Cu-Be/Cu-Zn层状金属基复合材料的冷轧变形行为及界面过渡层演变

Cold Rolling Deformation Behavior and Interface Transition Layer Evolution of Cu-Be/Cu-Zn Laminated Composite

高铍含量的铍铜(Cu-Be)合金时效后抗拉强度可达1400 MPa以上,伸长率却不到5%,呈现显著的强度-塑性倒置关系,严重影响了合金服役的安全可靠性。高强Cu-Be合金塑性变形时产生的局部应变集中现象是导致其低塑性的根本原因,将层状非均质构型设计的思想运用于Cu-Be合金,构建Cu-Be/Cu-Zn层状金属基复合材料,可以有效减少该现象的产生,有望获得高强塑性的层状金属基复合材料。运用塑性变形法制备层状金属基复合材料简单易行,受到广泛关注。前人对层状金属基复合材料轧制变形规律的研究主要集中在复合材料金属组元方面,对界面过渡层变形规律研究较少。本工作利用真空热压复合及后续冷轧变形的方式制备了Cu-Be/Cu-Zn层状金属基复合材料,利用光学显微镜(OM)、场发射扫描电镜(FE-SEM)结合能谱仪(EDS)、显微维氏硬度计对Cu-Be/Cu-Zn层状金属基复合材料冷轧变形行为及界面过渡层的演变进行了研究。研究结果表明,Cu-Be/Cu-Zn层状金属基复合材料冷轧前金属层间界面基本呈平直状,界面结合良好且无裂纹、孔洞等缺陷。当冷轧压下率不超过50%时,Cu-Be/Cu-Zn层状金属基复合材料发生不均匀的宏观变形,Cu-Zn层在板材厚度方向的变形量明显大于Cu-Be层和界面过渡层,当冷轧压下率为35%时,界面过渡层的厚度仅减小8.3%,不均匀的塑性变形导致Cu-Be/Cu-Zn界面由平直状态变为波浪状态;当冷轧压下率超过65%时,层状金属基复合材料内部发生均匀、协调的变形,各层厚度基本按照总冷轧压下率变化。不同冷轧压下率下,显微硬度最高的均为过渡层,其次是Cu-Be层,而Cu-Zn层的显微硬度最低。这是因为在层状金属基复合材料冷轧变形过程中,界面过渡层主要起到协调变形的作用,处于显著剪切应力状态,会产生额外的背应力强化。本工作探讨了界面过渡层在Cu-Be/Cu-Zn层状金属基复合材料冷轧过程中的宏观变形以及强化机理,有助于进一步阐明层状金属基复合材料塑性加工变形规律并合理制定其塑性加工工艺。

After aging treatment,the ultimate tensile strength of high strength beryllium copper alloy can reach 1400 MPa but the elongation is less than 5%.The significant strength and ductility trade-off presented in the beryllium copper alloy seriously affects the safety and reliability during the service.The local strain concentration which leads to the low plasticity can be suppressed by applying the laminated heterogeneous configuration design to the Cu-Be alloy.It is expected to acquire material with high strength-ductility through the preparation of Cu-Be/Cu-Zn laminated metal matrix composite.The preparation of laminated metal matrix composite through plastic deformation is easy to realize,which has caused widely concern.Previous researches of laminated metal matrix composite rolling deformation mainly focused on the deformation characteristics of metal components,but few works concerned the deformation characteristics of interface transition layers during rolling.In this work,we successfully prepared a Cu-Be/Cu-Zn laminated metal matrix composite by vacuum hot pressing and subsequent cold rolling.The cold rolling deformation behavior and interface transition layer evolution of Cu-Be/Cu-Zn laminated metal matrix composite were investigated by an optical microscope(OM),a field-emission scanning electron microscope(FE-SEM)with energy dispersion spectrum(EDS)and a Vic-kers hardness tester.The results show that the interfaces between the Cu-Be layers and Cu-Zn layers of the laminated metal matrix composite without cold rolling are of straight shape and the interface bonding is well,without cracks or voids.When the cold rolling reduction rate is less than 50%,inhomogeneous macroscopic deformation occurs in the composite.The deformation of Cu-Zn layers in the thickness direction is obviously larger than that of Cu-Be layers and transition layers.The thickness of transition layers is only reduced by 8.3%with the cold rolling reduction rate of 35%.The inhomogeneous plastic deformation changes the Cu-Be/Cu-Zn interfaces from straight to wavy.When the cold rolling reduction rate is above 65%,different layers of the laminated metal matrix composite deform uniformly and the thickness of the layers changes according to the cold rolling reduction rate.The transition layers possess the highest microhardness,followed by the Cu-Be layers and the Cu-Zn layers have the lowest microhardness in the case of the same cold rolling reduction rate.The high microhardness of the transition layers can be attributed to the significant shear stress state caused by coordinating the deformation of metal layers during the cold rolling of laminated metal matrix composite,which generates the extra back stress strengthening.In this work,the macroscopic deformation and strengthening mechanism of the transition layers in the Cu-Be/Cu-Zn laminated metal matrix composite during cold rolling is discussed,which contributes to better understanding of the plastic deformation characteristics and more reasonable formulating the processing during plastic forming of laminated metal matrix composite.