Sri Nugroho

English

博士学位論文の要旨及び審査結果の要旨 (Summary of Thesis(DR))othe

Sri, Nugroho

Tohoku University Repository (TOUR) / 東北大学機関リポジトリ

Processing and Characterization of BariumHexaaluminate Reinforced Alumina MatrixComposites (バリウムヘキサアルミネート分散強化型アルミナセラミックス複合材料の作製と評価)著者 Sri Nugroho号 53学位授与番号 4144URL http://hdl.handle.net/10097/42558すり ぬぐろほ氏 名SriNugroho授 与 学 位 博士(工学)学 位 授 与 年 月 日 平成21年3月25日学位授与の根拠法規 学位規則第4条 第1項研究科,専攻の名称 東北大学大学院工学研究科(博士課程)金属フロンティア工学専攻学 位 論 文 題 目Pr㏄essingandCharacterizationofBariumHexaalu㎡nateReinforcedAluminaMatrixComposites(バリウムヘキサアルミネート分散強化型アルミナセラミックス複合材料の作製と評価)指 導 教 員 昌東北大学教授 川崎 亮論 文 審 査 委 員 主査 東北大学教授 川崎 亮 東北大学教授 粉川 博之東北大学教授 藤田 文夫 東北大学准教授 陳 中春論 文 内 容 要 旨      Component forhigh temperature  st uctural applications, such as in gas turbine  and aerospace engines, heat exchangers, and hot gas  fillers are conventionally made from Fe-,  14-, Co-based  superalloys  with operating  temperatures around 1100°C that is near  their upper use temperature.  Accordingly, the use of  cooing air is  necessary, thus  resulting in reduced  efficiency and performance of the system.  Since these applications require long-term exposure tooxidizing  environments, the  materials have to be featured by a  combination f  mechanical (e.g., strength, fracture toughness, and creep resistance), chemical (e.g., oxidation a d corrosion resistance),  thermo-physically properties (e.g., thermal shock  resistance), and also long-term stability  cluing service at elevated temperatures. An  all-oxide c ramic composite consisting ofoxide  fibers,  oxide  matrix, and an  oxide  interphase(s), is a potential candidate due to its damage tolerance and inherent resistance to degradation in oxidizing atmospheres at high temperatures. B cause of a reduced need or no need for  cooing air, the applications  f all-oxide CMCs lead to an increase in thermal  efficiency and a  reduction in pollutant  emissions  (N0x,  CO, and unburied hydrocarbons). Oneof the  most popular  ll-oxide composites is  alumina fiber  einforced  alumina matrix  composites.  However, processing of this material faces ome  drawbacks, such as  (faculty in  dispersing fiber  homogeneously, need for surface treatment of he fiber, hard to consolidate due to  networking structure and high cost. In order to  overcome this problem,  in-situ synthesis is applied to obtaining  composites hat have similar  structure and properties as fiber-like  reinforced matrix composites.       In this  work,  barium  hexaaluminate  (Ba-p-Al203 or  Ba0.7.3Al203) was studied  further for potential pplication as  reinforcement for  alumina-matrix composites hrough insitu synthesis of  alumina-barium carbonate and  alumina-barium zirconate powders. Due to limited information on densification  behavior and mechanical properties data on bulk singe phase of  Ba-P-Alz03,— 626 —synthesis and  formation mechanism of  Ba-13-Al203  powder followed by  densification of synthesized powders by spark plasma sintering (SPS) and pressureless  sintering  (PLS) were  first  conducted. Then, using the same starting powders and processing, 30%vol  Ba-P-Al2031403 and  30%vol  [Ba-(3-Al203-Zr02]/Al203 composites were produced from in situ reaction of  (Al203-BaCO3) and  (Al203-BaZr03), espectively.       So  far,  some research works have concerned with the solid-state synthesis [1] and formation mechanisms  [2,3] of  Ba-p-Al203 phase.  