Imaging transient solidification behavior
- PDF / 6,192,750 Bytes
- 11 Pages / 585 x 783 pts Page_size
- 101 Downloads / 346 Views
ntroduction Solidification processing can be traced back more than 5000 years, and the melting and casting of metals and alloys have represented major technological advances for society. However, inception of modern solidification science began only in the late 1940s and early 1950s with Turnbull’s pioneering work on nucleation1–10 and a seminal paper by Tiller et al. on solute redistribution,11 showing that the complex process of alloy solidification could be described quantitatively. Since then, scientific advances in solidification have continued to provide innovative solutions for manufacturing and breakthrough technologies for industry and society. As an example, the evolution of nickel-based superalloys, in terms of the complexity of both alloy composition and solidification processing, has led to development of aircraft turbine blades with outstanding high-temperature strength and corrosion resistance, enabling modern jet engines with improved performance.12–14 During solidification, alloy microstructure is determined by processing conditions, including temperature gradient, concentration gradient, cooling rate, and growth velocity. These process conditions govern the solid–liquid interface morphology, with interface patterns ranging from planar to cellular to complex dendritic structures,15,16 and they play a critical role in the growth competition of grains and formation of grain
boundaries in polycrystalline and multiphase materials.17,18 Thus, control of the solidification conditions provides an initial opportunity to influence microstructure development, and hence properties and performance, in metallic components. Typically, metals and alloys are examined post-solidification by sectioning components to infer the dependence of microstructure and its evolution at elevated temperature on processing conditions. These destructive inquiries assume that the final state suitably represents an instantaneous condition at an earlier time during solidification.17 Recently, development of real-time monitoring techniques has permitted direct observations of metallic alloys during solidification with appropriate spatial and temporal resolutions to capture microstructure evolution and responses to process condition changes that control transient solidification behaviors. In this article, examples are given that demonstrate the impact of these in situ techniques on our understanding of microstructure and defect development during alloy solidification, providing a path toward process strategies that enable control of structure evolution and creation of optimal properties. In addition, we demonstrate utilization of measurements from these state-of-the-art in situ experiments to develop multiscale predictive models for structure evolution under various processing conditions.
Joseph T. McKeown, Materials Science Division, Lawrence Livermore National Laboratory, USA; [email protected] Amy J. Clarke, Department of Metallurgical and Materials Engineering, Colorado School of Mines, USA; [email protected] Jörg M.K. Wiezorek,
Data Loading...
