退火时间对块体纳米晶Fe3Al材料组织性能的影响

在800℃下对铝热反应法制备的含10%Ni的纳米晶Fe3Al材料进行了不同时间的等温热处理,保温时间分别为4、8、12、16、20、24和48 h。利用XRD和TEM分析了不同保温时间下材料的平均晶粒尺寸,并对硬度进行了测试,研究了晶粒尺寸变化趋势以及硬度变化规律,探讨了两者之间的变化关系。结果表明:材料的平均晶粒尺寸在不同时间的退火处理后,呈现出两次减小,两次增大,最后趋于平稳的过程。晶粒尺寸在4 h等温处理后达到最小值16 nm,在24 h等温处理后达到最大值35 nm。存在一个临界值dc=20 nm,当晶粒尺寸小于dc时,维式硬度和晶粒尺寸之间满足反Hall-Petch关系,当晶粒尺寸大于dc时,两者之间呈现正的Hall-Petch关系。16 h退火处理后维氏硬度最大为490 HV,24 h退火后维氏硬度最小为410 HV。

Effect of annealing time on microstructure and properties of bulk nanocrystalline Fe_3Al-based materials

Bulk nanocrystalline Fe3Al materials with 10%Ni element prepared by aluminothermic reaction were annealed at 800 ℃ for different time.The average grain size of the material was investigated by X-ray diffraction and transmission electron microscope and its hardness was also tested.Results show that the average grain size exhibits fluctuant changes with increasing annealing time less than 24 h and then becomes stable.The minimum average grain size of 16 nm is achieved after annealing for 4 h and the maximum value of 35 nm is obtained for the material after annealing for 24 h.There is a critical value dc,which is 20 nm,when the grain size is lower than dc,hardeness and grain size of the material show an opposite Hall-Petch relationship,when it is greater than dc,they show a positive Hall-Petch relationship.The hardness reaches the maximum value of 490 HV after annealing for 16 h and the minimum value of 410 HV after annealing for 24 h.