《功能材料制備與成形》課件塊體金屬納米材料的制備

1、2022/7/6納米材料的制備第十章2022/7/610.1、氣相法制備納米材料第十章2022/7/6氣體冷凝法：是指在低壓惰性氣體中將金屬加熱，使其蒸發(fā)后形成超微粒（11000nm）或納米微粒，然后冷凝為納米級(jí)的粉末顆粒的方法。10.1 低壓氣體蒸發(fā)法（氣體冷凝法）2022/7/6按照熱源：1）電阻加熱法；2）等離子噴射法；3）高頻感應(yīng)法；4）電子束法；5）激光法。10.1 低壓氣體蒸發(fā)法（氣體冷凝法）氣體冷卻法制備1）金屬粉末：Cu、 Al、。2）化合物粉末： TiN， AlN、。10.1 低壓氣體蒸發(fā)法（氣體冷凝法）2022/7/6影響粉末粒度的因素： 1）氣體壓力； 2）冷卻條件；10

2、.1 低壓氣體蒸發(fā)法（氣體冷凝法）惰性氣體的壓力，P平均顆粒直徑，nm2022/7/6 用兩塊金屬板分別作為陽(yáng)極和陰極，在兩電極間施加電壓0.31.5kV，在兩電極間充Ar氣，電場(chǎng)的作用下兩極間的Ar被離子化形成輝光放電，沖擊陰極靶材使靶材原子從其表面蒸發(fā)出來(lái)形成納米顆粒。10.2 濺射法蒸發(fā)材料電極板蒸發(fā)離子2022/7/610.2 塊體納米材料的制備第十章一、過(guò)冷金屬的晶粒細(xì)化機(jī)理什么是過(guò)冷金屬的晶粒細(xì)化? 當(dāng)金屬熔體過(guò)冷凝固時(shí)，其晶粒尺寸取決于過(guò)冷度 T=Tl - T. 對(duì)于 T T*, 晶粒尺寸發(fā)生超過(guò)幾個(gè)數(shù)量級(jí)的減小。T*臨界過(guò)冷度。 Walker(1959) 金屬Ni 過(guò)冷凝固時(shí)，

3、當(dāng) T T * =162KWhere T * is the critical undercooling for grain refinement of undercooled molten Ni Kattamis and Fleming(1970)晶粒細(xì)化在 Fe基和Ni基金屬與合金中出現(xiàn),Devaud and Turnbull (1987), Lau and Kui(1991)Grain refinement exists in semiconducting system Ge枝晶重熔（Re-melting): K.A. Jackson, J.D. Hunt. D.R. Uhlmann, a

4、nd T.P.Seward III Melt-back by composition inhomogeneity and capillarity effect M. Schwarz, A. Karma, K. Eckler, and D.m.Herlach動(dòng)力學(xué)形核（Dynamic nucleation）: G. Horvey: Proposal that the grain refinement may be induced by dynamic uncleation.晶粒細(xì)化機(jī)理（Mechanisms of Grain refinement） 實(shí)驗(yàn)過(guò)程 Materials:NiB0.1:

5、Pure Ni( 99.999%) and pure B(99.999%)Ni70Cu30: Pure Ni(99.999%) and pure Cu (99.99%)Experimental Procedure:實(shí)驗(yàn)結(jié)果Results and Disccusion 1. NiB 0.1 2. Ni70Cu30 Average grain size as a function as undercooling in Ni99.9 B0.1Fig. 2a Microstructure of an undercooled specimen with T = 70K, T = 70K, Fig. 2b

6、 Microstructure of an undercooled specimen with T = 119.6K. Refined equiaxed grains occupy a small region on the left of the micrograph at R1. The grain size then increases continuously as one moves to the right.T = 119.6KFig. 2c Microstructure of an undercooled specimen with T = 131.8K. The refined

7、 equiaxed grains (marked by R2) occupy a larger volume fraction comparing with that in Fig.2bT = 131.8KFig. 2d Microstructure of an undercooled specimen with T = 155.6K. It depicts the refinement has undergone completely. The entire cross-section is occupied by refined equiaxed grains. T = 155.6KFig

8、. 3a Microstructure of an undercooled specimen with T = 189.1K. It consists of large fan-shape grains. Grain refinement has not occurred yet. T = 189.1KFig. 3b Microstructure of an undercooled specimen with T = 189.6K. Grain refinement has already occurred at the left hand corner marked by D1. The r

9、est of the undercooled specimen consists of large fan-shape grains. The site of initial crystallization is at C1T = 189.6KFig. 3c Microstructure of an undercooled specimen with T = 190.1K. The equiaxed grains region (marked by D2) has enlarged comparing that in Fig.3b. T = 190.1KFig 3d Microstructur

10、e of an undercooled specimen with T = 190.6K. The region of refined equiaxed grains has almost enlarged to the entire undercooled specimen. The initial site of crystallization is at D3T = 190.6KFig. 3e Microstructure of an undercooled specimen with T = 191.3K. The grain refinement process has comple

11、tedT = 191.3K2 Ni70Cu30Microstructure of an undercooled apecimen with T = 129K.Microstructure of an undercooled apecimen with T = 138K.Microstructure of an undercooled apecimen with T = 211K.Microstructure of an undercooled apecimen with T = 138K.Microstructure of an undercooled apecimen with T = 15

12、5K.Microstructure of an undercooled apecimen with T = 153K.Microstructure of an undercooled apecimen with T = 153K.Microstructure of an undercooled apecimen with T = 153K.Microstructure of an undercooled apecimen with T = 153K. 結(jié)論 Ni99.9B0.1.發(fā)生了兩種方式的晶粒細(xì)化 當(dāng)T = 112.2K時(shí)，由于柱狀晶的重熔而產(chǎn)生的晶粒細(xì)化 當(dāng)T = 190.2K時(shí)，發(fā)生

