放電等離子燒結(jié)和快速熱壓工藝制備具有低或負(fù)熱膨脹系數(shù)鎢酸鋯塊體_英文_

1、GRIMA Joseph N 等:具有潛在負(fù)熱膨脹性和負(fù)壓縮性的三角形構(gòu)筑模塊的有限元分析 · 749 ·第 37卷第 5期放電等離子燒結(jié)和快速熱壓工藝制備具有低或負(fù)熱膨脹系數(shù)鎢酸鋯塊體NEUBAUER Erich1, GA VRILOVI Aleksandra2, ANGERER Paul2(1. 奧地利研究中心 (ARC,塞伯斯多夫 A-2444,奧地利; 2. 電化學(xué)表面技術(shù)中心 (CEST,維也納新城 A-2700,奧地利 摘 要:采用快速熱壓工藝 (放電等離子燒結(jié)和感應(yīng)加熱熱壓 ,利用 ZrW 2O 5粉料制備了負(fù)熱膨脹系數(shù) (coefficient of the

2、rmal expansion, CTE 鎢酸鋯 (ZrW2O 8 陶瓷體材料。這兩種工藝可在燒結(jié)過(guò)程中保留負(fù) CTE 材料鎢酸鋯所需的結(jié)構(gòu)和相組成。結(jié)果表明:改變工藝參數(shù),如熱壓溫度和保溫時(shí)間, 可以調(diào)節(jié) ZrW 2O 8陶瓷的 CTE 從 9×106/K到 +9×106/K變化。首次采用 ZrW 2O 8作為填料與輕金屬鈦復(fù)合制備了零膨脹復(fù)合材料。關(guān)鍵詞:鎢酸鋯;體材料;負(fù)熱膨脹材料;放電等離子燒結(jié)技術(shù);感應(yīng)加熱熱壓工藝;金屬基復(fù)合材料中圖分類號(hào):TB321 文獻(xiàn)標(biāo)志碼:A 文章編號(hào):04545648(200905074906BULK ZIRCONIUM TUNGSTAT

3、E WITH A LOW OR NEGATIVE COEFFICIENT OF THERMAL EXPAN-SION PREPARED BY SPARK PLASMA SINTERING AND RAPID HOT PRESSING PROCESSES NEUBAUER Erich1, GAVRILOVI Aleksandra2, ANGERER Paul2(1. Austrian Research Centers GmbH-ARC, A-2444 Seibersdorf, Austria; 2. CEST (Centre of Electrochemical Surface Technolo

4、gy Kompetenzzentrum für elektrochemische Oberflächentechnologie GmbH, A-2700 Wiener Neustadt, Austria Abstract: Zirconium tungstate (ZrW2O 8 ceramic materials with a negative coefficient of thermal expansion (CTE were prepared by rapid hot pressing techniques (spark plasma sintering, induc

5、tively heated hot pressing using ZrW2O 8 powder. The processes allow preserving the required structure and phase composition of the negative CTE ZrW2O 8 ceramics. It shows that the variation of the process parameters (hot pressing temperature,Keeping time allows a certain tailoring of the CTE in a r

6、ange from 9×106/K to +9×106/K. A first attempt was made to use the negative CTE ZrW2O 8 filler powder in a light mass matrix (titanium to obtain a zero CTE composite with metallic matrix.Key words: zirconium tungstate; bulk material; negative thermal expansion materials; inductively heated

7、 hot pressing process; spark plasma sintering pressing; metallic matrix compositesZirconium tungstate (ZrW2O 8 is one of the few mate-rials which show a strong negative coefficient of thermal expansion (CTE. Typically there are not many materials showing such behaviour. One of the main advantages of

8、 this ceramic compound is an isotropic shrinkage during heating up the material, compared to e.g . carbon fibers which show a negative CTE only parallel to the fiber axis. An isotropic CTE is particularly of interest for applica-tions where expansion effects caused by a temperature induced expansion

