【作者】 郭明星；

【导师】 汪明朴；

【作者基本信息】 中南大学 ， 材料物理与化学， 2008， 博士

【摘要】 本文研究了双束熔体原位反应-快速凝固法和简化内氧化法两种纳米弥散强化铜合金短流程制备技术，制备了Cu-TiB₂与Cu-Al₂O₃两个系列的纳米弥散强化铜合金，并对两种合金的力学性能、电学性能、加工性能以及组织结构演变规律进行了研究，主要研究结果如下：1、Cu-Ti和Cu-B双束熔体原位反应热力学研究表明，原位反应产物TiB₂相与TiB相均具有负的吉布斯自由能，但TiB₂相能量最低，TiB₂相是双束熔体原位反应中生成的主要强化相。单向扩散双束熔体原位反应动力学研究表明，反应前锋迁移速率方程可表达为（?），单位体积内TiB₂粒子形核数量方程可表达为（?），TiB₂粒子半径方程可表达2、扁型喷嘴反应器出射熔体的流动特性定常紊流边界理论研究表明，紊动射流熔体横向流速满足方程（?），平行于轴线的流速满足方程（?），射流熔体轴线流速u_m沿程变化满足（?），出射熔体卷吸量满足（?），射流熔体初始长度满足L₀=5.2（2b₀）。利用上述研究结果对双束熔体原位反应器进行了理论设计，确定了反应器实验室原型扁型喷嘴厚度2bo的合理取值范围（0．5mm<2b₀<3．0mm）、喷射角度θ取值范围（40-60°）以及反应腔体相关尺寸范围。对Shangguan模型进行外推，研究了凝固界面与前端粒子间相互作用以及熔体中粒子间的相互作用，发现冷却速率V只有在满足C_CI<V<V_CP时，原位反应生成的TiB₂粒子才能被凝固界面捕捉，且颗粒间相互排斥，不易团聚，最终能均匀分布于Cu合金基体内。根据理论设计以及反复实验成功设计了制备Cu-TiB₂合金的双束熔体原位反应-快速凝固联合装置实验室原型。3、依据理论分析与实验研究，确定了实验室研究条件下最佳原位反应参数，即：喷嘴厚度2b₀=1．0～2．5mm，θ=50°；熔炼温度：Cu-Ti合金1400～1500℃，Cu-B合金1300～1400℃；送气压力：0．2～0．35MPa。在上述研究的基础上，成功制备了三种浓度Cu-TiB₂合金，其综合性能分别为：Cu-0．45wt％TiB₂合金：HV=102，σ_b=389MPa，σ_0.2=330MPa，δ=21％，相对电导率=92％IACS；Cu-1．6wt％TiB₂合金：HV=142，σ_b=456MPa，σ_0．2=415MPa，δ=14％，相对电导率=81％IACS；Cu-2．5wt％TiB₂合金：HV=169，σ_b=542MPa，σ_0.2=511MPa，δ=12％，相对电导率=70％IACS。三种浓度合金基体内均弥散分布有大量纳米TiB₂粒子。4、利用TEM对Cu-TiB₂合金的TiB₂粒子尺寸和晶粒尺寸的分布进行了统计，发现合金基体内尺寸在50～75nm的TiB₂粒子频率最高。随着合金浓度增加，原位合成的纳米粒子体积分数不断增加，晶粒尺寸则不断减小。利用上述统计结果对Cu-TiB₂合金强化机制和导电机制进行了研究。结果表明，弥散强化和细晶强化是Cu-TiB₂合金的两种主要强化机制，其中弥散强化的贡献大于细晶强化的。低浓度Cu-0．45wt％TiB₂合金电导率计算值与实测值相差较小，随着所制备合金浓度的增加，材料的电导率的计算值与实测值相差也逐渐增加。影响Cu-TiB₂合金强度及电导率的主要因素是残余的溶质元素Ti、B以及原位反应合成的TiB₂粒子的含量和尺寸等。5、针对Cu-Al₂O₃合金传统内氧化工艺复杂，过程难以控制，产品质量不稳定，生产成本高等问题，进行了简化内氧化工艺研究。简化的工艺流程如下：Cu-Al母合金熔炼→雾化制粉→与适量氧化剂混合→在预先控制气氛条件下内氧化并在线进行真空热压→热挤压成棒材。省去了传统工艺中内氧化→破碎筛分→还原→破碎筛分→冷等静压制坯→真空烧结→包套、抽真空、封口等诸多繁杂工序，大大缩短了生产周期，避免了中间环节造成的氧污染，提高了产品质量。利用该简化工艺制备的两种典型浓度的Cu-Al₂O₃弥散强化铜合金在热挤压态性能分别为：Cu-0．23vol％Al₂O₃合金：HV=85，σ_b=260MPa，σ_0.2=195MPa，δ=30％，相对电导率=96．5％IACS；Cu-2．7vol％Al₂O₃合金：HV=145，σ_b=580MPa，σ_0.2=521MPa，δ=13％，相对电导率=82％IACS。6、Cu-Al₂O₃弥散强化铜合金冷轧过程中会出现加工软化现象，随着Al₂O₃浓度的增加，加工软化特性不断减弱。通过TEM观察建立了位错与弥散粒子间相互作用模型，认为加工软化的原因是：在大变形量冷轧过程中异号位错间发生湮灭，它使得相邻位错胞合并和长大，从而导致合金硬度下降，最终出现加工软化现象。单向轧制的弥散强化铜合金各向异性显著，横向强度均远低于纵向的，且沿横向拉伸过程中会出现独特的应力波动或陡降现象。金相和拉伸断口研究表明，单向轧制会使弥散强化铜合形成结合界面较弱的纤维组织，它使得横向拉伸时出现沿纤维界面劈裂现象。纤维组织和沿纤维界面劈裂是Cu-Al₂O₃合金产生各向异性的根本原因。交叉轧制可有效避免Cu-Al₂O₃合金各向异性。7、Cu-Al₂O₃弥散强化铜合金在室温沿纵横两个不同方向进行压缩时，随着应变速率的增加，流变应力均不断增加，但纵向压缩流变应力要高于横向的。利用滑移面和滑移方向旋转模型以及运动位错与弥散粒子相互作用模型可较好的解释这一规律。Cu-Al₂O₃合金高温热压缩变形是一个热激活过程；沿同一方向压缩时高浓度合金的激活能高于低浓度的，两种浓度合金沿纵向压缩的激活能均高于相应合金沿横向压缩的。根据Cu-Al₂O₃合金高温压缩实验求出的相关材料常数，建立了峰值屈服应力与应变速率以及温度之间的本构方程。对于Cu-0．23vol％Al₂O₃合金，高温变形本构方程为：横向：（?）=[sinh（0．0124836σ）]^4.39909exp（11．65218-99．848×10³／RT）纵向：（?）=[sinh（0．006078σ）]^8.86218exp（23．22611-183．614×10³／RT）对于Cu-2．7vol％Al₂O₃合金，高温变形本构方程为：横向：（?）=[sinh（0．007653σ）]^4.20761exp（14．84478-120．59×10³／RT）纵向：（?）=[sinh（0．005638σ）]^8.52908exp（26．31261-209．892×10³／RT）8．金相组织观察表明，当合金沿横向压缩时，随着热压缩温度的不断升高，纤维组织不断弱化，纤维边界以及内部出现的动态再结晶晶粒数量不断增加，不过高浓度合金动态再结晶相对较困难。当合金沿纵向压缩时，由于压缩方向平行于纤维组织的排列方向，纤维组织破碎严重。高温纵向压缩比横向压缩更容易沿界面产生裂纹。TEM组织观察表明，热压缩使合金亚晶尺寸不断减小，相邻亚晶粒间取向差不断增加，而位错密度却先增加后降低。更多还原

