【作者】 龙卧云；

【导师】 卢安贤；

【作者基本信息】 中南大学 ， 材料学， 2012， 博士

【摘要】 非晶合金原子在三维空间呈拓扑无序排列,不存在常规晶态材料固有的晶粒、晶界等缺陷,宏观上呈现出各向同性,具有许多优异的性能,是材料科学界研究的热点领域之一。其中,Zr-A1-Ni-Cu体系因不含贵金属元素及有毒元素,并且具有较高的非晶形成能力而备受关注。然而,用常规模铸法制备Zr-A1-Ni-Cu块体非晶合金需要较为苛刻的工艺条件,难以产业化。机械合金化是一种非平衡态下的粉末固态合金化技术,通过高能球磨使粉末经受反复的变形、冷焊、破碎,最终达到原子级合金化的过程,现已广泛用于非晶合金粉末的制备。本文利用机械合金化的方法,以商业金属元素粉末为原料,合成Zr-A1-Ni-Cu非晶合金粉末,并结合实验和热力学原理对其非晶化的机理进行了探讨。常规模铸法因受熔体冷却速度和合金体系非晶形成能力的影响而使所制备的非晶合金尺寸非常有限,粉末固结工艺可以避免这种缺陷,从而开拓了另一种合成块体非晶合金的路线。基于成本考虑,本文采用常规的低压烧结方式对所制备的Zr-基非晶合金粉末进行烧结处理,探索非晶合金粉末的烧结方法。本文利用机械合金化方法成功制备了Zr5oAl15-xNi10Cu25Yx非晶合金粉末,探索了Y取代Al对体系非晶形成能力的影响,确定了Y的最佳添加量,为利用合金元素添加的方法来提高体系的非晶形成能力提供有力的实验证明。研究了外部添加剂对体系热稳定性的影响,确定了体系的最佳添加剂类型及其含量。利用低压烧结处理将非晶合金粉末烧结成型,探索了添加剂类型、含量、烧结温度以及保温时间对制品形貌及基本力学性能的影响。主要结论如下：1.利用共晶点原则设计了Zr50Al15Ni10Cu25体系基础组成,并采用正交实验方法法,由机械合金化技术在较低的转速(170r/min)及20：1的球料比条件下球磨60小时后,由商业金属元素粉末合成了Zr50Al15-xNi10Cu25Yx系列非晶合金粉末。2.探索了Y元素部分取代A1对体系非晶化的影响,发现添加适量的Y可以增加系统无序度并消除体系中氧杂质的有害作用,提高Zr50Al15-xNi10Cu25Yx体系的非晶形成能力,Y的最佳添加量为1.25at.%,过少或过多的Y引入量都会降低体系的非晶形成能力。3.用热力学方法对Y的最佳添加量进行了简单的分析。结果表明,随Y含量的增加,体系的混合焓呈现单调递减趋势,而系统的混合熵则呈现出抛物线形变化规律,在x=7.5时达到最大值,通过对等效自由能数据进行曲线拟合后发现,系统在x=1.20时获得最低的等效自由能,热力学上最有利于非晶合金的形成。4.探索了外部添加剂对Zr50A115Ni10Cu25非晶合金体系热稳定性的影响,发现适量(5wt.%)的外部添加剂(Si3N4)能有效提高Zr50A115Nil0Cu25非晶合金粉末的析晶活化能,可以抑制Zr50A115Ni10Cu25系统在升温过程中的析晶,增强体系的热稳定性,有助于非晶合金粉末的加热固结成型。5.探索了zr50A115-xNi10Cu25Yx非晶合金粉末的低压烧结工艺,由于实验过程中所采用的烧结温度过高,导致了经低压烧结后非晶合金粉末已完全非晶化,未能成功获得zr50A115-xNi10Cu25Yx块体非晶合金材料。6.探索了外部添加剂颗粒在Zr50Al15_xNi10Cu25Yx非晶合金粉末的低压烧结过程中的作用,发现适当的外部添加剂能起到一定的骨架作用,强化非晶基体。其中,以Si3N4的添加总体效果最好,块体样品的最高抗弯强度达115.22MPa。但由于添加物颗粒较粗,手工碾磨的方式很能使其均匀分散在基体粉末中,严重影响制品性能。更多还原

