氫對金屬玻璃機械性質及結構之影響

Effects of Hydrogen on Mechanical Behavior and Structure of Bulk Metallic Glasses

莊智斌(Chih-Pin Chuang)

指導教授 ： 黃嘉宏 ； 喻冀平

國立清華大學/原子科學院/工程與系統科學系/博士(2012年)

https://doi.org/10.6843/NTHU.2012.00300

摘要

塊狀非晶合金,又稱”金屬玻璃”或”液態金屬”,是金屬材料領域內新開發的一類特殊材料。因為其特殊的非晶體結構，金屬玻璃具有優異的材料性能，例如: 高強度(~4-5 GPa, 鐵基金屬玻璃)，高彈性極限(~2%)，高抗腐蝕性及軟磁性。這些獨特的功能使其在先進工程材料領域有極大的應用潛力，尤其是在結構材料領域的應用。此外，研究人員發現部分塊狀金屬玻璃（BMG）成分有極佳的儲氫能力，可應用在與氫氣能源相關的產業，如氫儲存與氫燃料電池裡的質子交換薄膜。當氫吸附進入金屬材料裡，卻會造成材料機械性質的劣化，產生“氫脆”(hydrogen embrittlement)效應。如何解決“氫脆”現象一直是材料科學家和工程師研究的主題。不管對於以上任何一個角度來看，了解氫對非晶合金的力學性能和結構上的影響都是很重要的。
本研究主要探討氫對鋯基非晶合金的機械性質和微結構的影響。在對鋯基非晶彈性變形的研究中發現，在巨觀尺度下BMG的彈性型變，卻是由微觀尺度下的塑性變形所組成。通過高能X射線散射和各向異性PDF分析，結果顯示當金屬玻璃變形時，約有20~25％的體積是非彈性的型變, 只有約75%~80%的體積是彈性型變。正如同傳統的氧化物玻璃，金屬玻璃的變形是粘彈性的(viscoelastic)。在氫對金屬玻璃機械性質的研究中發現，氫會增加鋯基BMG的硬度，也會降低Zr基BMG的破裂韌性。高能X光散射實驗和非彈性中子散射實驗結果顯示，氫原子進入到金屬玻璃內部後會佔據四面體的間隙原子位置，也就是四面體的中心。而在不同原子所組成的四面體中，氫又會優先佔據主要是鋯原子組成的四面體。氫進入此四面體後，會與周圍鋯原子穩定結合。而進入非鋯原子組成的四面體裡的氫原子則會在停止充氫後慢慢的從材料中被釋放出來。同時，吸附在金屬玻璃內的氫原子會撐大基材的體積，造成金屬玻璃極大的殘餘應力，此殘餘應力造成材料局部的塑性變形，此效應可能是造成金屬玻璃氫脆化的主要原因。

關鍵字

金屬玻璃 ； 氫脆 ； 高能X光散射

並列摘要

Bulk-amorphous metallic alloys are a new class of materials that exhibit superior material properties, these unique features makes them perspective materials for various advanced engineering applications. In addition, some of the bulk metallic-glass (BMG) compositions have drawn much attention for their potential for hydrogen-energy-related applications, such as hydrogen purification/separation membranes. “Hydrogen in metals” has been a popular topic for material scientists and engineers for many decades. One of the main reasons is the infamous ability of hydrogen to degrade the mechanical properties of most metallic materials. Another reason is the potential of using metal hydrides for hydrogen-storage materials. For either perspective, it is very important to understand the effect of hydrogen on the mechanical behavior and structure of BMGs.
In the present research, the effect of hydrogen on the mechanical behavior and structure of Zr-based BMGs have been studied. The deformation of the Zr-based BMG was first examined. It is found that the elastic formation of BMG in macroscopic scale is not “elastic” in atomic scale. Through x-ray scattering and the anisotropic PDF analysis, it is shown that about 25% of the volume of a metallic glass is occupied by anelastic sites, which are soft and bear no static shear load. Just as other glasses, metallic glasses are fundamentally viscoelastic. The dissolved hydrogen was found to increase the hardness of the Zr-based BMG, roughly 40% right after hydrogen charging. The hydrogen will also embrittle the Zr-based BMG. The embrittlement is attributed to the rearrangement of the local atomic structure and the decohesion of atomic bond strength. The atomic pair-distribution-function (PDF) analysis and inelastic neutron scattering experiment reveals that hydrogen atoms preferentially occupy tetrahedral-like interstitial sites composed of mainly Zr atoms. The introduction of hydrogen atoms results in a ~ 15% volume expansion of the amorphous matrix. Such volume expansion produces a large residual strain at the hydrogen-charged area.

並列關鍵字

Bulk Metallic Glass ； hydrogen embrittlement ； high energy X-ray ； Pair-distribution Function Analysis

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