宽过冷液相区铁基非晶合金的形成和磁性

用熔体急冷法制备出具有明显的玻璃转变和较宽的过冷液相区的Fe-Co-(Nb)-Zr-B非晶合金,研究了热稳定性和软磁性能。结果表明,在Fe-Co-Zr-B四元合金中添加适量的Nb可以显著扩大过冷液相区,提高合金的热稳定性。当冷却速率降低时,急冷合金具有非晶和纳米晶的复相结构。非晶合金的饱和磁化强度随Nb含量的增加而减小。不同Nb含量的非晶合金的饱和磁致伸缩系数均较低。在低于晶化温度的温度下退火可以有效地降低矫顽力,改善软磁性能。晶化导致软磁性能降低。     

熔体热历史对Al-Cu合金定向凝固界面稳定性的影响

在温度梯度、抽拉速率等工艺参数相同的条件下，发现熔体热历史对Ａｌ４．６５％ Ｃｕ 合金定向凝固界面稳定性具有显著影响，它是非平衡溶质分配系数ｋ 增加界面稳定性和结晶过冷度Δｔ－ 降低界面稳定性的综合作用结果． 随着过热处理温度的提高，ｋ 对平衡溶质分配系数ｋ０ 的偏离增大， 导致液固界面稳定性增加；但当过热处理温度进一步提高到使合金熔体结晶的热力学过冷度Δｔ－ 明显增大时， 反而导致液固界面稳定性下降．     

软磁性Co基块体非晶合金的研究进展

Co基非晶合金不仅具有高热稳定、高强度、硬度,还显示出优异的软磁特性如低矫顽力、高磁导率、低铁损、低磁致伸缩系数等,尤其是高频下的导磁率、铁损性能极佳,有着重要的工业应用价值.但相对于软磁性Fe基非晶合金,Co基的合金体系较少、玻璃形成能力(GFA)和饱磁感应强度较低而影响了它们的广泛应用.近年,材料工作者研发出了一系列Co基块体非晶合金体系,并对它们的非晶形成机理、GFA、过冷液态稳定性、结晶化行为、磁性及力学性能等进行了广泛、深入的研究.本文对软磁性Co基块体非晶合金的研究进展进行了简述,并展望了其今后的发展方向.     

超快扫描量热揭示铝基金属玻璃过冷液态:接近液体脆度的理论极限（英文）

铝基非晶合金具有密度低、强度高、耐腐蚀等诸多优异性能;然而,铝基非晶合金形成能力差,一般需要非常高的冷却速率,这限制了铝基非晶合金的应用.玻璃形成理论认为形成能力与过冷液体密切相关.但在一般升温测量时,铝基非晶合金不显示玻璃转变或过冷液体,而是直接变成晶态.目前为止,关于铝基非晶合金的玻璃转变和过冷液体属性仍然是未知的.本文采用超快速差热分析方法(Flash DSC)使得升温速度达到10000 K s^-1,测量了20余种常见铝基非晶合金的玻璃转变行为和过冷液体特征.发现铝基非晶合金普遍具有很高的液体脆度系数(m),其中某些成分m>160,已经接近理论上预测的脆度系数上限m^175.通过系统研究这些成分的形成能力,发现铝基非晶合金的玻璃形成能力与脆度系数成反相关,而且这种相关不是线性的.只有m<100时,降低m才会对玻璃形成能力有明显影响;相反, m>100的玻璃形成力普遍较弱,而且随m变化不显著.因此,过高的液体脆度系数可能是铝基非晶合金形成能力差的一个重要原因.     

