【作者】 慕思国；

【导师】 唐谟堂； 郭富安； 彭长宏；

【作者基本信息】 中南大学 ， 有色金属冶金， 2008， 博士

【摘要】 为了解决Cu-Cr-Zr系合金的非真空熔铸和板带加工成型的技术难题,本文分别对Cu-Cr-Zr系合金的非真空熔铸、微观组织演变、热变形行为、带材特征织构等方面进行了理论探讨。设计了一套非真空熔铸系统,确定了最佳熔铸和形变热处理工艺参数。以吉布斯自由能为判据,从热力学上分析了铬和锆元素在熔炼环境下可能发生的化学反应;并从动力学方面研究了在熔炼环境下的合金组元之间扩散和化学反应过程。研究表明:在非真空熔炼和铸造过程中,铬和锆元素与氧气、氮气、氢气、石墨、炉衬材料等发生化学反应而造渣损失;提出了适合于非真空条件下Cu-Cr-Zr系合金的熔炼气氛、炉衬材料、脱氧剂等,设计了相应的熔炼设备。并进行了多次熔铸实验,Cr组元和zr组元的平均烧损率分别9.69%和9.70%,合金组织洁净。采用CALPHAD（Calculation of Phase Diagram）技术,对低溶质Cu-Cr-Zr体系进行了相平衡热力学计算,预测了合金在铸造、热轧和时效温度下可能的析出相和质量分数,以此指导研制合金的化学成分设计。计算结果表明:在低溶质Cu-Cr-Zr系合金的形变热处理过程中主要存在Cu相、Cr相和Cu₅Zr相;当Cr/Zr≥3.5时,Cr相为主要析出相;当Cr/Zr≤3.5时,Cu₅Zr相为主要析出相。利用OM（Optical Microscopy）和HRTEM（High ResolutionTransmission Electron Microscopy）观察了所设计合金在铸造、固溶和时效等工序中析出相的演变。研究结果表明:当Cr含量较高时,在铁模铸造过程会析出大量的Cr相,并偏聚于晶界,加快铸造过程的冷却速度会抑制Cr相的析出和偏聚。铸造时析出的Cr相在固溶处理过程中不会完全返溶,有的甚至聚集长大。在时效过程中,随着Cr含量的增加和Cr/Zr值的增大,析出温度降低、析出速度加快。Cr相在基体中主要以针状、棒状、球状和六边形四种形态存在,富锆相则以不规则形态存在;亚稳相CrCu₂（Zr,Mg）在425℃下时效时分解为Cr相、Cu₄Zr和富Mg相。在Gleeble-1500D热/力模拟机上对Cu-Cr-Zr系合金进行了热压缩实验,研究了其在变形温度700℃-820℃和应变速率0.01-10s^-1条件下的热变形行为。结果表明:热形变过程的流变应力可用双曲正弦本构关系来描述,平均激活能为597.53kJ/mol。根据材料动态模型,计算并分析了该合金的加工图,确定了热变形的流变失稳区,获得了实验参数范围内的热变形过程最佳工艺参数,其热加工温度800-820℃,应变速率为0.01-0.1s^-1。采用XRD（X-Ray Diffraction）技术,对Cu-Cr-Zr系合金的热轧、固溶、冷轧和时效等工序中织构的演变规律进行研究,检测不同工序下的板材沿0度（轧向）、45度和90度（横向）的室温拉伸性能及导电率,建立该系合金的微观组织-特征织构-室温力学性能之间的基本关系。研究结果表明:在Cu-Cr-Zr合金板带中,主要存在着Copper取向、Brass取向、S取向、Goss取向、立方和旋转立方取向。在冷轧过程中,随着冷变形量的增加,Copper取向逐渐向Brass取向转变,在时效过程中则出现了旋转立方取向。当主要取向为Copper取向时,合金板带0度方向（轧向）的强度和延伸率较高,导电率较低。当Copper和Brass取向体积分数相当时,合金板带在0度、45度和90度方向上的性能相差很小。在上述工作的基础上,对Cu-Cr-Zr系合金进行了制备工艺参数优化实验,获得了一套最佳熔铸、热轧、固溶、冷轧和时效工艺参数,并进行了200Kg规模的半工业化生产。更多还原

