Transition from Crystal to Metallic Glass and Micromechanical Property Change of Fe-B-Si Alloy During Rapid Solidification
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The effects of high undercooling and a large cooling rate can be achieved by the use of a containerless drop tube technique, which is conducive to rapid solidification and formation of a metastable phase. Here, the rapid solidification of Fe78Si13B9 (S1) and Fe78Si9B13 (S2) alloys was completed under microgravity condition. Based on theoretical calculations, a maximum undercooling of 433 K (0.29 TL) and 412 K (0.28 TL) was obtained, respectively. The microstructure evolution and the formation of an amorphous-nanocrystalline structure for the two alloys were compared and analyzed. The results show that S2 alloy has better amorphous forming ability and higher hardness. During the solidification of S1 alloy, the primary phase α-Fe grows by the manner of dendrites, and the secondary dendrite arm spacing decreases exponentially with increased undercooling. An amorphous-nanocrystalline structure is developed when the undercooling is increased up to 388 K; S2 alloy forms an amorphous-nanocrystalline structure at an undercooling of 275 K and is completely amorphized after exceeding an undercooling of 402 K. In addition, the hardness and elastic modulus are acquired by nanoindentation technology under different degrees of undercooling. The phase constitution, morphology, distribution, and grain refinement of the alloys have important effects on the micromechanical properties of these alloys.
This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 51734008, 51522102, and 51771154), the National Key R&D Program of China (Grant No. 2018YFB2001800), and the Fundamental Research Funds for the Central Universities. The authors are grateful to Dr. D.L. Geng and Miss W. Liu for their valuable help with the experiments.
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