【作者】 彭丽军；

【导师】 熊柏青；

【作者基本信息】 北京有色金属研究总院 ， 材料科学与工程， 2014， 博士

【摘要】 Cu-Cr-Zr系合金是一种典型的时效强化型合金,由于其具有高强度、良好的导电、导热等性能,广泛的应用于航空航天、电子电气、交通运输、新能源等领域。研究表明,在Cu-Cr合金中添加微量的Zr后,由于Cr与Zr之间存在交互作用,会使合金在时效过程中析出更加细小的Cr相和富Zr相,提高合金的强度。虽然目前关于Cu-Cr-Zr合金组织与性能的研究较多,对合金时效析出行为的研究也有一些结论。但是,时效过程中Cr与Zr交互作用机制尚不十分清楚。本文以上述背景为立题依据,采用结合试验结果-数据分析-理论研究的方法对Cu-Cr-Zr合金中Cr与Zr的交互作用机制进行了系统的研究。通过测定一系列Cu-Cr、Cu-Zr和Cu-Cr-Zr合金的抗拉强度和电导率,采用函数拟合和双因素试验的方差分析方法探明了Cu-Cr-Zr合金中Cr与Zr的交互作用方式。通过对Cu-Cr. Cu-Zr及Cu-Cr-Zr合金时效过程中析出相演变规律的研究,确定Cu-Cr-Zr合金中Cr与Zr交互作用的微观机制。通过对不同Cr、Zr含量的Cu-Cr, Cu-Zr和Cu-Cr-Zr合金的抗拉强度和电导率进行函数拟合和双因素试验方差分析,得到Cu-Cr和Cu-Zr合金在450-C时效,由每0.1at.%的Cr、Zr原子引起的强度增量分别为：16.27MPa和48.09MPa,相应的表达式为σcr=233.0+162.7Xcr和σZr=233.0+480.9Yzr;而每0.1at.%的Cr Zr原子引起合金电导率的降低值分别为：0.81%IACS和7.15%IACS,相应的表达式为λCr=100-8.1Xcr和λZr=100-71.5Yzr。由于Cu-Cr-Zr合金中Cr与Zr之间存在正向交互作用,使得Cu-Cr-Zr合金在450℃时效时,合金的极限强度、最大电导率分别大于对应相同Cr、 Zr含量引起的强度增值与纯铜强度的叠加和Cr、Zr引起的电导率降低量与纯铜电导率的叠加,且前后两者强度的差值约为5-25MPa,电导率的差值约为0.5-3%IACS.同时,还获得一种Cu-XCrCr-YzrZr (Xcr≤0.87at.%, YZr≤0.12at.%)合金经450℃时效处理后极限强度和最大电导率的估算表达式分别为σ=233.0+162.7Xcr+480.9YZr+64.9XcrYZr1/3MPa, λ100-8.1Xcr-71.5Yzr+8.94XcrYzrl/3%IACS,利用金相显微镜(OM)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等分析手段研究了Cu-Cr-Zr系合金的铸态组织及均匀化过程中组织演变规律和物理、机械性能变化,发现Cu-Cr合金的铸态组织主要由网状的Cr枝晶和基体组成;Cu-Zr合金的铸态组织主要由共晶组织和基体组成,其中共晶组织是由基体和层片状的Cu5Zr相组成；而Cu-Cr-Zr合金的铸态组织是Cu-Cr和Cu-Zr两种合金铸态组织的叠加,并没有发现Cr2Zr相。在Cu-Cr-Zr合金的均匀化退火过程中,存在两个相变过程,即共晶组织的溶解和Cr相的析出。随着均匀化退火温度的升高和时间的延长,共晶组织逐渐溶解,Cr相的析出体积分数逐渐减小,合金的维氏硬度呈先降低后增加,最后趋于稳定的趋势：而合金的电导率则呈相反的规律,先增加而后下降。通过实验得出合理的均匀化退火制度为900℃×12h。研究了Cu-Zr合金的时效析出行为和强化机制。研究结果表明,固溶态Cu-Zr合金在450℃、500℃时效的维氏硬度与时效时间的关系曲线均呈单峰型,而合金电导率与时效时间的关系曲线呈先增大后趋于稳定的趋势。Cu-Zr合金在450℃时效的析出序列为：过饱和固溶体→Zr的原子团簇→与基体半共格的Cu5Zr相。面心立方结构的Cu5Zr相与基体的取向关系为[112]cu||[011]Cu5Zr,(111)cu||(111)Cu5Zr。通过沿不同晶带轴对析出相形貌的观察,得出Cu5Zr相的真实形貌为具有一定厚度的圆盘状析出物,且沿基体的{111}cu面析出。利用Orowan强化机制估算的屈服强度值167.4MPa与试验结果169.1MPa相近。研究了Cu-Cr和Cu-Cr-Zr合金的时效析出行为及析出相与基体的取向关系。研究结果表明,固溶态Cu-Cr和Cu-Cr-Zr合金在450℃、500℃时效的抗拉强度与时效时间的关系曲线均呈单峰型。固溶态Cu-Cr和Cu-Cr-Zr合金450℃、500℃时效的电导率与时效时间的关系曲线均呈先剧增,后缓慢增加趋于稳定的趋势。Cu-Cr和Cu-Cr-Zr合金450℃的时效过程中Cr相的析出系列为：过饱和固溶体→G.P区→f.c.c Cr相→有序化→b.c.c Cr相。富Zr相的析出过程为过饱和固溶体→Zr原子团簇→亚稳定CuCrZr相→Cu5Zr相。Cu-Cr和Cu-Cr-Zr合金时效过程中Cr相与基体取向关系的变化过程为：立方-立方(cube-on-cube)关系→Nishiyama-Wasserman(N-W)关系→Kurdjumov-Sachs (K-S)关系。通过微观组织分析研究和验证了Cr与Zr之间的相互作用机制。结果表明,在Cu-Cr-Zr合金中,Zr元素能加速Cr元素的偏聚和促进析出相的析出以及有序化过程,缩短合金到达峰时效的时间,并且能有效的减小PFZ的宽度,抑制Cr相的长大,增加时效后期析出相的稳定性,提高合金的综合性能。本文研究发现,在低合金化Cu-Cr-Zr合金中Cr元素能与Cu、Zr元素形成亚稳定CuCrZr相,随后会在时效过程中分解成面心立方结构的Cu5Zr相和体心立方结构的Cr相,延迟Cu5Zr相的形成并抑制其长大。更多还原

【Abstract】 Age-hardened Cu-Cr-Zr system alloys have excellent mechanical properties, high thermal and electrical conductivity, which can be widely used in the field of aviation and navigation, electric power and transportation. The resluts show that the addition of Zr to Cu-Cr alloy can refine the Cr and Zr-rich phase and increase the tensile strength in the aging process, due to the interaction between Cr and Zr elements. Although the microstructure and properties of Cu-Cr-Zr system alloys have been investigated and some conclusions