However, to the best  knowledge of the present authors,  different from conventional  sold-state  r action technique, in this research, a high-energy  planetary ball milling method was  applied to reduce the  particle sizes and enhance the  reactivity of  constituent powders. Besides, the formation mechanism of  Ba-P-Al203 phase has  never been reported before from the  viewpoint of  morphological  evolution with temperature changes. Thus the first goals of this research are to synthesize monophasic  Ba-11-Al203 powder through  mechanically-activated millingand  sold-state  r action f  alumina and  barium carbonate powder  mixtures and to  get further  understanding of itsformation mechanism.  Ba-13-Al203 was ynthesized through  His  following equation:  7.3403 +  BaCO3  Ba0.7.3Al203 + CO2 (1) Based on  TG DSC and XRD results,  mechanically ctivated  milling results in  decrease in decomposition emperature of  BaCO3 and promotes  further reaction  between  Al203 and  BaCO3 powders [4]. Almost ingle phase  Ba-p-Al203 can be synthesized through high energy  ball milling for 9  —12 hours,  followed by heat reatment at 1500°C for 2 hours. The formation of  Ba-f3-Al203 phase  includes three stages: 0)decomposition of  BaCO3, (ii)  formation a d growth of spherical  BaGAl203  particles, and (iii)  reaction  between Al203 and  BaO•Al203 to form  F3a-13-Al203 with an elongated morphology.  Figure 1shows a  schematic illustration of the reaction sequence and  formation  mechanism of the  Ba-fi-Al203 phase during heat  treatment.Milled     re,er 600°C 800°C1500°C  1400°C  IL.-  1-  1111  4-1000°C         —a* 1300°C POT 1100°C 44" /..12,^Cf/11200°C• 0  Al203  C:tBaCO3  BaO.Al203  Ba-p,AI203  Fig.  1. Schematic  llustration  showing the formation ofelongated  Ba-f3-Al203 Ba-P-Al2031s very  cffticult to be  densified due to its peculiar layered  structure and its elongated morphology. Many attempts have been made to  obtain dense sample of  Ba-3-Al203 but the results were  unsatisfactory. Debsikdar [5] stated that the  Pressurekss-sintered  density ofthis material upto 1550°C for 24 h  was, less than  60°/0 . Work by He  et.al. [6] and Dunn  et.al. [7] in the— 627 — sane  year, almost dense  barium  hexaaluminate could be consolidated by PLS but it needs  very high  temperature of  sintering and long sintering time. Due to this drfficulty, to the best of our  knowledge, therefore, it is still  little research discussing the mechanical  properties of this  material.  Besides, densification by using SPS  methods i not  yet done. Based on the  formation mechanism of Ba-(24123 discussed above, dense  Ba-O-Al203sarnples wer  consolidated from  two different  powders compounds, i.e.,  [Ba0•1203 + Al203]  (route 1) and  Be-f3-A203 (route 2)  powders by SPS and PLS. A single phase of bulk  Ba-P-Al203  with  full density  can be  produced  from SPS-ed  route-1  powders at  1500°C-30min. SPSed route-2 powder at  15000G-60min only produced  91% of  theoretical  density.  Route-1  powder was easier to be densified than route 2, because it has  spherical and very fine powders. The phases for oute  1and route 2 are  [Ba-p-A2o3  + trace of  Al203] and  Ba-p-Al203,  respectively. Thehardness and fracture toughness of this material were 14.6 GPa and 1.6  MPa.m12, respectively. PLSat  1500"C for 2 h was not able to produce d nse bulk Ba-p-Al203 derived  neither from  route-1 nor  route•2 (with relative  d nsity less than 80%TD). The fracture  images showed that it has  transgranular mode of  fracture.       In  alumina based composites, theelongated second phases used as  reinforcementsare,generally,  altrninate compounds with a layered  p-alumina  structure (such as  Lakti0v3 [8],  Ba0-6.9Al203 [9],  SrA1-12019 [10]) or a  macjnetoplumbite  (MP) structure  (LaMgA11,019  [1 ]and  CaA1120,9 Tagaoka [9] has synthesized  22vo1%  Ba0.6.9  Al203/  Al203 composites by PLS however there is no further study on its mechanical properties. The main goals of  this chapter are to in-situ synthesize  and-characterize  30vol%  Ba-p-Al204Al203 composite by SPS and to examine its mechanical properties.      