Coaxial Laser Cladding of Cobalt-Base Alloy Stellite™ 6 on Grey Cast Iron Analysis of the Microstructural and Mechanical Properties Depending on the Laser Power

Abstract

A high-power diode laser was used to generate single- and multi-bead coatings of Stellite™ 6 by coaxial laser cladding over flat grey cast iron (EN-GJLP-200) as a preliminary study to develop a wear and corrosion resistant coating for brake disks on a cost-effective substrate. In this article, we have focused on a detailed quantitative analysis of the effect of different laser powers (1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 kW) on the bead geometry, dilution, microstructure, and hardness. Coatings dilution or composition depends directly on the laser power as well as bead geometry. The typical microstructure of the coatings comprises a solid solution of α (hcp)- and β (fcc)-Co with a dendritic structure as a metal matrix and an interdendritic lamellar eutectic, which contains predominantly β-Co, chromium carbides Cr7C3 and Cr23C6 as well as blocky tungsten carbide W2C. Coating hardness depends on the chemical composition and microstructure that is modified by the deposition parameters. Low laser power results in high carbide fraction and most refined microstructures, accounting for harder coatings.

Coaxial laser cladding of cobalt-base alloy StelliteTM 6 on gray cast iron/investigations on friction, wear versus commercial brake pad, and corrosion characteristics

“…101–103 In contrast, the coherent hard phase framework supports itself independently, as evidenced by the microstructural characterization. 38 This prevents individual hard phases from breaking out and further penetration into the interior of the coatings after the matrix areas near the surface are corroded out. 5…”

“…The methods of optical microscopy, scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray fluorescence spectroscopy (XRF) have been used to investigate the tribological and corrosive behavior, which are explicitly described in the preliminary study. 38…”

“…The corrosion behavior of uncoated and laser-cladded substrate was studied by carrying out potentiodynamic polarization according to the standard ISO 17475. 41 Before measuring, the specimen surfaces were prepared based on the metallographic treatment 38 to achieve a standard-compliant surface quality with R a <1 μm. The electrochemical corrosion studies were conducted with the potentiostat Interface 1010 and the corresponding analyzer Gamry Echem Analyst™ (v. 7.07) (co. Gamry Instruments Inc.).…”

“…The substrate material for tribological and electrochemical investigations consists of gray cast iron (EN-GJLP-200) itself, which is additionally coated with Stelliteä 6. 38 The friction partner is a commercially available brake pad material in a pin shape. This brake pad is classified as semi-metallic with a metal content of almost 50 wt.% (Table 1).…”

“…34,35,37 This study aims to evaluate a laser coating of Stelliteä 6 for gray cast iron (EN-GJLP-200) as brake disk to improve its wear and corrosion resistant, because only a few studies about this material assembly are available so far. From a preliminary microstructure characterization, 38 the tribological and electrochemical behavior were investigated, particularly TBL dynamics and corrosion kinetics.…”