Zr55Al10Ni5Cu30金屬玻璃具有良好的玻璃形成能力與過冷液態區高熱穩定性等性質,無論是液態凝固過程亦或是在結晶溫度以下加熱均不容易析出結晶相。然而,隨著組成中氧濃度的增加,將對金屬玻璃凝固行為及性質造成影響。 本研究針對高氧濃度鋯基金屬玻璃之玻璃形成能力、微結構、過冷液態區熱穩定性及機械性質進行探討。實驗配製之Zr55Al10Ni5Cu30合金,經氮氧分析儀測試結果,約含有1220 ppm的氧。再分別以單滾輪旋轉熔煉及熔射鑄造法製備Zr55Al10Ni5Cu30金屬玻璃薄帶及試棒。並經X光繞射分析結果說明,薄帶與試棒表面區域因凝固過程冷卻速率極快能迅速將熱排除,不受高氧濃度的影響仍舊能形成非晶質相。然而,試棒芯部區域冷卻速率較慢,易受氧觸發析出介穩態”big cube” f.c.c. NiZr2型結構的中間相。結晶相的析出不僅降低Zr55Al10Ni5Cu30金屬玻璃原有之玻璃形成能力,且受高氧濃度的影響亦將喪失金屬玻璃在過冷液態區良好的熱穩定性。最後,維克氏硬度測試結果,含有介穩態中間相之金屬玻璃其硬度值(Hv=575)約高於完全非晶質相Zr55Al10Ni5Cu30金屬玻璃(Hv=515)約10 %,且硬度值將隨著介穩態結晶相體積分率提高而增加。因此,欲製備完全非晶質相之金屬玻璃,除了符合Inoue經驗法則與Turnbull過共晶理論外,降低組成中之雜質與氧濃度為首要條件。
Among all BMGs, Zr-based alloys have superior glass forming ability and thermal stability. They can be readily produced into parts with cross sections larger than a few centimeters by conventional melting and casting techniques. But Zr-based BMGs lose their excellent GFA when the oxygen concentration level is high. The research on the effects of high oxygen concentration (1220 ppm) on thermal stability and mechanical properties of Zr-based BMGs. If we assume a homogeneous oxygen distribution in the volume, then at high oxygen level crystallites can preferentially form in the inner regions of the bulk samples where lower cooling rates lead to an enhanced formation of f.c.c. NiZr2 nanocrystals. In the outermost regions this process is suppressed due to a very rapid heat removal during cooling from the melt, resulting in an amorphous region.The formation of oxygen-induced Zr4Cu2O nuclei in amorphous matrix lead to reduce thermal stability and increase Vicker`s hardness of Zr-based BMGs.