S.S. Kim

Effect of V Addition on Hardness and Electrical Conductivity in Cu-Ni-Si Alloys

The effect of vanadium (V) addition on the microstructure, the hardness and the electrical conductivity of Cu-2.8Ni-0.7Si alloys was investigated. The V-free, the 0.1 wt% V-added, the 0.2 wt% V-added Cu base alloys were exposed to the same experimental conditions. After the cold rolling of the studied alloys, the matrix was recrystallized during the solution heat treatment at 950 °C for 2 h. However, small amounts of vanadium substantially suppressed the recrystallization and retarded the grain growth of the Cu base alloys. The added vanadium accelerated the precipitation of Ni2Si intermetallic compounds during aging and therefore it contributed positively to the resultant hardness and electrical conductivity. It was found that the hardness and the electrical conductivity increased simultaneously with increasing aging temperature and time with accelerated precipitation kinetics by the addition of vanadium. In the present study, the Cu-2.8Ni-0.7Si alloy with 0.1 wt%V was found to have an excellent combination of the hardness and the electrical conductivity when it was aged at 500 °C.

Effect of cathodic hydrogen charging on mechanical properties of Al 8090

It has been well established that precipitation hardened, high-strength Al alloys are often susceptible to external hydrogen embrittlement. Al 8090 has been developed to reduce the mechanical anisotropy and improve the toughness by introducing S{prime} (Al{sub 2}CuMg) precipitates. Recently, Chen et al. studied the effects of cathodic hydrogen charging on tensile properties of Al 8090 sheet, and observed that hydrogen embrittlement affects the tensile properties of Al 8090 significantly, suggesting that hydrogen embrittlement may play an important role in SCC of Al 8090. It has often been demonstrated that the presence of notch greatly alters the hydrogen-assisted mechanical behavior of metals. Therefore, the main objective of the present study was to examine the effects of cathodic hydrogen charging on tensile and fracture behaviors of Al 8090.

Fatigue-induced Grain Growth And Formation Of Slip Bands In Cu Processed By Equal Channel Angular Pressing

In order to elucidate the effect of the microstructure on fatigue behavior of ultrafine grained copper, fatigue tests were conducted using copper processed by equal channel angular pressing through 4, 8 and 12 pass numbers. The evolution of microstructure and surface damage during cyclic stressing was monitored. For samples processed by 8 and 12 passes, dynamically recrystallized grains were formed and these grew with subsequent stressing. Slip bands were initiated inside such grains. For samples processed by 4 passes, the formation of slip bands was likely to occur inside dynamically recovered coarse grains. The physical basis on the phenomena leading to the initiation of fatigue cracks was discussed from the viewpoint of microstructure and surface damage evolution.

Evaluation of crack growth rate and growth model of ultrafine grained copper

High-cycle fatigue tests were carried out on smooth specimens of ultrafine grained (UFG) copper produced by equal channel angular pressing for 12 passes. The growth behavior of a small surface-crack was monitored. A major crack, which led to the final fracture of the specimen, initiated from shear bands (SBs) at an early stage of stressing. Different tendencies of growth behavior occurred depending on the ranges of crack length. To understand the changes in growth rate and fracture surface morphologies, a quantitative model describing a crack growth mechanism were developed considering the reversible plastic zone size at a crack tip. In addition, the crack growth rate of UFG copper was evaluated by applying the small-crack growth raw.

The Relationship between Shear Bands and Crack Growth Behavior in Ultrafine Grained Copper Processed by Severe Plastic Deformation

Fatigue life of smooth specimens is approximately controlled by the growth life of a small crack. This means the growth behavior of small cracks must be clarified to estimate the fatigue life of plain members. However, there are few studies on the growth behavior of small cracks in ultrafine grained (UFG) metals. In the present study, fatigue tests for UFG copper have been conducted. The formation behavior of shear bands (SBs) and growth behavior of a small crack have been monitored to clarify the effect of SBs on the growth behavior of a major crack.