本文主要综述了目前制备纳米结构热障涂层的三种方法,即大气等离子喷涂、溶液前驱体等离子喷涂和悬浮液等离子喷涂,并对这三种方法的工艺过程、制备原理、涂层的微观结构特征和研究现状进行了归纳.最后,总结了纳米结构热障涂层研究目前存在的问题,并对其发展趋势进行了展望.
参考文献
| [1] | XU Z H,HE L M,MU R,et al .Influence of the deposition en ergy on the composition and thermal cycling behavior of La2 (Zr0.7-Ce0.3)2O7 coatings[J].Journal of the European Ceramic Society,2009,29(9):1771-1779.,2009. |
| [2] | EVANS A G,MUMM D R,HUTCHINSON J W,et al .Mecha nisms controlling the durability of thermal barrier coatings[J].Progress in MaterialsScience,2001,46(5):505-553.,2001. |
| [3] | SCHULZ U,LEYENS C,FRITSCHER K,et al .Some recent trends in research and technology of advanced thermal barrier coatings[J].Aerospace Science and Technology,2003,7(1):73-80.,2003. |
| [4] | MUMM D R,EVANS A G,SPITSBERG I T .Characterization of a cyclic displacement instability for a thermally grown oxide in a thermal barrier system[J].Acta Materialia,2001,49(12):2329-2340.,2001. |
| [5] | WRIGHT P K .Influence of cyclic strain on life of a PVD TBC[J].Materials Science and Engineering:A,1998,245(2):191-200.,1998. |
| [6] | 曹学强.热障涂层材料[M].北京:科学出版社,2007.23-25,231-245.CAO X Q.Thermal Barrier Coating Materials[M].Beijing:Sci ence Press,2007.23-25,231-245.,2007. |
| [7] | FENECH J,DALBIN M,BARNABE A,et al .Sol gel process ing and characterization of (REY) zirconia powders for thermal barrier coatings[J].Powder Technology,2011,208(2):480-487.,2011. |
| [8] | RAUF A,YU Q,JIN L,et al .Microstructure and thermal prop erties of nanostructured lanthana doped yttria stabilized zirconia thermal barrier coatings by air plasma spraying[J].Scripta Mate rialia,2012,66(2):109-112.,2012. |
| [9] | RAHELEH A P,REZA S R,REZA M,et al .Improving the thermal shock resistance of plasma sprayed CYSZ thermal barrier coatings by laser surface modification[J].Optics and Lasers in Engineering,2012,50(5):780-786.,2012. |
| [10] | JIN L,NI L Y,YU Q H,et al .Thermal cyclic life and failure mechanism of nanostructured 13wt% Al2O3 doped YSZ coating prepared by atmospheric plasma spraying[J].Ceramics Interna tional,2012,38(4):2983-2989.,2012. |
| [11] | PANZY,WANGY,WANGCH,etal .The effect of SiC par ticles on thermal shock behavior of Al2O3/8YSZ coatings fabri cated by atmospheric plasma spraying[J].Surface and Coatings 0Technology,2012,206:2484-2498.,2012. |
| [12] | ZHAO X D,ZENG K L,XIE J G,et al .Nanostructured lan thanum zirconate coating and its thermal stability properties[J].Journal of Iron and Steel Research International,2007,14(5):147-151.,2007. |
| [13] | LI J Y,DAI H,LI Q,et al .Lanthanum zirconate nanofibers with high sintering resistance[J].Materials Science and Engi neering B,2006,133:209-212.,2006. |
| [14] | CAO X,VASSEN R,FISCHER W,et al .Lanthanum cerium oxide as a thermal barrier coating material for high temperature applications[J].Advanced Materials,2003,15(17):1438-1442.,2003. |
| [15] | FAN Q B,ZHANG F,W F C,et al .Molecular dynamics calcu lation of thermal expansion coefficient of a series of rare earth zirconates[J].Computational Materials Science,2009,46(3):716-719.,2009. |
| [16] | LI Z P,GAO F .Bonding and hardness of LnMgAl11O19 (Ln=La; Pr; Nd; Sm; Eu; Gd)[J].Journal of Alloys and Compounds,2010,508(2):625-628.,2010. |
| [17] | 黄亮亮,孟惠民,陈龙.磁铅石结构六铝酸盐热障涂层的研究现状[J].材料工程,2013(12):92-99. |
| [18] | WANG Y H,OUYANG J H,LIU Z G .Influence of dysprosi um oxide doping on thermophysical properties of LaMgAl11O19ceramics[J].Materials & Design,2010,31(7):3353-3357.,2010. |