on aging behavior of alloys have been obtained, there are still some ambiguities about precipitation sequence of Cr precipitates and crystallographic structure of Zr-rich precipitates. Besides, the interaction mechanism between Cr and Zr elements is not clear. Thus, in the study, the interaction mechanism between Cr and Zr elements is studied by combining the experimental result, data analysis and theoretical research methods. The tensile strength and electrical conductivity of a series of Cu-Cr, Cu-Zr and Cu-Cr-Zr alloy are tested and the interaction of Cr and Zr is verified according to two-way analysis of variance. In addition, the mechanism of the interaction between Cr and Zr is analyzed by investigated the aging sequence of Cr and Zr-rich phase of Cu-Cr, Cu-Zr and Cu-Cr-Zr alloy.The tensile strength and electrical conductivity of a series of Cu-Cr, Cu-Zr and Cu-Cr-Zr alloy were analyzed by mathematical statistics and two-way analysis of variance. The results show that the added strength caused by addition of0.1at.%Cr and Zr is respectively16.27MPa and48.09MPa, corresponding equation ocr=233.0+162.7XCr and ozr=233.0+480.9Yzr, and decreased electrical conductivity caused by addition of0.1at.%Cr and Zr is respectively0.81%IACS and7.15%IACS, corresponding equation λcr=100-8.1Xcr and λzr-100-71.5Yzr. Additionally, since there is a positive interaction between Cr and Zr in the Cu-Cr-Zr alloy, the ultimate strength of Cu-Cr-Zr alloy is greater than superposition of strength increment caused by corresponding Cr and Zr and strength of pure copper, the electrical conductivity of Cu-Cr-Zr alloy has same change trend as the strength. The difference between before and later in ultimate strength and electrical conductivity are respectively5-25MPa and0.5-3%IACS. Meanwhile, the ultimate strength and electrical conductivity of a Cu-Xcr Cr-Yzr Zr can be respectively estimated by the equation of o=233.0+162.7Xcr+480.9YZr+64.9XCrYzr1/3MPa and λ=100-8.1Xcr-71.5Yzr+8.94XCrYzr1/3%IACS.The microstructure evolution and physical properties change of Cu-Cr-Zr system alloys were investigated in the homogenization process by OM, SEM and TEM, and the as-cast microstructure of Cu-Cr-Zr system alloys were studied as well. The results show that the as-cast microstructure of Cu-Cr alloy is mainly composed of Cu and a network Cr dendrite. The as-cast microstructure of Cu-Zr alloy is mainly comprised of Cu and eutectic structure which is made of Cu and CusZr phase with a fine lamellar structure. While the as-cast microstructure of Cu-Cr-Zr is comprehensive of as-cast Cu-Cr and Cu-Zr alloy, no Cr2Zr phase could be found. Dissolution of Zr-rich phases and precipitation of Cr phases are simultaneously found in the alloy during the homogenization. With the increasing of homogenization temperature and time, the volume fraction of the eutectic structure and Cr phase decrease gradually. The hardness of the alloy exhibite first a gradual decrease, then a rapid increase and