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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。
At 800 ℃, the 10% Ni nanocrystalline Fe3Al materials prepared by the aluminothermic reaction method were heat-treated at different temperatures for 4, 8, 12, 16, 20, 24 and 48 h, respectively. The average grain size of the material under different holding time was analyzed by XRD and TEM, and the hardness was tested. The variation trend of grain size and the variation of hardness were studied, and the relationship between them was discussed. The results show that the average grain size of the material decreases twice, increases twice and finally tends to be stable after annealing at different time. The grain size reached the minimum of 16 nm after isothermal treatment at 4 h and reached the maximum of 35 nm after isothermal treatment at 24 h. There is a critical value dc = 20 nm. When the grain size is smaller than dc, the anti-Hall-Petch relationship is satisfied between the Vickers hardness and the grain size. When the grain size is larger than dc, the positive Hall- Petch relationship. After 16 hours of annealing, the maximum Vickers hardness was 490 HV, and the minimum Vickers hardness was 410 HV after 24 h annealing.