Influence of Cooling Conditions in Casting Cu-Ni Alloy Based on Numerical Simulation

The most common and serious defect in Cu-Ni alloy casting is porosity. To solve the problem, accurate casting design and proper design of gating system are necessary. It can be predicted and designed by means of computer simulation of casting solidification. Based on the casting process of the Cu-Ni alloy, the simulation software of diathermanous—flowing—stress coupling ProCAST was used to simulate the Cu-Ni alloy solidification process about the defects and temperature field. By combining experimental results with the simulation results, the quality of casting on some cooling conditions were analyzed. Furthermore, a better cooling condition for solidification process of the Cu-Ni alloy was chosen to improve the quality of the casting. The simulation results indicate that the quality of Cu-Ni alloy casting is the best when it is on the cooling condition of the permanent mold with the insulated riser system.

INFLUENCE OF THE MICROSTRUCTURE OF Cu-Ni ALLOY ON ITS CORROSION RESISTANCE

The microstructures of two kinds of Cu-Ni alloys were observed by TEM.The results show that one of the alloys is a homogeneous solid solution.The other contains discontinuous precipitates at some grain boundaries,and the precipitate is a phase rich in Fe-Ni.By monitoring the corrosion potential(E_(con))in artifical seawater and exposure to natural seawater for a long time,it is found that the E_(con)of the former alloy steadily decreases,while the E_(con)of the latter decreases a little and fluctuates,and the corrosion rate of the former is clearly lower than that of the latter.Aanalyses of SEM and EDX show that the corrosion product film of the former is thin,uniform,compact and rich in nickel,and the film of the latter is thick,loose and covered with numerous deposits.Additionally serious intergranular corrosion occurs in the underlying substrate of the latter.The author proposes that the intergraular corrosion results from preferential dissolution of discontinuous precipitates at grain boundaries.In addition,the protective characteristics of corrosion product films are related not only to the enrichment of nickel but also to their compactness.

Application of the Embedded-atom Method to Liquid Binary Cu-Ni Alloys

A simple analytic embedded-atom model of monoatoms that includes more than nearest neighbours has been extended to study properties of binary liquid Cu-Ni alloys, here the two-body potential between different species of atoms is taken as a function of the two-body potential for the pure metals with a unique form which yields alloy models with the same invariance to electron density transformations as monoatomic models. Faber-Ziman structure factors have been computed by molecular dynamics simulation on the base of this model. The results are in good agreement with experimental data given by Waseda, thus supporting the overall validity of the approach, especially for cross potential of Cu-Ni pair. Further, a detailed description of structure of binary liquid Cu-Ni alloys with different compositions have been performed using pair analysis and bond orientational order method etc., and then the chemical short range order has also been examined to reveal the structural characterization.

Effect of Microstructure and Sulfide on Corrosion of Cu-Ni Alloys in Seawater

The microstructure and the corrosion product films have been investigated on Cu-Ni alloys by TEM, SEM, AES and electrochemical technique as well as natural seawater exposure tests. Experimental results showed that the alloys had two kinds of microstructure, i.e. recrystallizatjon and incomplete recrystallization. In synthetic seawater containing 2x10^-6 S^2-, the stability of the alloy increased with the increase of deformation and annealing temperature, i.e., the degree of recrystallization. After exposure to natural seawater for different periods of time, the corrosion product films of the recrystallized alloy were rich in Ni and compact, and there were cracks in the outer layer which contained a small amount of S; the films of the alloy of incomplete recrystallization became thick, loose and porous, and obviously of layered structure, and the intergranular corrosion took place in the underlying substrate Besides, a great amount of seawater substance existed in the outer layer and some sulfur was found within the grain boundaries that prefer to corrode. The accelerating effect of sulfides in corrosion of Cu-Ni alloys in seawater is attributed to the coexistence and absorption of sulfides and carbides promoting the preference of corrosion where they absorb, and the formation of dissolvable Cu2S results in keeping the surface of the alloys in the active state.

Effect of rare earth on the microstructure and mechanical properties of as-cast Cu-30Ni alloy

Cu-30Ni-xRE （x = 0-0.213） alloys were prepared by a metal mould casting method. The effect of RE on the microstructure and mechanical properties of the alloys was investigated using optical microscope, scanning electronic microscope with energy-dispersive spectrometer, X-ray diffraction, and mechanical test. The results show that RE has obvious effect on refining dendrite structure and grain size, as well as on purifying the melting of Cu-30Ni alloy. With the increase of RE content, the ultimate tensile strength, yield strength, and elongation increase at first and then decrease after adding RE more than 0.095 wt.%. Cu-30Ni-0.095RE alloy possesses preferable mechanical properties, i.e., the ultimate tensile strength, yield strength, and elongation are 308 MPa, 125 MPa, and 51.2%, respectively. The microstructure and mechanical properties are worsened with increasing RE content more than 0.095 wt.%. The improvement of mechanical properties of Cu-30Ni-0.095RE alloy is attributed to RE refining microstructure and purifying the matrix.

