Abstract
The results of microstructure and mechanical properties evaluation of a Stellite 6 (Co-6) alloy deposited on X22CrMoV12-1 substrate by the laser-engineered net shaping (LENSTM) technology are presented in this paper. The Stellite 6 alloy is widely used in industry due to its excellent wear resistance at elevated temperatures and corrosive environments. Specific properties of this alloy are useful in many applications, e.g., as protective coatings in steam turbine components. In this area, the main problems are related to the fabrication of coatings on complex-shaped parts, the low metallurgical quality of obtained coatings, and its insufficient adhesion to a substrate. The results of recently performed investigations proved that the LENS technology is one of the most effective manufacturing techniques of the Co-6 alloy coatings (especially deposited on complex-shaped turbine parts). The microstructural and phase analyses of obtained Stellite 6 coatings were carried out by light microscopy techniques and X-ray diffraction analysis. A chemical homogeneity of Co-6 based layers and a fluctuation of chemical composition in coating–substrate zone after the laser deposition were analyzed using an energy dispersive X-ray spectrometer coupled with scanning electron microscopy. The room temperature strength and ductility of the LENS processed layers were determined in static bending tests.
Highlights
Stellite 6 (Co-6) is one of the most popular cobalt-based alloys exhibiting a good hightemperature oxidation resistance, excellent thermal stability, good resistance to thermal fatigue, and good resistance to cavitation, corrosion, erosion, abrasion [1,2,3]
We have previously shown that the cracks are a common defect that occurs during laser deposition of Stellite 6 superalloy, and it is difficult to avoid [19,46]
The microscopic analysis of etched metallographic cross sections of the Co-6 coatings revealed that a microstructure both in a surface layer and entire volume of obtained samples consisted of equiaxed, fine dendrites with different sizes and eutectic carbides in the interdendritic spaces (Figure 3)
Summary
Stellite 6 (Co-6) is one of the most popular cobalt-based alloys exhibiting a good hightemperature oxidation resistance (at temperature up to 1095 ◦ C), excellent thermal stability, good resistance to thermal fatigue, and good resistance to cavitation, corrosion, erosion, abrasion [1,2,3]. The main alloying component of Stellite 6 is chromium (29% in weight), which provides better corrosion resistance and strength by the formation of M7C3, M23C6 carbides [4]. The other components of the alloy are 4.5% W, 1.5% Mo, 1.2% C, Co balance, in weight. Tungsten and molybdenum in Co-6 provide high strength by precipitation hardening. The CoCr-based alloys are used as coating or overlay material in pump seals, bearings, knives seats, blades in aviation engines, nozzle in diesel engines, etc. The CoCr-based alloys are used as coating or overlay material in pump seals, bearings, knives seats, blades in aviation engines, nozzle in diesel engines, etc. [5].
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