Papers by Author: Ping Liu

Abstract: The hot deformation behavior of Cu-Ni-Si-P alloy have been investigated by means of isothermal compression tests on a Gleeble-1500D thermal mechanical simulator in the temperature ranges of 873-1073 K and strain rate ranges of 0.01-5s^-1. The results show that the dynamic recryatallization occurs in Cu-Ni-Si-P alloy during hot deformation. The peak stress during hot deformation can be described by the hyperbolic sine function. The influence of deformation temperature and strain rate on the peak stress can be represented using the Zener-Hollomon parameter. Moreover, the activation energy for hot deformation of Cu-Ni-Si-P alloy is determined to be 485.6 kJ / mol within the investigated ranges of deformation temperature and strain rate. The constitutive equation of the Cu-Ni-Si-P alloy is also established. Keywords: Cu-Ni-Si-P alloy; Hot deformation; Dynamic recrystallization; Zener-Hollomon parameter.

Abstract: Based on Cahn-Hilliard nonlinear diffusion equation, the phase field model has been established for ternary alloy spinodal decomposition, which directly couples with Calphad thermodynamics and dynamics calculation and takes into account the effect of the coherent elastic energy. The simulated microstructures of spinodal decomposition were carried out in the isothermally-aged of Cu-6at.%Ni-3at.%Si alloy. The results indicate that the spinodal decomposition takes place at the early stage of Cu-6at.%Ni-3at.%Si alloy aging at temperatures of 723K, forming two-phases mixture of Cu-rich and Ni/Si-rich, and the decomposition microstructures are distributed in a semi-interconnected labyrinth-like form. Under the effect of the coherent elastic energy, the decomposition microstructures demonstrate the obvious anisotropic characteristics, and present interconnected rectangular stripes aligned along [10] and [01] directions. The growth of the decomposition microstructures is in accordance with the growth law of growth exponent n≈0.29, slightly less than the LSW’s prediction.

Abstract: The phase-field model is established for precipitation transformations in multi-component alloy, which incorporates the interfacial energy and elastic energy anisotropy. The mechanism of the precipitation phase transition is revealed by means of the simulation of δ-phase precipitation process in Cu-4.0at.%Ni-2.0at.%Si alloy, and furthermore, the δ-phase precipitation kinetics is built at the temperature of 450°C. Under the influence of both interfacial energy and elastic energy anisotropy, δ-Ni2Si is presented in disc-shaped precipitates. The simulation patterns show that when one precipitate hits another precipitate with a different orientation, it stops growing, consequently forming a “T”-shape precipitate configuration. When two precipitates with the same orientations grow and hit each other, they connect or coarsen only if the spacing between the precipitates is very small. Therefore, the coarsening behavior of disc-shaped precipitate should be completely different from that of spherical precipitates.

Abstract: The DPCC(deformation processed Cu-based in-situ composite) behaved better combined performance. In this paper, Cu-10Fe-1.5Ag and Cu-10Fe-1.5Ag-0.1Zr in-situ composites were prepared using different forming processes and annealing techniques. The microstructure evolution was explored by SEM during the plastic deformation. It was found that Fe fibers were produced during drawing process and changed from trees dendrite to fiber structure in the form of flake. The effect of Zr on thermal stability of composite was analyzed also. It was shown that the adding of Zr element was helpful to increase the thermal stability of Cu-Fe composite by multi elements compound.

Abstract: The behavior of plastic deformation of Cu-15Cr-0.1Zr in-situ composite under different degree of cold drawing deformation was analyzed by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that both Cu and Cr phases are elongated along cold drawn direction and appear a fibrous morphology; However, Cu phase shows a thread-like fibrous morphology and Cr phase shows a band-like fibrous morphology. The two phases have a coherent relationship of (111)Cu //(011)Cr; When the degree of deformation(ε)is equal to 6.43, the relationship shows// [111]Cu // [110]Cr //cold drawn direction. Furthermore, forming two different morphologies of Cu and Cr phases during cold drawing is also analyzed.

