Effect of Rare Earth Upon As-Cast Microstructure and High Temperature Performance of ZA40 Alloy
In testing comparison, this study is made on the modification effect of 0.05 wt.% La-rich rare earth (RE) upon as-cast microstructure, mechanical properties of materials at high temperatures (100, 150, 200°C) and wear resistance under different temperatures (100and 200°C) of ZA40 alloy containing Si. The addition of RE shows that it can not only effectively refine Al-rich and Cu-rich phase, but also reduce the amount of needle-like eutectic silicon, and then make the size of massive primary silicon phase smaller. Thus, there are the improvement of strength, ductility and wear resistance of materials at high temperature. The analyses are also conducted on the mechanism of underlying RE elements.
Effects of stabilizing heat treatment on microstructures and creep behavior of Zn–10Al–2Cu–0.02Ti alloy
Abstract The microstructures of as-extruded and stabilizing heat-treated Zn–10Al–2Cu–0.02Ti alloys were observed by scanning electron microscopy, transmission electron microscopy, electron probe microanalysis and X-ray diffraction analysis techniques. The change in structure after heat treatment and its effects on room temperature creep behavior were investigated by creep experiments at constant stress and slow strain rate tensile tests. The results show that after stabilizing heat treatment ((350 °C, 30 min, water-cooling)+(100 °C, 12 h, air-cooling)), the amount of α+η lamellar structure decreases, while the amount of cellular and granular structure increases. The heat-treated Zn–10Al–2Cu–0.02Ti alloy exhibits better creep resistance than the as-extruded alloy, and the rate of steady state creep decreases by 96.9% after stabilizing heat treatment.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME