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Microstructure and properties of molybdenum disilicide and its composites.

機(jī)譯：二硅化鉬及其復(fù)合材料的微觀結(jié)構(gòu)和性能。

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Molybdenum disilicide (MoSi2) is a candidate material for high temperature structural applications due to its high melting point and excellent oxidation resistance. A major impediment to implementing this material is its poor room temperature fracture toughness. This study incorporates the microstructure-mechanical property relationship for MoSi2, MoSi 2 alloys, and composites in an effort to determine the feasibility for improving room temperature fracture toughness without undermining the beneficial oxidation and creep properties.; The fracture toughness values reported in the literature vary significantly, and the first part of this study examines the origins for these differences. A diverse array of samples was collected from laboratories involved in exploring MoSi2. These samples were investigated for their microstructural features and indentation response. The non-ideal indentation cracking observed with some MoSi2 samples is based on the anisotropic single crystal properties. The orientation dependency for indentation deformation and fracture was observed for the (110) plane of MoSi2. Fracture toughness values were determined from the damage zone surrounding the indent irrespective of the formation of the ideal radial/median cracking system. Adjustments to fracture toughness values are made to account for the elastic/plastic response. Results from this study indicate that a finely dispersed secondary phase enhances tortuous crack paths and microcracking.; The indentation analysis used for MoSi2 was also applied to MoSi2-Al2O3 and MoSi2-SiC samples. The Al2O3 addition increases the dihedral wetting angles of the triple junction SiO2 in MoSi2 and retards grain growth. These microstructural changes result in differences in the indentation cracking behavior. The fracture toughness improvement for the hot-pressed MoSi2-SiC sample, which is confirmed by four-point bend tests, may be attributed to higher residual stresses that aid in the tortuous crack behavior. Alloying approaches using Al, Ti, or Re to improve fracture toughness met with limited success. The crystal structure changes, lattice spacing modifications, and second phase additions were not helpful in preventing crack propagation.; In addition, isothermal oxidation results of MoSi2 indicate a microstructural effect on the rates of oxidation. The oxidation kinetics are temperature dependent, changing from linear to parabolic at 500°C, and this change is attributed to the volatization of MoO3.
機(jī)譯：由于其高熔點和優(yōu)異的抗氧化性，二硅化鉬（MoSi2）是用于高溫結(jié)構(gòu)應(yīng)用的候選材料。實施該材料的主要障礙是其差的室溫斷裂韌性。這項研究結(jié)合了MoSi2，MoSi 2合金和復(fù)合材料的微觀結(jié)構(gòu)-機(jī)械性能關(guān)系，以試圖確定在不損害有益的氧化和蠕變性能的情況下提高室溫斷裂韌性的可行性。文獻(xiàn)中報道的斷裂韌性值差異很大，本研究的第一部分檢查了這些差異的成因。從參與探索MoSi2的實驗室收集了各種樣品。研究了這些樣品的微觀結(jié)構(gòu)特征和壓痕響應(yīng)。在某些MoSi2樣品中觀察到的非理想壓痕裂紋是基于各向異性的單晶特性。在MoSi2的（110）平面上觀察到壓痕變形和斷裂的取向依賴性。斷裂韌性值是從凹痕周圍的損壞區(qū)域確定的，與理想的徑向/中部裂紋系統(tǒng)的形成無關(guān)。調(diào)整斷裂韌性值以考慮彈性/塑性響應(yīng)。這項研究的結(jié)果表明，細(xì)分散的第二相增強(qiáng)了曲折的裂紋路徑和微裂紋。用于MoSi2的壓痕分析也適用于MoSi2-Al2O3和MoSi2-SiC樣品。 Al2O3的添加增加了MoSi2中三結(jié)SiO2的二面角潤濕角并阻礙了晶粒長大。這些微觀結(jié)構(gòu)變化導(dǎo)致壓痕裂紋行為的差異。通過四點彎曲試驗證實的熱壓MoSi2-SiC樣品的斷裂韌性得到了改善，這可能歸因于較高的殘余應(yīng)力，這有助于彎曲的裂紋行為。使用Al，Ti或Re改善斷裂韌性的合金化方法獲得的成功有限。晶體結(jié)構(gòu)的變化，晶格間距的改變和第二相的添加對防止裂紋擴(kuò)展沒有幫助。另外，MoSi 2的等溫氧化結(jié)果表明了對氧化速率的微觀結(jié)構(gòu)影響。氧化動力學(xué)與溫度有關(guān)，在500°C時從線性變化為拋物線，并且這種變化歸因于MoO3的揮發(fā)。

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  • 作者

    Newman, Aron English.;

  • 作者單位

    State University of New York at Stony Brook.;

  • 授予單位 State University of New York at Stony Brook.;
  • 學(xué)科 Applied Mechanics.; Engineering Metallurgy.; Engineering Materials Science.
  • 學(xué)位 Ph.D.
  • 年度 1998
  • 頁碼 122 p.
  • 總頁數(shù) 122
  • 原文格式 PDF
  • 正文語種 eng
  • 中圖分類 應(yīng)用力學(xué);冶金工業(yè);工程材料學(xué);
  • 關(guān)鍵詞

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