Calorimetric measurements on some undercooled metals and alloys

Undercooling was achieved directly in the cell of a high temperature calorimeter (Setaram HTDSC) for Ni, Fe, Cu, Pd and several alloys, using cooling rates between 1 and 15 K min⁻¹. The samples were immersed in alumina powder inside a standard alumina crucible under flowing helium. Ag, Au and Al were not undercooled significantly. The reproducibility of the measurements was within 1.5%. The heat of solidification of Ni at an undercooling of ΔT = 220 K was −17.5 ± 0.2 kJ mol⁻¹, which is the same absolute value of the heat of fusion at the equilibrium melting point T_m. This implies that the specific heat of the undercooled liquid is very close to that of the crystalline solid in this temperature range. Fe appears to display a similar behavior at ΔT = 220 K. The difference between the heat of fusion at T_m and the heat of solidification at an average value of ΔT = 95 K is significant for a Pd_77.5Cu₆Si_16.5 glass-forming alloy. From these data, we calculated an average specific heat difference between the liquid and crystal phases of 7 ± 5 J mol⁻¹ K⁻¹. The enthalpy data for Pd₈₂Si₁₈ comply with those of the ternary Pd---Cu---Si.     

Heat capacity of Ce1−xLaxCu4Al Kondo alloys

The temperature dependence of the specific heat C_p(T), for Ce_1−xLa_xCu₄Al alloys has been studied. The specific heat has been analyzed considering the electronic, phonon and Schottky contributions. In comparison to CeCu₄Al, the substitution of Ce by La reduces the electronic specific heat coefficient γ values. At low temperatures γ value depends strongly on the temperature range used for the extrapolation and on the magnetic field. The scheme of the energy levels created by the crystal electric field (CEF) splitting has been determined from the Schottky anomaly. The values obtained for the energy of the levels are similar for all the compositions.     

Damping capacity of TiNi-based shape memory alloys

The damping capacity mainly comes from the motion of martensite boundaries, which is larger than that from different phase interfaces in TiNi-based shape memory alloys. The fine and disperse precipitation in the TiNi matrix will increase the damping capacity of the TiNiNbMo alloy in the martensitic state but little affect the damping capacity during the martensite transformation. The dispersed Nb-rich particles and the internal stress fields around them influence the change tendency of damping capacity with the increasing of strain amplitude.     

CuAlMn形状记忆合金的高阻尼特性

用悬臂梁弯曲共振法研究了新型CuAlMn系形状记忆合金在马氏体态和母相态的阻尼特性.研究结果表明:室温马氏体态Cu-10.5%Al-6%Mn(质量分数)和室温母相态Cu-11%Al-8%Mn形状记忆合金在表面应变振幅为4.05MPa时,都具有很高的阻尼性能,内耗Q-1接近0.1; 两种形态的CuAlMn形状记忆合金的阻尼性能都随应力振幅增加而下降,且母相态合金阻尼性能下降速度更快.     

Thermodynamic properties of liquid glass-forming Ca–Mg alloys

The complex formation model was used to investigate the thermodynamic properties of liquid Ca–Mg glassy alloys. Our expressions reproduce the thermodynamic functions such as free energy of mixing, enthalpy of mixing, entropy of mixing and activity ratio. The study of long wavelength concentration–concentration fluctuations (S_CC(0)) provides structural information about liquid glass-forming Ca–Mg alloys. Chemical short range order parameter (₁) was obtained from S_CC(0) to quantify the degree of order. The study reveals that the formation of more than one type of complex may be related to the process of glass formation.     

Surface tension and mass density of liquid Cu–Ge alloys

We report a study on the mass density and surface tension of liquid Cu–Ge alloys in the temperature range between the liquidus line and 1373 K. The experiments have been carried out by means of the sessile-drop method. The temperature dependences of both properties are given in terms of linear relations for all alloys under investigation. Both, density and surface tension show remarkable deviations from linear mixing: The density is increased, and the surface tension reduced due to Ge acting as surfactant. The composition dependence of the surface tension is discussed in terms of a simple compound formation model which is well able to relate the results to previous findings on the short-range order of the alloys under investigation.     

镁及镁合金阻尼特性的研究进展

综述了镁及镁合金阻尼特性的研究进展及阻尼镁合金材料的研究现状,介绍了其阻尼性能的评价方法,阐明了其阻尼机制符合G-L位错钉扎模型、基面(0001)上的位错脱钉运动是造成镁合金在室温具有高应变振幅阻尼性能的主要原因,概述了应变振幅、温度、变形工艺、热处理、晶粒尺寸和取向以及合金元素对镁合金阻尼性能的影响.     