9、 of one component have to be com-pensated. In addition such materials can be used as filler for metallic matrices in order to obtain a material with metallic behaviour but significantly reduced CTE.Beside application of bulk ZrW2O 8 materials, promis- ing might be the introduction of ZrW2O 8 particl

10、es as filler in various metal matrices to reduce the coefficient of thermal expansion. Various attempts to introduce these material as particles in metals (e.g . Cu or Al, in poly-mers or even in cements were investigated 1 where it could be shown, that a 60% in volume of ZrW2O 8 could end up in a m

11、aterial with zero CTE.Attempts to combine ZrW2O 8 with Cu in the purpose to understand composite materials, combining high ther-mal conductivity and a low coefficient of thermal expan-sion shows only limited success up to now, due to reac-tion/decomposition between both constituents when hot isostat

12、ic pressing was observed. A partial decomposition at already low temperatures of 600 into ZrO 2 and WO3收稿日期:20090310。 修改稿收到日期:20090401。 第一作者:NEUBAUER Erich (1974 ,男,博士。 Received date:20090310. Approved date: 20090401. First author: NEUBAUER Erich (1974, male, Ph.D., researcher. E-mail: erich.neubaue

13、rarcs.ac.at第 37卷第 5期 2009年 5月硅 酸 鹽 學(xué) 報(bào)JOURNAL OF THE CHINESE CERAMIC SOCIETYVol. 37, No. 5 M a y , 2009山東廣和 放電等離子燒結(jié)系統(tǒng)(SPS、真空熱壓燒結(jié)爐、小型真空熔煉爐55556099硅 酸 鹽 學(xué) 報(bào)· 750 ·2009年was reported.2The crystal structure of ZrW2O 8 was reported by Sleight 3 and the synthesis of single crystals

14、 of this phase by using a layered self-flux technique was described in Ref. 4. Meanwhile other materials with similar thermal expan-sion behaviour as the ZrW2O 8 coming from group generally described by A2(MO4 3 were found from Ref. 5.There are different methods for the synthesis of bulk ZrW 2O 8 ce

15、ramics described in literature. One of them is based on sintering a powder mixture of ZrO2 and WO3 followed by sintering at temperatures between 1150 and 1200 for several hours. 6ZrW 2O 8 is a metastable phase at room temperature, while it shows stability in the temperature range from 1105 to 1 257.

16、 ZrW 2O 8 de-composes into zirconium oxide (ZrO2 and tungsten oxide (WO3 as it cools down slowly from its stable state. For the ZrW 2O 8 production ZrO2 and WO3 are used as the starting materials. After the formation of the phase at temperatures above 1150 a rapid cooling down is required. Such a pr

17、ocess can of course be used for a formation of a bulk material, but especially larger components are somehow difficult to realize. Other described routes are based on conventional sintering of ZrW2O 8 powders at temperatures above 1150 followed by rapid quenching. 7In this work, ZrW2O 8 ceramic mate

18、rials with a nega-tive coefficient of thermal expansion (CTE were pre-pared by rapid hot pressing techniques using ZrW2O 8 powder. A first attempt was made to use the negative CTE ZrW2O 8 powderas filler in a light mass matrix (tita-nium. The material properties were studied.1 Experimental procedure

19、1.1 Sample preparationWithin this work a powder technological approach was used for the preparation of bulk material from ZrW 2O 8 powder. As a starting material commercial avai- lable ZrW2O 8 powder (WahChang, USA with a particle size < 50µm and a mean particle size in the range of 817m was

20、 used. This material was compacted by two different process techniques: spark plasma sintering/field assisted sintering (SPS/FAST and inductive heated hot pressing (iHP. Both processes allow high heating/cool- ing rates. In the SPS process this requirement was met by a direct pulsed electric current

21、 which effectively heated the graphite die, while in the iHP method an induction coil provided rapid heating of the cylindrical graphite die. Both methods are characterized by a short cycle time due to the high heating/cooling rate which was in the range of 200400K/min. This allows the consolidation