13、了動(dòng)力學(xué)形核而產(chǎn)生的晶粒細(xì)化 Ni70Cu30 合金的晶粒細(xì)化機(jī)理 由于枝晶重新熔化而造成的晶粒細(xì)化。 共晶合金的晶粒細(xì)化2022/7/6當(dāng)共晶合金的過(guò)冷度達(dá)到一定的程度時(shí)，會(huì)后發(fā)生晶粒細(xì)化?如果細(xì)化，其行為怎樣？納米材料（Nanostructured materials） Gleiter: 首先通過(guò)快速凝固方法制備納米塊體材料2022/7/6 Powder sintering（粉末燒結(jié)） Thermal annealing of glassy metals（金屬玻璃的退火處理）Nanostructured materials have been Synthesized mainly by t

14、wo methods: Powder sintering （粉末燒結(jié)）As-prepared nanometer powders are compacted together and sometimes annealed at an elevated temperature to product bulk nanostructured materials dimension : f10mm 12mmTwo drawbacks: - There are many residual microvoids; - if the thermal annealing is also employed. N

15、onuniform grain growth easily occurs 2022/7/6Thermal annealing of an amorphous metal（金屬玻璃的退火結(jié)晶）W.L.Johnson et. al. and others They found nanocrystals dispersed in the amorphous matrix by annealing an amorphous specimen. 2022/7/6The drawback of this synthesis: 晶粒尺寸分布不均，有大有小. 而且容易晶粒長(zhǎng)大。 思路 對(duì)于共晶合金 當(dāng)液體過(guò)冷

16、至共晶溫度以下，由于具有不同固態(tài)晶體結(jié)構(gòu)的原子，它們?cè)噲D分別按照其自身的晶體結(jié)構(gòu)結(jié)晶，因此它們?cè)诮Y(jié)晶之前，將發(fā)生液相相分離（liquid-phase separation ，LPS) L0 L1 + L2 2022/7/6L0AB%BTL1L2Phase boundarySpinodal lineLSDLNGIf composition is also allowed to vary, a liquid miscibility gap can be traced out. 思路LPS 有兩種可能 2022/7/6L1L2AAB%BPhase boundarySpinodal lineLSDLN

17、GTBFree EnergyT0Liquid phase nuclea-tion and growth(LNG)- Liquid phase spinodal decomposition(LSD) 可能形成相互交叉的液相網(wǎng)狀?？赡苄纬蓫u狀的球形形貌 思路2022/7/6L1L2L0AB%BTPhase boundarySpinodal lineLSD J.W. Cahn 曾預(yù)測(cè) l (T )-1/2 l = 液相網(wǎng)絡(luò)的波長(zhǎng)T = 過(guò)冷度 因此，當(dāng)過(guò)冷度足夠大， l可能達(dá)到納米級(jí)，則可能結(jié)晶稱為納米塊體的材料。 Lee et. al. (J.Mater. Res. 13 3034(1998) 當(dāng)

18、 Pd80Si20 合金熔體過(guò)冷到其液相線以下時(shí)，發(fā)現(xiàn)其將發(fā)生液相的相分離，而且當(dāng)T = 240 K 時(shí)，其過(guò)冷液相 = 0.8m。2022/7/6 Yuen. et. al.(J. Mater. Res. 12. 314(1997)The molten PdNiP alloy also undergoes liquid phase spinodal decomposition deep in the undercooling regime. At T = 100K, l = 350nm, At T = 150K, l = 150nm.2022/7/6Therefore, l decrease

19、s rapidly with T 2. 實(shí)驗(yàn)過(guò)程Pd82Si18 合金制備2022/7/6高溫處理Tl過(guò)冷Tm過(guò)冷處理 at T for 912min晶屆TEM,SEM and X-ray 檢查High temperature furnace2022/7/62022/7/6TTime, min 4hrs 912minTm=1133KTm + 200KTT=Tm-T10K/minFig. 2 Heat treatment curve of undercooled specimen Crystallization peak3. RESULTS AND DISCUSSIONS2022/7/6Fig.

20、 3 A SEM micrograph displaying the morphologies of an undercooled specimen (T=280K) that had undergone liquid phase spinodal decomposition. There are two networks that are traced out by solid lines (l= 2.5mm)Pd3Si + Pd9Si2Pd + Pd9Si2T=280KFig. 4 A SEM micrograph depicting the spinodal network of an

21、undercooled specimen with T=320K. The liquid of networks have partially broken up. (l =120nm)2022/7/62022/7/6Fig.5 A TEM micrograph showing the microstructure of an undercooled specimen with T=320K(annealing time is 11min), it shows that the network is partial breaken up 2022/7/6 Compare these two p

22、ictures, since connectivity of the two networks has reduced substantially, it is apparent that an annealing period of 912min is already effective in breaking up the liquid networks for an undercooled specimen with T=320K.l=2.5ml=120nm2022/7/6Fig. 6 A TEM micrograph illustrating the microstructures o

23、f an undercooled specimen with T=350K. The constituent grains of the undercooled specimen are more or less granular, grain size 60nmPd3SiPdPd9Si2Fig. 8 Average grain size vs undercooling2022/7/6Networkgranular2022/7/6Fig. 7 A TEM micrograph illustrating the microstructures of an undercooled specimen with T=350K. Annealing period =21min. Average grain size is 70nm.It consists of more or less very fine equiaxed grains. Pd3SiPd9Si2PdFig. 9. A TEM dar