| Carbon structure materials have a wide application prospect in the field of ultra-high temperature extreme environment such as deep space,aerospace,etc.,but the high temperature oxidation becomes the bottleneck restricting its industrialization development.Although ZrB2-SiC coating has shown excellent oxidation protection capability in wide temperature range,however,because the oxygen resistance structure of the coating is dynamic change,SiC will undergo life oxidation when the temperature is over 1900k,which will cause its destructive dynamic evolution,weaken the oxidation defense ability and application prospect of the coating.Because the diffusion of oxygen to the substrate through the coating is the main reason for the dynamic evolution of the destructive property,it is necessary to improve the dynamic stability of the coating,it is necessary to improve the densification of the coating,reduce the defects in the coating and reduce the oxygen diffusion path.In order to achieve this goal,the low temperature hot pressing technology of plasma sintering is used to improve the densification of the coating,and the pre-oxidation treatment makes the coating self-destructive to form a film under lower oxidation,and improves the dynamic stability of the coating by the joint action of the coating itself and glass film.In view of the contrary quality change law between the carbon matrix and coating after oxidation,it has a great interference to the optimization of the oxygen resistance performance of the coating.In this paper,a high resistance oxygen evaluation model is proposed in this paper.A diversified data collection mode of"standard sample-coating sample-matrix sample"is established.The real protection capability behind distortion data can be effectively reduced by separating and analyzing oxidation dynamics of different samples.In this paper,ZrB2-SiC coating was prepared by plasma sintering.The effects of ZrB2 content and pre-oxidation process on the oxygen resistance of carbon matrix were studied.The oxidation resistance mechanism of ZrB2-SiC coating was studied by combining with XRD,SEM,TEM,EDS and other various surface analysis before and after the oxidation of the coating,and the film forming mechanism of the self-generated glass layer was clarified The relationship between the change of coating components and the pre-oxidation treatment and oxygen permeability was studied.The following contents and results are obtained:The results of 1973K constant temperature oxidation test show that ZrB2-SiC ultra-high temperature ceramic coating prepared by plasma sintering has a good composition adjustment ability.The coating has good combination with the substrate,and the increase of ZrB2 content promotes the densification of the coating.With the increase of ZrB2 content,the maximum oxygen permeability decreased from 2.91%to1.77%,and the cumulative antioxidant efficiency increased from 96.4%to 97.7%.In the active oxidation stage,due to the insufficient formation of composite glass layer,the oxidation of ZrB2 will aggravate the oxidation consumption of ZrB2 SiC coating.In the inert oxidation stage,the oxidation stability of the composite glass layer can be improved by increasing the content of ZrB2,which greatly reduces the oxidation consumption of the coating.The microstructure analysis shows that the composite glass layer formed on the surface of the coating is the main reason for the excellent oxidation protection effect of ZrB2-SiC ceramic coating.Meanwhile,the dispersion of Zr-oxides nanoparticles on the surface of the coating formed a more stable Zr-B-Si-O glass layer,which widened the melting zone of the glass layer,increased the viscosity of the glass layer and inhibited the oxygen permeability of the glass layer.Although the increase of ZrB 2content in the active oxidation stage aggravates the oxidation consumption of the coating,the oxidation consumption of the coating is inhibited in the inert oxidation stage,which is due to the dispersion strengthening effect of Zr-oxide nanoparticles.The oxidation data of the coating after pre-oxidation process show that the formation speed of the composite glass layer is accelerated with the increase of the pre-oxidation temperature.The structure factor of the coating decreased from 2.6%to1.6%and the inerting factor decreased from 1.2×10-6g·cm-2·s-1 to 0.9×10-6g·cm-2·s-1when the temperature of the pretreatment was low.This is mainly because during the pre-oxidation process,oxygen seeps into the coating to form SiO2 phase,effectively heals the internal defects,suppresses the destructive dynamic evolution,improves the density of the coating,and enhances the oxygen resistance ability of the coating structure.At this time,the complex glass layer formed on the surface has less defects due to low energy consumption,and the inerting oxygen resistance ability of glass layer is enhanced.The two factors enhance the oxygen resistance of the coating.The temperature of pre-oxidation continued to increase,the structure factor of coating increased from 1.6%to 2.3%,and the inerting factor increased from0.9×10-6g·cm-2·s-1 to 1.7×10-6g·cm-2·s-1.This is mainly because the oxidation activity of the coating increases,the formation speed of glass layer is accelerated,oxygen does not enter the coating in time,which can not effectively increase the density inside the coating,and the increase of the structure oxygen resistance performance of the coating is less.The surface glass layer has some defects such as pores due to its high oxidation activity,which provides oxygen diffusion channel for 1973K oxidation,and the internal oxidation intensifies,and the oxygen resistance of the coating decreases.The cumulative oxidation resistance efficiency of the coating treated with1200?was 98%.At this time,the protective effect of the coating was the most obvious and the dynamic stability of the coating was the strongest.The oxidation data of the coating after pre-oxidation treatment showed that the oxygen permeability of the coating decreased from 1.01%to 0.94%with the prolongation of the pre-oxidation time.This is mainly because Zr-B-Si-O composite glass layer gradually forms on the surface,and the dispersion of Zr-oxides in glass phase is more uniform,and the inerting oxygen resistance ability of glass layer is strengthened.At the same time,oxygen enters the interior through the diffusion channel of the coating,and the formation of SiO2 phase also heales the internal hole to a large extent,and the oxygen resistance ability of the coating structure is effectively strengthened.The two functions to improve the oxygen resistance of the coating.But the pre-oxidation time is too long,which increases the oxygen permeability of the coating from 0.92%to 0.96%.This is mainly because of the excessive consumpt ion of coating and the formation of defects such as holes,thus reducing the dynamic stability of glass layer.Even if the pre-oxidation has been obtained inside,the defects of glass layer show obvious oxygen permeability,which makes the structure oxygen resistance ability of the coating obviously decrease.After 6 hours of pre-oxidation treatment,the thickness of the oxide layer is only 100?m,and the coating has the strongest ability of oxygen resistance.There are 41 figures,3 tables and 115 references in this paper. |
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