基于动力学的大块金属玻璃形成能力研究

快速判定大块金属玻璃（BMG）的玻璃形成能力（GFA）是开发新型BMG的关键。基于加和性原则，用动力学理论解释了约化玻璃转变温度Trg作为合金玻璃形成能力的可行性和局限性，为制备非晶合金提供了理论依据，合金能形成BMG的最低Trg为0.4066，同时找到了玻璃形成能力最佳的两个理论约化玻璃温度，即Trg=1和Trg=0；提出了判定GFA大小及其稳定性的两个新的参量摩尔熔化热ΔHmg和稳定性CPS，并用它计算了BMG合金系的GFA大小及其稳定性，BMG的GFA大小顺序与井上明久（Inoue）的排列顺序吻合     

Ce-Ga-Cu系非晶合金的热力学研究

通过差示扫描量热仪(DSC)利用三线法求出Ce_(70)Ga_xCu_(30-x)(x=4,6,10,12,15)系非晶合金过冷液体、熔体和晶体的热容及液体和晶体的热容差(ΔCP),并计算出液体相对于晶体的过剩焓(ΔHexc)、过剩熵(ΔSexc)和Gibbs自由能之差(ΔGl-s)。结果显示,对应于Ce-Ga-Cu系非晶合金低的玻璃转变温度(Tg),其液体的Kuazmann温度(TK)也较低。Ce-Ga-Cu系非晶合金的热力学参数ΔHexc、ΔSexc和ΔGl-s都随着Ga含量的增加而减小,这与玻璃形成能力(GFA)的变化趋势不相符。这说明对于Ce-Ga-Cu非晶合金体系,热力学驱动力不是控制非晶形成的主要因素,其他因素(比如动力学因素)可能是形成能力的关键因素。     

Ni_(68)B_(21)Si_(11)三维金属玻璃的热稳定性

采用 Perkin-Elmer DSC7型差示扫描量热仪对深过冷快淬法制取的 Ni_(68)B_(21)Si_(11)三维金属玻璃进行等温、变温热分析,从液态合金的净化,非晶合金的预退火处理及冷却速率三个方面考察了 Ni_(68)B_(21)Si_(11)非晶合金的热稳定性。研究发现:由于大幅度地消除了合金内的预存晶核,深过冷快淬法形成的非晶合金的热稳定性显著提高,此法获得的 Ni_(68)B_(21)Si_(11)非晶合金在400K 下预期寿命提高了一个数量级;非晶合金的预退火处理将导致初始晶化温度 T_λ 和晶化热ΔH 下降;冷却速率对热稳定性影响较小。     

块体镁基非晶合金及其复合材料研究的新进展

介绍了块体镁基非晶合金及其复合材料的最新研究进展,并简要分析和总结了镁基非晶合金在成分选择和玻璃形成能力(GFA)判据上的新成果,最后针对镁基非晶合金本身存在的问题提出了今后的研究方向建议。     

熔体过热对Sb-Bi合金凝固组织的影响

以Sb-4.6%Bi合金为研究对象,在限定其它因素保持不变的情况下,考察了熔体过热温度对凝固过程的影响。,实验结果发现,随着熔体过热温度的提高,合金形过冷度增大,凝固组织显著细化,研究表明,熔体过冷倾向是熔体结构状态的一个必然反映,熔体结构状态随温度发生变化是导致合金结晶过冷度发生明显的变化的原因,随着过热温度的提高,Sb-4.6%Bi合金晶粒显著细化,其原因是经过热处理的合金熔体在较大的过冷度下凝固。     

金属熔体结构及其控制技术的研究进展

综述了国内外在熔体结构研究方面的现状与进展,介绍了通过控制合金熔体的预结晶状态来改善合金组织和性能的相关技术及成果。可以得出:温度和压力可使金属熔体发生液/液结构转变,金属熔体结构随温度的变化存在滞后性,利用熔体结构随温度变化的滞后性可控制合金的凝固过程、明显细化合金的凝固组织、大大提高合金的力学性能。     

Roles of alloying additions on local structure and glass-forming ability of Cu–Zr metallic glasses