| [19] | WANG Y H,OUYANG J H,LIU Z G .Preparation and ther mo physical properties of La1-xNdxMgAl11O19 (x =0,0.1,0.2) ceramics[J].Journal of Alloys and Compounds,2009,485(12):734-738.,2009. |
| [20] | GADOW R,LISCHKA M .Lanthanum hexaaluminate novel thermal barrier coatings for gas turbine applications materials and process development[J].Surface and Coatings Technology,2002,151 |
| [21] | ZHANG J F,ZHONG X H,CHENG Y L,et al .Thermal shock resistance of LnMgAl11O19 (Ln =La,Nd,Sm,Gd) with magnetoplumbite structure[J].Journal of Alloys and Com pounds,2009,482:376-381.,2009. |
| [22] | XIE X Y,GUO H B,GONG S K .Mechanical properties of LaTi2Al9O19 and thermal cycling behaviors of plasma-sprayed LaTi2Al9 O19/YSZ thermal barrier coatings[J].Journal of Ther malSprayTechnology,2010,19(6):1179-1185.,2010. |
| [23] | XIE X Y,GUO H B,GONG S K,et al .Lanthanum titanium aluminum oxide:A novel thermal barrier coating material for ap plications at 1300℃[J].Journal of the European Ceramic Socie ty,2011,31(9):1677-1683.,2011. |
| [24] | XIE Xiaoyun,GUO Hongbo,GONG Shengkai,XU Huibin.Hot Corrosion Behavior of Double-ceramic-layer LaTi2Al9O19/YSZ Thermal Barrier Coatings[J].中国航空学报（英文版）,2012(01):137-142. |
| [25] | XIE X Y,GUO H B,GONG S K,et al .Thermal cycling be havior and failure mechanism of LaTi2Al9O19/YSZ thermal bar rier coatings exposed to gas flame[J].Surface and Coatings Technology,2011,205:4291-4298.,2011. |
| [26] | XU Z H,HE L M,MU R D,et al .Double ceramiolayer ther mal barrier coatings based on La2 (Zr0.7 Ce0.3) 2O7/La2Ce2O7 de posited by electron beam physical vapor deposition[J].Applied Surface Science,2010,256(11):3661-3668.,2010. |
| [27] | WANG L,WANG Y,SUN X G,et al .Thermal shock behavior of 8YSZ and double ceramic layer La2Zr2O7/8YSZ thermal bar rier coatings fabricated by atmospheric plasma spraying[J].Ce ramics International,2012,38(5):3595-3606.,2012. |
| [28] | XU Z H,HE L M,MU R,et al .Thermal cycling behavior of YSZ and La2 (Zr0.7 Ce0.3)2O7 as double-ceramic-layer systems EBPVD TBCs[J].Journal of Alloys and Compounds,2012,525 |
| [29] | XU Z H,HE LM,MU R,et al .Double ceramic layer thermal barrier coatings of La2Zr2O7/YSZ deposited by electron beam physical vapor deposition[J].Journal of Alloys and Compounds,2009,473:509-515.,2009. |
| [30] | XU Z H,HE S M,HE L M,et al .Novelthermalbarrier coat ings based on La2 (Zr0.7 Ce0.3) 2O7/8YSZ double-ceramic-layer systems deposited by electron beam physical vapor deposition[J].Journal of Alloys and Compounds,2011,509(11):4273-4283.,2011. |
| [31] | CAO X Q,VASSEN R,TIETZ F,et al .New double ceramic layer thermal barrier coatings based on zirconia rare earth com posite oxides[J].Journal of the European Ceramic Society,2006,26(3):247-251.,2006. |
| [32] | MA W,DONG H G,GUO H B,et al .Thermal cycling behav ior of La2Ce2O7/8YSZ double-ceramic-layer thermal barrier coatings prepared by atmospheric plasma spraying[J].Surface and Coatings Technology,2010,204:3366-3370.,2010. |
| [33] | KUSANO E,KITAGAWA M,SATOH A,et al .Hardness of compositionally nano modulated TiN films[J].Nanostructured Materials,1999,12:807-810.,1999. |
| [34] | HERNANDEZ LOPEZ J L,BAUER R E,CHANG W S,et al .Functional polymers as nanoscopic building blocks[J].Materials Science and Engineering:C,2003,23:267-274.,2003. |
| [35] | LIMA R S,KUCUK A,BERNDT C C .Integrity of nanostruc tured partially stabilized zirconia after plasma spray processing[J].Materials Science and Engineering:A,2001,313:75-82.,2001. |
