Nucleation Behavior of a Single Al-20Si Particle Rapidly Solidified in a Fast Scanning Calorimeter.

Qin Peng,Markus Rettenmayr,Bin Yang,Dongmei Liu,Christoph Schick,Benjamin Milkereit,Olaf Keßler,Armin Springer

doi:10.3390/ma14112920

Abstract

Understanding the rapid solidification behavior characteristics, nucleation undercooling, and nucleation mechanism is important for modifying the microstructures and properties of metal alloys. In order to investigate the rapid solidification behavior in-situ, accurate measurements of nucleation undercooling and cooling rate are required in most rapid solidification processes, e.g., in additive manufacturing (AM). In this study, differential fast scanning calorimetry (DFSC) was applied to investigate the nucleation kinetics in a single micro-sized Al-20Si (mass%) particle under a controlled cooling rate of 5000 K/s. The nucleation rates of primary Si and secondary α-Al phases were calculated by a statistical analysis of 300 identical melting/solidification experiments. Applying a model based on the classical nucleation theory (CNT) together with available thermodynamic data, two different heterogeneous nucleation mechanisms of primary Si and secondary α-Al were proposed, i.e., surface heterogeneous nucleation for primary Si and interface heterogenous nucleation for secondary α-Al. The present study introduces a practical method for a detailed investigation of rapid solidification behavior of metal particles to distinguish surface and interface nucleation.

Highlights

In the production chains of metal components, e.g., in spray forming, rapid solidification of metal particles is a critical process
The rapid solidification of Al-20Si alloy was investigated by differential fast scanning calorimetry (DFSC) [22] at 5000 K/s cooling, which is in the range of the cooling rate in additive manufacturing (AM)
The results show that the microstructure of the rapidly solidified particle consists of primary Si, secondary α-Al, and (α-Al + Si) eutectics

Summary

Introduction

In the production chains of metal components, e.g., in spray forming, rapid solidification of metal particles is a critical process. Studies regarding the nucleation undercooling of Al-Si alloy particles during rapid solidification processes has been reported [15,18,19,20,21]. For an accurate description of the microstructure evolution during rapid solidification, the nucleation undercooling and nucleation mechanisms are crucial, as they provide access to the optimization of the process parameters. Accurate measurements of nucleation undercooling and cooling rate, as well as accurate descriptions of rapid solidification mechanisms are required for a better understanding of rapid solidification processes of metal particles at high cooling rates. The rapid solidification of Al-20Si (mass%) alloy was investigated by differential fast scanning calorimetry (DFSC) [22] at 5000 K/s cooling, which is in the range of the cooling rate in AM.

Materials and Methods

Discussion

Conclusions