To identify the structural role of alloying element M (M = Ti, Ga, Co, Fe) on the glass-forming ability (GFA) of Cu₅₀Zr₅₀ base alloy, the atomic structures of the binary and ternary metallic glasses were examined by extended X-ray absorption fine structure (EXAFS) spectroscopy. The EXAFS curve-fitting analysis indicates that the main structural difference among the metallic glasses is in the atomic packing density of Cu-centered clusters. The relative shortening of the Cu–M distance is closely related to the heat of mixing between Cu and M: the more negative the heat of mixing, the larger is the shortening of the Cu–M distance. Based on a systematic analysis of the component properties and GFA data for Cu–Zr based alloys, it is suggested that alloying elements that bring a more uniform distribution of atomic size and possess strong chemical interactions with the main components should be selected in developing large-size bulk metallic glasses.     

The Effect of Melt Treatment on Glass Forming Ability and Thermal Stability of Al‐Based Amorphous Alloy

Melt treatment is widely used to mediate the structure of materials. Recently, it is evidenced to be a new way to improve the glass forming ability (GFA) and thermal stability of the amorphous alloys. Bulk metallic glass was obtained through this process in the Al–Ni–La alloy system. In this work, the mechanism of melt treatment on the GFA and thermal stability of the Al–Ni–La alloy was studied. A Ni‐rich metastable high‐melting‐temperature‐phase is found to occur to this alloy system. The elimination of the Ni‐rich phase through the melt treatment is attributed to stabilize the thermal stability of the melt and, accordingly, enhances the GFA and thermal stability of the amorphous alloy.     

In-process rheometry as a PAT tool for hot melt extrusion

Real time measurement of melt rheology has been investigated as a Process Analytical Technology (PAT) to monitor hot melt extrusion of an Active Pharmaceutical Ingredient (API) in a polymer matrix. A developmental API was melt mixed with a commercial copolymer using a heated twin screw extruder at different API loadings and set temperatures. The extruder was equipped with an instrumented rheological slit die which incorporated three pressure transducers flush mounted to the die surface. Pressure drop measurements within the die at a range of extrusion throughputs were used to calculate rheological parameters, such as shear viscosity and exit pressure, related to shear and elastic melt flow properties, respectively. Results showed that the melt exhibited shear thinning behavior whereby viscosity decreased with increasing flow rate. Increase in drug loading and set extrusion temperature resulted in a reduction in melt viscosity. Shear viscosity and exit pressure measurements were found to be sensitive to API loading. These findings suggest that this technique could be used as a simple tool to measure material attributes in-line, to build better overall process understanding for hot melt extrusion.     

Validity of the energy and entropy interfacial tension models examined in view of the stability of metallic glasses

The thermal stability of metallic glasses as calculated from homogeneous nucleation and growth theory is compared with experimental observations. Calculations based on the “negative entropy” model in which interfacial tension scales with temperature predict that all metallic glasses which once attain atomic mobility at moderate temperatures should crystallize in minutes, contrary to observation. On the other hand, the calculations based on the “positive energy” model are more or less in harmony with the observed stability. It appears that a temperature independent contribution to the interfacial tension is necessary to account for the observed stability of many metallic glasses.     

Al基块体金属玻璃的研究进展

Al基金属玻璃具有高强度、高韧性、良好的耐蚀性,特别是其比强度高达330kN·m/kg,作为新结构材料在航空航天领域具有潜在的应用前景。近年不仅研发出了具有大过冷液相区以及能形成块体金属玻璃的Al基合金,还通过粉体温热固化成形工艺实现了Al基金属玻璃的大块体化,推动了其在实际生产中的应用。简述了有关Al基金属玻璃合金的玻璃形成能力、过冷液体热稳定性、力学性能及其粉末烧结体的组织和性能等方面的最新研究进展,并对其发展存在的问题进行了探讨。     

泡沫铝合金渗流铸造工艺的试验分析EI

采用正交实验方法 ,选择三种不同粒径的填料 ,系统研究了粒子预热温度、金属液浇注温度和充型压力对渗流铸造泡沫铝合金成型工艺的影响 ,并对试验结果作了理论分析。认为 ,合理选择粒子预热温度是生产泡沫金属铸件的前提 ,适当提高浇注温度是保证泡沫组织均匀良好的关键 ,保持适度的充型压力有利于提高材质通孔率和工艺稳定性。     

