【摘要】：針對非晶合金在過冷液相區(qū)進行熱塑性成形時的氧化問題,本研究分析了加熱條件、表面形貌和應(yīng)力狀態(tài)對Zr55Cu30Al10Ni5非晶合金氧化行為的影響,討論了其在過冷液相區(qū)的氧化機理,并評價了氧化后非晶合金樣品的綜合性能。通過改變加熱溫度和保溫時間,觀察在不同加熱條件下非晶合金的氧化行為。根據(jù)熱重曲線和等溫晶化曲線,發(fā)現(xiàn)其氧化動力學(xué)行為遵循多級拋物線速率定律,且其動力學(xué)行為轉(zhuǎn)變是由晶化引起的。氧化層表面會形成由單質(zhì)Cu和CuO組成的析出顆粒,氧化層的主要成分是t-ZrO2、m-ZrO2以及A1203。隨著氧化程度的加劇,氧化層結(jié)構(gòu)由單層向多層轉(zhuǎn)變。非晶合金在過冷液相區(qū)的氧化速率是由離子擴散控制的,Cu離子向外擴散而O離子向內(nèi)擴散。通過表面磨拋處理,使非晶合金獲得不同的表面形貌,分析表面形貌對氧化速率的影響。研究表明,隨著磨料粒徑增大,表面析出顆粒的尺寸和數(shù)量升高,而氧化層厚度也隨之增加。熱動力學(xué)分析證明,粗糙表面對氧化的促進作用是由表面劃痕尖銳度,而不是表面粗糙度直接決定的。從擴散動力學(xué)的角度,解釋了粗糙表面對非晶合金氧化的促進機理。通過在氧化過程中對樣品施加恒定的拉／壓載荷,分析應(yīng)力狀態(tài)對非晶合金氧化行為的影響。研究證實,壓應(yīng)力可以抑制非晶合金的氧化,而拉應(yīng)力則能促進非晶合金的氧化,但是兩者的作用效果都比較有限�；趯ρ趸昂蠓蔷Ш辖饦悠肺⒂^組織和化學(xué)成分的分析,討論其在過冷液相區(qū)的氧化機理。在氧化早期,氧化物通過晶格擴散以樹枝晶形態(tài)生長。當(dāng)基體層完全晶化以后,氧化層通過晶界擴散進行生長。Cu離子持續(xù)從氧化層中的晶界處向外擴散,導(dǎo)致氧化層中出現(xiàn)相互連通的縫隙。氣態(tài)O2分子通過這些縫隙進入氧化層內(nèi)部,一方面繼續(xù)推進氧化層的生長,另一方面也導(dǎo)致在已形成的氧化層中出現(xiàn)新的亞層結(jié)構(gòu)。采用納米壓痕、納米劃痕和動電位掃描評價氧化后非晶合金樣品的微觀硬度、摩擦系數(shù)和耐蝕性能,分析氧化對非晶合金性能的影響。研究表明,在氧化后,氧化層和基體層的微觀硬度顯著提高：表面摩擦系數(shù)下降,有利于降低成形過程中的流動阻力：腐蝕電位升高,表明其耐蝕性能得到了改善。綜上所述,Zr55Cu30Al10Ni5非晶合金在過冷液相區(qū)的氧化會顯著影響熱塑性成形產(chǎn)品的表面形貌、尺寸精度以及綜合性能。通過控制非晶合金熱塑性成形過程中溫度和時間等參數(shù),不僅能避免氧化造成的負面影響,還可能在成形的同時實現(xiàn)產(chǎn)品的強化。
[Abstract]:In this paper, the effects of heating conditions, surface morphology and stress state on the oxidation behavior of amorphous alloy Zr55Cu30Al10Ni5 in the supercooled liquid phase region were studied, and the oxidation mechanism of the amorphous alloy in the supercooled liquid phase region was discussed. The comprehensive properties of the oxidized amorphous alloy samples were evaluated. The oxidation behavior of amorphous alloys under different heating conditions was observed by changing the heating temperature and holding time. According to the thermogravimetric curves and isothermal crystallization curves, it is found that the kinetic behavior of oxidation obeys the law of multistage parabolic rate, and the transformation of kinetic behavior is caused by crystallization. Precipitated particles consisting of Cu and CuO are formed on the surface of the oxide layer. The main composition of the oxide layer is t _ 2O _ 2, mg _ 2-ZrO _ 2 and A _ 120 _ 3. With the aggravation of oxidation degree, the structure of oxide layer changes from single layer to multi-layer. The oxidation rate of amorphous alloy in the supercooled liquid phase is controlled by ion diffusion. The Cu ion diffuses outward and the O ion diffuses inward. The surface morphology of amorphous alloy was obtained by surface grinding and polishing, and the effect of surface morphology on oxidation rate was analyzed. The results show that the size and quantity of precipitated particles increase and the thickness of oxide layer increases with the increase of abrasive particle size. It is proved by thermodynamic analysis that the effect of surface roughness on oxidation is directly determined by the sharpness of the surface scratch rather than the surface roughness. From the point of view of diffusion kinetics, the mechanism of promoting oxidation of amorphous alloy by rough surface is explained. The effect of stress state on the oxidation behavior of amorphous alloy was analyzed by applying constant tension / compression load to the sample during oxidation. It is proved that compressive stress can inhibit the oxidation of amorphous alloy, while tensile stress can promote the oxidation of amorphous alloy, but the effect of both is limited. Based on the analysis of microstructure and chemical composition of amorphous alloy samples before and after oxidation, the oxidation mechanism in the supercooled liquid phase region was discussed. In the early stage of oxidation, oxide grows in dendrite form through lattice diffusion. When the substrate layer is completely crystallized, the oxide layer grows through the grain boundary diffusion. The Cu ion continues to diffuse outward from the grain boundary in the oxide layer, resulting in the formation of connected cracks in the oxide layer. Gaseous O2 molecules enter the oxide layer through these gaps, on the one hand continue to promote the growth of the oxide layer, on the other hand, lead to the formation of a new sublayer structure in the formed oxide layer. The microhardness, friction coefficient and corrosion resistance of the oxidized amorphous alloy samples were evaluated by nano indentation, nano scratch and potentiodynamic scanning, and the effect of oxidation on the properties of the amorphous alloy was analyzed. The results show that after oxidation, the microhardness of the oxide layer and the substrate layer is significantly increased, and the friction coefficient of the surface decreases, which is beneficial to the reduction of the flow resistance during the forming process. The increase of the corrosion potential indicates that the corrosion resistance of the oxide layer and the substrate layer is improved. In conclusion, the oxidation of Zr55Cu30Al10Ni5 amorphous alloy in the supercooled liquid phase will significantly affect the surface morphology, size accuracy and comprehensive properties of thermoplastic forming products. By controlling the parameters such as temperature and time during thermoplastic forming of amorphous alloy, the negative effects caused by oxidation can not only be avoided, but also the strengthening of the products may be realized at the same time.
【學(xué)位授予單位】：華中科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG139.8

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