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     

快速凝固Cu-Sn亚包晶合金的电阻率及力学性能

定量表征了快速凝固Cu-xwt%Sn(x=7, 13.5, 20)亚包晶合金的电阻率和力学性能,理论分析了冷却速率与合金性能之间的关系. 研究结果表明,在急冷快速凝固条件下,随着冷却速率的增大,合金组织显著细化、晶界增多,对自由电子的散射作用增强,Cu-Sn亚包晶合金的电阻率升高. 当晶界散射系数取r=0.992时,可用M-S模型分析其电阻率.同时,细晶强化作用增强,合金的显微硬度和抗拉强度呈线性增大,并且细晶区显微硬度略大于粗晶区显微硬度. 冷却速率的增大使合金的伸长率减小,其值在1.0%—4.6%范围.     

三元Co-Cu-Pb偏晶合金的快速凝固组织形成规律研究

在自由落体条件下实现了三元Co-Cu-Pb合金的液相分离与快速凝固. 实验发现,随液滴直径减小,Co₅₁Cu₄₇Pb₂合金液滴发生由枝晶→两层壳核→枝晶组织的转变,Co₄₇Cu₄₄Pb₉合金液滴的组织形态由壳核组织演化为均匀组织. 两种合金的快速凝固组织均由α(Co),(Cu)和(Pb)固溶体三相组成,α(Co)和(Cu)相主要以枝晶方式生长,(Pb)相分布在(Cu)枝晶间.关键词：液相分离偏晶合金快速凝固自由落体     

快速凝固Ti-Cu-Fe合金的相组成与组织演变规律

采用落管无容器处理技术实现了Ti_61.2Cu_32.5Fe_6.3三元包共晶合金在自由落体条件下的快速凝固,获得了直径为80—1120μm液滴的凝固组织.实验中获得的过冷度范围为34—293 K,最大过冷度达0.23T_L.研究发现,在自由落体条件下,由于受到无容器、微重力、超高真空等因素的影响,合金熔体的凝固组织中包含Cu_0.8Fe_0.2Ti相、CuTi₂相和CuT₃相,显著偏离了平衡状态.Cu_0.8Fe_0.2Ti为初生相,同时又与CuTi₂相形成两相共晶;CuTi₃相则呈现枝晶形貌,并发生了明显的溶质截留效应.随着过冷度的增大,共晶组织由层片共晶向不规则共晶转变,形貌由长条状共晶团变为椭球状共晶团,最终变为球状共晶胞;Cu_0.8Fe_0.2Ti相枝晶形貌由粗大枝晶变为碎断枝晶,进一步变成不规则的粒状晶粒;CuTi₃相枝晶则由碎块状转变为完整枝晶.     

Cu50Ni50合金快速凝固的分子动力学模拟

采用分子动力学模拟的方法研究了Cu₅₀Ni₅₀合金在不同冷却速度下的凝固过程,利用均方位移、径向分布函数和结构可视化等方法分析其微观结构.并对凝固模型进行拉伸模拟,通过应力应变曲线和直观结构变化分析其性能.研究表明：冷却速度对Cu₅₀Ni₅₀合金凝固形成的结构有较大影响,随着冷却速度的升高,凝固形成的结构中晶体含量减少,在较低的冷却速度下,如冷却1×10¹²K/s时,Cu₅₀Ni₅₀合金凝固形成晶体结构;在较高的冷却速度下,如1×10¹⁴K/s时,Cu₅₀Ni₅₀合金凝固形成非晶体结构,且非晶Cu₅₀Ni₅₀合金的抗拉性能要优于晶体Cu₅₀Ni₅₀合金.     

落管中Ni-Fe-Ti合金的快速凝固机理及其磁学性能

采用落管自由落体方法实现了Ni_(45)Fe_(40)Ti_(15)合金在微重力无容器条件下的快速凝固,获得了直径介于160—1050μm的合金液滴.理论计算表明冷却速率及过冷度随液滴直径减小而增大,并呈指数函数关系,实验获得的最大过冷度为210 K(0.14 T_L).随着过冷度增大,凝固组织中粗大的γ-(Fe,Ni)枝晶逐渐细化,二次枝晶间距减小,溶质Ti在γ-(Fe,Ni)相中的固溶度显著扩展.对不同直径合金液滴的凝固样品进行磁学性能分析,结果表明随着凝固合金液滴直径减小,其饱和磁化强度增大,矫顽力减小,矩形比下降,软磁性能明显提高.     

