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Study on the Constitutive Relationship of Cu-Nb Metal Matrix Composites during Hot Deformation

Author: ZouLiYing
Tutor: LuYaFeng
School: Northeastern University
Course: Materials Science
Keywords: Cu-Nb composites constitutive relationship hot deformation
CLC: TB331
Type: Master's thesis
Year: 2012
Downloads: 12
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Abstract

Cu-Nb composites have attracted interest for the advantages of excellent mechanical strength, high conductivity and high temperature resistance. Study on the mechanical behavior of Cu-Nb composites plays an important role in the development and application of the composites. Development of constitutive relation of composites during hot deformation will be helpful to quantitative analysis about the effect of deformation thermal parameters on mechanical behavior of composites, which will provide reliable data for the system of mechanical behavior of Cu-Nb composites.High temperature tensile tests of Cu-Nb composites were carried out in the temperature range of20℃～700℃and strain rate range of0.001s-1～10s-1by the Gleeble-3500hot working simulator. To indicate on the effect of morphology of Cu-Nb composites’ on the deformation mechanism, high temperature compression tests of pure Nb body materials were performed at the same conditions. The variations of flow stress with the thermal parameters were showed by true stress-strain curves. Introduced with the key parameter of strain, the models of constitutive relationship of Cu-Nb composites and pure Nb body materials were obtained on the base of Arrhenius equations. The main research results are shown as following:1. For Cu-Nb composites, flow stress decreased with the increasing of deformation temperature at the same condition of strain rate. The effect of softening process is mainly resulted by aggravation of atom movement and cancellation effect between the dislocations and decreasing of dislocation density. Flow stress increased with the increasing of strain rate at the same condition of deformation temperature. Decreasing of the softening phenomenon is due to increasing of generation, movement, probability of crossing and the equilibrium density of dislocation. For pure Nb body materials, flow stress decreased with the increasing of the deformation temperature at the same condition of strain rate. The variations of flow stress slightly result from the coupling effect of strain rate and deformation temperature.2. Obvious yield phenomenon of Cu-Nb composites during hot deformation is remarkably caused by the following reasons:(1) Dislocation density increased abruptly as tensile tests experienced the plastic deformation stage;(2) Dislocation movements were impeded by Nb fibers.3. When Cu-Nb composites were tested at ambient temperature, the process of dynamic recovery was predominantly observed. Above this temperature, the process of dynamic recrystallisation was found to be the dominant mechanism. Main softening mechanism of pure Nb materials was dynamic recovery from room temperature to700℃. It is resulted that Nb fiber was easier to experience dynamic recrystallisation than its body materials at the same deformation conditions. So Cu-Nb composites were apt to cause the process of dynamic recrystallisation.4.In view of the key parameter of strain, constitutive relationship models of Cu-Nb composites and pure Nb body materials were proposed on the base of Arrhenius equations. Based on this model, the constitutive relationships of Cu-Nb composites and pure Nb blocks containing deformation temperature, strain, strain rate and flow stress were constructed. A solving method of constitutive equations was suggested by Matlab platform and quantitative relation of constitutive relationship models were obtained at different deformation conditions. Moreover, the accuracy of the obtained constitutive equations was verified. In the constitutive relationship model of Cu-Nb composites, the fitting accuracy of98.5%data points was above90%. In the constitutive relationship model of pure Nb body materials, the fitting accuracy of all the data points was above85%. And the optimum fitting process could supply a effective method to estimate the mechanical behavior of Cu-Nb composites.

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