| [36] | KILLINGER A,GADOW R,MAUER G,et al .Review of new developments in suspension and solution precursor thermal spray processes[J].Journal of Thermal Spray Technology,2011,20(4):677-695.,2011. |
| [37] | BIANCHI L,MEILLOT E .Summary of the round table on the present and future of solution and suspension thermal spraying applications[J].Journal of Thermal Spray Technology,2012,21(6):1100-1103.,2012. |
| [38] | FAUCHAIS P,MONTAVON G .Latest developments in sus pension and liquid precursor thermal spraying[J].Journal of Thermal SprayTechnology,2010,19:226-239.,2010. |
| [39] | FAUCHAIS P,RAT V,COUDERT J F,et al .Operating pa rameters for suspension and solution plasma-spray coatings[J].Surface and Coatings Technology,2008,202(18):4309-4317.,2008. |
| [40] | Xianliang JIANG,Chunbo LIU,Feng LIN.Overview on the Development of Nanostructured Thermal Barrier Coatings[J].材料科学技术学报（英文版）,2007(04):449-456. |
| [41] | 何箐,屈轶,汪瑞军,王伟平.DZ40M合金表面纳米和垂直裂纹结构热障涂层的抗燃气热腐蚀性能[J].材料工程,2014(05):66-72,90. |
| [42] | WANG N,ZHAO W X,WANG P W,et al .To develop nano structured thermal barrier coatings[J].Journal of Modern Phys ics B,2006,20:4171-4176.,2006. |
| [43] | LIMA R S,MARPLE B R .Thermal spray coatings engineered from nanostructured ceramic agglomerated powders for structur al,thermal barrier and biomedical applications:a review[J].Journal of Thermal Spray Technology,2007,16(1):40-63.,2007. |
| [44] | LIN X H,ZENG Y,ZHOU X M,et al .Microstructure of alu mina 3wt.% titania coatings by plasma spraying with nanostruc tured powders[J].Materials Science and Engineering:A,2003,357:228-234.,2003. |
| [45] | GELL M,JORDAN E H,SOHN Y H,et al .Development and implementation of plasma sprayed nanostructured ceramic coat ings[J].Surface and Coatings Technology,2001,146 |
| [46] | LIMA R S,KUCUK A,BERNDT C C .Bimodal distribution of mechanical properties on plasma sprayed nanostructured partially stabilized zirconia[J].Materials Science and Engineering:A,2002,327(2):224-232.,2002. |
| [47] | GOBERMAN D,SOHN Y H,SHAW L,et al,Microstructure development of Al2 O3-13wt .%TiO2 plasma sprayed coatings de rived from nanocrystalline powders[J].Acta Materialia,2002,50(5):1141-1152.,2002. |
| [48] | LUO H,GOBERMAN D,SHAW L,et al .Indentation fracture behavior of plasma sprayed nanostructured Al2O3-13wt.% TiO2 coatings[J].Materials Science and Engineering:A,2003,346:237-245.,2003. |
| [49] | BANSAL P,PADTURE N P,VASILIEV A .Improved interfa cial mechanical properties of Al2O3-13wt.%TiO2 plasma-sprayed coatings derived from nanocrystalline powders[J].Acta Materia lia,2003,51(10):2959-2970.,2003. |
| [50] | LIANG B,DING C X .Phase composition of nanostructured zir conia coatings deposited by air plasma spraying[J].Surface and Coatings Technology,2005,191:267-273.,2005. |
| [51] | ZHOU Hong,LI Fei,HE Bo,WANG Jun,SUN Bao-de.Nanostructured yttria stabilized zirconia coatings deposited by air plasma spraying[J].中国有色金属学会会刊（英文版）,2007(02):389-393. |
| [52] | LIMA R S,MARPLE B R .Toward highly sintering resistant nanostructured ZrO2-7wt.%Y2O3 coatings for TBC applications by employing differential sintering[J].Journal of Thermal Spray Technology,2008,17:846-852.,2008. |
| [53] | WANG N,ZHOU C G,GONG S K,et al .Heat treatment of nanostructured thermal barrier coating[J].Ceramics Interna tional,2007,33(6):1075-1081.,2007. |
| [54] | JAMALI H,MOZAFARINIA R,RAZAVI R S,et al .Fabrica tion and evaluation of plasma-sprayed nanostructured and con ventional YSZ thermal barrier coatings[J].Current Nano science,2012,8(3):402-409.,2012. |
