,which can transfer stress and avoid stress concentration.There is a transition zone,which greatly improves the bonding strength of the body layer.Compared with Si-MoSi₂-HfB₂ternary coating,the double-layer coating has fewer holes and better bonding,which improves the laser ablation resistance of the coating.