Effect of WO3 Nanoparticle Loading on the Microstructural, Mechanical and Corrosion Resistance of Zn Matrix/TiO2-WO3 Nanocomposite Coatings for Marine Application

In this study, for marine application purposes, we evaluated the effect of process parameter and particle loading on the microstructure, mechanical reinforcement and corrosion resistance properties of a Zn-TiO2-WO3 nanocomposite produced via electrodeposition. We characterized the morphological properties of the composite coatings with a Scanning Electron Microscope (SEM) equipped with an Energy Dispersive Spectrometer (EDS). We carried out mechanical examination using a Dura Scan hardness tester and a CERT UMT-2 multi-functional tribological tester. We evaluated the corrosion properties by linear polarization in 3.5% NaCl. The results show that the coatings exhibited good stability and the quantitative particle loading greatly enhanced the structural and morphological properties, hardness behavior and corrosion resistance of the coatings. We observed the precipitation of this alloy on steel is greatly influenced by the composite characteristics

Effect of Prior Cold Work on Grain Refinement in ST 44-2 Mild Steel by Cyclic Re-Austenitizing

The effect of prior cold work on grain refinement in mild steel by cyclic re-austenization has been studied. Cyclic re-austenization consists of repeated heating to the austenite range, soaking for a short time at the peak temperature and then quenching in water. A steel grade, ST 44-2 (0.14-0.20%C, 0.18-0.28%Si, 0.40-0.60%Mn), was cold worked to various degrees of deformation and subjected to various isothermal heat treatments, keeping the holding time constant while the peak temperature was varied and vice-versa for a number of cycles. The higher the degree of cold work the finer the average grain size for a given number of cycles. Average grain size decreases with increasing number of cycles up to an optimum number and the optimum number of cycles decreases with increasing degree of cold work. The effect of cold work is more pronounced at lower temperature, shorter time and smaller number of austenitizing cycles. For a given condition of temperature and time, the higher the degree of cold work, the smaller the number of cycles required for optimum grain refinement. Keywords: Mild Steel, Grain Refinement, Cyclic Re-Austenitization, Cold-Work Journal of Applied Science, Engineering and Technology Vol. 6 (1) 2006 pp. 48-5

The effects of isothermal transformation on the fatigue strength of austempered ductile iron

The fatigue strength of austempered ductile irons was studied. Austempering was carried out by initial austenitising at temperatures of 850, 900 and 950°C for 1 hour followed by rapid quenching and holding in a salt bath maintained at temperatures of 280, 300, and 350°C for different time intervals (15,30,60,90 or 120 minutes). Fatigue test was prepared to standard and the number of cycles to failure for each specimen was plotted against the bending stresses for the specimen. Results showed that at low austenitising and low austempering temperatures, the fatigue limits were generally low. Increasing the austenitising temperature to 950°C while maintaining the austempering temperature at 3500C, the fatigue limits of both medium silicon and high silicon alloys increased. The highest fatigue strength 450Nmm-2 was obtained from alloy austenitised at 950°C and austempered at 350°C for 90 minutes. Keywords: fatigue, austempered ductile cast iron Botswana Journal of Technology Vol. 14(2) 2005: 21-2