Heat capacity and phase equilibria in rare earth alloy systems. R-rich R-Al alloys (R=La, Pr and Nd)

Molar heat capacities of the R-Al (R=La, Pr and Nd) R-rich alloys were determined at different temperatures by differential scanning calorimetry both by using the stepwise and the enthalpimetric methods. The results obtained for the molar heat capacity of Pr₃Al, βPr₃Al and Nd₃Al phases have been reported together with the values obtained for liquid La–Al alloys (x_Al=0.25). The characteristic temperatures obtained for the different invariant reaction involved in the R-rich region have been compared with the literature data. The ↔βPr₃Al transformation has been confirmed at 330°C and a value of Δ_trsH+0.09 kJ/mol of atoms obtained for the transformation enthalpy.     

Effects of Y on mechanical properties and damping capacity of ZK60 magnesium alloys

The microstructure,mechanical properties and damping capacity of ZK60-xY(x=0,1.5%,2.5%,4.0%,mass fraction) magnesium alloys were investigated by using the optical microscope(OM),X-ray diffractometer(XRD),universal tensile testing machine and dynamic mechanical analyzer(DMA).The mechanisms for damping capacity of referred alloys were discussed by Granato-Lücke theory.The results show that Y additions remarkably reduce grain size(the average grain size is 21.6,13.0,8.6 and 4.0μm,respectively),and the tensile properties are enhanced with grain refining(the yield tensile strength increases to 292 MPa from 210 MPa and ultimate tensile strength increases to 330 MPa from 315 MPa).For the ZK60-xY(x=0,1.5%,4.0%)alloys,the damping capacity decreases with the increase of Y content.However,for the ZK60-xY(x=2.5%)alloy,the damping capacity improves abnormally,which is possibly related to the formation of Mg3Y2Zn3(W)FCC phase in this alloy.     

Design optimization of cast Cu-Al-Be-B alloys for high clamping capacity

This paper investigated high-damping Cu-Al-Be-B cast alloys using metallographic analysis, X-ray diffraction (XRD) and electrical resistance measurements for transformation temperatures. The results showed that beryllium can stabilize β phase, resulting in a thermo-elastic martensite microstructure leading to high-damping capacity in cast Cu-Al-BeB alloys. Trace additions of boron to Cu-Al-Be alloys can significantly refine the grains, providing high strength and ductility to the alloys. A factorial design of experiment method was used to optimize the composition and properties of cast Cu-Al-BeB alloys. The optimal microstructure for thermo-elastic martensite can be obtained by adjusting the amounts of aluminum and beryllium to eutectoid or pseudo-eutectoid compositions. An optimized cast Cu-Al-Be-B alloy was developed to provide excellent mechanical properties, tensile strength σb = 767 MPa, elongation δ = 7.62 %, and damping capacity S. D.C =18.70%.     

深过冷条件下Cu—Co合金的二次液相分解与合金的凝固

采用熔融玻璃深过冷技术和金相分析法,对Cu-(10%-30%)Co合金液态深过冷条件下的二次液相分解和合金的凝固行为进行了分析,研究表明,由于液相分解后富C液相的溶解度随温度下降而降低,使Cu原子不断从富Cu原子不断从富C液相中分解出来,如果分解出的Cu原子不能扩散到富Cu原子不能扩散到富Cu液相中,会在富Co液相内形成富Cu液滴。但合金凝固后富Co相中富Cu相并非都来自于干净人液相分解,一部分是来自于富Co液相长大和富Co相选分结晶,冷却曲线的测定结果和分析显示,Cu-Co合金液相分解后,富Co液相的结晶温度与合金成分和实验条件有关,富Co液滴结晶完成后发生了包晶转变。     

The dynamic viscosity of liquid Cu–Si alloys

The dynamic viscosity of liquid Cu–Si alloys is measured in the Cu-rich composition range (up to 40 at.% Si). The Arrhenius-law describing the temperature dependence of the viscosity holds for all alloys investigated. The viscosity isotherms, both experimental and from thermodynamic model calculations, show a broad maximum covering the homogenity ranges of the intermetallic phases. An interconnection of such findings with the atomic structure of the liquid alloys is briefly discussed.     

Rapid solidification and liquid-phase separation of undercooled CoCrCuFexNi high-entropy alloys