The  sane  Al203 and  BaCO3 powders were used as starting material, with the  nominal composition of composites after  sintering is  30vol%Ba-P-Al203/Al203 (see q. 2). 7.3403+  BaCO3  —*  30vo1%[Ba0-7.3Al203]  +  Al203  +CO2 (2) Based on the result of  densification of bulk  Ba-P-Al203, powder of  [Ba0•1203+Al203] (resulted from heat treatment of  Al203 +  BaCO3 powder following eq.  2)  was used for SPS. The  Ba-p-Al203  reinforced  Al203  matrix composite with  100%TD can be fabricated by  SPS above 1400°C for  30rnin from  [Ba0•1203+Al203] as starling powders.  Rgure 2 shows dearly dense composite and  platelike morphology f  Ba-P-Al203 in the composite.  It is seen that alumina h s mooth surface and on the other hand  Ba-p-Al203 phase has rough surface and layered structure.  Ba-P-Al203 phase attached perfectly in the surrouncing alumina  m trix          • -  Ar2o):,   •  •  • •                      7777. •  t.                     •• •:                                                                                   . .                    . " ' „ • • , •               Fig. 2 Morphology of  Ba-p-Al203in the composite showing  platelike and layered  structure  628 —The hardness and fracture toughness of Ba-P-Al2031Al203 composite w re 18.03 GPa and 3.45  MPa.m1/2, respectively. The  inoorporalion of  Ba-f3-Al203 phase results ina slight improvement in  fracture toughness of the composite due to crack deflection and  crack bridging.       Recently, Chen  et.al. [13,14] have also worked on in situ synthesis of  alumina matrix composites by  reactive sintering  of  Al203 and  BaZr03  powder mixtures through this following equation:  Al203+  BaZ103  Ba0-7.3Al203+ Zr02  Al203 (3) The composite containing  30vol%  [Ba-P-Al203 +  Zr02] showed an  optimum combination of mechanical properties. In this  chapter,  further research onsynthesis of  30vol%  [Ba-p-Al203-Zr02]/Al203 composites by two different  densification pr cedures, i. . (process-1)  planetary ball milling + SPS and  (process-2) rotary ball  milling PLS, will be thoroughly studied. The  objective of this work is to examine the effect of processing  parameter (ball milling and  sintering methods) on  densification behavior, formation f  reinforcements,  microstructural  deve opment and mechanical properties during consolidation.  Ba-p-Al203002  reinforced  Al203 matrix composite with  almost 100%  TD could be in situ synthesized by using PLS at 1500°C - 2h  (process-1) or SPS at  minimum 1400°C-30  min(process-2). Process-2 could produce  Ba-P-Al203/  Z102/  Al203 composite with igher toughness (5  MPa.m12) than one by  process-2 (4.1  MParri12)  .  This might be due to the higher aspect ratio f  reinforcement formed and  crack propagation  mainly ininterface of  matrix/reinforcement. Compare with  Ba-p-Al203/Al203 composite (3.4  MPa.rn12),  Ba-13-Al2030021Al203 composite produced by process-1 or process-2, has higher fracture toughness. Besides due to  difference in aspect ratio and  crack  propagation s tes, it also  was due to the  existence of  Z102 particale embedded in  Ba-p-Al203 phase. The crack propagation behavior of three different  Ba-f3-Al203  reinforced  alumina matrix composites could be seen in the  figure 3 below. Fig. 3.  (a)  Ba-P-Al2031Al203  composite  (b)Ba-p-Al2032r02/Al203 composite by  process-1 (c)  Ba*Al203/Zr02/PJ203 composite by                                            process-2       The  formation f  Ba-p-Al203 and  Zr02 phases asreinforcement of the composite could improve fracture toughness of  composite through  crack bridging and crack  deflection mechanism. The microstructure of insitu synthesized  Ba-P-Al203002JAl203 composite s stable until 1400°C.