高温结构弛豫对非晶复合材料力学性能的影响

采用铜模吸铸法制备了Cu40Zr44Al8Ag8非晶复合材料(BMGCs),在玻璃转变温度(Tg)退火不同时间(5,10,15,20,25,40,60,85min)后,采用单轴压缩实验测试了试样退火前后的力学性能,并利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和同步差示扫描量热仪(DSC)等手段对退火前后试样的显微结构和断口形貌进行分析。结果发现:所制备铸态试样主要为非晶结构,非晶基体中弥散分布着少量的纳米级及微米级的Al3Zr金属间化合物。随着退火的进行,非晶复合材料中微米级晶体相的尺寸和形貌并不发生变化,这些晶体相是裂纹形成的源泉;但是纳米级晶体相不断增加,最终析出产物相为Al3Zr,Cu10Zr7和Ag3Al相。非晶复合材料中自由体积与析出晶体相共同控制着该BMGCs的力学性能。退火初期,试样的强度和塑性缓慢增长,至退火15 min时达到极值,最高强度达到1.77 GPa,最大塑性应变量达到1.67%;但是继续退火,试样内自由体积大量减少,强度和塑性均迅速下降;其断裂方式也由单一剪切面断裂转变为多剪切面断裂,最后发生脆性劈裂。     

大块锆基非晶合金电化学耐腐蚀行为的试验研究

利用电化学极化曲线方法研究了Zr41Ti14Cu12．5Ni5Be22．5Fe5非晶合金及成分相同的晶化合金及纯Zr在硫酸溶液中的腐蚀行为。利用减重法研究了Zr41Ti14Cu12．5Ni5Be22．5Fe5非晶合金及成份相同的晶化合金在浓硫酸溶液中的腐蚀行为。极化曲线测试结果表明，非晶合金及成分相同的晶化合金与纯金属Zr有很大差异：非晶合金过钝化电位最高，钝化区最长，而纯金属Zr过钝化电位最低；钝化区也最短。减重试验表明，非晶合金的腐蚀速率是成分相同晶化合金的1/4。以上结果表明非晶合金拥有优良的耐腐蚀性能。     

Zr基大块非晶的研究

利用射流成型法制备出Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅大块非晶.该合金系统具有很强的玻璃形成能力和宽的过冷区,其玻璃转化温度T_g=650.63K,晶化温度T_x=721.90K,过冷区△T_x=T_x-T_g=71.27K.Vicker硬度为558kg/mm²压缩断裂强度1730GPa,弹性模量82GPa.观察其断口有大量纹络状河流花样,并有融化的液滴存在.该合金系统大的玻璃形成能力应归功于合金组元的多样性、组元间大的原子半径比率、组元间大的混合负热及在冷却过程中过冷区粘度的急剧上升等因素.     

金属玻璃（Fe55Ni45）78Si8B14的低温结构弛豫

使用Bordoni型仪器测量了Fe—Ni基金属玻璃在结构弛豫过程中内耗和模量的变化,详细地研究了在低于500K的低温阶段模量的变化。结果表明,结构弛豫对温度的特性可划分为两个阶段:低温结构弛豫,主要由TSRO控制;高温结构弛豫,主要由TSRO和CSRO控制。低温结构弛豫的激活能约为17kJ/mol。     

