I摘 要 本文采用铜模吸铸法成功地制备了直径3 mm的Zr(65x)HfxCu17.5Ni10Al7.5原子比 大块非晶合金及非晶基复合材料利用 X 射线衍射XRD光学显微镜OM示差扫描量热仪DSC差热分析仪DTA电液伺服万能试验机MTS和扫描电子显微镜SEM等技术手段研究了不同含量的 Hf 替代 Zr 后对淬火态 Zr(65x)HfxCu17..5Ni10Al7.5x165合金的微观结构玻璃形成能力热稳定性晶化动力学压缩力学性能以及断口形貌的影响 XRD 和 OM 实验结果表明1 %的 Hf 替代 Zr 后形成了大块非晶合金而 2-10 %的 Hf 替代 Zr 后形成了大块非晶基复合材料该复合材料是由微米级的树枝晶弥散均匀分布在非晶基体上组成的且枝晶尺寸随 Hf 含量的增加而增大 DSC 和 DTA 的实验结果表明淬火态 Zr(65 x)HfxCu17.5Ni10Al7.5合金在x1565时其玻璃转变现象已不明显在 x110 时随着 Hf 含量的增加非晶基体的热稳定性逐渐提高故 Zr55Hf10Cu17.5Ni10Al7.5非晶复合材料具有最高的热稳定性但合金系玻璃形成能力随 Hf 含量的增加呈下降趋势 Hf 完全替代 Zr 后合金结构为完全晶态另外热分析结果还表明淬态结晶相的体积分数随 Hf 含量增加而增大 非等温晶化动力学实验结果表明大块非晶复合材料具有和单相大块非晶合金相同的动力学特征即玻璃转变和晶化都具有显著的动力学效应与淬火态Zr64Hf1Cu17.5Ni10Al7.5大块非晶合金相比Zr60Hf5Cu17.5Ni10Al7.5非晶复合材料的晶化表观激活能稍大进一步证实了大块非晶复合材料的热稳定性要高于单相非晶合金 压缩力学性能及断口形貌分析表明淬态结晶相的晶粒尺寸和体积分数对非晶复合材料的力学性能起着至关重要的作用相对于完全非晶合金 Zr64Hf1Cu17.5Ni10Al7.5而言大块非晶基复合材料 Zr63Hf2Cu17.5Ni10Al7.5和 Zr60Hf5Cu17.5Ni10Al7.5中枝晶相的存在阻止了单一剪切带的扩展诱发了更多剪切带的形成从而使得材料的塑性变形能力有了较大的提高而复合材料 Zr55Hf10Cu17.5Ni10Al7.5的枝晶相体积分数较高且晶粒尺寸较大从而导致其脆性断裂 关键词大块非晶合金 大块非晶基复合材料 热稳定性 晶化动力学 力学性能 IIAbstract In this dissertation, bulk metallic glass (BMG) and metallic glass matrix composites Zr(65 x)HfxCu17.5Ni10Al7.5 (at.%) with 3 mm diameter were successfully synthesized by using copper mold suction casting method. The effect of replacement of Zr with Hf on microstructure, glass formation, thermal stability, crystallization kinetics, compressive mechanical behavior and fracture feature of the as-quenched Zr(65x)HfxCu17.5Ni10Al7.5 (x=1-65) alloys were investigated by means of X-ray diffraction (XRD), optical microscopy (OM), differential scanning calorimetry (DSC), differential thermal analysis (DTA), mechanical testing system (MTS) and scanning electron microscopy (SEM). The results of XRD and OM indicate that the substitutions of 1 and 2-10 at.% Hf for Zr lead to the formation of BMG and metallic glass matrix composites, respectively. The composites are characterized by a homogeneous distribution of micron-scale dendrites embedded in the amorphous matrix, and the size of the dendrites increases gradually with the increase of Hf content from 2 to 10 at.%. A comparison of DSC and DTA traces shows that no discernible endothermic peaks of glass transition exist for the alloys with x=15-65. The thermal stability enhanced while the glass forming ability decreased with the substitution of Hf for Zr in Zr(65x)HfxCu17.5Ni10Al7.5 alloys when x=1-10. Among these alloys, composite Zr55Hf10Cu17.5Ni10Al7.5 has the best thermal stability with the supercooled