22、 of the ma-terial in several minutes up to less than half an hour. In addition to a better cost-effectiveness a low cycle time also allows to limit the tungstate decomposition which is usually critical during sintering. At the same time the application of a mechanical pressure up to 50MPa sup- ports

23、 the densification. Various samples with diameters between 10 and 40mm have been prepared by both methods under different conditions. The sintering condi-tions are summarized in Table 1.Table 1 Hot pressing and SPS/FAST conditions Sample No.Process Sintering tem-perature/Heating rate/(K·min1Kee

24、ping time/ min42 SPS/FAST700 400 1 26 SPS/FAST800 400 1 32 SPS/FAST900 400 1157 iHP 750 400 1 158 iHP 800 400 1 159 iHP 900 400 1 170 iHP 700 400 1 171 iHP 750 400 30 172 iHP 800 400 30 176 iHP 850 400 1 In addition to the bulk samples prepared from the ZrW 2O 8 powder, those particles were also use

25、d as a filler material in Ti matrix composite. The mean particle size of the titanium powder used was about 50m. Here the main idea was to introduce this negative CTE filler in a light mass structural part frequently used in aerospace applications. A special interest of zero CTE materials is coming

26、from structural applications where mounting ma-terials, e.g ., for mirrors, must ensure that there is no dis-tortion in case of a temperature change. To study the im-pact of ZrW2O 8 additions to a metallic matrix, Ti powder and ZrW2O 8 powder were mixed and subsequently con-solidated by iHP. The tem

27、perature for the HP was fixed at 700 , the holding time was 15min. The pressure ap-plied during the HP was 50MPa. Three different type of samples containing 20% in volume (the same below, 35% and 50% of ZrW2O 8 were prepared.1.2 CharacterizationThe quantitative determination of the phase content of

28、the samples and the corresponding crystallite size determi-nation was performed by means of the X-ray powder dif-fraction method (XRD at a powder diffractometer (Model X Pert, Philips, Netherlands, 2 Bragg-Brentano ge-ometry using copperK 1,2 radiation at 40kV and 40 mA. This device is equipped with

29、 an automatic divergence slit, a diffracted beam curved graphite monochromator, and a scintillation counter. The measurements were performed in step-scan mode over the range 5°85°2 with a step size of 0.02°and a counting time of 3 s/step. The actual calculations were performed using t

30、he Rietveld refine-ment method with constant monitoring of the “good-ness-of-fit” parameter which gives a good indication about the obtained relative optimization level and the R wp山東廣和 放電等離子燒結(jié)系統(tǒng)(SPS、真空熱壓燒結(jié)爐、小型真空熔煉爐55556099NEUBAUER Erich等:放電等離子燒結(jié)和快速熱壓工藝制備具有低或負(fù)熱膨脹系數(shù)鎢酸鋯塊體 · 751

31、83;第 37卷第 5期parameter, which indicates how well adapted the current parameter set corresponds to the measured XRD pattern. The overall refinement goodness-of-fit (GOF parameter was finally in the range from 1.2 up to 1.8, while the R wp parameter has slightly bigger values in the range from 2.33.8.

32、For the Rietveld refinement calculations the program package TOPAS (by Bruker, Germany was used. 8For the characterization of the thermal expansion be-haviour a dilatometer was used. The thermal expansion behaviour of the bulk ZrW2O 8 was measured in a range of 50 to approx. 250 (450 under vacuum co

33、 n-ditions. Two to three cycles have been measured in order to limit the effect of intrinsic stress coming from the rapid processing of the material. In the results the length change of the samples is shown.2 Results and discussion2.1 Ceramic bulk materialsPhase composition (mass fraction and crysta

34、llite size data of the compacted samples as obtained from the XRD measurements by Rietveld analysis is plotted as a func-tion of the sintering temperature in Figs.1 and 2. Each Fig.1 Phase composition of SPS compacted ZrW2O 8 samples sintered at different temperatures for 1min Fig.2 Crystallite size

