快速凝固Co-Cu包晶合金的电学性能

研究了Co-Cu包晶合金快速凝固过程中的相选择和组织形成特征, 探索了冷却速率、组织结构和晶体位向与合金电阻率之间的相关规律.实验发现, 快速凝固可使Co在(Cu)中的固溶度扩展至20%.Cu含量大于80%时, L+αCo→(Cu)包晶转变被抑制, (Cu)可从过冷熔体中直接形核析出.Cu含量在40%—70%范围时, Co-Cu合金的液相分离受到抑制, 凝固组织沿条带厚度方向分为两个晶区.细晶区中αCo和(Cu)相竞争形核并生长, αCo枝晶形态细密，细小的（Cu）等轴晶均匀分布于αCo的基体之中.粗晶区αCo相为领先相, 富Cu相分布于αCo枝晶的晶界处.随着冷速的增大, 合金组织显著细化, 晶界增多,对自由电子的散射作用增强, 合金电阻率显著增大.当晶界散射系数r＝0996—0999时, 可采用M-S模型综合分析快速凝固Co-Cu合金的电阻率. 关键词： 电阻率 快速凝固 相结构 晶体生长     

快速凝固Cu-Pb过偏晶合金的性能表征

研究了Cu-Pb过偏晶合金的急冷快速凝固组织特征,定量表征了快速凝固Cu-Pb过偏晶合金的电阻率和力学性能,理论分析了冷却速率和组织形态对合金性能的影响规律. 研究结果表明,在急冷快速凝固条件下,Cu-Pb过偏晶合金中的(Cu)相和(Pb)相均以枝晶方式生长,晶体形态以均匀细小的等轴晶为特征. 随着冷却速率增大,一方面,凝固组织显著细化,晶界增多,对自由电子的散射作用增强,合金电阻率显著增大;另一方面,细晶强化作用增强,合金的抗拉强度呈线性升高,同时,伴随着晶体缺陷数量的增多,合金的伸长率降低. 关键词： Cu-Pb过偏晶合金 快速凝固 电阻率 力学性能     

三元等原子比Fe_(33.3)Cu_(33.3)Sn_(33.3)合金的快速凝固机理与室温组织磁性研究

采用自由落体和熔体急冷两种实验技术实现了三元等原子比Fe_(33.3)Cn_(33.3)Sn_(33.3)合金的快速凝固,研究了其组织形成机理和室温磁性特征.实验发现,合金熔体在不同快速凝固条件下都没有发生液相分离,其室温组织均由初生αFe相枝晶以及CU_3SU和CU_6Sn_5二个包晶相组成计算表明,落管中合金液滴的表面冷却速率和过冷度分别达1.3×10~5 K·s~(-1)和283 K(0.19 T_L)当表面冷却速率增大至3.3×10~3 K·s~(-1),初生αFe相发生由粗大枝晶向碎断枝晶的演化.急冷快速凝固过程中,初生αFe相凝固组织沿辊面向自由面方向形成细晶区和粗晶区,其中细晶区以粒状晶为特征而粗晶区存在具有二次分枝的树枝晶随着表面冷却速率由8.9×10~6增大至2.7×10~7 K·s~(-1),αFe相平均晶粒尺寸显著减小,合金条带的矫顽力增大一倍多.     

过冷Ni-P合金的凝固行为

以揭示共晶系合金在不同过冷度下凝固时初生相的选择规律和凝固组织形成机理为目的, 用熔融玻璃净化和循环过热相结合的方法, 将Ni_100-xP_x(x=18, 19, 19.6, 20, 21, 原子百分比)合金过冷至平衡液相线以下不同的温度, 用高速红外测温仪记录了试样的凝固冷却曲线, 详尽分析了试样的凝固组织.结果表明, 过冷Ni-P合金快速凝固过程中析出的初生相为α-Ni/Ni₃P耦合共晶时, 整个凝固过程中仅出现一次再辉, 在所形成的异常共晶组织中α-Ni颗粒大小分布均匀;而当某一共晶相优先析出时, 另外一相需要在残留液相中重新形核, 致使凝固过程中出现两次再辉, 相应形成颗粒相大小截然不同的两类异常共晶组织;据此绘制了Ni-P合金初生相为共生共晶的区域. Ni-P合金中α-Ni的生长动力学明显快于Ni₃P, 使得在大过冷度下过共晶合金也以α-Ni作为初生相进行凝固.     