liquid region of 130 K. Fully crystalline structure was obtained when Zr was completely replaced with Hf. In addition, the results of thermal analyses present that the volume fraction of quenched-in crystalline increases significantly with the substitution of Zr by Hf. The results of non-isothermal crystallization kinetics demonstrate that the metallic glass matrix composite has the same kinetic characterization with single-phase BMG in that both glass transition and crystallization have a significant kinetic effect. Apparent activation energy for crystallization of BMG matrix composite Zr60Hf5Cu17.5Ni10Al7.5 is somewhat larger than that of BMG Zr64Hf1Cu17.5Ni10Al7.5, further confirming that the thermal stability of BMG matrix composite is higher than that of fully amorphous alloy. Study of compressive mechanical behavior and fracture feature reveals that the grain size and volume fraction of quenched-in crystalline play an important role in mechanical IIIproperties of BMG matrix composite. Compared with single-phase BMG Zr64Hf1Cu17.5Ni10Al7.5, the dendrites in BMG matrix composites Zr63Hf2Cu17.5Ni10Al7.5 and Zr60Hf5Cu17.5Ni10Al7.5 can hinder the propagation of shear bands and initiate the formation of multiple shear bands, therefore, causing an improvement of plasticity. However, composite Zr55Hf10Cu17.5Ni10Al7.5 exhibits brittle fracture behavior due to its large grain size and high volume fraction of quenched-in crystalline. Key words: Bulk metallic glass Bulk metallic glass matrix composite Thermal stability Crystallization kinetics Mechanical behavior 1 1 绪 论 1.1 大块非晶合金的发展概况 金属材料的应用和发展经历了漫长的岁月在以往的 8 千年中人类所使用的金属都是晶态材料而非晶态金属合金Amorphous metallic alloys亦可称为玻璃态合金Glassy alloys或非结晶合金Noncrystalline alloys[1]是指结构类似于玻璃的无固定形态的金属和合金它们是一种新型的功能材料主要特点是原子的三维空间呈拓扑无序状排列结构上没有晶界和堆垛层错等缺陷存在组成元素之间以金属键相连并在几个晶格常数范围内保持短程有序因此具有许多不同于传统晶态材料的优异性能 最初的非晶态金属合金是通过急冷的方法将气态或液态的金属冷冻成为刚性固体而其内部仍保持液态的结构1934 年德国的 Kramer 首次用蒸发沉积法制备出了非晶态合金 不久 Brenner 等用电解沉积法得到了 NiP 非晶合金[2]然而这些非晶都是附着于某种基底上的非晶膜很难单独研究它们的特性直到 1960 年美国加州理工学院的 Duwez [3]采用熔体快冷技术 104106 K/s 即直接将熔融金属快速冷却得到了非晶态合金这种方法从工艺上突破了制备非晶态合金的关键于是熔体急冷技术迅速成为人们研制金属玻璃的主要手段1969 年美国人 Pond 等发明了单辊快淬法生产连续的非晶条带从而为大规模生产非晶态合金创造了条件[4]但由于这些合金体系的非晶形成能力普遍较弱其制备需要大于 105 K/s 的临界冷却速率只能形成最大厚度为 10100 mm 的非晶带材或粉末[5]因而极大地限制了对这类材料的进一步研究和开发利用虽然在 80 年代人们也曾试图通过机械合金化[6-7]固相反应法[8-12]来制备一些三维大块非晶材料但是由于此类方法存在着一些难以克服的缺陷如原始低维非晶材料在制备过程中表面的氧化污染可使得固化后的块体非晶材料整体性能大幅下降所以也没有从根本上解决问题 多年来寻求具有很强非晶形成能力能够直接从液相获得三维尺寸都在毫米级以上的大块非晶合金Bulk amorphous alloys or bulk metallic glasses体系一直是科学家们追求。