| [55] | GIROLAMO G D,MARRA F,BLASI C,et al .Microstruc ture,mechanical properties and thermal shock resistance of plas ma sprayed nanostructured zirconia coatings[J].Ceramics Inter national,2011,37(7):2711-2717.,2011. |
| [56] | WANG L,WANG Y,SUN X G,et al .Microstructure and in dentation mechanical properties of plasma sprayed nano bimodal and conventional ZrO2-8wt% Y2O3 thermal barrier coatings[J].Vacuum,2012,86(8):1174-1185.,2012. |
| [57] | WU Z L,NIL Y,YU Q H,et al .Effect of thermal exposure on mechanical properties of a plasma-sprayed nanostructured thermal barrier coating[J].Journal of Thermal Spray Technolo gy,2012,21(1):169-175.,2012. |
| [58] | ZHOU C G,WANG N,WANG Z B,et al .Thermal cycling life and thermal diffusivity of a plasma sprayed nanostructured ther mal barrier coating[J].Scripta Materialia,2004,51(10):945-948.,2004. |
| [59] | KEYVANI A,SAREMI M,SOHI H M .An investigation on oxidation,hot corrosion and mechanical properties of plasma sprayed conventional and nanostructured YSZ coatings[J].Sur face and Coatings Technology,2011,206:208-216.,2011. |
| [60] | JAMALI H,MOZAFARINIA R,RAZAVI R S,et al .Compar ison of thermal shock resistances of plasma-sprayed nanostruc tured and conventional yttria stabilized zirconia thermal barrier coatings[J].Ceramics International,2012,38(8):6705-6712.,2012. |
| [61] | SUN J,ZHANG L,ZHAO D .Microstructure and thermal cyc ling behavior of nanostructured yttria partially stabilized zirconia (YSZ) thermal barrier coatings[J].Journal of Rare Earths,2010,28:198-201.,2010. |
| [62] | KEYVANI A,SAREMI M,SOHI H M,et al .A comparison on thermomechanical properties of plasma-sprayed conventional and nanostructured YSZ TBC coatings in thermal cycling[J].Journal of Alloys and Compounds,2012,541 |
| [63] | YU Q H,RAUF A,WANG N,et al .Thermal properties of plasma sprayed thermal barrier coating with bimodal structure[J].Ceramics International,2011,37(3):1093-1099.,2011. |
| [64] | LIANG B,DING C X .Thermal shock resistances of nanostruc tured and conventional zirconia coatings deposited by atmospher ic plasma spraying[J].Surface and Coatings Technology,2005,197:185-192.,2005. |
| [65] | ZHOU C G,WANG N,XU H B .Comparison of thermal cyc ling behavior of plasma sprayed nanostructured and traditional thermal barrier coatings[J].Materials Science and Engineering:A,2007,452 |
| [66] | ABBAS M,GUOH B,SHAHID M R .Comparative study on effect of oxide thickness on stress distribution of traditional and nanostructured zirconia coating systems[J].Ceramics Interna tional,2013,39(1):475-481.,2013. |
| [67] | WANG X Y,ZHU Y P,DU L Z,et al .The study on porosity and thermophysical properties of nanostructured La2Zr2O7 coat ings[J].Applied Surface Science,2011,257(21):8945-8949.,2011. |
| [68] | GONG W B,SHA C K,SUN D Q,et al .Microstructures and thermal insulation capability of plasma sprayed nanostructured ceria stabilized zirconia coatings[J].Surface and Coatings Tech nology,2006,201(6):3109-3115.,2006. |
| [69] | YU Q H,RAUF A,ZHOU C G .Microstructure and thermal properties of nanostructured 4wt.% Al2O3-YSZ coatings pro duced by atmospheric plasma spraying[J].Journal of Thermal Spray Technology,2010,19(6):1294-1300.,2010. |
| [70] | YU Q H,ZHOU C G,ZHANG H Y,et al .Thermal stability of nanostructured 13wt%Al2O3-8 wt% Y2O3-ZrO2 thermal bar rier coatings[J].Journal of the European Ceramic Society,2010,30(4):889-897.,2010. |
