. Intelligent Manufacturing and Equipment School, Shenzhen Institute of Information Technology, Shenzhen 518172, China . Sino-German Intelligent Manufacturing School, Shenzhen City Polytechnic, Shenzhen 518116, China . Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006, China . Guangdong Provincial Key Laboratory of Industrial Ultrashort Pulse Laser Technology, Shenzhen 518055, China . College of Materials Science and Engineering, Chongqing University, Chongqing 400045, China
The selective laser melting (SLM) technique applied to high-entropy alloys (HEAs) has attracted considerable attention in recent years. However, its practical application has been restricted by poor surface quality. In this study, the capability of laser polishing on the rough surface of a Co-free HEA fabricated using SLM was examined. Results show that the initial SLM-manufactured (as-SLMed) surface of the Co-free HEA, with a roughness exceeding 3.0 μm, could be refined to less than 0.5 μm by laser polishing. Moreover, the microstructure, microhardness, and wear resistance of the laser-polished (LP-ed) zone were investigated. Results indicate that compared with the microhardness and wear resistance of the as-SLMed layer, those of the LP-ed layer decreased by 4% and 11%, respectively, because of the increase in grain size and reduction of the BCC phase. This study shows that laser polishing has an excellent application prospect in surface improvement of HEAs manufactured by SLM.
Fig.1 (a) The surface for LP and the LP-ed/as-SLMed samples; (b) LP strategy.
Scanning times
Power/W
Scanning speed/(mm?s−1)
Hatch spacing/μm
Once/twice
200
40
37.5
Once/twice
200
50
37.5
Once/twice
200
60
37.5
Once/twice
200
70
37.5
Once/twice
200
80
37.5
Tab.1 Parameters of LP
Fig.2 Schematic of (a) Ra and (b) Sa.
Specimen
Sa/μm
Sz/μm
As-SLMed
3.18
92.98
LP-ed
0.43
9.32
Tab.2 Surface roughness Sa and Sz of the HEA samples before and after LP
Fig.3 (a) Influence of laser polishing parameters on Sa; (b) Average Sa of different samples.
Fig.4 3D surface profile of the (a) as-SLMed and (b) LP-ed samples.
Fig.5 OM and SEM images of the (a1,a2) as-SLMed surface and (b1,b2) LP-ed surface. The table below shows the results of the element distribution of points A, B, C, and D in (a2) and (b2).
Fig.6 Face scanning results of the element distribution of the (a) as-SLMed and (b) LP-ed surfaces.
Fig.7 (a) XRD patterns and (b) partial XRD patterns of as-SLMed and LP-ed surface.
Fig.8 (a) Optical microscopy and scanning electron microscopy images on the X–Z plane of the (b) LP-ed sample and (g) as-SLMed sample; (c) LP-ed layer; (d) HAZ; (e) high magnification of (c); (f) high magnification of (d).
Fig.9 Inverse pole figure with grain boundary of the X–Z plane of the (a1) LP-ed sample and (a2) as-SLMed sample; (b1,b2) grain boundary distribution of (a1) and (a2), respectively; (c1,c2) phase distribution of (a1) and (a2), respectively; (d1,d2) kernel average misorientation of (a1) and (a2), respectively.
Fig.10 Distribution of the (a) FCC and (b) BCC grain sizes. (c) Distribution of the total average grain sizes of the as-SLMed, LP-ed layer, and HAZ.
Area
/%
/%
/μm
/μm
LP-ed layer
87.5
82.4
5.5
2.9
HAZ
99.3
79.8
6.5
2.9
as-SLMed layer
74.8
75.7
1.6
0.7
Tab.3 Detailed information on the phases and HAGBs
Fig.11 Microhardness distribution on the X–Z plane of the LP-ed sample.
Fig.12 Coefficient of friction under reciprocating sliding for the LP-ed and as-SLMed surface.
Fig.13 Scanning electron microscopy images of wear scars on the (a1–a3) LP-ed surface and (b1–b3) as-SLMed surface.
Fig.14 3D morphology of wear scars on the as-SLMed and LP-ed surfaces. NM stands for noise management.
Fig.15 Schematic of laser polishing: (a) the principle of laser polishing and the effects of scanning times; (b) the effects of scanning speed.
Abbreviations
As-SLMed
Initial selective laser melting-manufactured
BCC
Body-centered cubic
CoF
Coefficient of friction
EBSD
Electron backscatter diffraction
FCC
Face-centered cubic
HAGB
High-angle grain boundary
HAZ
Heat-affected zone
HEA
High-entropy alloy
HDR
High dynamic range
IPF
Inverse pole figure
KAM
Kernel average misorientation
LP
Laser polishing
LP-ed
Laser-polished
OM
Optical microscopy
SEM
Scanning electron microscopy
SLM
Selective laser melting
XRD
X-ray diffraction
Variables
Ra
Surface roughness (arithmetic mean height of the profile)
Sa
Surface roughness (arithmetic mean height of the surface)
Sz
Surface roughness (maximal height)
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