https://scholars.lib.ntu.edu.tw/handle/123456789/74477
標題: | 添加稀土元素以改善Ti-40Al-15Nb鈦鋁介金屬合金之高溫機械性質研究 | 作者: | 顧鈞豪 | 關鍵字: | 鈦鋁介金屬合金;顯微結構;機械性質;氧化性質;相變態;分散強化;稀土;Titanium aluminide alloy;Microstructure;Mechanical properties;Oxidation properties;Phase transformation;Dispersion strengthening;Rare earths | 公開日期: | 2003 | 出版社: | 臺北市:國立臺灣大學材料科學與工程學研究所 | 摘要: | 添加微量稀土元素(Sc 或 Mm)與增加約1 at% Nb 之Ti-40Al-15Nb 合金的研究結果顯示鑄造後之Ti-40Al-16Nb合金與Ti-40Al-15Nb合金之顯微組織相似;但均質化後之Ti-40Al-16Nb 合金之顯微組織與均質化後之Ti-40Al-15Nb 合金相較有不同。其中Ti-40Al-16Nb合金在均質化後其B2 相基地被α2 相 所取代,且會有σ相析出於α2 相基地中。而添加0.39wt% Sc 或La-rich Mm之Ti-40Al-16Nb 合金的顯微結構與相特性分析可歸納如下:(i)鑄造後之Ti-40Al-16Nb-0.39wt%M (M = Sc or Mm)合金具有α2 相基地,且包含有α-Ti 相與B2 相和少量之γ 相析出。藉由內氧化所形成之Sc2O3 與部分氧化之La 氧化物粒子可在本研究中觀察到,但在雙相γ-TiAl 合金之文獻中所觀察到的Ti3(Al,Sc)介金屬相析出物並未在此研究中發現。而部分氧化之Sc 在α-Ti 中之固溶量係高於Mm,(ii)添加Sc 或La-rich Mm具有可降低α-transus temperature 之效果,亦即可以穩定α2 相並抑制B2 相或γ相的生成,(iii) 在均質化後σ相和γ相會析出於α2 相基地中,而B2 相則會消失。且存在於α-Ti 中部分氧化之Sc 在均質化之後會進一步氧化成Sc2O3。而就氧化析出粒子在Ti-40Al-16Nb 合金中之分佈型態而言,添加La-rich Mm之合金的析出粒子較添加Sc 之合金 所形成之氧化粒子分佈得較均勻且呈較不連續狀。在Sc 與La-rich Mm添加對Ti-40Al-16Nb 合金高溫性質之影響方面,結果顯示合金藉由添加微量之Sc 或La-rich Mm得以改善合金在900℃∼1150℃之高溫機械性質與800℃、1000℃的高溫抗氧化 性。藉由此合金成分之設計可使此合金的壓縮應力峰值較Ti-40Al-15Nb 合金高出450 MPa 左右,且900℃以上之高溫強度亦有明顯增加。造成此合金之高溫機械性質明顯改善之原因係歸因於此合金中析出具有熱穩定性佳的微細氧化粒子析出,且這 些氧化粒子是阻止差排移動的有效障礙物。此外微量Sc 或Mm 之添加可減少合金的氧化速率、增加氧化層與合金間之黏著強度和改變高鈮含量TiAl 合金之氧化物型態。此具有氧化物粒子散佈強化之TiAl 基介金屬合金可以有效的將TiAl 合金的應用 溫度由一般預期之700℃提高至900℃左右。 The effect of a slight increase in Nb content of approximately 1 at% and the effect of adding a minor Sc or La-rich misch metal (Mm) on the microstructure and phases of Ti-40Al-15Nb alloy show that the microstructures of the as-cast Ti-40Al-16Nb and the as-cast Ti-40Al-15Nb alloy are the same, but slightly differs from the homogenized Ti-40Al-15Nb alloy, in which the B2 phase matrix of the Ti-40Al-16Nb alloy is replaced by á2 phase and ó phase precipitates after homogenization at 1100℃ for 72h. Microstructural analysis and phase characterizations of the Ti-40Al-16Nb alloy with 0.39 wt% Sc or La-rich misch metal additions are summarized as follows: (i) The as-cast Ti-40Al-16Nb-0.39wt%M (M= Sc or Mm) alloys have an á2 matrix and contain á-Ti and B2 phase precipitates but few ã phase precipitates. The Sc2O3 or partial oxidized (La,Al)1-xOx oxide dispersoids, formed by internal oxidation, are observed in this work; but Ti3(Al,Sc) presented in the dual phases of γ-TiAl are not found. The solubility of the partially oxidized Sc in á-Ti is higher than that of Mm. (ii) Adding Sc and La-rich Misch metal decreases the á-transus temperature of the TiAl-Nb alloys, possibly stabilizing the á2 phase and inhibiting the B2 or ã phase formation. (iii) After homogenization, the ó phase and ã phase precipitate in the á2 phase matrix, but the B2 phase is absent. The partially oxidized Sc in á-Ti may be further oxidized to Sc2O3 after homogenization. The distributed morphology of the oxide dispersoids in the TiAl-Nb alloy with added La-rich Mm is more uniform and discontinuous than that in the TiAl-Nb alloy with added Sc after the homogenization. Experimental results about effects of a minor addition of Sc or La-rich misch metal on the high-temperature compressive properties and isothermal oxidation behavior of a TiAl alloy with a high niobium content indicate that the high-temperature mechanical properties at temperatures from 900℃ to 1150℃ and the oxidation resistance of the alloy at 800℃ as well as 1000℃ are improved by alloying with a minor Sc and La-rich misch metal. Adding a slight amount of Sc or La-rich misch metal may significantly enhance 2 the high-temperature compressive peak stress of the high niobium content TiAl alloy. The peak flow stress increment measured from high temperature compression testing at 900℃ is around 450MPa and the high temperature strength at temperatures above 900℃ is also enhanced. The significant improvement in high-temperature mechanical properties is attributed to the precipitation of fine oxide particles with high thermal stability in the alloys. These particles form an effective barrier to the moving dislocations. Furthermore, adding either a minor Sc or La-rich Mm to the alloy reduces the oxidation rate, increases the strength of adhesion between the oxide layers and the alloys and changes the morphology of the oxide layers formed in the TiAl alloy with a high niobium content. The TiAl alloys with oxide dispersoids strengthening may effectively increase the application temperature from intended temperature 700℃ to 900℃. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/12436 | 其他識別: | 912216E002024 | Rights: | 國立臺灣大學材料科學與工程學研究所 |
顯示於: | 材料科學與工程學系 |
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912216E002024.pdf | 10.85 MB | Adobe PDF | 檢視/開啟 |
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