【Abstract】 Two kinds of short flow technologies, in situ reaction of double beam melts-rapid solidification and simplified internal oxidation technology, for the preparation of dispersion strengthened cooper alloys, have been investigated systematically in this paper. And both Cu-TiB₂ and CU-Al₂O₃ nano dispersion strengthened cooper alloys have been prepared by these technologies respectively. The mechanical properties, electricity properties, processability and the evolving law of structure have been studied deeply. The main results can be summarized as follows:1. The investigation of thermodynamics of in-situ reaction of Cu-Ti and Cu-B melts demonstrates that, the Gibbs free energy values of both TiB₂ and TiB phases are negative, TiB₂ phase is the main strengthening phase generated in the in-situ reaction, since the energy of TiB₂ phase is lower. According to the unilateral diffusion kinetics of the in-situ reaction of double-beam melts, the penetration rate of reaction front forTiB₂ particles can be described by the equation （?）. Thenucleation number Z（x） of TiB₂ particles per unit volume is givenby Z（x） =（?） and the radius of the particles is givenby r（x）=（?）2. The investigation of the flow characteristics of melts ejected by in situ reactor with flat nozzles using the turbulent theory indicates that, the current velocity ofturbulent jet melt in transverse direction satisfies the equation（1/a）（v/u_m）= （?）F’（（?））-1/2F（（?）） .The current velocity parallel to the axis satisfies the equation u/u_m= F’（（?））. The axiscurrent velocity u_m for jet melt satisfies （u_m）/（u₀） = 2.28（?）. The entrainment amount of ejected melt satisfies q/q₀= 0.62（?）. The initial segment of jet melt satisfiesL₀ = 5.2（2b₀）. On the basis of the above mentioned results, in-situ reactor of double beam melts has been designed. The proper spans of the thickness 2bo for the flat-shaped ejection nozzle（ 0.5mm < 2b₀ < 3.0mm）, ejection angleθ（40-60°） andrelative sizes of reaction cavity have been determined. The Shangguan model was extrapolated to consider the effect of cooling rate on interaction between freezing interface and front-end particles, and the interaction of particles in melts at the same time, the results indicate that only if the cooling rate V can satisfy the relationship ofV_CI < V < V_CP, TiB₂ particles synthesized by in situ reaction of Cu-Ti and Cu-B meltscan be trapped by freezing interface, and uniformly distribute in the copper matrix. At last, the device of combined in situ reaction with rapid solidification were successfully assembled, and can be used to prepare Cu-TiB2 alloys.3. According to the theory analysis and experiment results, The optimum conditions of ejecting double beam by in situ reactor are as follows: 2b₀=1.0-2.5mm,θ=50°, Cu-Ti melt temperature=1400-1500℃, Cu-B melt temperature=1300-1400℃, air pressure=0.2-0.35MPa. The corresponding properties of CU-TiB₂ alloys prepared by using these optimum conditions are as follows: Cu-0.45wt%TiB2 alloy: HV=102,σ_b =389MPa,σ_0.2=330MPa,δ=21%, relative electric conductivity=92%IACS; Cu-1.6wt%TiB₂ alloy: HV=142,σ_b=456MPa,σ_0.2=415MPa,δ=14%, relative electric conductivity=81%IACS ;Cu-2.5wt%TiB₂ alloy:HV=169,σ_b=542MPa,σ_0.2 =511MPa, 8 =12%, relative electric conductivity =70%IACS. A large number of nano TiB₂ particles can be observed in the matrix of Cu-TiB2 alloys.4.Through