Young-Gil Kim

Effect of aluminium on deformation mode and mechanical properties of austenitic FeMnCrAlC alloys

Abstract This work is concerned with the effects of Al on the deformation mode and tensile properties of Fe19Mn5Cr(0–5.5)Al0.25C alloys. The deformation mode at room temperature shifted from (e + α′) martensites to deformation twinning to slip with increasing Al content. Al increased the stacking fault energy at a rate of 10 mJ mm−2 wt.%−1, which is sufficiently high to give birth to the large variation of the deformation mode. On the other hand, bct α′ martensites were induced during deformation at low temperatures, together with deformation twins. The formation of bct α′ martensites was preceded by the prior formation of deformation twins. Fe19Mn5Cr3.5Al0.25C alloy composition exhibited excellent elongations exceeding 65% at both room temperature and 77 K. It was found in this work that the sequential formation of strain-induced deformation twins and α′ martensites was responsible for exhibiting excellent elongations at both room temperature and 77 K.

Properties of austenitic Fe-25Mn-1Al-0.3C alloy for automotive structural applications

Abstract Austenitic Fe-25Mn-1Al-0.3C steel, cold-rolled and annealed at about 800 °C, exhibited 2.5 times higher tensile strength than current automotive ferritic sheet steel, while possessing comparable formability. The formation of strain-induced deformation twinning gave rise to an optimum combination of high strength and good formability.

Tensile properties and microstructure of microalloyed CuAlNiX shape memory alloys

Abstract The effects of microalloying additions (0.3Ti, 3Ti-0.2Mn, and 0.3Ti-0.6Zr) to a β Cu-13Al-3Ni shape memory alloy on the tensile properties, shape recovery capacity and microstructure were investigated. It was found that the tensile properties,(σt, σf and ϵf) lie roughly on a straight line according to a Hall-Petch relationship. The highest fracture stress (903 MPa) and fracture strain (8.6%) were obtained in the Cu-13.4Al-3.05Ni-0.24Ti-0.63Zr alloy. Fractography revealed a change from the intergranular to the transgranular fracture mode. Grain boundary cracking was markedly suppressed by the microalloying additions and the fracture model lso changed from brittle to ductile with decreasing grain size of the β phase. The investigated alloys were fully martensitic consisting of internally faulted M18R and internally twinned N2H types.

Effect of applied pressure during solidification on the microstructural refinement in an AlCu alloy

The solidification microstructure can be refined by increasing the cooling rate during solidification. Applying high pressure during solidification can promote the solidification rate by increasing the heat transfer coefficient at the metal/mold interface and changing thermodynamic properties such as solid-liquid transition temperature. Based upon these advantages of high pressure solidification, various investigators have reported substantial refinement of microstructures and improvement of mechanical properties. However, the cooling rate and the degree of the microstructural refinement have not been reported consistently. The purpose of the present study is to investigate the effects of pressure up to 1.7GPa during solidification of an hypoeutectic Al-Cu alloy. Experimental observation of the microstructural refinement in high pressure solidified Al-5.4wt%Cu was compared with the mathematical simulation of the heat transfer behavior during high pressure solidification.

Microstructure and properties of grain-refined Cu-Zn-Al-X shape memory alloys

This work was concerned with the effects of adding the microalloying elements of nickel, silicon, zirconium and titanium to the Cu-25Zn-4Al (wt%) shape memory alloy on the microstructure and properties

A computer aided diffraction analysis in a Cu-base precipitation hardened alloy

Electronic and electric materials such as lead frame and connector alloys require high strength and good electrical conductivity. Among the various strengthening mechanisms, precipitation hardening is a unique method to increase electrical conductivity as well as strength. Electrical conductivity can be increased along with an increase in strength due to the removal of interstitially dissolved elements in the matrix. Cu-base alloys are widely used for electronic and electrical applications due to the high electrical conductivity. The authors previously reported a computer-simulated electron diffraction pattern analysis and its applications to managing steels and Cu-base shape memory alloys. This work is concerned with the application of the computer simulated electron diffraction analysis to the CDA 19015 alloy to determine the orientation relationship between the copper matrix and Ni[sub 2]Si precipitates.

Microstructure and crystallographic features of lath martensite in Fe10Cr10Ni2W maraging steel

Abstract The crystallographic characteristics of martensitic laths in Fe10Cr10Ni2W maraging steel have been investigated using electron diffraction patterns. The microstructure of the solution-treated and subsequently quenched maraging steel consists of fully lath martensite with a high dislocation density. A twin relationship between some adjacent martensitic laths is observed. It is identified that the twinned laths are transformed from the austenite of two specific variants with a Kurdjumov-Sachs orientation relationship.

Effects of Deformation-Induced Twinning and Martensitic Transformation on the Cryogenic Mechanical Properties of Fe-19Mn-5Cr-(0-5)Al-0.2C Alloys

The microstructures and cryogenic mechanical properties of Fe-19Mn-5Cr-(0,3,5)A10.2C alloys have been investigated from room temperature to 77 K. Addition of Al greatly increased austenite stability against e martensite transformation. The fully austenitic Fe19Mn-5Cr-3A1-0.2C alloy showed a UTS of 1120MPa and high elongations of about 75% at both RT and 77 K, due to the formation of strain-induced deformation twins during tensile testing. The alloy also exhibited a high impact energy of 160 J at 77 K.