用拉伸膨胀等方法研究非晶薄带的结构弛豫及晶化

主要介绍用拉伸膨胀法测量非晶薄带弛豫和晶化过程的结果及其可靠性,并结合电阻和X射线衍射实验讨论得到的重要结论。     

超声振动对Zr基大块非晶合金结构与显微力学行为的影响

在室温条件下对铸态Zr52Cu23Al14.5Ni10.5大块非晶合金进行5 h超声振动处理,通过X射线衍射(XRD)、高分辨透射电镜(HRTEM)、差示扫描量热分析(DSC)以及纳米压痕测试,研究长时间超声处理对大块Zr基非晶合金结构与显微力学行为的影响。结果表明,经过5 h超声振动处理后,Zr基非晶合金仍保留非晶态结构,没有发生晶化;超声振动对大块非晶合金的热力学特征温度如玻璃化转变温度(Tg)、晶化开始温度(Tx)以及晶化峰值温度(Tp)的影响都不大,但可诱导结构弛豫,使其自由体积明显减少;相比铸态合金,超声处理后的合金,其纳米压痕实验的载荷—位移曲线上的锯齿流变现象明显减少,显微硬度和弹性模量均明显提高,分别从铸态的5.7 GPa和102 GPa提高到6.5 GPa和122 GPa。表明超声振动处理是一种室温调控大块非晶合金力学性能的有效手段。     

TiCu金属玻璃及其氢化物的结构

氢可用来作为探测金属玻璃结构信息的探针。从氢化和未氢化的TiCu金属玻璃的径向分布函数实验结果表明,在8.5×10~3Pa H_2和80℃条件下氢化,根据测得的原子最近邻间距推知,钛原子和铜原子的最近邻间距有显著变化。由此可认为,氢主要占据由钛原子和铜原子组成的四面体间隙位置。     

氢在金属玻璃Fe39Ni39Si8B12Mn2中的扩散及其对弹性模量的影响

用排水集气法分别测量了淬态和退火处理Fe₃₉Ni₃₉Si₈B₁₂Mn₂金属玻璃在室温附近不同温度下的氢的扩散系数,由此计算出扩散激活能。退火处理导致的结构弛豫均使频率因子D₀和激活能变小。测量了样品在弯曲振动模式下共振频率,发现氢可以降低金属玻璃的杨氏模量,且充氢后时效过程中共振频率随时间的变化规律和时效过程中样品含氢量的曲线相似,即由氢降低的杨氏模量和含氢量成正比。     

金属玻璃中与氢有关的内耗

使用Bordoni型的仪器在声频范围内研究了铁镍基金属玻璃的低温含氢内耗,并研究了退火处理对内耗的影响。结果表明低温含氢内耗是Snoek 型弛豫,并观察到了反常模量亏损和反常弛豫强度现象,提出τ缺陷增强 Snoek 弛豫模型解释了反常弛豫强度现象。     

钨骨架/Zr基非晶合金材料的静态力学行为

利用渗流铸造法制备出直径为8 mm、钨颗粒体积分数达40％的钨骨架/Zr基非晶合金复合材料,在室温下通过电子万能试验机对材料进行静态压缩实验.通过扫描电子显微镜(SEM)技术对复合材料的原始组织和断裂特征、裂纹扩展等情况进行研究.结果表明:材料在静态加载条件下屈服强度不具有应变率效应,其值基本保持不变;材料塑性良好,具有应变强化效应.复合材料断裂模式为一种混合断裂模式,在变形带间交界处发现若干裂纹.非晶基体阻碍钨骨架中裂纹的扩展,钨骨架防止复合材料发生大范围的流变.     

Structural Relaxation of La55Al25Ni10Cu10 Bulk Metallic Glass

The relaxation process and glass transition kinetics of the La₅₅Al₂₅Ni₁₀Cu₁₀ bulk metallic glass (BMG) below the calorimetric glass transition were investigated by differential scanning calorimetry. Enthalpy relaxation was observed in isothermal annealing experiments below the glass transition temperature T _g . The time-dependent enthalpy relaxations were well described by a stretched exponential relaxation function, with an exponential index 0.78. An apparent activation energy E = 60.8 kJ/mol was derived from the temperature dependence of the relaxation time. The equilibrium free volume concentration at a temperature about 30 K below T _g is 10⁻¹⁷ to 10⁻¹³, calculated using an empirical Vogel–Fulcher–Tammann (VFT) type equation. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