【Abstract】 Metallic glasses have extraordinary disordered atomic configuration and no crystalline defects such as grain boundaries in conventional crystal metals. The structurally and chemically homogeneous glassy phase characteristics of metallic glasses provide many excellent properties compared to crystalline counterparts. Metallic glasses have been one of research fronts in materials science, of which, Zr-Al-Ni-Cu amorphous alloy has attracted more attentions because there exist no precious metal elements or toxic elements. Furthermore, the alloy has strong glass forming ability. The preparation of metallic glasses by conventional molding is affected by many rigorous preparation requirements, and it is hard to industrialize the production. Mechanical alloying (MA) is a powder metallurgy processing technique that includes repeated cold welding, fracturing and rewelding of powder particles in a high-energy ball mill. Currently, MA has now been widely used to synthesize amorphous alloy powders. In this paper, amorphous Zr-Al-Ni-Cu alloy powders are prepared by MA at low vacuum with commercial pure element powders. The progress and mechanism of amorphization in mechanical alloying has been investigated by X-ray diffractometry, differential scanning calorimetry, scanning/transmission electron microscopy and the corresponding thermodynamic principle.It can easily obtain bulk samples with complex shapes by powder consolidation techniques. A number of studies have been carried out on the consolidation of amorphous alloy powders using various consolidation techniques. Powder consolidation is a relatively new method to obtain large-sized amorphous alloy with excellent properties. Based on cost considerations, the high-cost methods such as ultra-high-pressure consolidation, extrusion consolidation and spark-plasma sintering are not adopted in the research. In order to reduce the preparation cost, this paper explores a more economical consolidation method for Zr-based amorphous alloy powders by conventional low-pressure sintering.The study successfully prepared Zr-Al-Ni-Cu-Y amorphous alloy powders by mechanical alloying, and explored the beneficial effects of Al partially substituted by Y in Zr5oAl15Ni10Cu25on glass forming ability. The optimum substitution amount of Y is1.25at%, which provides a convincing experimental evidence for improving glass-forming ability of Zr-based amorphous alloy by minor alloying elements additions. The influence of external additive particles on the thermal stability of amorphous powders was investigated, and the optimum type and content of additive particles for Zr-Al-Ni-Cu have been determined. The amorphous alloy powders were consolidated by low-pressure sintering process. And then the paper explored the influence of additive particles and sintering temperature on morphology and mechanical properties of bulk Zr-Al-Ni-Cu-Y composite. The main conclusions of this paper are listed as below.1. Numerous experiments have indicated that an amorphous alloy can exhibit high glass forming ability when its composition lies along the binary eutectic line with low melting temperature in hypoeutectic composition. Based on these studies, a new composition Zr5oAl15Ni10Cu25is presented. And Zr5oAl15-xNi10Cu25Yx amorphous alloy powders can be synthesized from low purity commercial powders by mechanical alloying after60hours milled under the condition of low rotational speed (170r/min) and ball-to-powder weight ratio of20:1.2. The influence of Al partial substituted by Y in Zr5oAl15Ni10Cu25on glass forming ability is investigated. It can be found out that an appropriate amount of Y addition can make the atoms in Zr5oAl15Ni10Cu25arrange more disordered and scavenge the oxygen impurity in the system via the formation of innocuous yttrium oxides, thus improve the glass forming ability of Zr50Al15-xNi10Cu25Yx. The optimum addition amount of Y is1.25at%. Below or beyond that amount, the glass-forming ability of the system will decline.3. In order to optimize the addition amount of yttrium, a simple analysis based on the thermodynamic principle is carried out. It can find that the the mixing enthalpy of the system is monotonously decreased with the Y content increased, but the mixing entropy first increases and then decreases. The maximal mixing entropy appears at x=7.5. As can be seen from the fitting curve of equivalent free energy, free energy approaches to its lowest value at x=1.25, that is to say, the yttrium amount is appropriate for amorphous alloys formation from the point of view of thermodynamic principle.4. The impact of external additive particles on the thermal stability of Zr50Al15-xNi10Cu25Yx amorphous alloy has been explored. Results show that an appropriate amount (5wt.%) of the external additive particles (Si3N4) can effectively increase the crystallization activation energy of the amorphous matrix and thus improve the thermal stability. And good thermal ability is helpful for the consolidation of the amorphous alloy powders under heating process.5. The consolidation of Zr50Al15-xNi10Cu25Yx amorphous alloy powders by low-pressure sintering has been explored. Because of the sintering temperature is much higher than the crystallization temperature, all amorphous powders have been crystallized in the sintering process and no bulk amorphous alloys are obtained.6. The role of external additive particles on consolidating Zr5oAl15-x Ni10Cu25Yx amorphous alloy powders by low-pressure sintering process is investigated. It is found out find that the external additive particles can act as a framework in the amorphous alloy powders, thus strengthen the amorphous matrix. Among the three different additives, Si3N4has the best performance for consolidating Zr50Al15-xNi10Cu25Yx amorphous alloy powders. The highest flexural strength value is up to115.22MPa. Because of the particle size of the additives are large than the amorphous powders, it is hard to disperse the external additive particles homogeneously in the amorphous powders by means of hand milling. The inhomogeneous external particles can greatly restrict the structure and performance of the products.更多还原