材 料 科 学 与 工 程 前 沿

1、材 料 科 学 与 工 程 前 沿航空航天高温结构材料High-Temperature Structural Materials in Aerospace北京航空航天大学 材料学院六、Nb-Si基高温合金T/W ratio 20Wrought superalloyCast superalloyDS- superalloySingle-cystal superalloy13206508501050125014501650T/W ratio 8T/W ratio 10T/W ratio 1519401960198020002020TemperatureWhat materials could be

2、 qualified？T/W :Thrust to Weight Ratio for Aero-Engine Superalloy can not meet design requirements of aeroenginesCeramics matrix composites Good strength and oxidation resistance at HT; Brittle, difficult to processC/C composites Low density, good strength at HT; Poor oxidation resistance & Difficul

3、t to processNb/Si based intermetallics (composites) Good formability, and Comprehensive advantage in mechanical performance at HT Poor ductility and oxidation resistance Potential candidates are as follows元素周期表Nb具有良好的室温塑韧性，机械加工性和高的熔点（2447C，超过Ni约1000C)，以及热传导率大, 热膨胀系数小, 弹性系数大, 密度小, 到熔点都保持稳定b.c.c.承温能力：

4、12001700C.可以采用多种方式强化、韧化和改善抗氧化 性:1、强化 Nb及合金的特点固溶强化 Mo, W, Hf, Cr, Al, Si 等能与Nb形成置 换固溶体，W、Mo最强金属间化合物NbSS/Nb3Al (Nb-Al二元合金)和 NbSS/Nb5Si3（Nb-Si二元合金)， NbSS 提供韧性而Nb3Al和Nb5Si3提供高温强度 韧/脆两相结构，NbSS：Solid solution，固溶体特殊热加工定向凝固（DS: directional solidification），热等静压(HIP: hot isostatic pressing), 热挤出（HE: hot extru

5、sion), 粉末冶金等 Nb及合金的特点2、 韧化 合金化-Hf、Ti元素对NbSS韧化 减少Si含量-Si减少， Nb5Si3减少，塑韧性上升 改变组织形态-Mo，W等元素倾向形成片状组 织改善NbSS和Nb5Si3形态 3、抗氧化：基体抗氧化+涂层 Cr-NbCr2有利于抗氧化 Si-SiO2有利于抗氧化，Ti有利于抗氧化 Nb及合金的特点合金元素对Nb性能的影响1、Nb-Si binary diagram Nb5Si3High melting point: 2520 CModerate density: 6.1 gcm-3Toughness: KIC= 13 MPam1/2NbSSGo

6、od ductility at RTNbSS + Nb5Si3Alloys with NbSS and Nb5Si3:Can be stable up to very high temperature ( 1670C)（一）航空领域中使用的Nb-Si合金Nb-18Si-15W-10Mo-10Ti (AIST, JUTEMI and TOHUKU Uni. In Japan)Target Appl. Temperature: 1500CAlloyed with high W and MoHigh strength: 650MPa at 1500C Poor toughness, ductilit

7、y and oxidation resistanceHigh density:910 g/cm3 国内外研究现状Nb-24.7Ti-16Si-8.2Hf-2.0Cr-1.9AlTarget Appl. Temperature: 1200CAlloyed with high Ti and HfHigh toughness: 20MPam1/2Low creep rateLow density: 6.58 g/cm3Poor oxidation resistance国内外研究现状Nb-18Ti-17.22Si-8.7Hf-20Cr-2.5AlTarget Appl. Temperature: 12

8、00CAlloyed with high Cr and TiGood oxidation resistance Low density: 6.57.5 g/cm3Poor mechanical properties国内外研究现状高温强度室温断裂韧性高温抗氧化性Balance the toughness, strength and oxidation resistance by optimizing and controlling microstructure of NbSS, Silicide and Cr2Nb phasesNb-Si based alloysNbSS- Toughness