finally an almost saturated value. While the electrical conductivity of the alloy showes a contrary tendency. The proper homogenizing process is900℃x12h.The aging behavior and strengthening mechanism of Cu-Zr alloy were investigated. The results showed that hardness-time curve of Cu-Zr alloy exhibites a single peak aged at450℃and500℃, while electrical conductivity-time curve showes a rapid increase first and trendes a stable value finally. The precipitation sequence of Cu-Zr alloy aged at450℃is supersaturated solid solution→Zr atomic cluster→semi-coherent CusZr phase. The orientation relationship with [112]Cu‖[011]Cu5Zr,(111)Cu‖(111)Cu5Zr existes between CusZr phase and matrix. Furthermore, the morphology of CusZr phase is identified as a kind of disk-precipitate with a certain thickness, whose habit plane is parallel to the{111}cu plane of the matrix. The yield strength aged at450℃for8h is calculated to be167.4MPa according to the Orowan strengthening, which is quite consistent with the experimental data (169.1MPa). The aging behavior of the Cu-Cr system alloys and the orientation relationship between Cr phase and matrix were studied. The results showed that the tensile strength-time curve of Cu-Cr system alloy exhibite a peak aged at450℃and500℃. For Cu-Cr alloy, the peak strength effect occurres after aging at450℃for8h. The addition of Zr to Cu-Cr alloy can shorten the time to the peak and increased the tensile strength in the aging process. The electrical conductivity of Cu-Cr system alloys exhibite first a gradual increase, then a rapid increase and finally an almost saturated value. The addition of Zr ato Cu-Cr alloy showe the same change rule of electrical conductivity as the Cu-Cr alloy. The precipitation sequence of Cr phase in the Cu-Cr and Cu-Cr-Zr alloys is supersaturated solid solution→G.P zones→f.c.c Cr phase→order f.c.c Cr phase→b.c.c Cr phase. The precipitation process of Zr-rich phase in the Cu-Cr-Zr alloy is supersaturated solid solution→Zr atomic cluster→metastable CuCrZr phase→CusZr phase. In the evolution of decomposition, the change process of the orientation relationship between Cr phase and matrix is cube-on-cube→Nishiyama-Wasserman→Kurdjumov-Sachs.The interaction mechanism between Cr and Zr on the aging process of Cr precipitates was investigated in detail in the Cu-Cr-Zr alloy. The results show that the addition of Zr to Cu-Cr alloy could accelerate the segregation of Cr elements and enhance the precipitation of Cr phase and the ordering process in the early aging stage. The Zr addition also shortens time to reach the peak, restrained the growth of Cr precipitates and decreases the width of precipitate free zone (PFZ) to increase the stability of Cr phases and the comprehensive properties of the alloy effectively. While the Cr, Zr and Cu elements forme a metastable CuCrZr phase, decomposed into Cu5Zr phase and Cr phase in the aging process, which postpones the formation of CusZr and restrained the growth of this phase.更多还原