Multi-scale dendritic patterns sequentially superimposed in a primary semi-solid matrix

Abstract

• The base of conventional dendritic arms is constituted by a primary semi-solid matrix. • The sequential formation of multi-scale dendrites were in-situ and real time verified. • The formation mechanism for multi-scale dendrites is attributed to temperature superimposition. • Multi-scale dendrites are important to microstructures and segregation control. The principle and control for solidification present crucial challenges. Through in situ and real time observation on the solidification of M50 bearing steel, here we discovered that the base of conventional dendritic arms is constituted by a primary semi-solid matrix. Due to the superimposition of temperature fluctuations from the large to the subtle scale, multi-scale dendritic patterns will sequentially emerge and evolve in the primary semi-solid matrix. These findings redefine the essence of multi-scale dendrites as the multi-scale segregation patterns in the primary semi-solid matrix, reconstitute the time and space sequence in the formation of multi-scale dendrites, and reveal the superimposition of temperature fluctuation as the driving principle. These new understandings will fundamentally influence the solidification field. These results also indicate important engineering applications, such as designing multi-scale dendrites, controlling the dendritic segregation and eliminating the detrimental eutectics.