■ Title : Strategy for alloy design to simultaneous increasing strength and its trade off properties
■ Speaker : Dr. Han‐Seung Jeon (KIMS)
■ Date and time : 11/26 (Tue) 10:00 AM
■ Venue : Applied Engineering Building (W1), #2429
■ Host : Prof. Seungbum Hong
■ Abstract : Improving the strength, ductility, formability and conductivity of metals is the ultimate goal of almost every metal research. However, ductility, formability, and conductivity have a trade-off relation that decreases with increasing strength. The reason for this is that only part of mechanisms to increase trade-off properties are complementary or conflicting to the strengthening mechanism. In particular, the ductility and formability of metals depend greatly on the degree of incompleteness of the material, that is, it depends on the instability of grain boundary, which is the stress concentration factor, grain boundary segregation, non-uniform strain between grains, irregular coarse precipitates or inclusions, and the presence of pores.
To simultaneously increase strength and its trade-of properties including ductility, formability and conductivity, the many metallurgical method based on morphological control was been reported. This article has addressed the microstructural view of strengthening metals and at the same time improving their trade-off properties, ductility and conductivity.
First, we discussed whether it is possible to simultaneously increase the strength and its trade off properties, ductility and conductivity in single-phase pure metals. As one of example, the defect-free nanocrystalline copper not only increases the strength but also improves the formability, and stabilization of the grain boundary can increase the strength without sacrificing ductility. The second part deals with how the morphology and distribution of the second phase in a matrix in a multiphase alloy can simultaneously improve the strength and the trade-off properties of the strength. By reducing the interfacial energy or the particular interfacial energy between the second phase and the alloy matrix, the miniaturization and uniform dispersion of the dispersed phase in the matrix were achieved, thereby increasing the strength and improving the conductivity and ductility. We also introduced a method of miniaturizing grains to reduce the inevitably occurring artefacts in the manufacture of alloys, such as coarse grains or columnar structures. The third part indicated that the introduction of secondary nanoscale particles in addition to the main strengthening phase could improve not only strength but also ductility and conductivity. Finally, the discontinuous precipitation mechanism occurred frequently in precipitation-hardening alloys, however, which has been studied only to suppress the mechanical properties because it was known to mechanically detrimental mechanism can be new way to simultaneously improve strength, ductility and conductivity.