深过冷Cu60Sn30Pb10偏晶合金的快速凝固

实现了大体积Cu60Sn30Pb10偏晶合金的深过冷与快速凝固.实验获得的最大过冷度为173 K(0.17TL).凝固组织发生了明显的宏观偏析,XRD分析表明,试样上部是由固溶体(Sn),(Ph)相和金属间化合物ε(Cu3Sn)相组成的三相区,下部为富(Ph)相区.在小过冷条件下,三相区中ε(CuSn)相的凝固组织为粗大的枝晶,随着过冷度的增大,ε(Cu3Sn)相细化成层片状组织.且层片间距随过冷度的增大而减小,而(Sn),(Ph)两相始终以离异共晶的方式存在.富(Pb)相区中分布有少量的ε(Cu3Sn)枝晶,枝晶长度随过冷度的增大而增大,且在大过冷条件下发生碎断.(Sn)相在ε(Cu3Sn)相表面形核、长大,其形态类似于包晶凝固组织.     

强磁场对Mn-Sb包晶合金相变及凝固组织的影响

以Mn-56.5 wt%Sb包晶合金为研究对象, 进行了不同磁场、不同冷速条件下的凝固实验. 通过对液相线温度、包晶温度的考察, 发现强磁场可以提高Mn-56.5 wt%Sb合金的液相线温度, 且该上升值随磁感应强度的增加而增加, 当所施加的磁感应强度为11.5 T时, 液相线温度升高大约3 ℃, 但施加磁场后包晶反应温度没有明显改变. 对该合金的凝固组织进行定量金相分析发现, 施加磁场后MnSb相明显减少, 该结果与磁场对相变温度的影响相一致. 另外通过X射线衍射分析发现, 强磁场诱发包晶反应生成相MnSb的c轴垂直于磁场方向取向, 而Mn₂Sb相的(311)面平行于磁场方向取向. 对不同冷速凝固的Mn-56.5 wt%Sb合金组织进行定量金相分析结果显示, 强磁场对合金凝固过程的作用效果受到冷却速度的影响. 随着冷却速度的增加, 强磁场对该合金凝固组织中MnSb相的相对含量变化影响效果减弱.关键词：强磁场包晶合金凝固相变温度     

急冷快速凝固过程中液相流动与组织形成的相关规律

研究了Fe58wt%Sn过偏晶合金的急冷快速凝固和组织形成特征． 实验发现, FeSn过偏晶合金的急冷快速凝固组织由规则排布的纤维状β-Sn相和分布其间的α-Fe相及少量金属间化合物相组成, β-Sn相的几何排列方向与合金条带表面成0—15°的夹角．根据急冷条件下金属熔体的热传导方程和Navier-Stokes方程, 对过偏晶合金的凝固行为和组织形成过程进行了理论分析, 揭示出熔体内部的动量传输对过偏晶合金的液相分离行为具有显著的影响．两相分离发生于液池底部约200μm的急冷区内, 分离的L2液滴在辊面驱关键词：液态相分离液相流动快速凝固晶体生长     

Al-Cu-Ge合金的热物理性质与快速凝固规律研究

Al-Cu-Ge合金是典型的三元共晶体系,在工业上有重要的应用价值,对其进行研究有助于了解该合金的热物理性质和提高该合金的结构性能.本文选择了Al55Cu10Ge35,Al70Cu10Ge20和Al80Cu10Ge10三种成分合金作为研究对象,对合金的固态比热和热膨胀系数进行了测量,并对比分析了合金在近平衡凝固和落管快速凝固条件下的组织特征和凝固路径.研究发现,合金比热随Al含量的增大和Ge含量的减少而增大.这三种成分合金的软化温度均为666 K,物理热膨胀系数α在370—650 K温度范围内基本一致,约为1.5×10-5K-1.近平衡凝固条件下合金凝固过程中最后一步反应生成的均为(Al)+(Ge)二相共晶而不是三元共晶,这表明(Al)、(Ge)和CuAl2相在这三种成分的Al-Cu-Ge合金中难以同时形核并协同生长.然而,在快速凝固条件下,初生相的形核和生成受到抑制,合金中更易于形成二相共晶和三元共晶组织.     