| [71] | CHEN H,HAO Y F,WANG H Y,et al .Analysis of the mi crostructure and thermal shock resistance of laser glazed nano structured zirconia TBCs[J].Journal of Thermal Spray Technol ogy,2010,19(3):558-565.,2010. |
| [72] | CHEN D Y,JORDAN E H,GELL M .Effect of solution con centration on splat formation and coating microstructure using the solution precursor plasma spray process[J].Surface and Coatings Technology,2008,202(10):2132-2138.,2008. |
| [73] | MAX Q,ROTH J,XIAO T D,et al .Solution precursor plas ma spray:a promising new technique for forming functional nanostructured films and coatings[J].Ceramic Engineering and Science Proceedings,2008,25(4):381-387.,2008. |
| [74] | JORDAN E H,XIE L D,GELL M,et al .Superior thermal barrier coatings using solution precursor plasma spray[J].Jour nal of Thermal Spray Technology,2004,13(1):57-65.,2004. |
| [75] | XIE L D,MAX Q,JORDAN E H,et al .Deposition mecha nisms of thermal barrier coatings in the solution precursor plas ma spray process[J].Surface and Coatings Technology,2004,177 |
| [76] | XIE L D,MA X Q,JORDAN E H,et al .Identification of coat ing deposition mechanisms in the solution precursor plasma spray process using model spray experiments[J].Materials Sci enceand Engineering:A,2003,362:204-212.,2003. |
| [77] | BHATIA T,OZTURK A,XIE L D,et al .Mechanisms of ce ramic coating deposition in solution precursor plasma spray[J].Journal of Materials Research,2002,17(9):2363-2372.,2002. |
| [78] | XIE L D,MAX Q,ALPER O,et al .Processing parameter effects on solution precursor plasma spray process spray patterns[J].Surface and Coatings Technology,2004,183(1):51-61.,2004. |
| [79] | GELL M,XIE L D,MAX Q,et al .Highly durable thermal barrier coatings made by the solution precursor plasma spray process[J].Surface and Coatings Technology,2004,177 |
| [80] | XIE L D,JORDAN E H,PADTURE N P,et al .Phase and mi crostructural stability of solution precursor plasma sprayed ther mal barrier coatings[J].Materials Science and Engineering:A,2004,381:189-196.,2004. |
| [81] | CHEN D Y,GELL M,JORDAN E H,et al .Thermal stability of air plasma spray and solution precursor plasma spray thermal barrier coatings[J].Journal of the American Ceramic Society,2007,90(10):3160-3166.,2007. |
| [82] | PADTURE N P,SCHLICHTING K W,BHATIA T,et al .Towards durable thermal barrier coatings with novel microstruc tures deposited by solution precursor plasma spray[J].Acta Ma terialia,2001,49(12):2251-2257.,2001. |
| [83] | JADHAV A,PADTURE N P,WU F,et al .Thick ceramic thermal barrier coatings with high durability deposited using so lution precursor plasma spray[J].Materials Science and Engi neering:A,2005,405:313-320.,2005. |
| [84] | XIE L D,CHEN D Y,JORDAN E H,etal .Formation of ver tical cracks in solution precursor plasma sprayed thermal barrier coatings[J].Surface and Coatings Technology,2006,201:1058-1064.,2006. |
| [85] | GELL M,XIELD,JORDANEH,etal .Mechanisms of spall ation of solution precursor plasma spray thermal barrier coatings[J].Surface and Coatings Technology,2004,188 |
| [86] | WU F,JORDAN E H,MA X,et al .Thermally grown oxide growth behavior and spallation lives of solution precursor plasma spray thermal barrier coatings[J].Surface and Coatings Tech nology,2008,202(9):1628-1635.,2008. |
| [87] | PAWLOWSKI L .Finely grained nanometric and submicrometric coatings by thermal spraying:a review[J].Surface and Coatings Technology,2008,202(18):4318-4328.,2008. |