微重力条件下Cu-Zr共晶合金的液固相变研究

采用落管方法实现了液态Cu-10 wt.%Zr亚共晶、Cu-12.27 wt.%Zr共晶和Cu-15 wt.%Zr过共晶合金在微重力无容器条件下的快速共晶与枝晶生长.Cu-12.27 wt.%Zr共晶合金的凝固组织随液滴直径减小由层片规则共晶向不规则共晶转变,且层片间距减小;Cu-10 wt.%Zr亚共晶合金的初生(Cu)相随液滴直径减小由粗大树枝晶向棒状晶转变,且所占体积分数增加,部分区域形成花状凝固组织,(Cu)相枝晶辐射向外生长;Cu-15 wt.%Zr过共晶合金初生相则为金属间化合物Cu_9Zr_2相,呈条状生长,随液滴直径减小冷却速率增大,凝固组织由宏观弯曲生长向球状晶胞转变.理论计算表明,三个合金液固相变枝晶与共晶的生长均由溶质扩散控制.测定Cu-10 wt.%Zr亚共晶合金初生(Cu)相显微硬度随液滴直径减小而增大,三个合金的共晶相随合金初始成分增大而增大.     

Tb0.3Dy0.7－xPrx(Fe0.9Al0.1)1.95合金的磁致伸缩、自旋重取向和穆斯堡尔谱研究

系统研究了室温下Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95 (x=0，0.1，0.2，0.25，0.3，0.35)合金中稀土元素Pr替代Dy对晶体结构、磁致伸缩、各向异性和自旋重取向的影响. 结果发现，x≤0.1时，Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95完全保持MgCl₂立方Laves相结构，0.1<x≤0.3，有杂相出现并且随Pr替代量逐渐增多；晶格常数a随Pr含量x的增加缓慢增大. 磁致伸缩测量发现，随着替代量x的增多磁致伸缩减小；x>0.2时超磁致伸缩效应消失. 然而，x=0.1时合金的磁致伸缩略大于没有替代的，而且磁致伸缩随磁场更易趋于饱和，说明Pr替代有助于降低磁晶各向异性. 内禀磁致伸缩λ₁₁₁随Pr替代量x的增加接近线性增加. 由相对磁化率随温度的变化关系可以看出，自旋重取向温度随Pr替代量的增多呈先增后降趋势，在x=0.1处出现极大值. 穆斯堡尔效应表明，随Pr含量的增加Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95合金中易磁化轴可能在{110}面上绕主对称轴作微小转动，发生自旋重取向. 与Al元素替代效应相比，Pr替代Dy对自旋重取向的影响相对较小.     

k光子Jaynes-Cummings模型的亚Poisson光子统计特性研究

本文利用量子电动力学理论,首次对 k 光子 Jaynes-Cummings 模型中单模激光场的稳态亚 Poisson 光子统计性质进行了系统研究.结果表明:在一般情况下,激光上能级相对泵浦参量 x_a 具有一个确定的阈值 x_at;当 x_a>x_at时,光场呈现亚 Poisson 光子统计;当 x_a>>x_at时,光场呈现出深度且完全恒定的亚 Poisson 光子统计.在特殊情况下,阈值 x_at-0,这时在激光腔内将直接诱发亚 Poisson 光子统计.随着 k(k≥2)值增加,阈值 x_at降低,光场亚 Poisson 光子统计程度增强.     

急冷条件下Cu-Pb偏晶合金的相分离研究

研究了Cu-Pb偏晶合金的急冷快速凝固和组织形成规律，并通过将金属熔体的热传导方程和Navier-Stokes方程相耦合, 理论分析了合金熔体的冷却速率、液固相变时间等物理参量与液相分离之间的相关性. 研究结果表明，在急冷快速凝固条件下，熔体的快速冷却对偏晶合金组织形成的影响要比熔体内部液相流动的影响更为显著. 快速凝固使液相分离受到抑制，Cu-Pb偏晶合金均可获得均匀的微观组织结构. 随着冷速的增大，晶粒尺寸明显减小，凝固组织显著细化，晶体形态由粗大枝晶向均匀细小的等轴晶过渡. 提高冷却速率，缩短液固相变时间是重力场中抑制液相分离、获得均匀偏晶组织结构的重要条件. 关键词： 偏晶合金 快速凝固 液相分离 微观结构     

GeSn合金的晶格常数对Vegard定律的偏离

在Si (001)衬底上, 以高质量的弛豫Ge薄膜作为缓冲层, 先后生长Sn组分x分别为2.5%, 5.2%和7.8%的完全应变的三层Ge_1-xSn_x合金薄膜. 在Si (001)衬底上直接生长了x分别为0.005, 0.016, 0.044, 0.070和0.155的五个弛豫Ge_1-xSn_x样品. 通过卢瑟福背散射谱、高分辨X射线衍射和X射线倒易空间图等方法测量了Ge_1-xSn_x合金的组分 与晶格常数. 实验得到的晶格常数相对Vegard定律具有较大的正偏离, 弯曲系数b=0.211 Å.     

