Nd60Al10Fe20Co10金属玻璃的变形行为

利用材料测试系统(MTS)、X-Ray衍射(XRD)和扫描电镜(SEM)等手段研究了Nd基大块金属玻璃的变形行为和断裂特征.Nd基大块金属玻璃样品在室温下是脆性断裂,大约在500 K时变形模式从非均匀变形转变为均匀变形,在523 K以上表现出显著的塑性变形.在5×10-4 m/s的应变速率下,这种Nd基大块金属玻璃材料在523 K～600 K之间出现明显的屈服应力下降现象,随后进入1种稳定的粘性流动状态,而且这种屈服下降现象与温度和应变速率有关.这种在过冷液相区的变形行为与其他大块金属玻璃变形特征相似.合金的这种塑性变形行为表明了其存在稳定的过冷液相区,同时对其变形行为的研究有助于进一步了解Nd基大块金属玻璃的反常热稳定性.     

Kinetics of Glass Transition and Crystallization in Carbon Nanotube Reinforced Mg-Cu-Gd Bulk Metallic Glass

Mg65Cu25Gd10 bulk metallic glass and its carbon nanotube reinforced composite were prepared. Differential scanning calorimeter （DSC） was used to investigate the kinetics of glass transition and crystallization processes. The influence of CNTs addition to the glass matrix on the glass transition and crystallization kinetics was studied. It is shown that the kinetic effect on glass transition and crystallization are preserved for both the monothetic glass and its glass composite. Adding CNTs in to the glass matrix reduces the influence of the heating rate on the crystallization process. In addition, the CNTs increase the energetic barrier for the glass transition. This results in the decrease of GFA. The mechanism of the GFA decrease was also discussed.     

Al—Zn—Li—Mg—Cu合金在433K的时效行为

采用透射电镜（TEM）和Vickers硬度计研究了Al-Zn-Li-Mg-Cu合金在433K的人工时效行为,结果表明,在等温时效动曲线上存在双阶硬化行为。第一阶段硬化起因子合金基体上沉淀析出的δ′相（AlLi） 时效强化效果来自δ′相;随着时效的进行,到达第二时效硬化峰,在合金基体上除了δ′相外,大量析出一种具有准晶结构的沉硬化相（命名为X相）,此时,时铲强化效果来处自δ′相和X相,在X相的周围存在无δ′相析出区,表明X相含有Li原子,X相呈棒状,棒的长轴与基体的＜110＞Al方向一致,EDS测试表明,X相富集Cu,Zn和Mg。     

块体非晶合金在低温下的剪切带特征

通过宏观洛氏压痕实验在低温(193K)下对玻璃转变温度和本征脆性具有显著差别的5种典型非晶合金(Mg65Cu25Gd10,La55Al25Cu10Ni5Co5,Pd43Cu27Ni10P20,Zr47.9Ti0.3Ni3.1Cu39.3Al9.4,Fe52Cr15Mo9Er3C15B6)的剪切带特征进行了研究。考查了剪切带间距和数量与归一化温度和材料本征脆性的关联,并根据放射状剪切带的夹角讨论了不同合金的压力敏感系数及其影响因素。     

Microstructure and mechanical properties of Zr-Cu-Al bulk metallic glasses

Zr49Cu46Al5 and Zr48.5Cu46.5Al5 bulk metallic glasses（BMGs） with diameter of 5 mm were prepared through water-cooled copper mold casting. The phase structures of the two alloys were identified by X-ray diffractometry（XRD）. The thermal stability was examined by differential scanning calorimetry（DSC）. Zr49Cu46Al5 alloy shows a glass transition temperature, Tg, of about 689 K, an crystallization temperature, Tx, of about 736 K. The Zr48.5Cu46.5Al5 alloy shows no obvious exothermic peak. The microstructure of the as-cast alloys was analyzed by transmission electron microscopy（TEM）. The aggregations of CuZr and CuZr2 nanocrystals with grain size of about 20 nm are observed in Zr49Cu46Al5 nanocrystalline composite, while the Zr48.5Cu46,5Al5 alloy containing many CuZr martensite plates is crystallized seriously. Mechanical properties of bulk Zr49Cu46Al5 nanocrystalline composite and Zr48.5Cu46.5Al5 alloy measured by compression tests at room temperature show that the work hardening ability of Zr48.5Cu46.5A15 alloy is larger than that of Zr49Cu46Al5 alloy.     