| [88] | KOZERSKI S,LATKA L,PAWLOWSKI L,et al .Preliminary study on suspension plasma sprayed ZrO2 + 8wt.% Y2O3 coat ings[J].Journal of the European CeramicSociety,2011,31(12):2089-2098.,2011. |
| [89] | PAWLOWSKI L .Suspension and solution thermal spray coat ings[J].Surface and Coatings Technology,2009,203(19):2807-2829.,2009. |
| [90] | BASU S,JORDAN E H,CETEGEN B M .Fluid mechanics and heat transfer of liquid precursor droplets injected into high-tem perature plasmas[J].Journal of Thermal Spray Technology,2008,17(1):60-72.,2008. |
| [91] | MA X Q,WU F,ROTH J,et al .Low thermal conductivity thermal barrier coating deposited by the solution plasma spray process[J].Surface and Coatings Technology,2006,201(7):4447-4452.,2006. |
| [92] | CARPIO P,RAYON E,PAWLOWSKI L,et al .Microstruc ture and indentation mechanical properties of YSZ nanostruc tured coatings obtained by suspension plasma spraying[J].Sur face and Coatings Technology,2013,220 |
| [93] | WALDBILLIG D,KESLER O .Effect of suspension plasma spraying process parameters on YSZ coating microstructure and permeability[J].Surface and Coatings Technology,2011,205:5483-5492.,2011. |
| [94] | TINGAUD O,BERTRAND P,BERTRAND G .Microstructure and tribological behavior of suspension plasma sprayed Al2O3 and Al2O3 YSZ composite coatings[J].Surface and Coatings Technology,2010,205(4):1004-1008.,2010. |
| [95] | VANEVERY K,KRANE M J,TRICE R W .Parametric study of suspension plasma spray processing parameters on coating mi crostructures manufactured from nanoscale yttria stabilized zir conia[J].Surface and Coatings Technology,2012,206:2464-2473.,2012. |
| [96] | VAβEN R,KAβNER H,MAUER G,et al .Suspension plasma spraying:process characteristics and applications[J].Journal of Thermal SprayTechnology,2010,19:219-225.,2010. |
| [97] | STUKE A,KASSNER H,MARQUIS J L,et al .Suspension and air plasma sprayed ceramic thermal barrier coatings with high infrared reflectance[J].International Journal of Applied Ceramic Technology,2012,9(3):561-574.,2012. |
| [98] | GUIGNARD A,MAUER G,VAβEN R,et al .Deposition and characteristics of submicrometer structured thermal barrier coat ings by suspension plasma spraying[J].Journal of Thermal Spray Technology,2012,21:416-424.,2012. |
| [99] | TARASI F,MEDRAJ M,DOLATABADI A,et al .Phase for mation and transformation in alumina/YSZ nanocomposite coat ing deposited by suspension plasma spray process[J].Journal of Thermal SprayTechnology,2010,19(4):787-795.,2010. |
| [100] | TARASI F,MEDRAJ M,DOLATABADI Aet al .Enhance ment of amorphous phase formation in alumina YSZ coatings deposited by suspension plasma spray process[J].Surface and Coatings Technology,2013,220 |
| [101] | TARASI F,MEDRAJ M,DOLATABADI A,et al .Amor phous and crystalline phase formation during suspension plasma spraying of the alumina zirconia composite[J].Journal of the European Ceramic Society,2011,31(5):2903-2913.,2011. |
| [102] | CHEN D Y,JORDAN E H,GELL M .Suspension plasma sprayed composite coating using amorphous powder feedstock[J].Applied SurfaceScience,2009,255(11):5935-5938.,2009. |
| [103] | BERGHAUS J O,MARPLE B R .High velocity oxy fuel (HVOF) suspension spraying of mullite[J].Journal of Ther malSprayTechnology,2008,17:671-678.,2008. |
| [104] | GADOW R,KILLINGER A,RAUCH J .New results in high velocity suspension flame spraying (HVSFS)[J].Surface and CoatingsTechnology,2008,202(18):4329-4336.,2008. |
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