【作者】 李庆丰；

【导师】 袁晓光； 邱克强；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2009， 博士

【摘要】 Mg基非晶合金由于具有高的比强度、良好的耐蚀性、低廉的价格而在精密仪器、微成型材料和3C产品中具有广泛的应用前景。但是由于通常Mg基非晶合金没有宏观上的塑性变形,断裂韧性也与SiO₂等理想脆性材料相当,使Mg基非晶合金的应用存在困难,因此提高Mg基非晶合金的塑性成为Mg基非晶合金研究的焦点。本文通过合金元素的力学特性和对Mg基非晶形成能力的分析,确定了以Mg-Cu-Nd、Mg-Ni-Cu-RE（RE=Y,Nd）、Mg-Zn-Ca和Mg-Ni-Zn-Y合金为主要研究对象,通过铜模铸造方法制备了不同直径的圆柱样品。采用扫描电镜、X射线衍射仪、差示扫描量热仪、透射电镜和拉压力学试验机等设备对合金的组织形貌、相结构、非晶合金的热力学稳定性、熔化行为和力学性能进行研究,获得了以下结果:在Mg-Cu-Nd三元合金系中,建立了非晶合金形成能力在2mm以上的成分区域。合金元素Ag可以提高Mg-Cu-Nd合金的非晶形成能力与力学性能。其中Mg₅₇Cu_30.5Nd₁₀Ag_2.5的非晶形成能力达到5mm,塑性变形量达到为1.5%。对Mg-Cu-Ni-Nd四元合金的研究结果表明,Mg_62.6Cu_10.5Ni₁₄Nd_12.9的临界制备尺寸至少可以达到直径5mm。而Mg₆₀Ni₁₀Cu₁₆Nd₁₄合金不仅具有较高的非晶形成能力（-5mm）,而且具有高达8.5%的塑性应变,这是目前所发现的塑性应变量最大的Mg基非晶合金,采用TEM分析表明,两种不同成分的非晶相所引起的剪切滑移过程的变化是引起塑性变形的主要原因。对Mg-Cu-Ni-Nd-Y五元合金的研究结果表明,Mg_58.5Cu_27.5Ni₃Nd₅Y₆可以形成直径达13mm的非晶合金,提出了采用计算应力与实验应力的相对差值估算实验应力的可靠性问题。计算结果表明,Mg_58.5Cu_27.5Ni₃Nd₅Y₆具有最小的相对误差,表明具有很好的实验应力再现性能。对Mg-Zn-Ca三元合金研究结果表明:非晶形成能力最佳的合金成分为Mg₆₈Zn₂₈Ca₄,其强度和塑性应变分别为828MPa和1.28%。在Ca含量控制在3-5at.%时,通过调节Mg和Zn的含量可以获得具有高性能的Mg基非晶合金及其复合材料。对Mg-Ni-Zn-Y四元合金的研究结果表明,当合金成分在Mg为73-81at%、Ni为8-12% at%、Zn为3-5at%、Y为6-10% at%范围时,可以形成具有长程有序相（LPO）韧化的Mg基非晶合金复合材料。合金成分中形成LPO相的最小Y/Zn值为0.57,而LPO相中的Y/Zn比值略大于1。其中Mg₈₁Ni₈Zn₅Y₆合金的压缩强度为550MPa,塑性应变为21%。这是目前所发现的塑性变形量最大的Mg基非晶合金复合材料。更多还原

【Abstract】 Mg-based bulk metallic glasses （BMGs） have potential application in precision instruments, micro-forming materials and 3C products due to their high special strength, good corrosion resistance and low cost. However, it is impossible to use such kind of materials because most of Mg-based BMGs exhibit no macro-plastic deformation under compression and the fracture toughness is comparable to the ideal brittle materials, such as SiO₂. Therefore, how to improve the ductility of Mg-based BMGs has become a key issue in this area.By considering mechanical properties and the effect on glass-forming ability （GFA） of choosing elements, glass-forming alloys were designed based on Mg-Cu-Nd, Mg-Ni-Cu-RE （RE=Y, Nd）, Mg-Zn-Ca and Mg-Ni-Zn-Y, respectively. As-cast samples with different diameters were fabricated by copper mould casting method. The microstructure, thermal properties related to amorphicity, melting behavior and mechanical properties of as-cast samples were examined by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, differential scanning calorimetry （DSC）, transmission electron microscopy （TEM） and compression-tension tester, respectively. The main experimental results are as following:The glass-forming region with BMG diameter up to 2 mm was located in Mg-Cu-Nd ternary phase diagram. The addition of Ag element can improve both the GFA and mechanical properties of Mg-Cu-Nd alloys. Furthermore, we found that the GFA reflected by critical cast diameter and plastic strain for Mg₅₇Cu_30.5Nd₁₀Ag_2.5 alloy are as high as 5 mm and 1.5%, respectively.For Mg-Cu-Ni-Nd alloys, at least 5 mm in diameter for glass formation was obtained for the Mg_62.6Cu_10.5Ni₁₄Nd_12.9 alloy. While the Mg₆₀Ni₁₀Cu₁₆Nd₁₄ alloy exhibits not only good GFA, but also excellent plastic strain up to 8.5%, which is the largest strain found up to now according to the literature. Such large plastic strain was attributed the two different compositional amorphous phase existed in matrix, as testified by TEM, which was able to change the shear process and such result in the plastic deformation of the related BMG. The GFA and the mechanical properties of Mg-Cu-Ni-Nd-Y alloys were investigated. The glass formation for Mg_58.5Cu_27.5Ni₃Nd₅Y₆ alloy is as high as 13 mm in diameter. Furthermore, we suggest that the reliability in fracture stress can be evaluated by the relative difference between calculated stress and experimental stress. The smallest value was found for Mg_58.5Cu_27.5Ni₃Nd₅Y₆ BMG, which demonstrates that the fracture stress of this alloy can be reproduced.The GFA for Mg-Zn-Ca alloys was investigated and the best one with composition of Mg₆₈Zn₂₈Ca₄ was located. The fracture stress and plastic strain for Mg₆₈Zn₂₈Ca₄ BMG are 828MPa and 1.28%, respectively. The glass formers and amorphous matrix composites with relative better mechanical properties can be obtained by adjusting Mg and Zn content when Ca content is between 3⁵at.% for Mg-Zn-Ca alloys.The long period ordered （LPO） structure can be formed in the amorphous matrix when Mg, Ni, Zn and Y are in the range of 73-81at%, 8-12% at%, 3-5 at% and 6-10% at%, respectively, which can improve the ductility of Mg-based BMGs. The critical Y/Zn ratio for LPO formation is 0.57 in the composition of alloys, whereas the value of Y/Zn ratio in the LPO is general larger than 1. The fracture stress and plastic strain for Mg₈₁Ni₈Zn₅Y₆ are 550MPa and 21%, respectively. The plastic strain is the largest one found up to now among Mg-based amorphous matrix composites.更多还原