Influence of Ni Content on Microstructure and Properties of NiTi Alloy Coatings Fabricated by Laser Cladding

Yuqiang Feng; Zexu Du; Zhengfei Hu

doi:10.3788/CJL202249.0802022

Chinese Journal of Lasers, Volume. 49, Issue 8, 0802022(2022)

Influence of Ni Content on Microstructure and Properties of NiTi Alloy Coatings Fabricated by Laser Cladding

Yuqiang Feng, Zexu Du, and Zhengfei Hu^*

Shanghai Key Laboratory for R&D and Application of Metallic Functional Materials, School of Materials Science and Engineering, Tongji University, Shanghai 201804, China

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Figures & Tables(22)

Fig. 1. SEM morphologies of original powders. (a) Pure Ni powder; (b) NiTi alloy powder

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Fig. 2. IPG YLS-10000 laser cladding equipment. (a) Laser and working stage; (b) schematic of laser cladding process

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Fig. 3. Friction and wear tester

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Fig. 4. Corrosion resistance test. (a) Gamry electrochemical workstation; (b) equivalent electric circuit diagram

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Fig. 5. Morphologies of laser cladding sample. (a) Morphology of coating surface; (b) cross-sectional metallographic image

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Fig. 6. XRD patterns of coating and mixed powder

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Fig. 7. Morphologies of bonding area of cladding layer. (a) Metallographic image of bonding area; (b) EDS line scanning results of bonding area

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Fig. 8. Average grain sizes of dendrites in different coating areas

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Fig. 9. SEM image of cladding layer

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Fig. 10. Structural diagram of coating

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Fig. 11. Microhardness of cladding layer versus depth

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Fig. 12. Friction coefficient of cladding layer versus time

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Fig. 13. Surface morphologies of samples after friction and wear test. (a) 316L substrate; (b) 55NiTi coating；(c) 55NiTi + 5Ni coating

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Fig. 14. Electrochemical polarization curves of coatings and substrate

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Fig. 15. Nyquist diagrams of cladding layers in NaCl solution

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Table 1. Chemical compositions of 316L stainless steel (mass fraction, %)
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Table 1. Chemical compositions of 316L stainless steel (mass fraction, %)
Element Fe Cr Ni Mo Mn Si P C S
Value Bal. 16.320 10.120 2.040 0.920 0.340 0.026 0.016 0.015

Table 2. Chemical compositions of pure Ni and 55NiTi alloy powders (mass fraction, %)
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Table 2. Chemical compositions of pure Ni and 55NiTi alloy powders (mass fraction, %)
Powder Ni Ti Fe Nb Co C Si O
Pure Ni Bal. - 0.003 - 0.020 0.020 0.003 0.006
55NiTi 56.460 Bal. 0.005 0.010 0.005 0.005 - 0.037

Table 3. Process parameters for laser cladding

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Table 3. Process parameters for laser cladding

Parameter	Value
Laser power /kW	2.0
Scanning speed /(mm·s^－1)	2.0
Laser beam spot diameter /mm	7.2
Working distance /mm	10
Overlap ratio /%	55
Powder feed rate /(r·min^－1)	50
Carrier gas flow rate /(L·min^－1)	8
Shielding gas flow rate /(L·min^－1)	5

Table 4. Calculation results of dilution rates of cladding layers
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Table 4. Calculation results of dilution rates of cladding layers
Cladding layer h /μm H /μm Dilution rate
55NiTi 1140 1436 0.44
55NiTi + 5 Ni 955 1660 0.36

Table 5. EDS scanning results of different regions marked in Fig. 9

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Table 5. EDS scanning results of different regions marked in Fig. 9

Coating	Region	Atomic fraction of Ni /%	Atomic fraction of Ti /%	Atomic fraction of Fe /%	Atomic fraction of Cr /%	Major Phase
55NiTi+5Ni	A	33.48	31.43	22.99	12.10	NiTi
	B	63.17	22.93	11.45	2.45	Ni₃Ti
	C	44.26	36.24	16.73	2.77	Ni₃Ti + NiTi

Table 6. Friction coefficients and wear mass losses of coatings and substrate

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Table 6. Friction coefficients and wear mass losses of coatings and substrate

Material	Mass before friction /g	Mass after friction /g	Wear mass loss /mg	Friction coefficient
Substrate	78.9182	77.8951	23.1	0.801
55NiTi coating	80.7855	80.7736	11.9	0.517
55NiTi + 5Ni coating	79.5127	79.5020	10.7	0.492

Table 7. Tafel fitting results of polarization curves of coatings and substrate
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Table 7. Tafel fitting results of polarization curves of coatings and substrate
Material E_corr /V I_corr /(μA·cm^－2) Corrosion rate /mpy
Substrate 0.16 51.65 27.32
55NiTi coating －0.24 9.20 5.45
55NiTi + 5Ni coating －0.19 4.36 1.97

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Yuqiang Feng, Zexu Du, Zhengfei Hu. Influence of Ni Content on Microstructure and Properties of NiTi Alloy Coatings Fabricated by Laser Cladding[J]. Chinese Journal of Lasers, 2022, 49(8): 0802022

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