Abstract: The deformation processed Cu-based in-situ composite was a kind of structural function materials with high physical and mechanical performance and used widely in large scale integrated circuit. Especially, the sheet material of Cu-Fe in-situ composites was interested to researchers because the Fe was cheaper and the use of sheets was more widely in electron industry. In this study, the sheets of Cu-10Fe-1Ag in-situ composite were achieved by cold rolling which the thickness was from 6mm to 2.56mm, 1.28mm, 0.64mm and 0.32mm. Corresponding, the rolling ratio was 4.9, 5.3, 5.9 and 6.6. The maximum strength was 722Mpa at the rolling ratio 4.9. The conductivity was measured also with maximum 59.5% IACS. The experimental results show that the tensile strength and electrical resistance increase with the increasing of rolling strain. Although the conductivity of Cu-Fe in-situ composites was not very high, the matching of strength and conductivity was favorable. It is feasible that the high performance Cu-based in-situ composite can be obtained by cold rolling with merits of materials cheaper, melting simple and usage wide

Abstract: The effect of aging temperature and aging time on properties of Cu-3.2Ni-0.75Si-0.3Zn alloy were studied. The alloys were isochronally or isothermally aged after solution treatment. The cold rolling prior to the aging treatment was used to increase the precipitation rate .The microstructure of the alloy was studied by means of transmission electron microscope (TEM). The results show that the fine and dispersed precipitates are fully coherent with the Cu matrix and make the alloy possesses higher hardness and conductivity after the alloy was solution at 1173K and then aged at different time. The precipitates responsible for the age-hardening effect was Ni2Si.The transformation kinetics were studied by analyzing the electrical resistance variation of the solution Cu-3.2Ni-0.75Si-0.3Zn alloy in the process of aging.

Abstract: The micro structural evolution and the mechanism of recrystallization grain growth were studied during re-aging process in Cu-Ni-Si alloy containing finely pre-aging δ-Ni2Si precipitates using computer simulations based on a diffuse-interface phase-field kinetic model. In this model, the temporal evolution of the spatially dependent field variables is determined by numerically solving the time-dependent Ginzburg-Landau (TDGL) equations for the structural variables. The simulation results quantify the effects of the precipitation on recrystallization. It is shown that the finely dispersed pre-aging δ-Ni2Si precipitates exert a strong pinning effect on the recrystallization grain boundaries. The recrystallization grain growth for r = 3 fa = 0.015 can be described as R =1.04∗t 0.33 at the beginning, followed by a gradual transition to growth stagnation. The final grain size follows a Zener type relation lim 0.49 1.41 a R r f =     for 0.01 ≤ fa ≤ 0.21 and r = 2.5 or 3.

Abstract: A method of the aluminizing treatment on the surface of Cu-Al-Y alloy with addition of rare earth compound CeCl3 in 1173K was carried out. The followed internal oxidation of the aluminized Cu-Al-Y alloy was also carried out in the commercial nitrogen gas medium to generate Al2O3 dispersed hardening copper matrix composites. The hardness distribution in aluminized layer and microstructure were studied. Results show that the addition of rare earth oxide CeCl3 has great accelerating effect on the aluminizing, the aluminized layer deeper and uniform than that not add CeCl3 at the same condition. It is possible to generate Al2O3 particles dispersed hardening layer depth reached about 200μm in the surface of specimens with aluminizing and internal oxidation technique.

Abstract: By means of a vacuum induction furnace, Cu-Ag-Cr alloy were produced. The wear property and mechanism of Cu-Ag-Cr alloy are studied, and its property was compared with a Cu-Ag alloy. The microstructure of the Cu-Ag-Cr alloy before wear tests was analyzed by transmission electron microscopy. Worn surfaces of the Cu-Ag-Cr alloy were analyzed by scanning electron microscope (SEM) and energy dispersive X-ray spectrum (EDS). Wear tests were conducted under laboratory with a special sliding wear apparatus that simulated the tribological conditions of sliding current collectors on contact wires, and alloy wire was slid against a copper-based powder metallurgy strip under unlubricated conditions. The results show that the wear rate of Cu-Ag-Cr alloy increase with the increase in the sliding speed and the sliding distance. Adhesive wear, abrasive wear and electrical erosion wear are the dominant mechanisms under the electrical current sliding processes. At lower sliding speed, adhesives wear and abrasive wear are the major wear damage, while electrical erosion wear and adhesive wear are the major at higher sliding speed. Under the same conditions, the wear resistance of the Cu-Ag-Cr alloy is 2~3 times of the Cu-Ag alloy.