Processing and Characterization of Laser-Cladded Coating Materials

Abstract

The feasibility of laser cladding as a surface modification process was experimentally investigated. Emphasis was placed on identification of the effects of independent critical process parameters such as laser power, process speed (interaction time), and feed rate of cladding powder mixture on the microstructure, compositional homogeneity, geometry (e.g., thickness and width), and mechanical properties of the developed coatings. Rapidly solidified coatings metallurgically bonded to AISI 1018 steel substrates were formed in situ by using a 10 kW continuous wave C0 2 laser to melt a thin layer of the substrate as well as a powder mixture consisting of Fe, Cr, C, and W with a weight ratio of 10:5:1:1 delivered to the substrate by means of blown shielding gas and a pneumatic screw feed system. Various diagnostic methods, indentation hardness measurements, and scratch-resistance testing of the laser-cladded coating materials revealed a high degree of grain refinement, increased solid solubility and uniform distribution of alloying elements, high hardness, and appreciable resistance against plastic shear deformation when the important process parameters were optimized. Microstructure studies demonstrated that coatings with very fine or relatively coarse dendritic, feathery, and particulate type microstructures were obtained, depending on the processing conditions. This investigation verified that due to the inherent rapid solidification and high concentration of key elements in the surface, hard coating materials of novel microstructures and physical properties which can be tailored to the surface requirements of the application can be produced with minimum dilution and thermal distortion. Implications of the laser cladding process in tribological applications are also interpreted qualitatively in light of the obtained results.

Microstructural evolution of a laser-cladded coating

“…%) 2.71C, 16.21Cr, 4.64W, 2.71Ni, Fe bal. The result means that ␥-austenite is a nonequilibrium phase with extended alloy element contents, in agreement with the other studies dealing with similar Fe-based alloys [4,5]. The existence of austenite is attributed to low Ms temperature, high concentration of austenite stabilizing elements, and rapid cooling rate.…”

Multiphysics simulation of laser–material interaction during laser powder depositon

“…Compared with conventional machining process used for 3D shaping of mechanical parts, it can reduce considerably the amount of material wasted due to chip formation [1]. The laser cladding process is defined as the process in which laser beam is used to fuse a material which has different metallurgical properties than the substrate, whereby only a very thin layer of the substrate has to be melted in order to achieve metallurgical bonding with minimal dilution of added material and substrate so that the original properties of the coating material are maintained [2]. In practice, laser cladding makes possible to solve problems such as wear of diesel engine exhaust valves [3], wear of tools made of high speed steel [4], reparation of mold steels [5], corrosion of gas turbine blades [6], and other problems that would be impossible solving using conventional methods, like heat treatment [7].…”

Microstructural Evolution of Hypoeutectic, Near-Eutectic, and Hypereutectic High-Carbon Cr-Based Hard-Facing Alloys

“…A coated surface obtained by GTA technique has the potential to produce a fine microstructure with high hardness and wear resistance for synthesis onto various substrate materials. [14][15][16][17] In this article, the gas tungsten arc welding (GTAW) process is used as a high-energy density beam to form a high-carbon Cr-based hard-facing alloy cladding above the S45C steel with chromium and chromium carbide (Cr:C = 4:1) alloy fillers. These claddings were designed to observe hypoeutectic, near-eutectic, and hypereutectic structures with various (Cr,Fe) 23 C 6 and (Cr,Fe) 7 C 3 carbides at room temperature.…”