应变速率对锆基非晶复合材料力学性能的影响

采用铜模吸铸法制备出直径3mm的[Zr0.72+x(Cu0.59Ni0.41)0.28-x]88Al12(x=0.05、0.10)棒状非晶复合材料。考察应变速率对合金压缩力学性能的影响。结果表明,随应变速率的增大,合金的塑性变形区域减小,锯齿流变现象逐渐消失;在相同成分下,随应变速率的增大,弹性模量逐渐升高,塑性应变和抗压强度则逐渐降低,屈服强度和断裂强度也基本呈下降趋势。在x=0.05、应变速率为0.55×10-4s-1时,塑性应变、抗压强度和断裂强度均为最大值,分别为6.77%、1 758MPa和1 629MPa。     

Production and Mechanical Properties of Roll Bonded Bulk Metallic Glass/Aluminum Laminates

Twin roll casting has been used to produce sheet of Mg₆₀Cu₂₉Gd₁₁ bulk metallic glass (BMG). Sheet can be produced with thicknesses between 1 and 4 mm, the width of sheet produced can be between 25 and 75 mm. The dimensional stability of the produced sheet in a cast run is ±1 mm in the width direction and ±0.05 mm in the thickness direction. As with all magnesium-based BMGs the sheet produced is strong yet brittle at room temperature. The maximum flexural stress of a twin roll cast Mg₆₀Cu₂₉Gd₁₁ BMG strip is 150 MPa with a flexural strain of 0.005. The Charpy impact energy of a Mg₆₀Cu₂₉Gd₁₁ BMG strip is 0.02 J. In order to improve the toughness values of the Mg₆₀Cu₂₉Gd₁₁, BMG strip laminates of BMG and aluminum alloy (UNS A91100) were produced via roll bonding. The introduction of aluminum layers to the sheet structure provides a barrier to shear band movement stopping the sudden catastrophic failure of the sheet. After rolling the BMG was examined via X-ray diffraction (XRD) to confirm that the BMG layer remained amorphous. The flexural stress, flexural strain, and Charpy impact energy properties of BMG-Al laminates are improved when compared to monolithic glass properties. The flexural stress values for laminates compared to the monolithic glass improve by 60 pct from 150 to 250 MPa. The flexural strain values improve by over an order of magnitude from 0.005 to 0.14. The Charpy impact energies increase by 2 orders of magnitude from 0.02 to 2.5 J.     

冷却介质对退火态Cu50Zr42Al8块体非晶合金力学性能的影响

考察在过冷液相区内790K+30min保温后炉冷和液氮冷却对Cu50Zr42Al8压缩断裂行为的影响。5mm铸态非晶复合棒的屈服强度、断裂强度和杨氏模量分别为1670MPa,1849MPa和104.4GPa,塑性应变为1.9%。经炉冷和液氮冷却试样的压缩断裂强度和杨氏模量下降,分别为912,678MPa和38,56.5GPa。液氮冷却试样为部分非晶结构,炉冷试样完全晶化。晶化相均为正交晶相Cu10Zr7,四角晶相CuZr2和DO3结构的AlCu2Zr三种脆化相。     

Primary Transformation Kinetics in Zr-Al-Ni-Cu-Pd Bulk Metallic Glass Correlated with Relaxation State

The primary transformation kinetics of nanoicosahedral quasicrystalline (QC) phase formation were investigated in Zr₆₅Al_7.5Ni₁₀Cu_12.5Pd₅ bulk metallic glass (BMG) in various relaxation states. A less relaxed (unrelaxed) BMG exhibited higher activation energy for atomic diffusion in the glassy structure than that of a relaxed one, which represents a change in the nucleation and grain growth kinetics of the primary phase with the relaxation state. Actually, the grain growth rate of a QC particle near the crystallization temperature was approximately 1 × 10^?9 m/s in the less relaxed BMGs, which was less than half of that in the relaxed BMGs. In contrast, the calculated homogeneous nucleation rate significantly increased in the less relaxed samples. It increased with the volume fraction transformed in the early stage. It is concluded that the relaxation state of glassy alloys markedly affects the primary transformation kinetics. The current study also indicates a necessity of development of the relaxation state for structure controlling in industrial applications of BMGs.     

