| 摘要: | 在某些鋯基塊狀非晶質合金中，可以自基地裡析出ZrCu B2相，而此ZrCu B2相在受到剪切帶的應力時會產生相變化而吸收剪切帶的能量並有效地阻止其傳播，進而阻止材料被破壞而大幅提升非晶質合金的塑性。然而Zr48Cu47.5Al4Co0.5合金於鑄造過程中，其ZrCu B2相之析出尺寸無法有效控制，常會發現大區塊團聚及不均勻分佈之析出相。所以本研究利用凝固製程中接種之概念，在Zr48Cu47.5Al4Co0.5合金中添加微米等級的鉭金屬顆粒(5 ~ 30 µm)，利用鉭之高熔點及與基材不互熔的特性，可將鉭顆粒均勻地散布在基材中成為ZrCu B2相的析出成核點，使ZrCu B2析出相散布均勻，再搭配不同冷卻銅模溫度來控制ZrCu B2相的尺寸，藉此更有效地提升其塑性。
Zr48Cu47.5Al4Co0.5外添加 0 ~ 0.75 vol.% 鉭顆粒之合金在冷卻銅模溫度-30 °C條件下，其XRD圖皆具有非晶質結構之基地及ZrCu B2析出相的特徵峰，但其中添加0.75 vol.% 鉭顆粒之合金在冷卻銅模溫度高於-20 °C的條件下則結晶。在OM的觀察下可發現，Zr48Cu47.5Al4Co0.5加入鉭顆粒後使ZrCu B2析出相散布更均勻，同時可發現鉭顆粒被ZrCu B2相包覆於中心處；隨著鉭顆粒的增加提供了更多的成核點而析出更多的ZrCu B2相。然而，添加0.75 vol.% 鉭顆粒之合金隨著冷卻銅模溫度的上升而析出大量的ZrCu B2相並產生團聚現象。DSC的結果顯示，隨著鉭顆粒的添加及冷卻銅模溫度的上升其結晶放熱峰值有下降的趨勢，代表合金基地非晶相體積分率下降及ZrCu B2相體積分率提高。雖然添加鉭金屬顆粒對於Zr48Cu47.5Al4Co0.5合金的硬度值並沒有影響，基材硬值度約為515 ± 5 Hv，而ZrCu B2相硬度約為344 ± 2 Hv，但於冷卻銅模溫度為-30 °C的條件下，添加0.75 vol.% 鉭顆粒之鋯基非晶質合金棒材的機械性質有非常顯著的提升，其降伏強度為1750 MPa、破裂強度為1890 MPa、塑性變形量提升到14 %，相較其基材的塑性變形量7.5 %，增加了6.5 %。
;In some Zr-based bulk metallic glass composites (BMGCs), the ZrCu B2 phase can be precipitated from the matrix. When the ZrCu B2 phase subjected to the stress from the shear banding, it will absorb the energy of shear band and transform into ZrCu B19′ phase, and so as to improve the plasticity of Zr-based BMG. However, the particle size and distribution of ZrCu B2 phase in Zr48Cu47.5Al4Co0.5 BMG cannot be well controlled in general casting. Large agglomerated and inhomogeneous distributed ZrCu B2 phase were usually found in the Zr48Cu47.5Al4Co0.5 BMG samples. Therefore, the concept of inoculation in conventional solidification process is applied in this study. The Ta particles (size of 5–30 µm) with 0 ~ 1.0 vol.% were added into Zr48Cu47.5Al4Co0.5 BMG matrix as the inoculant. By using the ultrahigh melting point of tantalum and immiscible with Zr-base substrate, the Ta particles can be uniformly dispersed in the Zr-based alloy melt as the nucleation sites for precipitating ZrCu B2 phase, and form a homogeneously distributed ZrCu B2 phase in the matrix of Zr48Cu47.5Al4Co0.5 BMG. Then, the different cooling rates of solidification process are further used to control the particle size of ZrCu B2 phase.
Based on the results of XRD analysis, Zr48Cu47.5Al4Co0.5 alloy rods with 0 ~ 0.75 vol.% Ta particle additions made by the copper mold at the temperature of -30°C present amorphous structure co-existing with ZrCu B2 phase. However, when the temperature of copper mold increases to higher than -20 °C, the sample with 0.75 vol.% Ta particle additions will be totally crystallized. After adding Ta particles, the precipitates of ZrCu B2 phase in the Zr48Cu47.5Al4Co0.5 alloy matrix exhibit more even distribution and round shape. But when decrease the cooling rate of solidification, the large amount of ZrCu B2 precipitates will agglomerate and form a large particle. According to the results of DSC analysis, with increasing the amount of Ta particles and decreasing the cooling rate of solidification, the enthalpy value of crystallization exothermic peak decreases, which means that the volume fraction of amorphous matrix decreased and the precipitate of ZrCu B2 phase increased.
The results of compression test reveal that the sample of Zr48Cu47.5Al4Co0.5 added with 0.75 vol.% Ta particle performs the highest mechanical properties, 1750 MPa yield stress, 1890 MPa fracture stress, and 14 % plastic strain. This is 6.5 % improvement of plastic strain in comparison with its base alloy. |