9、at RTNb5Si3- Strength at HTCr2Nb- Oxid. Resist. Our work on Nb-Si based alloys focus: Target Appl. Temperature: 1250C1350C To balance the toughness, strength & oxidation resistance Application: Vane of aero-engineR & D of Nb-Si based alloys in present workNb-Si-Ti-Cr系合金宏合金化、组织和性能Typical compositions

10、 of studied alloys: Based on Nb-Si-Ti phase diagram, Cr is added to investigate relationship between composition and phases of NbSS、Nb5Si3 and Cr2Nb, and optimize phases constitution and proportion Ti：22 at%, toughening Nb and decreasing eutectoid temperature of Nb3Si NbSS+Nb5Si3;Si ：12 at% 16at%，hy

11、po-eutectic, avoid large primary Nb5Si3;Cr：2 at% 17 at%，determining phase evolution of NbSS/Nb5Si3/Cr2Nb;Assistant elements：2Hf + 2Al;Compositions: Nb-(12,14,16)Si-22Ti-2Hf-2Al-(2,6,10,14,17)Cr Tri-phase NbSS+Nb5Si3+Cr2 Nb obtained with Cr 6 at.% NbSS+Nb5Si3+Nb3SiNbSS+Nb5Si3+Cr2NbNbSS+Nb5Si3+Cr2NbNb

12、SS+Nb5Si3+Cr2NbNbSS+Nb5Si3+Cr2NbNbSS+Nb5Si3+Cr2NbNbSSTypical Microstructures of as-cast 16 at% Si alloys with different Cr content16Si-2Cr(a)16Si-17Cr(f)16Si-6Cr(b)16Si-10Cr(c)16Si-14Cr(d)16Si-14Cr(e)16Si-14Cr(e)12Si-2Cr(a)14Si-6Cr(e)14Si-2Cr(d)12Si-17Cr(c)12Si-10Cr(b)14Si-17Cr(f)14Si-17Cr(f)Nb3SiEu

13、tectic of NbSS+Nb5Si3Typical Microstructures of as-cast 12, 14 at% Si alloys with different Cr contentTri-phase NbSS+Nb5Si3+Cr2 Nb obtained with Si+Cr 21 at.% 16Si-2Cr16Si-6Cr(a)(b)16Si-10Cr(c)16Si-14Cr16Si-17Cr16Si-17Cr(d)(f)(e)Typical Microstructures of heat-treated 16 at% Si alloys with different

14、 Cr content16Si2Cr 6Cr 10Cr 14Cr 17Cr14Si12SiAbbreviations: Slab (S), Block (B), Particle (P), Dendritic(D), Colony (C), Eutectic of NbSS+Nb5Si3 (EU), Matrix (M) Line 2Nb5Si3 initiationNbSS(D)+Nb3Si(M)EU (C)Line 3 Nb3Si endingNbSS(D)+Nb3Si+EU (C)NbSS(D) + Mixture EU(C)+Cr2Nb(P)NbSS(D)+Nb5Si3(M)+EU(C

15、) Line 1Cr2Nb initiation Hyper-eutectic-like regionNb5Si3(B/S) + Mixture Nb5Si3 (P) + Cr2Nb(P) + NbSS (P) Line 4 Eutectic-like composition Mixture EU (C)+Cr2Nb(P) 2Cr 6Cr 10Cr 14Cr 17CrFig. 10 Schematic maps of phases evolution under as-cast (a) and heat treated (b) conditions铸态相组成与微观组织与Si和Cr的关系1250

16、C14Si-xCr HT16Si-xCr HT12Si-xCr HT0.2% yield strength increases with an increasing Si content, and a decreasing Cr content; 2. The strength of 16Si-2Cr is the maximum, about 320MPa at 1250C.KQ decreases with an increasing Si and Cr contents, and heat treatment improves fracture toughness;2. Heat-tre

17、ated alloy with 2% Cr shows the best toughness, 1415 MPam1/2 14Si-xCr HT16Si-xCr HT12Si-xCr HT14Si-xCr AC16Si-xCr AC12Si-xCr ACWeight change shows a decreasing tendency with an increasing Cr content16Si-17Cr shows the minimum weight change of about 50mg/cm2 for 100hThe weight gain of the substrate w