Effect of Au Content on Thermal Stability and Mechanical Properties of Au-Cu-Ag-Si Bulk Metallic Glasses

The thermal stability, glass-forming ability (GFA), and mechanical and electrical properties of Au-based Au _x Si₁₇Cu_75.5–x Ag_7.5 (x = 40 to 75.5 at. pct) metallic glasses were investigated. The glass transition temperature (T _g ) and crystallization temperature (T _x ) decreased with increasing Au content. The ultralow T _g values below 373 K (100 °C) were obtained for alloys with x = 55 to 75.5. The alloys with x = 45 to 70 exhibited a high stabilization of supercooled liquid and a high GFA, and the supercooled liquid region and critical sample diameter for glass formation were in the range of 31 K to 50 K and 2 to 5 mm, respectively. The compressive fracture strength (σ _c,f ), Young’s modulus (E), and Vicker’s hardness (H _v ) of the bulk metallic glasses (BMGs) decreased with increasing Au content. A linear correlation between Au concentration and the characteristic temperature, i.e., T _g and T _x , and mechanical properties, i.e., σ _c,f , E, and H _v , as well as electrical resistivity can be found in the BMGs, which will be helpful for the composition design of the desirable Au-based BMGs with tunable physical properties.     

Chemical Short-Range-Ordering Effect on Structural Relaxation in Metallic Glasses

A model is proposed to address chemical effects on structural relaxation in metallic glasses. The atomic short range ordering (SRO) is described under the quasi-chemical approximation (QCA). Local chemical deviations from the ideal SRO are considered as an excess enthalpy. The simplified analysis of a disordered region’s evolution is based on the notion of the collective bond exchange between neighboring atoms. The approach suggests a bimolecular mechanism with possibly large apparent activation energy for structural relaxation near the glass transitions. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Relaxation Behavior of Ca-Based Bulk Metallic Glasses

The relaxation behavior of Ca₆₀Mg₂₀Zn₂₀, Ca₆₀Mg₂₀Cu₂₀, Ca₆₅Mg₁₅Zn₂₀, Ca₅₀Mg₂₀Cu₃₀, and Ca₅₅Mg₁₈Zn₁₁Cu₁₆ bulk metallic glasses was determined in the glass transition region using differential scanning calorimetry (DSC) with heating rates from 1 to 160 K/min. The activation enthalpy of structural relaxation and the fragility index m were found to be smaller in the glassy state (onset of the glass transition) than in the supercooled liquid state (end of glass transition). The Ca-based glass-forming liquids showed strong behavior of the relaxation time, with the fragility indexes m in the range of 33 to 40. The strong liquid behavior implies sluggish kinetics of crystallization in the supercooled liquid region and explains the very good glass-forming ability (GFA) of these alloys. The critical cooling rate for amorphization R _c of the Ca-based bulk metallic glasses was estimated to be in the range of 0.3 to 10 K/s, which is similar to R _c values for the best Pd- and Zr-based metallic glass-forming alloys discovered so far.     

Preparation and Mechanical Properties of Misch Metal Based Bulk Metallic Glasses

Bulk metallic glasses(BMGs)have been devel-oped in many alloy systems during past decade.Among these systems,rare-earth(RE)metal-basedBMGs are ones of those found earliest and with betterglass forming ability(GFA).For example,La-basedBMGs were the first a…     

Stored Mechanical Work in Inhomogeneous Deformation Processes of a Pd-Based Bulk Metallic Glass

We investigated the effect of anelastic rearrangements in a Pd-based metallic glass during inhomogeneous plastic deformation producing shear bands at room temperature. Therefore, we subjected bulk metallic glasses to uniaxial stresses and characterized the influence of deformation on the global configurational energy state with ultrasonic and calorimetric methods. The results provide evidence that even in an inhomogeneous plastic deformation process at room temperature, a certain amount of energy can be stored which is thermally relaxed below the glass transition temperature.