【Abstract】 The smelting process, microstructure evolution, hot deformation behavior and plate texture of Cu-Cr-Zr alloys were mainly investigated in this paper so to resolve the anti-vaccum melting and process technology of the alloys. The melting process experiments were studied by self-designed non-vacuum melting furnace and casting equipment. The melting, deformation and heat treatment process parameters were optimized by condition experiments. Specific contents and new conclusion are as follows:The Gibbs free energy changes of reactions of copper, chromium and zirconium with some compnents such as O₂, N₂, crucible and furnace lining materials, were calculated at the melting temperature. The possibilities of the relevant reactions were analyzed by the Gibbs free energy changes. The dynamic studies of diffusion and chemical reaction process show that chromium and zirconium can react with O₂ and N₂ under protective atmosphere; the zirconia and magnesia have a good stability for Cr and Zr, therefore, they can be used as crucible and furnace lining materials for Cu-Cr-Zr alloy melting. The favorable factor of the smelting process such as smelting atmopshere, refractory material, deoxidizing agent and so on were put forwarded and relevant equipment were deisgned. The smelting experiment results indicated that the melting loss rate of Cr and Zr elements are 9.69 wt.% and 9.7%, respectively. The casted microstructure of the alloy is clean.Phase equilibrium thermodynamics calculation for low solute Cu-Cr-Zr system is practiced. Precipitated phase and its mass fraction in the process of casting, hot-rolling, and aging are predicted by means of CALPHAD technology. The calculation results can give guide to the optimization of alloy chemical constitution and it is demonstrated that the main phase occurred in the process of thermomechanical treatment are （Cu）, Cr and Cu₅Zr phase. The Cr phase is the main precipitated phase while the value of Cr/Zr≥3.5, and Cu₅Zr is the main precipitated phase while the value of Cr/Zr≤3.5.The microstructure evolution of Cu-Cr-Zr alloys in the process of casting, solution and aging treatment was studied by optical microscope （OM） and high resolution transmission electron microscope（HRTEM）, It is found that when the content of Cr is higher, a large number of Cr phase congregated together in the grain boundary during the course of iron mould casting. The increase of cooling speed can inhibit the precipitation and gathering of Cr phase. The precipitated Cr phase cannot completely resolute into matrix after solution treatment. Furthermore, some precipitated Cr phases congregate and grow up. The precipitation temperature decreases with the increase of Cr content and Cr/Zr value while the precipitation speed is on the contrary in the course of aging. Cr phase exists in the matrix mainly with the shape of acerose, claviform, globosity and hexagon. Zr phase occurs with irregular shape, The CrCu₂（Zr,Mg） phase maybe decompose into chromium-rich phase and zirconium-rich phase at aging temperature above 425°C.The deformation behavior of Cu-Cr-Zr alloy was investigated by compression tests with Gleeble-1500D thermal simulator system. The tests temperatures are 700℃, 750℃, 800℃and 820℃, respectively. The strain rates are 0.01s^-1, 0.1s^-1,1s^-1 and 10s^-1. The results show that the flow behavior could be described by the hyperbolic sine constitutive equation, and an active energy of 597.53 kJ/mol was calculated. The processing maps were calculated and analyzed according to the dynamic materials model. And the processing parameters of hot deformation in the range of this experiment were attained by the maps. The optimal hot deformation temperature was 800-820℃and the strain rate was 0.01-0.1s^-1.The instability zones of flow behavior can also be recognized by the maps.Texture evolution of Cu-Cr-Zr alloy at different processing stage was investigated by mean of orientation distribution functions（ODF）, the volume fraction of the typical orientations also were calculated. Electrical conductivity, tensile strength and micro-hardness also were investigated at different process. The results show that the cold deformation texture, consisted of copper orientation（mainly {113}<332>）, Brass orientation, S orientation and Goss orientation, was very strong, especially the Copper orientation and the Brass orientation. In addition, Copper orientation transformed to Brass orientation with the increase of cold deformation rate. Brass orientation dominates in the aged alloy, and the S orientation and Copper orientation was relatively lower, and no {113}<332> orientation was observed. The volume friction of the {113}<332> orientation was more than 60% in cold rolling samples after aging. When Copper texture was mainly orientation, the tensile strength and elongation of the strip increased at the orientation from 0 degree to 90 degree, the electrical conductivity decreased. When volume fraction of Copper orientation equal to that of Brass orientation, the tensile strength, elongation and electrical conductivity have little different on the orientation from 0 degree to 90 degree.Base on the abve investigation, the preparation processing parameters are optimized by conditions experiments, and a suit of optimal processing parameters with respect to different working procedure of melting, casting, hot-rolling, solution treatment, cold-rolling and aging are obtained. These results provide instructive attemps for the semis-inductrial production of 200kg.更多还原