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The synthesis of nano cobalt boride with high energy ball milling and the development of mechanical properties of low carbon steel surfaces with coating

Thesis Type: Doctorate

Institution Of The Thesis: Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey

Approval Date: 2014

Student: MUSTAFA BARIŞ

Supervisor: ADNAN AKKURT

Abstract:

In this study, one of the transition metal borides compound-Co2B was mechanochemically synthesized in nano scale via planetary ball mill by 250, 300 and 350 rpm rotation rate. Furthermore 20:1, 30:1 and 40:1 ball to powder rates and optimum operating parameters were determined. Co, B2O3 and Mg initial powders were utilized in synthesize experiments as an initial material under argon atmosphere. The released Co2B/MgO powder mixtures from the experiments were leached with acetic acid to dissolution MgO. As a result of that pure Co2B nano particles were obtained in solid form. Synthesized Co2B nanoparticles were characterized by XRD, SEM, VSM, BET and specific density analysis. In addition the effect of synthesis parameters on products were introduced. The surface of S235JRC low carbon steel were coated with synthesized Co2B by different laser power using CO2 laser and the wear properties of coated layers were investigated. The laser cladded samples were cut with laser, wire erosion, abrasive water jet and abrasive disc methods and effect of the these operations on the coatings were investigated. It was determined that the synthesized Co2B nano particles have ferromagnetic characteristics and high surface area. FeN0,0760, Fe15,1C, FeCo and B2C5N2 phases were found on the surface of low carbon steel after laser cladding vii experiments. According to laser power, the composite coating layers average thickness were 35, 51 and 71 μm and hardness of the coatings were 2,83; 3,30 and 3,43 times harder than the substrate. Compared with the substrate, wear tests showed that the wear resistance of the composite coatings were improved significantly and laser coatings experiments with 174 and 220 W laser power exhibited best results. It was observed that the most suitable cutting method for coated materials is the abrasive disc cutting in the cutting tests.