35、 of SPS compacted ZrW2O 8 samples sintered at different temperatures for 1 min line corresponds to a specific phase as indicated .In the samples compacted by SPS technique four dif-ferent phases were observed as shown in Fig.1, and could be subsequently identified in the ICDD database: zirco-nium tu

36、ngstate, ZrW2O 8 (ICDD-PDF 000501868, zirconium oxide, ZrO2 (ICDD-PDF 010716426, monoclinic tungsten oxide, WO3 (ICDD-PDF 01087 2404, orthorhombic tungsten oxide, WO2 (ICDD-PDF 000481827. With an increasing sintering temperature from 700 up to 900 the mass content of the major phase ZrW2O 8 is rapid

37、ly decreasing while the mass frac-tion of the monoclinic WO2 phase almost symmetrically increasing. The ZrO2 phase and orthorhombic WO2 phase contributions remained constant.However, a linear dependence of the crystallite size for different sintering temperatures is observed for the ZrW 2O 8 phase a

38、s shown in Fig.2, where the observed crystallite growth starts with 90nm at 700 and end s with 160nm at 900.The iHP technique which was performed in the tem-perature range from 700 up to 900 led to different phase formations. Five phases were formed: ZrW2O 8 (ICDDPDF 000501868, ZrO2 (ICDDPDF 01071 6

39、426, tetragonal WO3 (ICDDPDF 000050388, mon- oclinic WO3 (010872404, and monoclinic tungsten oxide, WO2 (ICDDPDF 010860134. In this case, the major ZrW2O 8 content is decreasing almost linearly across the overall temperature range as shown in Fig.3. However, higher sintering temperatures induced the

40、 for-mation of the two monoclinic phases. A significant change in crystallite size is observed only for the ZrW2O 8 phase as show in Fig.4, where the observed growth starts with 58nm at 700 and end s with 182 nm at 900. The tetragonal WO3 phase shows slightly slower growth, with crystallite size of

41、9nm in the beginning to the 32nm at the highest temperature. The remained phases show almost no changes in the crystallite size for the different sintering temperatures. Fig.3 Phase composition of inductively hot pressed ZrW2O 8 samples at different temperature for 1min山東廣和 放電等離子燒結(jié)系統(tǒng)(SPS、真空熱壓燒結(jié)爐、小型真

42、空熔煉爐55556099硅 酸 鹽 學(xué) 報(bào)· 752 ·2009年 Fig.4 Crystallite size of inductively hot pressed ZrW2O 8 sam- ples at different temperature for 1minFigures 5 and 6 show the results of the thermal expan-sion measurements of iHP ZrW2O 8 samples. In Fig.5 the elongation (with respect to the

43、 initial length of the sample is shown for different compacted materials compacted by iHP at a temperature range between 700 to 900 for 1 min. At the same time it can be observed that the slope of the elongation is steadily increasing with the increasing Fig.5 Relative length change of ZrW2O 8 sampl

44、es compacted by inductively hot pressing at different temperatures for 1min Fig.6 Relative length change of ZrW2O 8 samples compacted by inductively hot pressing at different temperatures and holding time of the hot pressing temperature. But in all the samples still a negative CTE up to approximatel

45、y 140 is o b-served. At this temperature the phase change from alphato beta takes place resulting in a significant jump of the elongation value up to positive values for those samples compacted at temperatures above 800 . A similar situa-tion is observed if the holding time is significantly in-creas

46、ed as shown in Fig.5. The most favorable thermal behavior was found at a HP temperature of 800.Comparing the results of SPS compacted samples and iHP compacted samples no significant differences are observed in the expansion behavior at 800 for 1 min as shown in Fig.7. Here a CTE of around 9×10

