材 料 科 學(xué) 與 工 程 前 沿

1、材 料 科 學(xué) 與 工 程 前 沿航空航天高溫結(jié)構(gòu)材料High-Temperature Structural Materials in Aerospace北京航空航天大學(xué) 材料學(xué)院六、Nb-Si基高溫合金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具有良好的室溫塑韌性，機(jī)械加工性和高的熔點(diǎn)（2447C，超過Ni約1000C)，以及熱傳導(dǎo)率大, 熱膨脹系數(shù)小, 彈性系數(shù)大, 密度小, 到熔點(diǎn)都保持穩(wěn)定b.c.c.承溫能力：

4、12001700C.可以采用多種方式強(qiáng)化、韌化和改善抗氧化 性:1、強(qiáng)化 Nb及合金的特點(diǎn)固溶強(qiáng)化 Mo, W, Hf, Cr, Al, Si 等能與Nb形成置 換固溶體，W、Mo最強(qiáng)金屬間化合物NbSS/Nb3Al (Nb-Al二元合金)和 NbSS/Nb5Si3（Nb-Si二元合金)， NbSS 提供韌性而Nb3Al和Nb5Si3提供高溫強(qiáng)度 韌/脆兩相結(jié)構(gòu)，NbSS：Solid solution，固溶體特殊熱加工定向凝固（DS: directional solidification），熱等靜壓(HIP: hot isostatic pressing), 熱擠出（HE: hot extru

5、sion), 粉末冶金等 Nb及合金的特點(diǎn)2、 韌化 合金化-Hf、Ti元素對(duì)NbSS韌化 減少Si含量-Si減少， Nb5Si3減少，塑韌性上升 改變組織形態(tài)-Mo，W等元素傾向形成片狀組 織改善NbSS和Nb5Si3形態(tài) 3、抗氧化：基體抗氧化+涂層 Cr-NbCr2有利于抗氧化 Si-SiO2有利于抗氧化，Ti有利于抗氧化 Nb及合金的特點(diǎn)合金元素對(duì)Nb性能的影響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）航空領(lǐng)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 國(guó)內(nèi)外研究現(xiàn)狀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國(guó)內(nèi)外研究現(xiàn)狀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國(guó)內(nèi)外研究現(xiàn)狀高溫強(qiáng)度室溫?cái)嗔秧g性高溫抗氧化性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、組織和性能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鑄態(tài)相組成與微觀組織與Si和Cr的關(guān)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.氧化動(dòng)力學(xué)曲線Solidification paths of Nb-Si and Nb-Si-Mo Nb-Si NbSS +Nb3SiNbSS+Nb5Si3Nb-Si-Mo EutecticEutectoidEutectic structure NbSS/Nb5Si3組織控制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室溫彎曲斷裂形貌NbSS/Nb5Si310mm(h)100mm20mm20mm(g)Bridging ligamentBranching Ma

20、in crackMain crackNb5Si3Nb5Si3Nb5Si3Nb5Si3Cr2NbCr2NbCr2NbCr2NbNb5Si3Nb5Si3Nb5Si3NbSSNbSSAABBCCCC室溫彎曲斷裂形貌NbSS/Nb5Si3/Cr2Nb橋接、分叉，界面分離、繞過機(jī)制(a)(b)(c)(d)AABBNb5Si3Nb5Si3Nb5Si3Nb5Si3Cr2NbNb5Si3Cr2NbCollapsed Nb5Si3Crack BCrack CCrack A高溫壓縮斷裂形貌硅化物壓塌，裂紋在硅化物內(nèi)或界面擴(kuò)展Cast blades of Nb-16Si-22Ti-2Cr-2Al-2HfGE公司制備

21、的Nb-Si超高溫金屬間化合物高溫結(jié)構(gòu)材料的葉片目前還沒有裝機(jī)試車的報(bào)道預(yù)計(jì)2012年出現(xiàn)低壓渦輪葉片，2015年出現(xiàn)更復(fù)雜的高壓渦輪葉片室溫塑性和強(qiáng)韌性匹配；抗氧化性和涂層設(shè)計(jì)；定向凝固葉片加工技術(shù)。 進(jìn)一步開展的工作七、Ir基高溫合金Ir的一般特性金屬Ir ：熔點(diǎn)高，比重大，原子鍵結(jié)合力強(qiáng), 組織穩(wěn)定，有一定的塑韌性. 易于加工.第五周期的過度族元素，晶體結(jié)構(gòu)fcc，比重22.4g/cm3,熔點(diǎn)2716K，價(jià)格高，120140元/克航天領(lǐng)域上的應(yīng)用適合于19002200C之間液態(tài)火箭使用的是Ir/Re雙層結(jié)構(gòu)，Re合金（Re-W，-Mo 熔點(diǎn)2500C2800C）上涂一層5075m的Ir;

22、Ir的作用：高熔點(diǎn)不熔化，抗氧化性好！良好的物理和冶金性能，一定的力學(xué)性能。為什么要提高火箭的燃燒溫度？推進(jìn)器的理想火焰溫度為2500C3000C，才能使比沖(specific impulse)達(dá)到最大（單位質(zhì)量推進(jìn)劑推力對(duì)時(shí)間的積分），有效載荷增大，效率高。比沖提高1%，火箭有效承載能力提高7%。經(jīng)過一定的冷卻措施和采用還原性富燃燃?xì)猸h(huán)境(非標(biāo)準(zhǔn)化學(xué)當(dāng)量的燃料) ，燃燒室壁材料的使用溫度在19002200C 。Ir/Re結(jié)構(gòu)進(jìn)展：用化學(xué)方法溶去內(nèi)芯得到Ir/Re雙層結(jié)構(gòu)比沖比Silicide/Nb的高2.56.9%，有效承載能力高1750%，遠(yuǎn)地點(diǎn)軌道發(fā)動(dòng)機(jī)的累積點(diǎn)火時(shí)間已達(dá)14000秒，地

23、面實(shí)驗(yàn)累積點(diǎn)火時(shí)間已達(dá)21000秒 Mo or C 內(nèi)芯CVD法沉積5075m的Ir內(nèi)襯CVD法沉積Re合金外層Ir與過度金屬的相圖Ir-NbIr-ZrIr-HfIr-TaIr與過度金屬的相圖相變和組織特征1、與Hf、Zr、Nb和Ta發(fā)生共晶反應(yīng)，共晶溫度2100C以上；2、共晶反應(yīng)為 L IrSS + Ir3Me （共格關(guān)系）IrSS：Ir的固溶體，f.c.cIr3Me: Ir與金屬M(fèi)e之間的金屬間 化合物，具有L12結(jié)構(gòu)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