【作者】 陈莉；

【导师】 袁泽喜；

【作者基本信息】 武汉科技大学 ， 材料学， 2008， 硕士

【摘要】 元素（特别是微量元素）在晶界上的偏聚对工程材料的力学行为有着深刻的影响，因此研究元素在晶界上的偏聚有着重要的实际意义。而溶质原子的晶界偏聚可分为平衡晶界偏聚和非平衡晶界偏聚两大类，本文以2.25Cr-1Mo钢为试验材料，借助Gleebl-1500热模拟实验机，俄歇电子能谱仪，扫描电子显微镜，冲击试验机等研究P原子在晶界处的非平衡晶界贫化规律，及P原子的偏聚对试验材料韧脆转变温度的影响。试验材料在520℃，40 MPa的压应力下时效不同时间后经AES检测发现，P原子在晶界处发生了明显的非平衡晶界贫化现象，其临界时间为30 min，此时晶界处P原子的偏聚量达到最小值14.18％（at.）。运用Xu模型，计算得出在贫化阶段P-空位复合体的扩散系数数量级为10-21 m²·s^-1；在反贫化阶段，P原子的扩散系数数量级为10-15 m²·s^-1。相较于无应力下的扩散系数，压应力使复合体的扩散系数降低了5个数量级，而磷原子的扩散系数则增加4个数量级。且俄歇试样的冲击断口形貌与晶界处P原子的偏聚量有很好的对应关系。Xu模型能很好解释P原子的非平衡晶界贫化。而试样经650℃，560℃及480℃时效不同时间后，进行系列冲击试验，得到各时效温度下试样的韧脆转变温度。通过冲击试验结果及断口扫描照片分析，随着时效温度的降低，2.25Cr-1Mo钢的韧脆转变温度逐渐升高。根据平衡晶界偏聚理论，随着时效温度的降低，磷的平衡偏聚量逐渐升高。这说明时效温度越低，磷的平衡偏聚量越大，晶界脆性越大，而对应材料的韧脆转变温度越高。更多还原

【Abstract】 The segregation of elements, especially the trace elements at grain boundaries, has animportant influence on the mechanical behavior of engineering materials. So it has basilicpractical meaning to study the segregation of elements at the grain boundaries. The segregationof solute atoms at grain boundaries may be classified into equilibrium segregation and nonequilibriumsegregation. In the present work, a 2.25Cr-1Mo steel was selected as theexperimental material. The non-equilibrium grain boundaries dilution of phosphorus at grainboundaries and the influence of phosphorus segregation on the ductile-to-brittle transitiontemperature （DBTT） were investigated in virtue of Gleeble-1500 thermal simulation machine,AES, SEM and impact machine, et al.The non-equilibrium dilution of phosphorous at the grain boundaries occurs obviously byAES after experimental materials ageing different times at 520℃and 40MPa compressivestress. And the critical time for this non-equilibrium segregation is 30 min. At this time, thesegregation concentration of phosphorus achieves minimal value 14.18at.%. Calculated by Xu’smodel, the order of diffusion coefficients of phosphorous-vacancy complexes are 10-21 m²·s^-1 indilution process. The order of diffusion coefficients of phosphorous are 10-15 m²·s^-1 in dedilutionprocess. Compared with the diffusion coefficients under no external stress, it is foundthat the compressive stress decreases the diffusion coefficient of phosphorous-vacancycomplexes by 5 order of magnitude and increases the diffusion coefficient of phosphorous by 4orders of magnitude. And the fracture appearances of AES samples correspond to the grainboundaries segregation results of phosphorus. Xu’s model can effectively explain the nonequilibriumgrain boundaries dilution of phosphorus.Series of Charpy impact tests are carried after samples respectively ageing at 650℃, 560℃and 480℃, and ductile-to-brittle transition temperature is known. By the values of impact testand the analysis on SEM pictures of impact fracture, the DBTT of 2.25Cr1Mo increases withthe reduce of ageing temperature. According to equilibrium grain boundary segregation theory,the segregation concentration of phosphorus increases with the descending of ageingtemperature. So we can conclude that the lower the aging temperature, the greater theequilibrium segregation concentration of phosphorus and the brittleness of grain boundaries is,and the DBTT of materials is higher.更多还原