18、ith Mo(Al,Si)2 coating is 7.8 mg/cm2 after oxidation for 100 h.氧化动力学曲线Solidification paths of Nb-Si and Nb-Si-Mo Nb-Si NbSS +Nb3SiNbSS+Nb5Si3Nb-Si-Mo EutecticEutectoidEutectic structure NbSS/Nb5Si3组织控制Alloying with Mo changes the solidification paths and results in the formation of NbSS/Nb5Si3 lamel

19、lar structureMoe1p1e2p2-(Nb,Mo)5Si3NbssNbDS eutectic structures of NbSS/Nb5Si3Growth directionFull lamellated eutectic of NbSS/Nb5Si3 in Nb-18Si-10Mo alloy can obtained by directional solidification (Growth rate: 5mm/h)NbSSNb5Si3室温弯曲断裂形貌NbSS/Nb5Si310mm(h)100mm20mm20mm(g)Bridging ligamentBranching Ma

20、in crackMain crackNb5Si3Nb5Si3Nb5Si3Nb5Si3Cr2NbCr2NbCr2NbCr2NbNb5Si3Nb5Si3Nb5Si3NbSSNbSSAABBCCCC室温弯曲断裂形貌NbSS/Nb5Si3/Cr2Nb桥接、分叉，界面分离、绕过机制(a)(b)(c)(d)AABBNb5Si3Nb5Si3Nb5Si3Nb5Si3Cr2NbNb5Si3Cr2NbCollapsed Nb5Si3Crack BCrack CCrack A高温压缩断裂形貌硅化物压塌，裂纹在硅化物内或界面扩展Cast blades of Nb-16Si-22Ti-2Cr-2Al-2HfGE公司制备

21、的Nb-Si超高温金属间化合物高温结构材料的叶片目前还没有装机试车的报道预计2012年出现低压涡轮叶片，2015年出现更复杂的高压涡轮叶片室温塑性和强韧性匹配；抗氧化性和涂层设计；定向凝固叶片加工技术。 进一步开展的工作七、Ir基高温合金Ir的一般特性金属Ir ：熔点高，比重大，原子键结合力强, 组织稳定，有一定的塑韧性. 易于加工.第五周期的过度族元素，晶体结构fcc，比重22.4g/cm3,熔点2716K，价格高，120140元/克航天领域上的应用适合于19002200C之间液态火箭使用的是Ir/Re双层结构，Re合金（Re-W，-Mo 熔点2500C2800C）上涂一层5075m的Ir;

22、Ir的作用：高熔点不熔化，抗氧化性好！良好的物理和冶金性能，一定的力学性能。为什么要提高火箭的燃烧温度？推进器的理想火焰温度为2500C3000C，才能使比冲(specific impulse)达到最大（单位质量推进剂推力对时间的积分），有效载荷增大，效率高。比冲提高1%，火箭有效承载能力提高7%。经过一定的冷却措施和采用还原性富燃燃气环境(非标准化学当量的燃料) ，燃烧室壁材料的使用温度在19002200C 。Ir/Re结构进展：用化学方法溶去内芯得到Ir/Re双层结构比冲比Silicide/Nb的高2.56.9%，有效承载能力高1750%，远地点轨道发动机的累积点火时间已达14000秒，地

23、面实验累积点火时间已达21000秒 Mo or C 内芯CVD法沉积5075m的Ir内衬CVD法沉积Re合金外层Ir与过度金属的相图Ir-NbIr-ZrIr-HfIr-TaIr与过度金属的相图相变和组织特征1、与Hf、Zr、Nb和Ta发生共晶反应，共晶温度2100C以上；2、共晶反应为 L IrSS + Ir3Me （共格关系）IrSS：Ir的固溶体，f.c.cIr3Me: Ir与金属Me之间的金属间 化合物，具有L12结构Ni-based superalloys (widely used)Pt-based superalloysMetals-based Superalloys that ha