快速凝固Cu-1.5%Be合金的制备

采用单辊旋淬法制备了快速凝固Cu-1.5%Be合金(Be质量分数1.5%)薄带。根据热传输平衡方程对快速凝固冷却速率进行了估算,并借助X射线衍射仪、扫描电子显微镜对该合金的微观结构及相选择进行了分析。结果表明:当辊面线速度在29.93~39.19 m/s范围内时,合金冷却速率可达到9.80105~1.63106 K/s;随着辊轮转速的提高和喷注气压的减小,合金条带厚度和晶粒度逐渐变小;随着冷却速率的增加,溶质截留效果显著,合金相结构由复相向单相转变,当辊面线速度达到34.54 m/s时,Cu-1.5%Be合金可形成过饱和的-Cu固溶体组织,且组织细小均匀,可获得纳米晶;条带横断面显微组织由接近辊面一侧的细小等轴晶区、中间的柱状晶区和靠近自由表面的等轴晶区组成。     

电阻率与强度性能的关联及铜合金性能分区

铜合金以低电阻率为特征,由于电阻率与强度存在着共同的微观结构机理,两者往往协同变化,而导致难以对合金进行性能的全面评估和选材.本文以Cu-Ni-Mo合金作为研究对象,以团簇结构[Mo_1-Ni_(12)]构建固溶体的近程序结构模型,解析了电阻率和强度依赖于成分的定量变化规律,并定义了拉伸强度/电阻率的值为代表合金本质特性的"强阻比",得到了完全固溶态Cu-Ni-Mo合金的强阻比为7×10~8MPa/?·m,完全析出态的强阻比为(310—490)×10~8MPa/?·m.进而应用强阻比对常用铜合金进行了性能分区,给出铜合金材料选材的依据,得出了基于Cu-(Cr, Zr, Mg, Ag, Cd)等二元基础体系的铜合金适用于高强高导应用,而基于Cu-(Be, Ni, Sn, Fe, Zn, Ti, Al)等为基础二元体系的铜合金不能实现高强高导.该强阻比为310的特征性能分界线的发现为合金性能的全面评估提供了量化依据,可指导高强高导铜合金的选材和研发.     

Damage mechanism of nickel-based creep-resistant alloys strengthened by the Laves phase at the grain boundary

ABSTRACT

This study proposes a design guideline for polycrystal Ni-based model alloys with high ductility and 100-MPa creep rupture strength beyond 800°C and 10^5?h. These alloys are strengthened by both the precipitation of fine γ′ particles inside the grain and the Laves phase at the grain boundary. For investigating the damage mechanism, transformation from the non-equilibrium Laves phase to the σ phase at the grain boundary and formation of the equilibrium needle-like Laves phase inside the grain are promoted by increasing the Fe concentration. The rupture time of Fe-free alloys significantly increases because of the equilibrium Laves phase at the grain boundary owing to a suitable Mo equivalent. In particular, W addition can help achieve high-temperature creep strength. The precipitate-free zone (PFZ) is predominantly formed by prior migration at the grain boundary without precipitation. Creep rupture occurs at the precipitation/matrix interface in the PFZ. Therefore, transformation control from the Laves to the σ phase at the grain boundary suppresses creep degradation. Consequently, a Ni-based alloy with strength >100?MPa and rupture elongation >20% at 800°C and 10^5?h is fabricated using Larson–Miller parameter conversion, and the alloy design guideline’s validity is confirmed.     

Correlation study of structural,electrical and mechanical properties of quenched tin–zinc–cadmium solder alloys

It is important, for electronic application, to decrease the melting point of SnZn₉ solder alloy because it is too high as compared with the most popular eutectic Pb–Sn solder alloy. Adding Cd causes structural changes such as phase transformations, dissolution of atoms and formation of Cd crystals in the quenched SnZn₉ alloy, and its physical properties are affected by this change. For example, the melting point is decreased towards the melting point of the Pb–Sn eutectic alloy, or even much less. The structure, electrical and mechanical properties of quenched Sn_{91? x} Zn₉Cd _x (x?=?0 or x?≥?5) alloys have been investigated. Adding Cd to a quenched SnZn₉ alloy increases its electrical resistivity and decreases its elastic modulus and internal friction. The Sn₇₁Zn₉Cd₂₀ alloy has the lowest melting point (162 °C) and electrical and internal frictions as compared with commercial Pb–Sn solder alloys.     