— 629 — References: 1. Masato Machida,  Koichi Eguchi, and Hiromichi  Arai, Journals  ofArnerican  Ceramics  Society  71[12]  1142-47  (1988). 2.  G.  Groppi, C.  Cristiani, P. Forzatti and M. Belloto, J. Mater.  Sci  29  (1994), p.  3441 3. N.  Iyi, S. Takekawa and S.  Kimura,  Journal of  Solid State  Chemisfry,  Volume 83, Issue 1,  November 1989, Pages 8-19 4.  Sri  Nuqrono, Zhongchun Chen, Akira Kawasaki, MOD.  Jarligo, submitted in the Journal  ofAlloys and  Compounds, under  review. 5. JC. Debsikdar, OS.  Sowemimo, journal  ofmaterial science  l tters  11  (1992) 637-638. 6.  G.  He, T. Goto, T.  Narushima  and  Y. lguchi,  Solid State  Ionics,  Volume 121, Issues 1-4, June 1999, Pages 313-319 7. S. Dunn, R.V.  Kumar and D.J. Fray Solid State  Ionics  124  (1999),  p.133. 8. C.B. Solano, L  Esquivias,  J.  Am. Ceram. Soc., 82 [5]  1318-24  (1999) 9. T. Nagaoka, Y.  Iwamoto,  J.  Am.  Ceram. Soc.,  83  [7]  1613-16  (2000) 10. M. Yasuoka, K. M.E.  Brito, S. Kanzaki, J. Mi. Ceram. Soc.  78  (1995)  1853. 11. P.E.D. Morgan,  J.A. Miles,  J. Am.  Ceram. Soc.  69  (1986) C157 12. L. An, H.C. Ha,  H.M. Chan, J.  Am.  Ceram. Soc.  81  [12]  3321-24  (1998) 13. Z. Chen,  K.K.  Chawla, M.  Koopman, Mater.  Sd.  Eng.  A. 367 (2004)  24-32. 14. Z.  Chen, T. Okazawa, K Ikeda,  Ceram.  Trans.  192  (2006)11-21. —  630  —論文審査結果の要旨地球温暖化 防止は急務の課題 で あ りCO2ガ スの排 出量 を低減す るためエ ネル ギー機器 の作動 温度の高温化が急 ピッチで進 められ てい る。そのための鍵 は高温構造用セラ ミックスであ り、耐熱温度の限界に近づいた超耐熱合金 の代 替材料 として不可欠 となっている。 しか し、大 きな問題 点は破壊靱性値が低い こ とであ り、機器 の信頼性を確保す るた めにはその改善が必 要 となる。バ リウムヘキサアル ミネー トは層状構 造を もつ 酸化物セ ラ ミックスであ り層 間剥離が容易 なことか ら、強度や破壊靱性は低い もの の選択的に亀裂 を伝播 させ るこ とが期待 できる。 したがって、高温構造用セ ラミックスに分散す る ことができれ ば、急峻 に立ち上が るR一 曲線挙動 を実現で きる可能性 があ り破壊靱性 の向上 に有効 と考 えられ る。一方、バ リウムヘ キサ アル ミネー トは難焼結性で あ り、そ の単相焼結 体の作製例 は少 な く、破壊靱性 な どの基本的性質 のデー タが乏 しい。 また、それ らの均一分散混合 も困難 なこ とか ら新 しい創製 プ ロセ スの研究開発 も必要 とされている。以上 の観点か ら、本研究では、大気 中の高温構 造用 セ ラ ミックスを想 定 してA1203セラ ミックス をマ トリックスに選択し、バ リウムヘ キサ アル ミネー ト単相焼結体の合成 と評価 を行 った上で、in-situ反応焼結 プ ロセ スによってバ リウムヘ キサアル ミネ・一・一ト分散強化型Al203複合セ ラ ミックスの作製 を試 みたものである。破壊靱 性値お よび機械 的性 質の評価 とともに高靭性化 メカニズムについて も言及 して いる。第1章 は序論 であ り、研 究の背景お よび 目的 を述べてい る。第2章 では、メカ ノケ ミカル反応 を利用 した高エネルギー ボール ミル法 と熱処理 を組み合わせ 、バリウムヘキサ アル ミネー ト単相粉 末の合成 を試みた。詳細 に合成過程 を調べ 、形成 メカニズムを明らかにする とともに単相粉末の合成 に成功 した ことを述 べている。第3章 では、パ ルス通 電焼結法 によ りバ リウムヘ キサアル ミネー ト単相粉末 の焼結固化 を試 み、焼結体の機械的性質 の評価 を行った。バ リウムヘ キサアル ミネー ト単相粉末の焼結緻密化 は非常 に困難であった が、 中間生成物 としてのBaO-A1203にAI203を混合す ることによ り、若干A1203が残 るがほぼ理論密度の単相焼結体を得 られ るこ とを明 らかに した。加 えて、機械 的性質 として硬 さお よび破壊靭性値 を求 めている。第4章 では、上記結 果 を基 にバ リウムヘ キサアル ミネ ー ト分散強化型A'1,0,複合セ ラミックスをin-situ反応焼結 によ り合成 した。期待 した破壊靱性の向上は少 なかったが、アスペ ク ト比が低 いことが一因で ある と考察 してい る。第5章 では、A120,とBaZiO3混合粉 末のin-situ反応 焼結 によ りバ リウムヘキサアル ミネー トとZrO2分散強化型Al203複合セ ラ ミックスを合成 し、その評価 を行 った。常圧焼結法 に よって も緻密 化できることを示 し、異方性粒成長 によって高いアスペク ト比が得 られることを明 らか に した。 これ によ り亀裂架橋、デ フ レクシ ョンな どの靱化 メカニズムが有効 に働 き十 分な破壊靱性値の改善がで きることを明 らか に した。第6章 は、本研究 をま とめた総括 であ る。以上要す るに本論文 は、in・situ反応焼結 プロセ スによるバ リウムヘ キサアル ミネー ト分散強化型A1203複合セ ラ ミックス作製の基礎研 究 を実施 し、合成機構 の詳細な考察 とともに高靱性化 メカニズムを示 した もので、基礎 的研 究ばか りでな く工学的応用 についても言及 してお り、材料 システム 、工学の発展 に寄与す るこ とが少な くない。よって、本論文は(工 学)の 学位 と して合格 と認 める。631

Processing and Characterization of Barium Hexaaluminate Reinforced Alumina Matrix Composites (バリウムヘキサアルミネート分散強化型アルミナセラミックス複合材料の作製と評価)

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Processing and Characterization of Barium Hexaaluminate Reinforced Alumina Matrix Composites (バリウムヘキサアルミネート分散強化型アルミナセラミックス複合材料の作製と評価)

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