چكيده به لاتين
The laser alloying process can be used to create a coating to increase the hardness and corrosion resistance of parts operating at high temperatures. In this research, laser alloying has been performed by pulsed laser to obtain coating of cobalt, chromium and alumina reinforcing particles on the surface of AISI1045 steel base metal. Since the shape and size of the microstructure and the distribution of reinforcing particles affect the hardness of the coating, the factors controlling these changes have been investigated.
X-ray diffraction (XRD) and X-ray energy spectroscopy (EDS) to detect the phases. Optical microscopy (OM) has been applied to study the geometry of alloyed sections. Scanning electron microscopy (SEM) and Vickers hardness have been used to study the microstructure and analyze the hardness distribution of the coating, respectively.
This research has been done in two phases. In the first phase, carbon was used as the reducing agent to in-situ reducing the levels of cobalt oxide and chromium oxide to achieve the Co_20% Wt Cr composition. After activation of oxide powders at 8.12.24.and 36 hours, the powders were not reduced. Then, by combining activated powders and glue, a suspension was prepared and placed on the surface of the base metal. After drying, the sample was exposed to laser beam. No coating was formed on the surface of the base metal due to spraying because of the reduction reaction.
In the second phase of the experiment, aluminum was added to the powders as reducing agent in 1/2, 5/8 and 3/4 stoicheiometry ratios. As the temperature of the milling chamber increased due to the aluminothermic reaction, the carbothermic reaction was activated and the oxide powders were reduced after 40 hours of milling. After the preplacing of powders and laser alloying, a coating containing cobalt, chromium and alumina is formed on the surface of the base metal. Coating control factors, such as the relative speed of the laser and the pulse length, play an important role in the coating hardness. As the relative speed of the laser beam increases, the depth of the coating increases and the hardness increases due to the accumulation of alumina particles. Decreasing the laser pulse length also reduced the size of the dendrites, and higher hardness was observed in samples with shorter pulse lengths. Overall, the results showed that the best coating mode with high hardness of 950 Vickers is achieved under the condition of 155 W Average Power 15 Hz frequency and 10 ms duration pulse. The optimum travel speed in this study was found to be 1 mms-1.