24、ve been used in high temperature area are as follows: The main characterizations in the microstructure and strengthening behavior are as follows: the microstructure is composed of coherent g(f.c.c)/ g(L12), where the g is Ni or Pt solid solution, and the gis intermetallics Ni(Pt)3Al with an L12 stru

25、cture, 2) the g is matrix and the gis strengthening phase, 3) the high-temperature strength reaches the peak value when the volume fraction of the strengthening phase gis in a range of 6070%, and 4) the strengthening mechanisms involve in the solid solution, coherent and precipitating hardening. App

26、lication Temperature: Below 1200CIr based solid Solution, IrSSIrSS + Ir3HfIr3HfStrengthening mechanism: Solid solution and coherent What kind of metal-based superalloy could be qualified for temperatures larger than 1800C？Alloying and Microstructure DesignWhat kind of alloying elements are Potential

27、 candidates to make the solid solution hardening and coherent hardening effect as stronger as possible?Hf, Zr and Nb etc.,Large atomic radius difference between Ir and Hf, Zr, Nb: 416%Crystal structure difference: Ir (f.c.c), Hf (h.c.p), Zr and Nb (b.c.c)Limited solubility of Hf, Zr and Nb in IrLarg

28、er lattice parameter misfit between coherent structure of f.c.c and Ir3Hf/Ir3Zr/Ir3NbHigh temperature propertiesMost of Ir-based alloys with an L12 phase-dominant f.c.c/L12 dual-phase microstructure, which is as same as the microstructure of Ni-based superalloys0.2% yield strength 5001000MPa below 1

29、200C 200MPa at 1800C for Ir-Zr and Ir-Hf alloysThe HT strength is not high enoughThere may be some different strengthening mechanisms between Ir and Ni and Pt, to understand the difference, following issues should be study: 1) Which one is strengthening phase, L12 or f.c.c? 2) How many strengthening

30、 phase in a dual-phase fcc/L12 structure can obtain the highest strength at the elevated temperaturesIdea for design of Ir-based alloysMulti-component alloying alloying element =2, large size misfit parameter and small solubility limitation)Hf, ZrMicrostructure : Monolithic f.c.cf.c.c/L12 dual-phase

31、 structure with various phase fraction, monolithic L12Ir-3Hf-3Zr - saturated monolithic Ir f.c.c Ir-4Hf-4Zr - dual-phase f.c.c/L12 structureIr-5Hf-5Zr - dual-phase f.c.c/L12 structure Ir-7Hf-7Zr - dual-phase f.c.c/L12 structure Ir-15Hf-5Zr - dual-phase f.c.c/L12 structureIr-15Hf-10Zr - monolithic L1

32、2Typical compositions of studied alloys:Works on： Microstructual evolution as a function Hf and Zr conntents Strength at HT as a function of phase volume fraction Phases constitution0100200300400500600700204060801001202?INTENSITY, I/cps, 100Ir-3Hf-3ZrIr-7Hf-7ZrIr-15Hf-15Zrf.c.cL12Fig. 3 X-ray diffra

33、ction patterns of the Ir-Hf-Zrternary alloys heat-treated at 2000C for 24 hoursIr-15Hf-10ZrAverage lattice misfit between f.c.c and L12:1.61%Ir-3Hf-3ZrIr-15Hf-10ZrIr-5Hf-5ZrIr-15Hf-5ZrIr-4Hf-4Zr(a)(b)(c)(f)(e)L12L12L12L12L12(d)Ir-7Hf-7ZrMicrostructureIsothermal section of Ir-Hf-Zr ternary at 2000 C AlloyIr-3Hf-3ZrIr-4Hf-4ZrIr-5Hf-5ZrIr-7Hf-7ZrIr-15Hf-5ZrIr-15Hf-10ZrHV834760702665442408DEV35.122.419.825.138.928.7Table 1 Vickers hardness of the Ir