形变热处理对Cu-0.8Cr-0.1Zr合金微观组织及性能的影响

Mechanical Properties and Microstructure Evolution in Cu-0.8Cr-0.1Zr Alloy with Thermomechanical Treatment

采用电子背散射衍射(EBSD)分析、透射电镜(TEM)观察、维氏硬度测试等手段,研究了Cu-0.8Cr-0.1Zr合金在固溶处理、二次冷轧及时效处理等工艺过程中的微观组织及性能变化,定量分析了形变热处理对合金力学性能的影响作用及其机制。结果表明,在经过变形率为50%的冷轧后,合金晶粒内部引入大量位错,其位错密度相比于固溶态合金提高了约14倍;在时效过程中,Cr,Zr元素从基体中脱溶析出,形成纳米尺度的面心立方结构富Cr相粒子。位错的增殖以及富Cr相粒子的脱溶析出显著提高了Cu-0.8Cr-0.1Zr合金的力学性能,在峰时效态Cu-0.8Cr-0.1Zr合金中,位错强化和沉淀强化引起的硬度增量分别达到HV 69和HV 68。此外,Cr,Zr溶质原子在时效过程中的脱溶析出,导致Cu-0.8Cr-0.1Zr合金的导电性能得以改善。在450℃时效1 h后,合金电导率由冷轧态的41.3%IACS提高至82.1%IACS。固溶态合金在经过变形率为50%的冷轧和峰时效(450℃时效3 h)后,其力学性能和电学性能达到良好匹配,其维氏硬度达HV 190,电导率达82%IACS。

The mechanical properties and microstructure evolution of Cu-0.8Cr-0.1Zr alloy in the process of solution treatment,secondary cold rolling and aging treatment were investigated by electron back-scattered diffraction(EBSD),transmission electron microscopy(TEM)and Vickers measurement.The effects of thermomechanical treatment on mechanical properties and electrical conductivity in the alloy were analyzed.The results showed that there was a large amount of micrometer-scale dendritic and particulate second phase internally in the cast alloy crystal grains.Through energy dispersive spectroscopy(EDS)analysis,the dendritic and particulate particles were known as Cr and Zr-rich second phase,respectively.The microstructure of the alloy after solid solution treatment was mainly composed of equiaxed grains,indicating that the alloy had a recrystallization reaction during the solution treatment at 950℃,and the average grain size of the solid solution alloy was about 19.0μm.The dendritic second phase almost disappeared after solution treatment,indicating that Cr and Zr elements gradually dissolved into the matrix during solution treatment.After cold rolling with deformation rate of 50%,the grains of the alloy elongated along the rolling direction and formed strip structure.According to the grain size distribution,the average grain size of cold rolled alloy was about 15.4μm,the Kernel average orientation difference(KAM)of the cold rolled alloy was about 3.34°,which was much higher than that of the solid solution alloy(0.24°),indicating that a large number of dislocations were introduced into the grains of Cu-0.8Cr-0.1Zr alloy during cold rolling.The dislocation density of the alloy was estimated by Williamson Hall model.A large number of dislocations were introduced into the alloy grain,and the dislocation density in cold rolling state increased by~14 times compared to solution-treated sample.The nanoscale Cr-rich phase with a face-centered cubic structure was precipitated from the copper matrix during aging,and the crystallographic orientation relationship between the Cr phase and the copper matrix was:■.With dislocation density before aging treatment(9.96×10^(14)m^(-2)),the dislocation density of the alloy after aging treatment was 9.19×10^(14)m^(-2),there was no obvious change,which indicated that there was no obvious recovery recrystallization reaction during aging.The mechanical property of the Cu-0.8Cr-0.1Zr alloy could be improved by the increase in dislocations and the precipitation of Cr-rich phases.The strengthening contribution from dislocation strengthening and precipitation strengthening in peak-aged Cu-0.8Cr-0.1Zr alloy was HV 69 and HV 68,respectively.The strengthening contribution from dislocation strengthening and precipitation strengthening in peak-aged Cu-0.8Cr-0.1Zr alloy was HV 69 and HV 68,respectively.The calculated contribution value of precipitation strengthening(HV 68)was slightly larger than that of the alloy after peak aging(HV57),which was mainly caused by the reduction of the solid solution strengthening effect of the alloy due to the desolvation and precipitation of solute atoms.In the aging process,the precipitation strengthening effect of precipitates was enhanced,while the solid solution strengthening effect was gradually reduced,resulting in that the hardness increment in the aging process was less than the contribution value of precipitation strengthening.In terms of conductivity,the conductivity of Cu-0.8Cr-0.1Zr alloy was significantly improved after aging treatment.In the initial stage of aging,the alloy conductivity increased rapidly.After aging at 450℃for 1 h,the conductivity of the alloy was increased from 39.7%IACS of the solid solution state to 82.1%IACS,and the conductivity of the alloy increased(41±1.4)%IACS,which was mainly attributed to the precipitation of Cr and Zr elements in the copper matrix.The desolvation of Cr and Zr elements from the matrix during aging could effectively improve the purity of copper matrix and reduce the scattering effect of solute atoms on free electronic,so that the alloy could obtain excellent electrical conductivity.With the further extension of aging time,the solid solution atoms were difficult to be further desolved and precipitated,and the conductivity of the alloy did not change significantly.Through the analysis of the strengthening mechanism of the alloy,the high hardness(HV 190)of the alloy sample in peak aging state was mainly due to the contribution of precipitation strengthening and dislocation strengthening.In addition,the deformation could promote the aging behavior of the alloy.The diffusion rate of Cr and Zr elements in copper matrix was lower than that at defects(such as dislocations),and the diffusion activation energy of Cr and Zr in copper matrix was higher than that at defects(such as dislocations),which indicated that Cr and Zr were easier to diffuse in dislocations.A good combination of physical and mechanical properties were attained after cold rolled(rolling reduction was 50%)and peak-aged(aged at 450℃for 3 h)in the Cu-0.8Cr-0.1Zr alloy.The hardness and conductivity of peak-aged alloy were HV 190 and 82%IACS,respectively.