| Al2O3 coating is a typical representative of wear-resistant oxide ceramic coating under severe wear service conditions.Previous studies on Al2O3 coatings mainly include the optimization of spraying,post-treatment process and coating composition.The methods are as followings:increasing the substrate deposition temperature,on-line assisted deposition of dry ice,post-processing by laser remelting,nanostructure,adding elemental phases(such as aluminum,graphene,carbon nanotubes)or compounds(such as Zr O2,YSZ,Ti O2),etc.The common problem of the above studies is that it is difficult to simultaneously improve the high temperature mechanical properties,thermal conductivity and wear resistance of the coating.In order to solve the problem that the long-term high temperature creep will obviously reduce the coating strengthening effect,based on the deep eutectic solidification mechanism,the in-situ deposition of Al2O3-Y3Al5O12(YAG)amorphous ceramic coating was deposited by large undercooling degree of plasma spraying with excellent high temperature microstructural stability combined with good plastic toughness,thermal conductivity and crack arrest properties.However,in the preparation process of sprayable powder,it is necessary to gradually increase the temperature and cyclic calcination treatment to produce high temperature solid-phase reaction.Besides,plasma spheroidization link is also needed,which has cumbersome process and high cost,and affects the consistency and reliability of coating quality.To solve the above problems,in this study,plasma sprayed Al2O3-Gd Al O3(GAP)amorphous ceramic coating was prepared.It not only realizes the stable integration of strength,toughness,thermal conductivity and high temperature microstructure similar to Al2O3-YAG amorphous ceramic coating,but also sprayable powder was composed of original phase without high temperature solid phase reaction.The sphericity and fluidity were good,and the deposition process was greatly simplified.Simultaneously,the consistency and reliability control of coating preparation quality were greatly improved,and the time and economic cost of coating preparation were effectively reduced.It has good advantages and potential in large-scale engineering applications.The main results are as follows:(1)Using submicron Al2O3/Gd2O3 powder as raw material,prepared by spray ranulation technology and calcined at 900?@2 h(without solid-phase reaction occurred),sprayable Al2O3/Gd2O3 powder with good sphericity fluidity was obtained.Al2O3 and Gd2O3 raw materials in a single particle were evenly mixed.The Al2O3-GAP coating was in situ deposited by plasma spraying.The amorphous phase in the coating was the main phase(>90%),and a small amount of?-Al2O3 and GAP grains were evenly distributed in the amorphous matrix.The nanoindentation hardness,elastic modulus,and structure/property uniformity of the three coatings were analyzed by multiple sets of nanoindentation tests.The nanoindentation hardness of the Al2O3-GAP coating was 9.25±0.57 GPa and the elastic modulus was 140.77±7.10 GPa.The microstructure uniformity of Al2O3-GAP coating was better than that of Al2O3 and Al2O3-YAG coating.(2)The crystallization kinetics of Al2O3-GAP amorphous coating showed that the crystallization temperature was 1179.2 K,and Gd4Al2O9(GAM),GAP and?-Al2O3 phases were precipitated successively.The crystallization activation energies of GAM,GAP and?-Al2O3 based on the Kissinger equation were 847.6,915.8 and 868.7 k J·mol-1,respectively.The calculation of crystallization activation energy showed that GAM phase was easier to nucleate than GAP and?-Al2O3 phases,the grain growth process of GAP and?-Al2O3 was more difficult than the nucleation process,and the growth process of GAM was more sensitive than the nucleation process.Among more than thirty reported typical amorphous materials, the Al2O3-GAP amorphous coating had the highest crystallization activation energy. The research showed that the microstructure of the coating at high temperature had good stability and was suitable for reliable service at higher temperatures.(3)The friction and wear properties analysis of the coatings paired with graphite showed that the Al2O3-GAP coating had better wear surface integrity than the Al2O3 and Al2O3-YAG coatings.After the Al2O3-YAG coating and the Al2O3-GAP coating were worn,the surface was intact and free of cracks.In addition,Al2O3- GAP/graphite had the lowest friction coefficient,the smallest fluctuation and the lowest wear surface temperature.Based on the wear assessment test of coating/graphite,the wear failure mechanism of Al2O3-GAP/graphite was proved. Al2O3-YAG and Al2O3-GAP coatings have similar wear mechanisms.The coating showed that cracks initiate,then peeled off,and finally expanded into peeling pits.Together with abrasive particles,they aggravated the abrasive wear effect. |
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