Laser Surface Modification Of00Cr13Ni4M0o Hydro Turbine Blade Stainless Steel

To improve the wear and corrosion resistance of00Cr13Ni4Mo hydro turbine bladestainless steel, the Ni60coatings adding carbide(TiN or CrN) and nitride(WC) werefabricated on its surface, whose phase, microstructure, microhardness, wear and corrosionresistance were investigated. Furthermore, we analysed the influence of different ceramicphase contents on the microstructure and performance of the coatings.The optimized laser power, scanning velocity and laser spot diameter in this thesiswere2.5kW,5mm/s and4.5mm, respectively. The laser alloying coating of Ni60+TiN wasobviously stratified and the top layer was consisted of agglomerated TiN particles withhigh microhardness. Compared with00Cr13Ni4Mo stainless steel matrix, the wear weightloss of the Ni60+10%TiN alloyed coating reduced from110mg to1.2mg, the corrosioncurrent in3.5wt.%NaCl solution decreased from480nA/cm~2to128nA/cm~2, while thecorrosion potential increased from-468.1mV to-380.3mV. However, the higher thecontent of TiN, the more serious the particle agglomeration, with the enhancing pittingcorrosion leading to bad corrosion resistance because of increased roughness.The laser alloying coating of Ni60+CrN was dense. Compared with stainless steelmatrix, the wear weight loss of the Ni60+20%CrN alloyed coating reduced from110mgto3.2mg, the corrosion current in3.5wt.%NaCl solution decreased from480nA/cm~2to51nA/cm~2, while the corrosion potential increased from-468.1mV to-287.1mV. Thelaser alloying coating of Ni60+20%CrN offered the most optimal comprehensiveperformance.The wear weight loss of Ni60coating was7.6mg, while the corrosion current in3.5wt.%NaCl solution was387nA/cm~2and the corrosion potential was-359.2mV. Themicrohardness of the coating increased after adding15%WC and resulted in the decreaseof wear weight loss from7.6mg to2.5mg, but the corrosion resistance reduced greatly.The microhardness and wear resistance of the coating improved when WC and TiN wereadded at the same time. The wear weight loss was0.2mg when the added content of TiNreached30%. The corrosion resistance of the coating improved comparing to that ofNi60+15%WC coating because of the weakened intergranular corrosion, but it was still poorer than that of pure Ni60coating because of serious galvanic corrosion. Themicrohardness and wear resistance of the coating decreased with addition CrN comparedwith addition of WC, the wear weight loss was2.8mg when the added content of CrNreached30%. Galvanic corrosion of Ni-based solid solution weakened due to the increaseof chromium and the corrosion resistance of the coating enhanced as well. The corrosioncurrent in3.5wt.%NaCl solution was219nA/cm~2and the corrosion potential was-440.5mV. So, the composition of the optimized laser cladding coating wasNi60+15%WC+30%CrN.