Processing Window and Microstructure of NiCoCrAlY Coating Deposited on Cast Iron Using Multilayer Laser Cladding

Abstract

Cast iron is an iron-carbon alloy widely used in mechanical engineering. Nickel-base or cobalt-base alloy coatings prepared by laser cladding can improve the surface properties of cast iron, thereby increasing the service life of the components; however, due to the poor weldability and high carbon content of cast iron, the use of laser cladding to prepare alloy coatings faces many difficulties. To reduce the brittleness of the bonded interface, laser cladding was applied to the surface of cast iron using a multilayer deposition strategy. Through testing of the single-track laser cladding, the causes of defects in the coating are analysed, including poor bonding, slag inclusions, and pores. An analytical model based on mass and heat conservation is developed, and a processing window of laser tracks without defects is determined thereby. NiCoCrAlY alloy coating prepared by overlapping laser tracks mainly consists of γ-(Fe, Ni) dendrites and interdendritic M7C3 and M23C6 carbides. Although there are no cracks in a single laser track, cracks are detected when laser tracks are overlapped under the same process parameters. The increase in laser power helps to reduce cracking susceptibility on this occasion. The morphology of the grain in NiCoCrAlY alloy coating is mainly epitaxially grown columnar crystals. The increase in microhardness of the coating is mainly attributed to ductile dendrites, precipitated carbides, and grain refinement.

Effects of Laser Scanning Speed on Microstructure, Microhardness, and Corrosion Behavior of Laser Cladding Ni45 Coatings

“…e dendrite region was composed of the c-nickel phase, while the interdendritic region was composed of Cr-rich carbide and boride precipitates that are needle-, blocky-, floret-, and fine spherical-shaped. Liu et al [31] investigated the microstructure of NiCoCrAlY coating deposited on cast iron using multilayer laser cladding. ey described the dendrite in NiCoCrAlY alloy coating as the c-(Fe,Ni) solid solution, and the phases in the interdendritic region as M 7 C 3 and M 23 C 6 carbides, where M represents Cr, Fe, or Ni.…”

The Model for Estimating the Failure Mechanism of Tensioned Plasma-Sprayed Zirconia Ceramic Hard Coating

“…1.4 × 10 −5 [31] Cobalt significantly reduces dislocation motion through grain boundaries and provides creep resistance of NiCoCrAlY solid solutions over a long period when subjected to high stresses [32]. Furthermore, the aluminum content of 8 wt.% to 15 wt.% in the solid solution reduces the growth rate of the crystalline phase [33], mainly composed of α-Al 2 O 3 .…”