Abstract
Micron-size Ni-base alloy (NBA) powders were mixed with both 1.5 wt.% (hereinafter %) micron-size CeO(2) (m-CeO(2)) and also 1.5% and 3.0% nano-size CeO(2) (n- CeO(2)) powders. These mixtures were coated on low-carbon steel (Q235) by 2.0 kW CO(2) laser cladding. The effects on the microstructures, phases and electrochemical corrosion of the coatings upon the addition of m- and n- CeO(2) powders to NBA (m- and n- CeO(2) /NBA) have been investigated. The results showed that a smooth coating was prepared under suitable processing parameters (P= 2.0 kW, V= 180 mm min(- 1)) by adding 1.5% n- CeO(2). In addition to the primary phases of γ-Ni, Cr(23)C(6) and Ni(3)B in the Ni-base alloy coating, CeNi(3) was formed in Ni-base alloy coatings with both n- CeO(2) and m-CeO(2) particles, and CeNi(5) appeared in the coating upon decreasing the size of CeO(2) particles. Well-developed dendrites were observed in the Ni-base alloy coating; directional dendrites grew at the interface in the coating upon the addition of m-CeO(2), whereas fine and multioriented dendrites grew upon decreasing the size of CeO(2) particles to the nanoscale. Actinomorphic dendrites and compact equiaxed dendrites grew from the interface to near the surface upon increasing the content of n- CeO(2) from 1.5 to 3.0%. In strongly acidic HNO(3) solution, the severe corrosion of dendrites occurred and there were many corrosion pits in the Ni-base alloy coating; intercrystalline corrosion also has a dominant role upon the addition of m-CeO(2), whereas uniform corrosion occurs in the coating as the size of CeO(2) particles is decreased to nanoscale.