Metastable phase separation and rapid solidification of undercooled Co-Cu alloy under different conditions

The metastable liquid phase separation and rapid solidification behaviours of Co_61.8Cu_38.2 alloy were investigated by using differential thermal analysis (DTA) in combination with glass fluxing, electromagnetic levitation (EML) and drop tube techniques. It is found that the liquid phase separation process and the solidification microstructures intensively depend on the experimental processing parameters, such as undercooling level, cooling rate, gravity level, liquid surface tension and the wetting state of crucible. Large undercooling and surface tension difference of the two liquids tend to facilitate further separation and cause severe macrosegregation. On the other hand, rapid cooling and low gravity effectively suppress the coalescence of the minority phase. Severe macrosegregation patterns are formed in the bulk samples processed by both DTA and EML. In contrast, disperse structures with fine spherical Cu-rich spheres homogeneously distributed in the matrix of Co-rich phase have been obtained in drop tube.     

Radiation annealing of rapidly solidified Sn–6.7Sb–5.3Zn alloy by low-dose gamma ray

The radiation annealing of a rapidly solidified Sn–6.7Sb–5.3Zn (in atomic percent) melt-spun alloy was caused by low-dose gamma ray irradiation. This is observed from the increase in both the volume of unit cell and particle size of the Sn matrix, as revealed from X-ray diffraction analysis, and the decrease in the resistivity. The alloy was irradiated by gamma ray at doses 5, 10, 20, 40, 50, 60, 70, 80, and 100 Gy. The electrical resistivity was measured for the alloys subjected to these doses and it was found that the resistivity decreased by increasing the dose to a minimum value of 50 Gy and then increased by increasing the dose.     

Effect of solidification temperature range on the dendritic growth mode

Electromagnetic levitation technique was used to undercool bulk samples of Co-20% Cu and Co-60% Cu alloys and high undercoolings up to 303 and 110 K were achieved,respectively.The dendritic growth velocities were measured as a function of undercooling.The dendrite growth velocity of the Co-20% Cu alloy was much higher than that of the Co-60% Cu alloy.The experimental data were analyzed on the basis of the LKT/BCT dendritic growth model by taking into account non-equilibrium interface kinetics.It has been re...     

Electron transport in Chevrel phase superconductors,Cu1.8Mo6S8−y Se y , 0⩽y⩽8 and Cu1.8Mo6S8−y Te y , 0⩽y⩽4—Fit to Cote-Meisel theory

Normal state electrical resistivity of the Chevrel phase compounds of the type Cu_1.8Mo₆S_8−y Se _y , 0⩽y⩽8 and Cu_1.8Mo₆S_8−y Te _y , 0⩽y⩽4 is analysed on the basis of the generalized diffraction model which incorporates a postulate on electron-phonon interaction,viz phonons with wavelength exceeding the electron mean-free path are ineffective electron scatterers. Fit obtained by this model was found to be superior to other models based on the interbands-d scattering of electrons.     

Electrical resistivity of liquid Sb–Zn alloys

Using the DC four-probe method, temperature dependence of the electrical resistivity (ρ???T) of Sb_{100? x} Zn _x (x?=?25,?40,?50,?57,?61,?80 at%) alloys was investigated in the temperature range of 500–860°C. The results showed that resistivity of each liquid alloy decreased non-linearly with temperature increasing above their liquidus (T _L) until reaching critical temperature, at which the resistivity–temperature coefficients dρ/dT–T converts from negative into positive. The phenomena of liquid phase transformation might relate with the dissociation of covalent bonds, chemical orders and associations in Sb–Zn melts.     

微重力下Fe-Al-Nb合金液滴的快速凝固机理及其对显微硬度的影响

采用落管无容器处理技术实现了Fe_(67.5)Al_(22.8)Nb_(9.7)三元合金在微重力条件下的快速凝固,获得了直径为40—1000μm的合金液滴.实验中合金液滴的过冷度范围为50—216 K,冷却速率随着液滴直径的减小由1.23×10~3K·s~(-1)增大到5.53×10~5K·s~(-1).研究发现,Fe_(67.5)Al_(22.8)Nb_(9.7)合金液滴的凝固组织均由Nb(Fe,Al)_2相和(αFe)相组成,且随着液滴直径的减小,初生Nb(Fe,Al)_2相由树枝晶转变为等轴晶,共晶组织发生了约3倍的细化且生长特征由层片共晶向碎断共晶转变;硬质初生Nb(Fe,Al)_2相的析出有效提高了合金的显微硬度.与电磁悬浮条件下同过冷合金的凝固组织对比发现,落管条件下的合金液滴凝固组织更细化,使得合金显微硬度提高了2%—6%.