Fluxing and cyclic superheating technique was used to investigate the rapid solidification behavior of CoCrCuFe_xNi (x = 1.0, 1.5, 2.0, molar concentration) high-entropy alloys in this study. The microstructures of CoCrCuFe_xNi (x = 1.0, 1.5, 2.0) high-entropy alloys solidified at different undercoolings (ΔT) were investigated. Liquid-phase separation leading to Cu-rich and Cu-depleted regions, were obtained in the solidified microstructure from highly undercooled melt. This occurs when the melt undercooling exceeds a critical undercooling (ΔT_crit) of 160 K for CoCrCuFeNi, 190 K for CoCrCuFe_1.5Ni and 293 K for CoCrCuFe₂Ni alloy. However, typical dendrites and interdendritic regions were observed in rapid-solidified CoCrCuFe_xNi alloys prepared from melts with a small undercooling (ΔT < ΔT_crit). Conversely, a large amount of Cu-rich spheres and even egg-type structures were observed in alloys solidified from melts with large degree of undercooling, ΔT in excess of the critical value, ΔT_crit. A large amount of Cu-rich nano-phases were found in the matrix, possibly, due to the precipitation of Cu-rich phase from the supersaturated solid solution obtained during solidification. The positive enthalpies of mixing between Cu and the other elements in the multi-component alloys resulted in the occurrence of liquid-phase separation prior to the liquid–solid transformation starts. The sluggish diffusion effect of high-entropy alloys and rapid solidification play an important part in the precipitation of nanophase during the solid-state transformation in the Cu-based matrix. Similar to other immiscible alloys, liquid-phase separation occurred when a critical undercooling was exceeded. Differently, nanophases were found in the microstructures of multi-component CoCrCuFe_xNi (x = 1.0, 1.5, 2.0) alloys.     

Numerical modeling of damping capacity of Zn-Al alloys with fully lamellar microstructures

The damping behaviors of Zn-Al alloys with fully lamellar microstructures were simulated with the cell method. The influences of the grain boundary condition, the strain amplitude, the number of the lamellae in the grain （N） and the content ratio of Zn and Al in Zn-Al alloys on the damping capacity were investigated. The results indicate that the grain boundary condition has great influence on the damping capacity of Zn-Al alloys, and also affects the relationship between the damping capacity and the number of lamellae （N）. The variation of damping capacity with the strain amplitude is increasing exponentially with the strain amplitude and the damping capacity increases with the increasing of content of Zn.     

固溶处理对ZK系镁合金力学及阻尼性能的影响

采用光学显微镜、X射线衍射仪、显微硬度计、拉伸试验以及动态热机械分析仪等研究了固溶处理对ZK系（ZK21,ZK40,ZK60）镁合金组织、力学及阻尼性能的影响。结果表明:经固溶处理后,ZK系合金的晶粒尺寸略有长大,第二相溶解、晶格畸变增加。晶界处脆性相的溶解产生的固溶强化效应导致固溶态合金的抗拉强度和显微硬度明显高于铸态。固溶处理后合金的与应变振幅无关阻尼下降、与应变振幅相关阻尼上升,且临界应变振幅明显增大。同一应变振幅下固溶态合金阻尼性能低于铸态;第二临界应变振幅(ε_cr2)增大使固溶态ZK系合金可以在更大应变振幅范围下使用。ZK系镁合金上述阻尼性能的变化可以用Granato-Lücke理论和塑性阻尼理论来解释。      

Corrosion of metals and alloys in mixed gas environments at elevated temperatures

The attack of nickel, cobalt, iron, and alloys of these metals containing chromium and aluminum, by gases containing sulfur-oxygen, carbon-oxygen, and nitrogen-oxygen has been studied at temperatures of 600 and 900°C. The degradation of these metals and alloys was characterized by using standard analytical techniques with emphasis on optical metallography. Three types of accelerated degradation were identified for the attack of alloys by gases containing another oxidant in addition to oxygen. One type of degradation occurred because of the formation of reaction products composed of mixtures of phases involving both of the oxidants. Another type resulted from the reaction of second oxidant phases with oxygen. The third form of degradation involved the development of less protective phases due to thermodynamic instabilities. Thermodynamic stability diagrams are used to help account for the effects produced by different elements in the alloys.     

Ag—Cu—Zr合金的热处理

报道Ag—Cu—Zr合金的固溶时效热处理制度的选择。     

Surface and transport properties of Cu-Sn-Ti liquid alloys

The lack of experimental data and / or limited experimental information concerning both surface and transport properties of liquid alloys often require the prediction of these quantities. An attempt has been made to link the thermophysical properties of a ternary Cu-Sn-Ti system and its binary Cu-Sn, Cu-Ti and SnoTi subsystems with the bulk through the study of the concentration dependence of various thermodynamic, structural, surface and dynamic properties in the frame of the statistical mechanical theory in conjunction with the quasi-lattice theory （QLT）. This formalism provides valuable qualitative insight into mixing processes that occur in molten alloys.     

耐热镁合金及其开发思路

简述了耐热镁合金的特点和概况,介绍了舍金化耐热镁合金、镁基复合材料和快速凝固镁合金3大领域,重点分析了开发新型耐热镁合金的思路、方法与需要注意的问题,并提出了一些建议,为进一步拓宽镁合金在汽车、航天航空、3C产品等领域的应用提供理论依据。