原位富铁纳米颗粒在铜合金中的形成机制

发布时间：2018-06-12 15:47

本文选题：Cu-Fe合金 + 纳米颗粒　；参考：《北京科技大学》2016年博士论文

【摘要】：本文分析了富Fe纳米颗粒在铜合金中熔体中的析出行为,探讨了Cu-Fe难混溶合金中富Fe纳米颗粒均匀在铜合金中分布的可能性,进行热力学及动力学分析。分析凝固条件、对流强弱、合金元素含量变化以及合金元素添加对液态合金中纳米相析出形貌及微观结构的影响。讨论富Fe纳米颗粒在铜合金熔体中的形成机制。通过定向凝固技术制备Cu-Fe合金,富Fe纳米颗粒均匀弥散分布在基体中,讨论富Fe纳米颗粒对单晶Cu-Fe合金力学性能的影响。研究发现,Cu-Fe及Cu-Fe-Co合金在直径φ3mm和φ6mm石英管中凝固后的析出相均为富Fe析出相,富Fe析出相与Cu基体保持良好的共格与半共格关系。根据析出相形状,富Fe析出相可以分为三类,第一类为圆形富Fe析出相,颗粒尺寸为2-50nm；第二类为类圆形富Fe析出相,析出相边界出现不同程度凹陷,颗粒尺寸为50-100nm；第三类为花瓣状富Fe析出相,颗粒尺寸大于200nm。添加Co元素对Fe在Cu合金中的析出有很大的影响。一方面,Co元素的添加使富Fe析出相的微观结构发生变化,富Fe纳米颗粒在20nm左右时,颗粒内部出现孪晶。另一方面Co元素的添加使得Fe析出相的数量增多,这是由于在富Fe纳米在熔体中生长时,由于溶质再分配及对流的同时作用,富Fe纳米颗粒可能发生花瓣晶熔断,富Fe纳米颗粒的尺寸得到有效控制并且数量也增多。在Cu-Fe合金中,富Fe纳米颗粒尺寸为60nm时,纳米颗粒内部开始出现孪晶结构。在Cu-Fe-Co合金中,富Fe纳米颗粒的尺寸约为12nm时就出现孪晶结构。凝固过程中,富Fe纳米颗粒分别以(110)Fe晶面和(112)Fe晶面发生孪生。以(110)Fe为孪生面的孪生机制为生长孪生,以(112)Fe为孪生面的孪生机制为形变孪生。在小对流凝固Cu-2wt%Fe合金条件下,纳米级的花瓣晶熔断现象被发现。较大的花瓣状富Fe纳米颗粒被分为几个尺寸较小的纳米颗粒,这种现象是由熔体对流和溶质再分配共同的作用下造成的。结合DSC实验和淬火Cu-Fe合金TEM分析可知,富Fe纳米颗粒是在Cu合金熔体中形成,在Cu合金凝固之前。大量的富Fe纳米颗粒在Cu熔体中做布朗运动使纳米颗粒弥散分布在基体中成为可能。通过连续定向凝固技术制备单晶Cu-1 wt%Fe合金。定向凝固条件下,Cu-1wt%Fe合金基体中弥散分布大量与基体共格的富Fe纳米颗粒。相比纯铜,Cu-1 wt%Fe合金均表现出较好的综合力学性能。Cu-1 wt%Fe合金相比纯Cu抗拉强度由131.21MPa提高至194.46MPa,延伸率由43.76%提高至44.72%。纳米颗粒共格界面能够改善位错在基体中的分布。一部分位错能够沿着共格界面发生滑移,一部分位错能够进入到纳米颗粒内部,位错塞积现象得到了改善,位错在基体中的分布情况得到了改善,因此能够在提高材料强度的同时,把对基体塑性的损害降到了最低。
[Abstract]:In this paper, the precipitation behavior of Fe rich nanoparticles in the melt of copper alloy is analyzed, and the possibility of uniform distribution of Fe rich nanoparticles in copper alloy is discussed. The thermodynamic and kinetic analysis is carried out. The effects of solidification conditions, convection intensity, the content of alloy elements and the addition of alloy elements on the morphology and microstructure of nanophase precipitates in liquid alloys were analyzed. The formation mechanism of Fe rich nanoparticles in copper alloy melt is discussed. Cu-Fe alloy was prepared by directional solidification, and the Fe-rich nanoparticles were uniformly dispersed in the matrix. The effect of Fe-rich nanoparticles on the mechanical properties of single crystal Cu-Fe alloy was discussed. It is found that the precipitated phases of Cu-Fe and Cu-Fe-Co alloys in diameter 蠁 3mm and 蠁 6mm quartz tubes are Fe-rich precipitates, and the Fe-rich precipitates have a good coherent and semi-coherent relationship with Cu matrix. According to the shape of the precipitated phases, the Fe-rich precipitates can be divided into three types: the first is circular Fe-rich precipitates with particle size of 2-50nm, the second is circular Fe-rich precipitates with different depressions at the boundary between 50 and 100 nm. The third is petal-rich Fe precipitated phase with particle size larger than 200 nm. The addition of Co has a great effect on the precipitation of Fe in Cu alloy. On the one hand, the microstructures of Fe-rich precipitates are changed with the addition of Co elements, and the twins appear in the Fe rich nanoparticles at 20nm or so. On the other hand, with the addition of Co, the amount of Fe precipitates increases, which is due to the fact that, when Fe rich nanometers grow in the melt, due to the simultaneous action of solute redistribution and convection, the Fe rich nanoparticles may be fused by petal crystal. The size of Fe rich nanoparticles was effectively controlled and the number increased. In Cu-Fe alloy, when the size of Fe rich nanoparticles is 60nm, the twin structure begins to appear in the nanoparticles. In Cu-Fe-Co alloy, when the size of Fe-rich nanoparticles is about 12nm, the twin structure appears. During the solidification process, Fe rich nanoparticles were twinned in the crystal planes of Fe (110) and (112) (Fe), respectively. The twinning mechanism of 110Fe as the twinning plane is taken as the growth twin, and the twinning mechanism of 112Fe as the twinning plane is regarded as the deformation twinning. In the condition of small convection solidification of Cu-2wt alloy, the melting phenomenon of nano-petal crystal was found. The larger petal-shaped Fe rich nanoparticles are divided into several smaller nanoparticles, which is caused by the combination of melt convection and solute redistribution. According to DSC test and TEM analysis of quenched Cu-Fe alloy, Fe-rich nanoparticles were formed in Cu alloy melt before Cu alloy solidification. The Brownian motion of a large number of Fe rich nanoparticles in Cu melts makes it possible for the nanoparticles to be dispersed in the matrix. Single crystal Cu-1 wt alloy was prepared by continuous directional solidification. There are a large number of Fe rich nanoparticles in the matrix of Cu-1wt alloy under directional solidification. Compared with pure copper alloy, Cu-1 wt alloy showed better comprehensive mechanical properties. Compared with pure Cu alloy, the tensile strength of pure Cu alloy increased from 131.21 MPA to 194.46 MPA, and the elongation increased from 43.76% to 44.72 MPA. Nanocrystalline coherent interface can improve the dislocation distribution in the matrix. Part of the dislocation can slip along the coherent interface, part of the dislocation can enter into the nanoparticles, the phenomenon of dislocation plug accumulation has been improved, and the distribution of dislocation in the matrix has been improved. Therefore, the damage to the matrix plasticity can be minimized while the strength of the material is improved.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG292;TB383.1

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