Effect of carbon addition on microstructure and mechanical properties of Ti-based bulk metallic glass forming alloys

A kind of novel Ti-based composites was developed by introducing different amounts of carbon element to the Ti50 Cu23 Ni20 Sn7 bulk metallic glass forming alloys. The thermal stability and microstructural evolution of the composites were investigated. Room temperature compression tests reveal that the composite samples with 1% and 3% （mass fraction） carbon additions have higher fracture strength and obvious plastic strain of 2 195 MPa, 3. 1% and 1 913 MPa, 1.3% respectively, compared with those of the corresponding carbon-free Ti50 Ni20 Cu23 Sn7 alloys. The deformation mechanisms of the composites with improved mechanical properties were also discussed.     

Undercooling and rapid solidification of Nb-Si eutectic alloys studied by long drop tube

Niobium-silicide alloys have great potential for high temperature turbine applications. The two-phase Nb/Nb5Si3 in situ composites exhibit a good balance in mechanical properties. Using the 52 m drop tube, the effect of undercooling and rapid solidification on the solidification process and micro-structural characterization of Nb-Si eutectic alloy was studied, The microstructures of the Nb-Si composites were investigated by optics microscope （OM）, X-ray diffraction （XRD） and scanning electron microscope （SEM） equipped with X-ray energy dispersive spectrometry （EDS）. Up to 480 K, deep undercooling of the Nb-Si eutectic samples was successfully obtained, which corresponds to 25% of the liquidus temperature. Contrasting to the conventional microstructure usually found in the Nb-Si eutectic alloy, the microstructure of the undercooled sample is divided into the fine and coarse regions. The most commonly observed microstructure is Nb＋Nb5Si3, and the Nb3Si phase is not be found. The change of coarseness of microstructure is due to different cooling rates during and after recalescence. The large undercooling is sufficient to completely bypass the high temperature phase field.     

离子辐照对Zr50.7Cu28Ni9Al12.3非晶合金力学性能的影响

非晶合金有潜力成为新一代核材料,离子辐照对其力学性能的影响决定了其使用价值。在不同剂量的Au离子辐照下,探讨了Zr_(50.7)Cu_(28)Ni_9Al_(12.3)非晶合金力学性能的变化过程。原子力显微镜以及正电子湮没寿命谱分析表明,在离子辐照后,非晶合金的自由体积尺寸增大、密度下降,总自由体积增加。透射电子显微镜分析表明,辐照剂量在达到50 dpa时非晶合金开始有纳米晶析出,随着辐照剂量的增加,纳米晶尺寸在增加、密度变大。纳米压痕试验表明,离子辐照后非晶合金的硬度减小,在高剂量时硬度又有增加的趋势。离子辐照下非晶合金的硬度变化是自由体积以及纳米晶竞争的结果。自由体积使非晶合金软化,纳米晶析出使非晶合金硬化。     

结构弛豫对Zr_(64.13)Cu_(15.75)Ni_(10.12)Al_(10)块体非晶合金硬度和剪切带特征的影响

通过接近玻璃转变温度的等温退火获得不同弛豫状态的Zr64.13Cu15.75Ni10.12Al10块体非晶合金样品。利用维氏显微硬度计和洛氏硬度计研究结构弛豫对合金硬度和压痕周围剪切带特征的影响规律。结果表明:在590K等温退火处理使Zr64.13Cu15.75Ni10.12Al10块体非晶合金发生焓弛豫行为,其维氏显微硬度随退火时间的延长较快增加后趋于稳定,而大载荷洛氏硬度对结构弛豫不敏感。通过洛氏压痕周围剪切带特征的研究,定量比较了结构弛豫对剪切带间距、数量的影响规律。     

氢对锆基块体非晶合金形变和开裂的影响

通过充氢和未充氢缺口拉伸试样和三点弯曲试样在SEM下的原位加载，研究了氢对Zr65Al7．5Ni10Cu17．5块体非晶合金形变和开裂过程的影响，结果表明，无论是否有氢，块体非晶的剪切带发展到临界尺寸，剪切裂纹就沿剪切带形核、扩展，它一旦张开就导致快速的断裂，断口边缘观察到的无特征区是剪切带，而不是剪切裂纹断口；剪切断口形貌和拉伸断口形貌没有本质区别，只有当长时间充氢才能形成氢鼓泡，如鼓泡很小或尚未形成，则氢对剪切带以及裂纹的形核、扩展没有明显影响；如存在较大的氢鼓泡，则当剪切带尚未充分发展时微裂纹就形核，导致低应力脆断。