Microstructure and Mechanical Properties of TiB2 Reinforced TiAl-Based Alloy Coatings Prepared by Laser Melting Deposition
WANG Hu1,2, ZHAO Lin1(), PENG Yun1(), CAI Xiaotao1, TIAN Zhiling1
1.Welding Research Institute, Central Iron & Steel Research Institute, Beijing 100081, China 2.College of Materials Engineering, North China Institute of Aerospace Engineering, Langfang 065000, China
Cite this article:
WANG Hu, ZHAO Lin, PENG Yun, CAI Xiaotao, TIAN Zhiling. Microstructure and Mechanical Properties of TiB2 Reinforced TiAl-Based Alloy Coatings Prepared by Laser Melting Deposition. Acta Metall Sin, 2023, 59(2): 226-236.
TiAl-based alloy coating produced by laser melting deposition exhibits excellent properties of high temperature and corrosion resistance and has a wide application potential across many fields. However, the wear resistance of the coating is poor, which limits its long-term usage in harsh and complex working environments. In this study, TiB2 reinforced TiAl-based alloy composite coatings are prepared by laser melting deposition to improve their wear resistance, and a theoretical reference for further exploring the applications of TiAl-based alloy composites in surface engineering is presented. TiAl-based alloy coatings with different TiB2 contents (0, 10%, 20%, 30%, mass fraction) were prepared on the surface of TC4 alloy using the laser melting deposition process. The effects of TiB2 content on the microstructure and mechanical properties of the coatings were systematically studied using XRD, OM, SEM, microhardness tester, indentation method, wear tester, and laser confocal microscope. Planar, columnar, and equiaxed crystal distributions were observed along the thickness direction from the bottom. With an increase in TiB2 content, the height of columnar crystal gradually decreased. TiB2/TiAl composite coatings are composed of a TiAl alloy matrix phase (γ + α2) and a TiB2 enhanced phase. Most of the directly added TiB2 particles do not melt, but the outer layer of the directly added TiB2 particles dissolves within the molten TiAl alloy, following which primary and secondary TiB2 are precipitated in situ. The primary TiB2 has a particle form and the secondary TiB2 has a needle or flake form. With the increase of TiB2 content from 0 to 10%, the matrix of the coating is noticeably refined, but an increase in TiB2 content (20% and 30%) do not produce further refinement. With the increase of TiB2 content from 0 to 30%, the surface hardness of the coating increases from 530.5 HV to 738.4 HV, the fracture toughness decreases from 7.75 MPa·m1/2 to 3.17 MPa·m1/2, the wear rate decreases from 3.98 mg/mm2 to 0.42 mg/mm2, and the wear degree and roughness of the wear surface also decrease. Furthermore, the wear mechanism of the coating without TiB2 is mainly microscopic cutting, supplemented by multiple plastic deformations. When the mass fraction of TiB2 is 10%, the wear mechanism of the coating is mainly microscopic cutting, supplemented by microscopic fracture. As the TiB2 content increases, the wear mechanism gradually turns to microscopic fracture. When the mass fraction of TiB2 is 30%, the wear mechanism of the coating is mainly microscopic fracture, supplemented by microscopic cutting.
Fig.1 SEM images of TiAl powders (a) and TiB2 particles (b)
Fig.2 XRD spectra of coatings with different TiB2 contents
Fig.3 OM (a) and back-scaterred electron (BSE) (b) images of middle region of the TiAl alloy coating
Fig.4 Low (a-c) and high (d-f) magnified BSE images of middle region of coatings with 10% (a, d), 20% (b, e), and 30% (c, f) TiB2
Mass fraction of TiB2 / %
Position
Ti
B*
10
A
20.82
79.18
B
18.74
81.26
C
15.76
84.24
D
14.99
85.01
20
A
15.87
84.13
B
17.75
82.25
C
16.84
83.16
D
15.81
84.19
30
A
14.73
85.27
B
15.44
84.56
C
17.69
82.31
D
16.14
83.86
Table 1 EDS results of the second phases in the composite coatings in Fig.4
Fig.5 OM images near the interface of coatings with different TiB2 contents (a) 0 (b) 10% (c) 20% (d) 30%
Fig.6 Microhardness distributions of coatings with different TiB2 contents
Fig.7 Indentation morphologies of coatings with different TiB2 contents (a) 0 (b) 10% (c) 20% (d) 30%
Mass fraction of TiB2 / %
Average crack length / mm
Fracture toughness / (MPa·m1/2)
0
0.195
7.75
10
0.545
5.02
20
1.204
3.49
30
1.672
3.17
Table 2 Fracture toughness values of coatings with different TiB2 contents (indentation method)
Fig.8 Wear rates of coatings with different TiB2 contents
Fig.9 Wear morphologies of coatings with different TiB2 contents (a) 0 (b) 10% (c) 20% (d) 30%
Fig.10 High power morphology of the spalling pit produced by abrasive particles under abrasive conditions
Fig.11 Roughnesses of wear surface of coatings with different TiB2 contents (Ra—contour arithmetic mean deviation, Rz—ten-point height average)
Fig.12 3D morphologies of wear surface of coatings with different TiB2 contents (a) 0 (b) 10% (c) 20% (d) 30%
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