铜基层状强韧化材料的制备及力学行为的研究

IMR OpenIR

	铜基层状强韧化材料的制备及力学行为的研究
	刘华赛
学位类型	博士
导师	张广平
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料物理与化学
关键词	层状材料微观结构/力学性能衬度强度塑性疲劳 Laminated Composite Microstructure/mechanical-property Contrast Strength Ductility Fatigue
摘要	"材料强度与塑性的倒置关系一直是制约高性能金属结构材料发展的关键因素。大量的研究表明，引起超细晶和纳米晶材料塑性下降的根本原因是由于随着材料微观结构尺度的降低，其应变硬化能力逐渐丧失，导致塑性失稳易于在材料中过早产生。因此，如何阻止或者延迟超细尺度金属材料中过早局部颈缩或者剪切带的发生成为提高高强材料塑性的关键。本研究提出了两种超细尺度金属强韧化的方法，通过大压下量的冷轧焊合方法分别制备了铜/铝和铜/铜两种铜基层状复合材料，结合不同退火工艺，调制了复合材料的微观结构和界面结合特性，系统地研究了两种层状复合材料中经不同累积轧制应变的铜层的微观结构与微织构演化规律、拉伸强度与塑性、疲劳抗力与损伤行为等，探讨了两种材料的强韧化机理。采用冷轧焊合及随后退火处理的方法制出了界面结合紧密的铜/铝层状复合材料。经过三道次的冷轧焊合后，铜层晶粒尺寸可细化到1.88 mm，并呈现出拉长位错胞，等轴位错胞和超细晶的混合结构。随着退火温度的升高，铝层被逐渐消耗生成金属间化合物，金属间化合物层的厚度逐渐变厚，直至280°C退火时，铝层被完全消耗形成Al2Cu和Al4Cu9的混合金属间化合物层。铜/铝层状复合材料的界面强结合度随退火温度的升高不断增加。在相同强度水平下，铜/铝层状复合材料的塑性明显高于相同条件下制备的冷轧纯铜；随着界面结合强度的增加，复合材料的塑性不断提高。铜/铝层状复合材料的塑性可以通过较薄的铝层及结合强度较好的铜/铝界面阻止或推迟较厚铜层的局部颈缩而得到提高。为此，提出了一种通过约束颈缩的方法获得高强高韧金属层状材料的新思路。提出了一种“同材层状化”的新方法，通过冷轧焊合加工及随后退火处理，在具有单一晶粒尺度结构的纯铜中制备出具有明显晶粒尺度层状衬度的新型层状复合材料。微观结构研究表明，不同道次轧制的铜层再结晶过程均为不连续再结晶过程；在回复与再结晶过程中，它们始终保持着明显的微观结构衬度。经过280 °C保温5小时的退火，Cuhard-460/Cusoft-100 层状复合材料中形成了明显的晶粒尺度层状衬度，其中8道次冷轧铜层为平均晶粒尺寸600 nm的超细晶层，3道次冷轧铜层为平均晶粒尺寸5 mm的细晶层。随着轧制道次的增加，轧制织构所占的比例逐渐升高。3道次和8道次冷轧铜层的轧制织构比例最终分别达到了~65%和~90%，其中S织构和Brass织构占主要地位，Copper织构的含量不高。通过冷轧焊合和适当的退火处理，获得了强度-塑性匹配良好的Cuhard-460/Cusoft-100层状复合材料，从而实现了在同一种材料中通过微观结构/力学性能的层状化（MPL）来提高材料强韧性的设计思想。拉伸实验表明，MPL-Cu/Cu复合材料的组元层微观结构和力学性能上的差异对材料实现高强度高塑性具有显著的影响。与3道次和8道次冷轧铜以及MPL-Cusoft/Cuhard复合材料相比，MPL-Cuhard/Cusoft复合材料具有更加优异的强度-塑性匹配。原位拉伸实验及SEM观察表明，MPL-Cuhard/Cusoft复合材料中薄的相对较软的铜层（3道次冷轧铜层）可以阻止厚的相对较硬的铜层（8道次冷轧铜层）中剪切带在厚度方向上穿过整个样品横截面，使厚的相对较硬的铜层中形成多重剪切带，从而延迟或抑制过早的塑性失稳，使MPL-Cuhard/Cusoft复合材料获得更高的延伸率。冷轧态纯铜、铜/铝和铜/铜层状复合材料在相同的抗拉强度水平下，铜/铜层状复合材料在高周疲劳区具有较高的疲劳强度。局部界面脱层导致的裂纹偏折与扩展延迟以及复合材料内层新裂纹的再萌生是复合材料具有高疲劳性能的主要原因。随着退火温度的升高，三种材料的应力幅-疲劳寿命曲线趋于重合，它们的疲劳极限也趋于一致。具有晶粒尺度层状衬度的MPL-Cu/Cu复合材料的疲劳性能与冷轧铜相比同样得到提高；同时，MPL-Cuhard/Cusoft的疲劳性能要明显高于MPL-Cusoft/Cuhard的疲劳性能，这种在单一材料中引入晶粒尺度/力学性能的层状衬度使疲劳裂纹无法自由扩展，使得材料内层中疲劳裂纹发生局部偏折及扩展延迟，从而提高了MPL-Cu/Cu复合材料的疲劳抗力。"
其他摘要	"A typical “banana-shaped” strength-ductility trade-off has become a key factor, which limits the development of high-performance structural materials. A number of investigations have shown that nanocrystalline (NC) and ultrafine grain materials (UFG) produced by severe plastic deformation (SPD) method have very high strength, but limited tensile ductility. The physical reason for the paradox is attributed to the fact that the decrease in microstructure scales inevitably results in the degradation of strain hardening ability, which triggers plastic strain localization in the form of necking or shear banding. Thus, how to prevent or delay the onset of the premature local necking or shear banding and sustain a large uniform deformation may be a clue to improve plasticity of the NC/UFG material. In this research, two new methods to improve ductility of high-strength metals with ultrafine grain size were proposed. Cold roll-bonding (CRB) process was used to produce Cu/Al and Cu/Cu laminated composites. Different annealing treatments were used to adjust microstructures and interface bonding strengths of the laminated composites. The evolution of microstructures and microtextures of the Cu layers in the composites, tensile strength and ductility, fatigue property and damage behavior of the laminated composites were investigated systematically. Strengthening and toughening mechanisms of the two kinds of the composites were elucidated. A Cu/Al alloy laminated composite with thicker Cu and thinner Al layers with high interface bonding strength could be fabricated through the CRB process and subsequent annealing treatment. After 3-pass roll bonding, the grain size of the Cu layer was about 1.88 mm, and there existed a mixture of elongated dislocation cells, equiaxed dislocation cells and UFG in the 3-pass rolled Cu layer. With increasing annealing temperature, the thinner Al layer was consumed gradually to generate the brittle intermetallic compounds layer. After annealing at 280 °C, the Al alloy was consumed completely to form Al2Cu and Al4Cu9. With increasing annealing temperature, the interface bonding strength