【作者】 李桂华；

【导师】 王伟民； 边秀房；

【作者基本信息】 山东大学 ， 材料学， 2010， 博士

【摘要】 本文主要选择Al-TM-RE(TM表示过渡族金属元素,RE表示稀土元素)基非晶合金为研究对象,分别研究了其非晶形成能力(GFA)与元素添加、热膨胀行为和耐腐蚀性的关系。此外,还研究了不同退火气氛(氢气(H2)、空气(air)、氩气(Ar)和氮气(N2))对Al基非晶合金的晶化、微观硬度和耐腐蚀性的影响。利用X射线衍射仪(XRD)、差示扫描量热仪(DSC)和高温粘度仪分析了Si元素的添加对Al-Fe-La合金非晶形成能力和热稳定性的影响,发现Al88-xFe6La6Six(x=0,0.5,1-4)合金系都为完全的非晶结构,且Al86Fe6La6Si2合金的GFA最好,Al87Fe6La6Si1合金的热稳定性最好。这是因为适量Si的加入会引起：(1)大的原子尺寸差进而增加了Al-Fe-La非晶合金的密排密度；(2)更负的混合焓；(3)化学钝化熔体中引起异质形核的杂质(如氧和碳),从而提高了合金的GFA。但是当Si含量大于2 at.%时会降低合金的热稳定性和GFA,这是因为多余的Si会与其他元素形成硅化物,引起异质形核,从而降低了GFA。另外,随着Si含量的增加,Al-Fe-La合金的晶化过程发生改变,由两次晶化过程转变为三次晶化过程。利用XRD、DSC、透射电子显微镜(TEM)、交流梯度磁力计(AGM)和微观硬度仪等研究了相似元素Ni-Co和La-Ce替代对Al86Ni9La5非晶合金的GFA、磁性和硬度的影响。研究发现试样的GFA的大小关系为：Al86(Ni0.5Co0.5)9(La0.5Ce0.5)5<Al86Ni9La5<Al86Ni9(La0.5Ce0.5)5,说明相似元素替代只能有限的提高合金的GFA。另外,三种合金在室温下都显示了抗磁性行为,这主要与Al-Ni-La合金的微观结构,即相似元素替代后二十面体结构和析出相的数量有关。利用高温粘度仪和热膨胀仪研究了Al86Ni9La5和Al86Ni9(La0.5Ce0.5)5非晶合金的动力学粘度和热膨胀行为,从自由体积出发,发现无论在液态或非晶态,Al86Ni9(La0.5Ce0.5)5合金中含有的自由体积都比Al86Ni9La5合金的少,表明Ce的加入降低了Al-Ni-La合金的自由体积,提高了原子尺寸的连续性,从而提高了GFA。同时也证实了熔体结构和非晶结构存在着相关性。另外,还研究了Al84Ni10RE6(RE=Y,Ce,Gd和Er)非晶合金的热膨胀行为。发现Al86Ni9La5、Al86Ni9(La0.5Ce0.5)5和Al84Ni10RE6(RE=Y,Ce,Gd和Er)六种Al基非晶合金的线性热膨胀系数(αas)与液相线温度(T1)的比值θ′,即αas／T1,与合金的GFA成正的相关性。还发现在Cu基和Gd基非晶合金中也存在这一现象,说明在同一合金系中,可以用新参数θ′来判断合金的GFA,θ′越大,GFA越好。此外,根据自由体积理论,GFA好的合金一般含有较小的自由体积。利用XRD、DSC、电化学工作站、扫描电镜(SEM)、能谱分析(EDS)和X-ray光电子能谱(XPS)研究了Al94-xNixGd6(x=6,8,10,12)非晶合金的GFA和电化学行为。研究发现：(1)随着Ni含量的增加,Al-Ni-Gd合金的热稳定性和GFA是逐渐增加的,Al-Ni-Gd合金的GFA的大小关系为：Al82Ni12Gd6>Al84Ni10Gd6>Al86Ni8Gd6>Al88Ni6Gd6；(2)Al-Ni-Gd合金在3.5 wt.%NaCl和0.1 mol／L NaOH溶液中的耐腐蚀性要优于在0.1 mol／L HCl溶液中的耐腐蚀性；(3)Al-Ni-Gd合金的非晶形成能力越好,合金的耐腐蚀性越优异；(4)阳极极化区间内在-0.5～-0.25V范围内的电流密度峰总是出现在含有Cl-的电解液中,这是Ni2+的氧化和Cl-共同作用的结果。在不同退火气氛(H2、air、Ar和N2)下对Al86Ni9La5非晶合金进行退火,并用XRD和TEM分析其析出相。研究发现：(1)在523 K(第一次晶化峰Tp1附近)退火时,初晶相Al与退火气氛无关；(2)在584 K(第二次晶化开始温度Tx2附近)退火时,晶体的最终产物为：Al、Al11La3和Al3Ni相,也与退火气氛无关；(3)在523 K退火时,H2和air能明显提高Al86Ni9La5非晶合金的共晶过程,引发亚稳相Al3Ni2的形成,所研究的气氛对晶化影响的大小关系为：H2>air>Ar>N2。随后利用硬度计和电化学工作站研究了退火后合金的微观硬度和电化学行为,发现在523 K下,与在Ar和N2中退火的条带相比,在H2和air中退火的条带显示了较高的硬度和较好的耐腐蚀性。退火试样性能的改善与在退火过程中形成的纳米晶相相关,这有助于该合金在海水环境中应用的研究。更多还原