The local structure nature for a Ti-based bulk metallic glass

In the present work, the local atomic structures of a Be-containing Ti-based bulk metallic glass (BMG) have been characterized using electron spectrum for chemical analysis and Raman scattering, including directional bonds and medium range order. It might suggest that a coefficient could be extracted from Raman scattering to characterize the glass forming ability (GFA), which could be employed to interpret the enhanced GFA by Be addition of Ti-based BMG. Additionally, compared with the crystallized sample, the glassy sample exhibits larger average bond length and larger content of local bond distortion using Raman scattering.     

Complete Composition Tunability of Cu(Ni)-Ti-Zr Alloys for Bulk Metallic Glass Formation

In the Cu-Zr-Ti ternary system, a new composition zone of bulk metallic glasses (BMGs) formation was discovered, locating at the 55-57 at. Pct Cu, 30-31 at. Pct Ti and 13-14 at. Pct Zr, and near Cu-Ti binary subsystem rather than the Cu-Zr binary. For these alloys, BMG rods of 2 mm in diameter can be fabricated by using copper mould casting. It is expected that these BMG-forming alloys correlate with (L→CuTi+Cu2TiZr+Cu61Zr14) eutectic reaction that the undercooled melt undergoes during solidification. Adopting "3D pinpointing ap-proach", compositional dependence of glass-forming ability (GFA) in Cu(Ni)-Ti-Zr pseudo ternary system was revisited. Optimized BMG-forming composition is located at Cu50.4Ni5.6Ti31Zr13, with a critical diameter of 6 mm for complete BMG formation. Its GFA is significantly superior to Vit 101 (Cu47Ni8Ti34Zr11) previously developed by Caltech group. The effect that the GFA of the ternary base alloy was improved by substitution of Ni for Cu is attributed to a role of retarding the crystallization of Cu51Zr14 intermetallics.     

Liquid dynamics and glass formation of Gd55Co20Al25 metallic glass with minor Si addition

Liquid dynamics plays an essential role in glass formation.Here we observed a distinct change of liquid dynamics in Gd55Co20Al25 metallic glass induced by microalloying Si element.In the equilibrium melt,minor Si(0.5 at.％)addition leads to a more fragile liquid behavior and a smaller strength of liquid-liquid transition with the transition strength(ΔF)decreasing from 0.76 to 0.35.However,in the supercooled liquid,Si-doped liquid exhibits a remarkable enhanced fragile-to-strong transition(FST),and the value of FST factor f increases sharply from 1.63 to 3.84,resulting in a stronger liquid behavior and more sluggish crystallization kinetics for Gd55Co20Al24.5Si0.5 metallic glass.Moreover,minor Si addition promotes the formation of a crystal-like structure with a size of 1-2 nm.The interactions between the crystal-like structures and other local favored clusters frustrate the further growth of crystal-like phases,thus sta-bilizes the amorphous structure.As a result,the glass-forming ability(GFA)was largely improved.The critical diameter of Gd55Co20Al25 metallic glass increased from 2 to 7 mm with 0.5 at.％Si addition with-out deterioration of the magnetocaloric effect.This study provides valuable insight for understanding the distinct effect of microalloying on GFA of metallic glasses from the aspect of the evolution of the liquid.     

泡沫铝合金制备工艺研究

采用正交实验方法，选择三种不同粒径的填料，系统研究了粒子预热温度、金属液浇注温度和充型压力对渗流铸造泡沫铝合金成型工艺的影响，并对试验结果作了理论分析。认为，合理选择粒子预热温度是生产泡沫金属铸件的前提，适当提高浇注温度是保证泡沫组织均匀良好的关键，保持适度的充型压力有利于提高材质通孔率和工艺的稳定性。