Effect of alloying elements on room temperature tensile ductility in magnesium alloys

The impact of alloying elements on the room temperature tensile behaviour was investigated for a wide range of strain rates using eight types of extruded Mg-0.3 at.% X (X = Ag, Al, Li, Mn, Pb, Sn, Y and Zn) binary alloys with an average grain size of 2–3 μm. The solid solution alloying element affected not only tensile plasticity but also rate-controlling mechanism for these fine-grained magnesium alloys. Most of the alloys exhibited an elongation-to-failure of 20–50% , while the alloys with a high m-value exhibited large tensile plasticity, such as an elongation-to-failure of 140% in a strain rate of 1 × 10^?5 s^?1 for the Mg–Mn alloy. This elongation-to-failure is more than two times larger than that for pure magnesium. This is due to the major contribution of grain boundary sliding (GBS) on the deformation. Microstructural observations reveal that grain boundary segregation, which is likely to affect gain boundary energy, plays a role in the prevention or enhancement of GBS. The present results are clearly expected to open doors to the development of magnesium alloys with good secondary formability at room temperature through the control of alloying elements.     

Crystal structure and physical properties of magnetic shape memory alloys Ni50 − x Cu x Mn29Ga21

The phase composition, crystal structure, and physical properties (magnetization, electrical resistivity, thermoelectric power, relative elongation, and thermal expansion coefficient) of the stoichiometric alloy Ni₅₀Mn₂₅Ga₂₅ and nonstoichiometric alloys Ni_{50 ? x} Cu _x Mn₂₉Ga₂₁ (x = 0, 1, 2) with the thermoelastic martensitic transformation have been investigated. The influence of the chemical composition on the transformations and physical properties of the alloys has been determined.     

The Hall effect in amorphous (Zr0.64Ni0.36)1−x M x alloys (M=Al,Ga)

Values of the room temperature Hall coefficients and electrical resistivity of amorphous melt spun (Zr_0.64Ni_0.36)_1–x Al _x and (Zr_0.64Ni_0.36)_1–x Ga _x alloys forx=0–0.25 are reported. Addition of Al or Ga to Zr_0.64Ni_0.36 dramatically increases the already positive Hall coefficient of this alloy and also increases the electrical resistivity and crystallization temperature.     

Microstructural evolution and thermal stability of Fe–Zr metastable alloys developed by mechanical alloying followed by annealing

The effect of Zr (up to 1 at.%) addition on the formation of Fe–Zr metastable alloys and their thermal stability were investigated for their possible nuclear applications. Fe–xZr (x = 0.25, 0.5, 1%) alloys were synthesised by mechanical alloying under a high-purity argon atmosphere using stainless steel grinding media in a SPEX 8000M high energy mill. The milling was conducted for 20 h with a ball-to-powder weight ratio of 10:1. The formation of metastable solid solutions after milling was confirmed from the change in the Gibbs free energy analysis as per Miedema’s model. The microstructural characterisation was carried out by analysis of X-ray diffraction, atomic force microscopy and transmission electron microscopy. The effect of Zr on the thermal stability of Fe–Zr alloys was investigated by extensive annealing experiments followed by microstructural analysis and microhardness measurements. The stabilisation was found to occur at 800 °C and thereafter, no significant change in the crystallite size was observed for the samples annealed between 800 and 1200 °C. The supersaturated solid solution, especially 1% Zr alloy, found to be highly stable up to 800 °C and the microhardness value of the same measured to be as high as 8.8 GPa corresponding to a crystallite size of 57 nm. The stabilisation effect has been discussed in the light of both the thermodynamic and kinetic mechanisms and the grain size stabilisation is attributed to the grain boundary segregation of Zr atoms and/or Zener pinning by nanoscale precipitation of the Fe₂Zr phase.     

Influence of precipitate-assisted nucleation on the microstructure and mechanical properties of Al-Mg-Si-Cu-Zn alloys

The influence of precipitation on the recrystallization nucleation and mechanical properties of Al-Mg-Si-Cu-Zn alloys was investigated by means of tensile tests, SEM, TEM, XRD and EBSD. The results reveal that there are distinct contributions from the various precipitates that form during annealing and that these critically influence the evolution of microstructure and its associated texture, as well as mechanical behaviour. In contrast to alloy sheets A, B, and C annealed at a lower temperature or for a shorter time, the T4P alloy sheet D with an annealing at 450°C for 3?h not only possesses almost identical strength and elongation, but also a higher average r (0.659) and n (0.313) values, and also a lower Δr (0.091) value. After solution treatment, the four alloy sheets are comprised of equiaxed grains with somewhat different grain sizes and different textures, but texture volume fraction and grain size in alloy sheet D both are decreased due to the effect of precipitate-assisted nucleation during solution treatment. The corresponding nucleation and growth mechanisms of recrystallization grains were established and the relationship between textures and r value in the four alloy sheets was also analyzed on the basis of a Visco-plastic self-consistent (VPSC) model.