statistic analysizing of the sizes of TiB₂ particles and grains in the matrix of CU-TiB₂ alloys prepared under their optimum conditions, it is found that, the frequency of TiB₂ particles with the size of 50-75nm is the highest, and with increasing of solute concentration, the volume fraction of nano TiB₂ particles is also increased, yet the grain sizes decrease. On the basis of the above statistic results, both the strengthening and the conductivity mechanisms have been studied. The results show that: dispersion strengthening and fine-grained strengthening are main strengthening mechanisms for Cu-TiB₂ alloys prepared by this technology, and the strength value contributed from dispersion strengthening is higher than that of fine-grained strengthening. The difference between the calculated and measured electric conductivity values for the Cu-0.45wt%TiB2 alloy is much smaller, yet, with increasing of TiB₂ particles concentration, their differential values are also increased gradually. The influencing factors for electric conductivity of Cu-TiB₂ alloys prepared by this technology mainly include the residual amount of Ti and B solute elements, the content, size and distribution of in situ synthesized TiB₂ particles.5. Because the traditional internal oxidation process is very complicated, products are not stable enough, and their costs are also very high, the simplified internal oxidation process is quite needed to be studied. Through investigation, the simplified internal oxidation process is determined as follows: melting of Cu-Al master alloy→preparing powder by gas atomization→mixing of Cu-Al powder and oxidant→hot pressing（internal oxidation & proforming）→hot extrusion. Some steps in the traditional technology are saved, such as internal oxidation→crushing and screen separation→reduction→crushing and screen separation→cool isostatic compression→vacuum stintering→canning, vacuum-pumping, sealing-off and other procedures, which cuts down the production period, avoids the oxygen pollution and improves the product quality. The properties of the CU-Al₂O₃ alloys under extrusion condition fabricated by the simplified process are as follows: Cu-0.23vol%Al₂O₃ alloy: HV=85,σ_b=260MPa,σ_0.2=195MPa, 8=30%, relative electric conductivity=96.5%IACS; Cu-2.7vol%Al₂O₃ alloy: HV=145,σ_b=580MPa,σ_0.2=521MPa,δ=13%, relative electric conductivity=82%IACS.6. With increased cold rolling deformation, a work softening phenomenon can be observed in the CU-Al₂O₃ alloys. The higher concentration of Al₂O₃ particles is, the poorer work softening is. In order to explain this phenomenon, the microstructure changes of Cu-Al₂O₃alloys were analyzed by TEM as a function of deformation, and the models of interaction between dislocation and dispersion particles were also introduced. The reason for the work softening is: annihilation of unlike dislocations during the cold-rolling with large deformation amount, leads to the agglomeration and growing of adjacent dislocation cells, which results in the decrease of alloy hardness, and the appearance of work softening phenomenon. The anisotropy of unidirectional rolled CU-Al₂O₃ alloy is significant, and the strengths in transverse direction are quite lower than those in longitudinal direction. In addition, the phenomenon of stress fluctuation or steep dropping appears in its transverse tension curve. The research of metallographic and tensile fracture analysis demonstrates that, fibre structure with lower bond strength boundary is formed in the CU-Al₂O₃ alloy after unidirectionaly rolling, and leading to the splitting of fibres along their interface during the transverse tension, which are the essential reasons for the stronger anisotropy of unidirectional rolled CU-Al₂O₃ alloy. Tandem rolling can avoid the anisotropy of CU-Al₂O₃ alloy effectively.7. With the increasing of strain rate, the stresses of CU-Al₂O₃ alloys compressed in the longitudinal and transverse directions at room temperature are increased. However, the stresses in the longitudinal direction are higher than those in the transverse direction, which can be explained by the rotation model of gliding plans and glide directions, and the model of interaction between moving dislocation and dispersion particles. Through the quantitative research in the effect of strain rate and compression temperature on peak yield stress, it is found that hot compression deformation of CU-Al₂O₃ alloy is a thermal activation process; the higher Al₂O₃ particle concentration is, the higher activation energy of the alloy is. And the activation energy of Cu-Al₂O₃ alloy compressed in longitudinal direction is higher than that in the transverse direction. According to the relative material parameters obtained from the compression experiment, the deformation constitutive equations of CU-Al₂O₃ alloy describing the relationship of yield stress peak value, strain rate and temperature are given as follows: u-0.23vol%Al₂O₃ alloy:Transverse direction（?） = [sinh（0.0124836σ）]^4.39909 exp（11.65218-99.848×10³/T） Longitudinal direction（?）= [sinh（0.006078σ）]^8.86218 exp（23.22611-183.614×10³/RT）Cu-2.7vol%Al₂O₃ alloy:Transverse direction（?） = [sinh （0.007653σ）]^4.20761 exp （14.84478 -120.59×10³ / RT）Longitudinal direction（?） = [sinh（0.005638σ）]^8.52908 exp（26.31261-209.892×10³/RT）8. The observation of metallographical structure demonstrates that, with increasing of deformation temperature, fibre structure is gradually weakened, and the number of dynamic recrystallization grains appearing among the fibers or on its boundary are also increased. However, dynamic recrystallization is difficult to happen in the high concentration CU-Al₂O₃ alloy. During the compression along its longitudinal direction, because the compression direction is parallel to the arrangement orientation of fibres, the fibres are damaged seriously. The generation of crack along the fibre interface is more difficult to occur in the transverse compression than in the longitudinal direction. The observation of TEM microstructure demonstrates that, hot compression makes the subgrain sizes decrease, and the orientation difference between the adjacent subgrain increase, yet, with the increasing of strain rate, the dislocation density first increases, then followed by decrease.更多还原