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. 2017 Mar 10;10(3):279.
doi: 10.3390/ma10030279.

Laser Cladding of Ultra-Thin Nickel-Based Superalloy Sheets

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Free PMC article

Laser Cladding of Ultra-Thin Nickel-Based Superalloy Sheets

Tobias Gabriel et al. Materials (Basel). .
Free PMC article

Abstract

Laser cladding is a well-established process to apply coatings on metals. However, on substrates considerably thinner than 1 mm it is only rarely described in the literature. In this work 200 µm thin sheets of nickel-based superalloy 718 are coated with a powder of a cobalt-based alloy, Co-28Cr-9W-1.5Si, by laser cladding. The process window is very narrow, therefore, a precisely controlled Yb fiber laser was used. To minimize the input of energy into the substrate, lines were deposited by setting single overlapping points. In a design of experiments (DoE) study, the process parameters of laser power, laser spot area, step size, exposure time, and solidification time were varied and optimized by examining the clad width, weld penetration, and alloying depth. The microstructure of the samples was investigated by optical microscope (OM) and scanning electron microscopy (SEM), combined with electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDX). Similarly to laser cladding of thicker substrates, the laser power shows the highest influence on the resulting clad. With a higher laser power, the clad width and alloying depth increase, and with a larger laser spot area the weld penetration decreases. If the process parameters are controlled precisely, laser cladding of such thin sheets is manageable.

Keywords: laser cladding; microstructural characterization; selective coating; thin sheet material.

Conflict of interest statement

The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Figures

Figure 1
Figure 1
SEM picture of the powder used as coating material.
Figure 2
Figure 2
Schematic laser cladding setup.
Figure 3
Figure 3
Definition of the quality criteria clad width ①, weld penetration ②, and alloying depth ③.
Figure 4
Figure 4
Position of the cross-sections and the measurement of the clad width.
Figure 5
Figure 5
Pareto charts of the standardized effects of the five varied parameters. Statistical significance is given for values higher than the vertical, dashed line.
Figure 6
Figure 6
(a) Clad width (OM); (b) weld penetration (SEM Secondary Electron (SE)); (c) alloying depth (EDX image); and (d) EDX line scan. Co is shown in blue, Ni in green. On the left, an example of a good weld is shown and, on the right, a poor one.
Figure 7
Figure 7
Cross-section of the specimen C4-4 (SEM BSE). Five different areas, numbered from 1 to 5, can be recognized in the microstructure of the clad.
Figure 8
Figure 8
(a) Cross-section and (b) lengthwise section combined image quality and orientation map (EBSD). On the lengthwise section, cladding direction is from left to right.
Figure 9
Figure 9
Lengthwise section of a coated line (SEM BSE) with increasing magnification from (a) to (c), cladding direction is from left to right; (d) elemental distribution of the transition between substrate and coating material; and (e) detail of elemental distribution with Nb-enriched zones in area 2 (both EDX, wt%). These Nb-enriched zones are identified as Laves phase.
Figure 10
Figure 10
(a) Intergranular enrichments of Si, Cr, and W (light gray) in area 5; and (b) line-orientated inter- and intragranular enrichments in area 4 (both SEM BSE).

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