Structure Transition Mechanism in Undercooled CuNi Alloys

Taking a Cu55Ni45 alloy as experimental alloy systems,we systematically studied the method of obtaining deep undercooling of alloy melt.Stable deep undercooling of alloy melt was obtained by the combination of molten glass purification and cyclic overheating.Combined with the nucleation and growth mechanism of undercooled melt,the microstructure evolution and grain refinement mechanism of the alloy were systematically studied in a wide undercooling range.The grain refinement solidification structure under large undercooling was analyzed by EBSD technology.Combined with the typical characteristics of recrystallization in metallographic pictures,it was finally confirmed that the grain refinement was caused by recrystallization.

Correlation of seawater corrosion and processing of Cu Ni alloy tubes

The investigations on the effect of the initial surface and microstructure on the seawater corrosion of Cu Ni alloy tubes were carried out by processing, electrochemical methods and natural seawater exposure as well as SEM. Deformation had more impact on the final microstructure of the tubes than the annealing time did, and at the deformation of 32% and annealing temperature 550～600 ℃ for 1 h the tubes was completely recrystallized microstructure. As increasing the volume fraction of recrystallization, the homogeneity of microstructure and the corrosion resistance increased. The residual carbon film produced on the inner surface of the tubes during the processing, had higher corrosion potential than the alloy substrate and good electronic conductivity, so accelerating the dissolution of the substrate in seawater, and the non protective and loose corrosion product film formed. Immersed in natural seawater, the tubes of incomplete recrystallization, consisting of deformed and recrystallized grains, displayed intergranular corrosion, which resulted from corrosion micro cells built between deformed and recrystallized grains and the preferable transportation of electrons on the boundaries of both the grains. In contrast, the recrystallized alloy tubes formed the uniform and compact corrosion product film under which no corrosion was found.

温度对B30铜镍合金在海水中电化学行为的影响

采用线性极化、动电位极化、交流阻抗、循环阳极极化等测试方法,研究了温度变化对B30铜镍合金在海水中电化学行为的影响。结果表明:随着温度的升高,B30铜镍合金在海水中的腐蚀电流密度增大,生成的表面膜稳定性下降,点蚀倾向加重。

船用辅冷凝器B30合金管腐蚀失效分析

某船用辅冷凝器B30合金管发生了大面积早期失效。通过失效B30合金管的腐蚀形貌、腐蚀产物及极化曲线分析其失效原因。结果表明:B30合金管发生了选择性腐蚀,其内表面局部区域发生的严重腐蚀是由点蚀引起的脱镍腐蚀,点蚀坑内的酸化环境使脱镍腐蚀更加严重;由于铜的电位正于镍的,铜在晶粒边界附近发生回沉积。

Effect of Hydrodynamic Conditions on Corrosion Inhibition of Cu-Ni(90/10)Alloy in Seawater and Sulphide Containing Seawater Using 1,2,3-Benzotriazole

Electrochemical studies of the effect of hydrodynamic conditions on corrosion inhibition of Cu-Ni （90/10） alloy in synthetic seawater and sulphide containing synthetic seawater by 1,2,3-benzotriazole （BTAH） are presented. Impedance, potentiodynamic polarization and cyclic voltammetric （CV） studies are employed in the present investigation. The studies are carried out by using Cu-Ni （90/10） alloy rotating disc electrode at different rotation speeds and at different immersion periods. Reynolds numbers at each rotation speed infer that the flow of seawater is laminar. With increasing rotation speed of the electrode immersed in seawater without sulphide and BTAH, both the charge transfer resistance （Rot） and film resistance （Rf^lm） are increased. However, in the presence of sulphide ions and without BTAH, both the Rot and Rf,m are found to decrease with increasing rotation speed at identical immersion periods. Interestingly, when BTAH is added to seawater or seawater containing sulphide, both the Rot and Rf,m are increased to such a great extent that an inhibition efficiency of 99.99% is obtained. In the presence of BTAH, the phase angle Bode plots are more broadened and the maximum values of phase angle are increased to a value close to 90~ as the rotation speed is increased. The BTAH film is highly protective even under hydrodynamic condition also. Potentiodynamic polarization studies infer that BTAH functions as a mixed inhibitor under hydrodynamic conditions also. CV studies reveal that the protective BTAH film is stable even at anodic potentials of ＋850 mV vs Ag/AgCI.

Protective Characteristics and Formation Mechanism of the Corrosion Product Films of B30 Tubes Exposed to Seawater

The corrosion product films of two kinds of B30 tubes(similar to CDA 715)exposed to seawat- er for various periods of time were investigated by SEM,AES and XPS.The results show that the pro- tective corrosion product film is thin,uniform and adherent.FeOOH is found to be present in the film surface,which confirms the hypothesis that iron hydroxide segregates at the surface of the film.The FeOOH promotes Ni enrichment in the corrosion layer by preventing Ni from running off.The corro- sion product film with no protectiveness is of lay- ered structure,loose and bad adherence.The for- mer film is formed through direct oxidation and the latter by precipitation and redeposition from dis- solved species.