increased. At the same strength level, the uniform elongation of the laminated composite is evidently larger than that of the corresponding cold-rolled Cu. The ductility of the composite increases with increasing the interface bonding strength. The layer interface in the composite could strongly constrain and delay the development of premature local necking of the cold-rolled Cu layer. Thereby, a potential way to improve plasticity of the high-strength metal without losing strength was proposed. A new strategy to produce microstructure/mechanical-property laminated (MPL) composite from a single material is proposed. Through the CRB process and subsequent annealing treatment, a pure Cu with single scale of grain microstructure could be produced into a laminated microstructure with different grain size scales. The recrystallization of the 3-pass and 8-pass rolled Cu layers in the MPL-Cu/Cu composite was a discontinuous process, and the microstructure contrast between constituent layers was generated during the recovery and recrystallization processes. After annealing at 280 °C for 5 hours, the most obvious microstructure contrast could be seen clearly between the constituent layers, among which the 8-pass rolled Cu layer was the UFG layer with an average grain size of ~600 nm and the 3-pass rolled Cu layer contained the equiaxed fine grains (FG) with an average grain size of ~5 mm. With increasing rolling passes, the rolling texture of the Cu layer could be strengthened. In the 3-pass and 8-pass rolled layers, the rolling texture was ~65% and ~90%, respectively, and among which the Brass (B) and S texture components were the major rolling texture, Copper (C) component was weak in the both Cu layers. Through the CRB process and the subsequent annealing treatment, the MPL-Cuhard-460/Cusoft-100 composite provides a better strength-ductility combination by introducing the laminated microstructure with different scales of grains into the single-microstructure scale. Tensile tests have shown that microstructure and mechanical-property contrasts between constituent layers had a significant influence on achieving strengthening and toughening materials. Compared with the 3-pass and 8-pass cold rolled Cu and the MPL-Cusoft/Cuhard composite, MPL-Cuhard/Cusoft has a better strength-ductility combination. In-situ tensile testing and SEM observations revealed that the thinner-softer Cu layer (the 3-pass rolled layer) in the MPL-Cuhard/Cusoft composite could prevent the shear band from traversing other layers in the thickness direction, which triggered the formation of multiple shear bands in the thicker-harder Cu layer (the 8-pass layer). As a result, delaying and suppressing premature plastic instability became more effective, and MPL-Cuhard/Cusoft could have a larger elongation. The experimental results show that the ultimate tensile strength of the Cu/Cu and Cu/Al laminated composites was nearly close to that of the cold-rolled Cu sheet, while the Cu/Cu laminated composite had the enhanced fatigue strength in the high cycle fatigue regime compared with the cold-rolled Cu. The local interface delamination-induced retardation and deflection of fatigue cracking and the secondary initiation of fatigue cracks at the inner layer surfaces are found to be the main mechanisms for the enhanced fatigue resistance. With increasing annealing temperature, the three stress amplitude- nmber of cycles to failure (S-N) overlap each other, and their fatigue strengths are nearly the same. The fatigue strength of the MPL-Cuhard/Cusoft composite annealing at 280 °C for 5 hours has a much higher fatigue strength than that of the MPL-Cusoft/Cuhard composite and the cold-rolled Cu. The fact that the fatigue cracks in the MPL-Cu/Cu composite could not spread freely in the through-thickness of the composite led to the deflection the retardation of fatigue cracking inside the composite, which effectively improved the fatigue endurance of the composite."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64437
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	刘华赛. 铜基层状强韧化材料的制备及力学行为的研究[D]. 北京. 中国科学院金属研究所,2012.