47、6/K at 50 can be d erived. Taking a look at the sample compacted at 900 for 1min a difference to those samples com-pacted by iHP can be found as shown in Fig.8. With this sample a positive expansion behavior is measured result-ing in a positive CTE at 50 of around +9 ×106/K. One possible explan

48、ation of this difference could come from a certain difference in the real sample temperature (iHP is measuring the sample temperature at the die outer side, therefore a certain shift of the real sample temperature could take place (in this case a lower sample temperature would be the result. Fig.7 C

49、oefficient of thermal expansion of SPS/FAST sample 26 compacted at 800 for 1min Fig.8 Coefficient of thermal expansion of SPS/FAST sample 32 compacted at 900 for 1min山東廣和 放電等離子燒結(jié)系統(tǒng)(SPS、真空熱壓燒結(jié)爐、小型真空熔煉爐55556099NEUBAUER Erich等:放電等離子燒結(jié)和快速熱壓工藝制備具有低或負(fù)熱膨脹系數(shù)鎢酸鋯塊體 · 753 ·第 37卷第 5期Ano

50、ther explanation for the difference in the expan-sion and CTE at this temperature could come from thephase composition in the material. The main differencesin the decomposition of ZrW2O 8 into different phases with increasing temperatures is summarized by quantita-tive analysis of the phase composit

51、ion and crystallite size of the different phases as shown in the previous section. 2.2 Ti-ZrW2O 8 compositesThe XRD investigations of the ZrW2O 8/Ti metal- based composite samples display that the titanium matrix is consisting of titanium phase (-Ti, ICDDPDF 01 0713948 only in the sample with a low

52、content of ZrW 2O 8 (20%. At higher contents the phase Ti6O (ICDDPDF 010721472 is observed. This TiO2 phase is closely related to the hexagonal titanium structure. The O 2 anions occupy a fraction of the octahedral holes in the closed package of the titanium lattice. For the forma-tion of this phase

53、 during the sintering process a defined oxygen content originating from the tungstate is neces-sary. However, the XRD diffractograms of Ti and Ti6O are very similar due to the close structural relation of the corresponding phases: they display only a slight shift of the diffraction angles of the pea

54、ks. Therefore the exact quantitative determination of the ratio Ti/Ti6O by means of the Rietveld refinement was not possible.Besides various contents of the ZrW2O 8 phase (ICDDPDF 000501868 no other phases were identi-fied. It is most reasonable, that in addition to the oxides of tungsten and zircon

55、ium, titanium oxide phases with a lower Ti/O ratio are also present.In a similar way as for the ceramic bulk materials the expansion behaviour for a TiZrW 2O 8 with different com-posites was analyzed. In the following figure the CTE of a composite material containing 20% and 50% is shown for three m

56、easurements (2 runs from 50 to 250, one run from 50 to 450 in Figs. 9 and 10, respectively. Fig.9 CTE of sample iHP793 TiZr20 at 700 for 15min While the CTE at room temperature of pure titanium is 8.6×106/K a positive effect of the ZrW2O 8 addition on lowering of the CTE could be observed. In c

57、ase of 50% ZrW 2O 8 a room temperature CTE of around 4×106 /KFig.10 CTE of sample iHP793 TiZr50 at 700 for 15min can be obtained. Nevertheless taking the rule of mixture a higher reduction is expected. A main reason why the ex-pected reduction was not achieved could be the used hot pressing con

58、ditions which have not been optimized so far (porosity etc . In order to obtain a good densification in the composite material (typical hot pressing temperature of pure Ti is mostly above 900 a temperature of 700 with a dwell time of 15 minutes was chosen to avoid too severe decomposition or reactio

59、n. But even at this temperature a certain reaction/decomposition is indicated by the results of the XRD. Not all of the phases formed could be identified but it is evident, that from the initial amount of ZrW2O 8 a certain amount decomposed or re-acted with the matrix (see Table 2. Due to a significant reduced amount of the ZrW2O 8 phase in the Ti composite the expected zero CTE in a com