【Abstract】 In the present thesis, Al-TM-RE-based (TM:transition metal; RE:rare earth) amorphous alloys were mainly chosen for the study of the relationships between glass-forming ability (GFA) and elements addition, thermal expansion behavior and corrosion resistance, respectively. In addition, the effect of different annealing atmospheres (H2, air, Ar and N2) on crystallization behavior, microhardness and corrosion resistance of Al-Ni-La amorphous alloy was also investigated.The effect of Si addition on the GFA and thermal stability of melt-quenched Al-Fe-La alloys has been investigated systematically by using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and viscometer. Results show that all the Alg88-xFe6La6Six (x= 0,0.5,1-4) alloys are full amorphous structure, moreover Al86Fe6La6Si2 alloy has the best GFA, and Al87Fe6La6Si1 alloy has the best thermal stability. That is because appropriate Si addition can induce:(1) larger packing density of the Al-Fe-La amorphous alloys due to large atomic size difference; (2) a larger negative heat of mixing; (3) the passivation of impurities (such as oxygen and carbon) which trigger heterogeneous nucleation in the melt, which increases the GFA. However, when Si content (csi) is beyond 2 at.%, the addition of Si reduces the GFA and thermal stability of the alloys. The reason is that the redundant Si atoms incline to form silicides with Al and Fe, i.e. increase the number of final phases which may serve as heterogeneous nucleation sites, then deteriorate the GFA. In addition, it is also found that the addition of Si influences the crystallization behaviors of the alloys, transforming from two-step crystallization process to three-step crystallization process.The effects of similar element pairs:La-Ce and Ni-Co, on the GFA, magnetic properties and hardness of Al-Ni-La alloy were investigated using XRD, transmission electron microscopy (TEM), DSC, magnetometer and hardness-tester. The results show that the GFA of the samples in the order of Al86Ni0.5Co0.5)9(La0.5Ce0.5)< Al86Ni9La5< Al86Ni9(La0.5Ce0.5)5, implying that similar element substitution has a limited enhancing effect on the GFA of the present Al-Ni-La alloy. In addition, the measured samples display a diamagnetic behavior at room temperature. The variations of diamagnetic behavior as well as the microhardness of the samples are strongly dependent on the microstructure, i.e. the amounts of the icosahedral structure and precipitates, after the similar element substitution in Al-Ni-La alloy.The dynamic viscosities and thermodynamic dilatometric behaviors of Al86Ni9La5 and Al86Ni9(La0.5Ce0.5)5 amorphous alloys were investigated using viscometer and conventional dilatometer. Results show that based on free volume theory, less free volume is found in Al86Ni9(La0.5Ce0.5)5 alloy than Al86Ni9La5 alloy in both melt and glassy states, suggesting that the partial substitution La by Ce decreases the quantity of free volume in Al-Ni-La system by improving the continuous degree of atomic size, which leads to the improvement of GFA. Meanwhile, it can be confirmed than the properties of a glass are closely related to the properties of a liquid. In addition, the dilatometric of Al-Ni-RE (RE=Y, Ce, Gd and Er) amorphous alloys were also investigated. It is found that the ratio of the linear thermal expansion coefficient (aas) and the liquidus temperature (T1) (aas/T1), defined byθ’, has a good positive correlation with GFA in Al86Ni9La5, Al86Ni9(La0.5Ce0.5)5 and Al-Ni-RE (RE=Y, Ce, Gd and Er) amorphous alloys. A similar phenomenon is also found in Gd-and Cu-based amorphous alloys. Consequently, the parameterθ’ can be applied to predict the GFA in the system with same main element. Based on the free volume model, it is found that the amorphous alloy which exhibits better GFA contains less free volume.The GFA and corrosion behaviors of Al94-xNixGd6 (x=6,8,10,12) amorphous alloys were investigated using XRD, DSC, electrochemistry experiment, SEM, EDS and XPS. The results show that:(1) with the increasing of Ni content, the thermal stability and GFA of Al-Ni-Gd alloys increase continually, and the GFA is in the order of Al82Ni12Gd6> Al84Ni1oGd6> Al86Ni8Gd6> Al88Ni6Gd6; (2) the corrosion resistance of Al-Ni-Gd alloys is better in 3.5 wt.% NaCl and 0.1 mol/L NaOH solutions than in 0.1 mol/L HC1 solution due to the formation of wide passive region; (3) the higher the GFA of Al-Ni-Gd alloy, the better the corrosion resistance; (4) the current density peak at-0.5 -0.25 V always appears in the Cl- containing solutions, which results from the co-function of the oxidation process of Ni2+ and Cl-.The Al86Ni9La5 amorphous ribbons were annealed in different annealing atmospheres (H2, air, Ar and N2), and the precipitated phases were investigated using XRD and TEM. Results show that:(1) during annealing at 523 K (about the peak temperature of first crystallization Tp1), the primary crystallized Al is independent on the annealing atmospheres; (2) during annealing at 584 K (about the onset temperature of second crystallization Tx2), the final crystalline phases, i.e. Al+Al11La3+Al3Ni, are also independent on the different annealing atmospheres; (3) during annealing at 523 K, H2 and air can promote the eutectic crystallization process, and induce the formation of metastable Al3Ni2 phase, and the promoting effect of different annealing atmospheres is in the order of H2> air> Ar> N2. In addition, the microhardness and corrosion resistance in the 3.5 wt.% NaCl solution of the annealed samples were also investigated by micro-hardness tester and electrochemistry experiment. Comparing with the ribbons annealed at 523 K in Ar and N2, the ribbons annealed in H2 and air show a higher microhardness and a better corrosion resistance. The property promotion caused by annealing process can be ascribed to the formation of nano-crystalline phases, which is possibly helpful to develop the alloy’s application in the seawater environment.更多还原