| ZHAO Qing-shan,SONG Xue-ping,LI Lai-jun,CAO Wen-hui,CHAI Ting-xi.Comparative Study on Mechanical Impact and Thermal Shock Properties of Ni60 and NiCr-Cr3C2 Coatings[J],52(4):436-445 |
| Comparative Study on Mechanical Impact and Thermal Shock Properties of Ni60 and NiCr-Cr3C2 Coatings |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.04.040 |
| KeyWord:coating HVOF die steel mechanical impact thermal shock |
| Author | Institution |
| ZHAO Qing-shan |
School of Mechanical Engineering, Lanzhou Petrochemical University of Vocational Technology, Gansu Lanzhou , China |
| SONG Xue-ping |
School of Mechanical Engineering, Lanzhou Petrochemical University of Vocational Technology, Gansu Lanzhou , China |
| LI Lai-jun |
School of Mechanical Engineering, Lanzhou Petrochemical University of Vocational Technology, Gansu Lanzhou , China |
| CAO Wen-hui |
School of Mechanical Engineering, Lanzhou Petrochemical University of Vocational Technology, Gansu Lanzhou , China |
| CHAI Ting-xi |
Peili School of Mechanical Engineering, Lanzhou City University, Gansu Lanzhou , China |
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| Abstract: |
| The work aims to improve the service life of hot-work dies (5CrNiMo) by selecting coating material reasonably. Ni60 and NiCr-Cr3C2 coatings were prepared through the supersonic flame spraying technology, and the microstructure, mechanical properties, mechanical impact and thermal shock properties of those coatings were studied. It was found that the two powders were spherical and the particle size ranged from 15 μm to 45 μm, which met the basic requirements of supersonic flame spraying. After spraying, the Ni60 coating had a compact structure without obvious cracks, and the porosity and surface roughness of the coating were 1.05% and 0.106 μm, respectively. However, there were many microcracks at the interface between the coating and matrix. Compared with the Ni60 coating, the porosity and surface roughness of the NiCr-Cr3C2 coating were slightly higher (3.08 % and 0.147 μm, respectively), while there were no obvious cracks in the coating and the interface between NiCr-Cr3C2 coating and the matrix, indicating that the mechanical bite between NiCr-Cr3C2 coating and the matrix was stronger. During the spraying process, Cr3C2 hard particles had higher compressive stress in the impact process, which promoted the shot peening effect. And there was no obvious cracks in the interior of the coating and interface of the 20% NiCr-80% Cr3C2 coating and matrix. Therefore, 20% NiCr-80% Cr3C2 coating had higher surface microhardness (818.9HV) and bonding strength (64.04 MPa) than Ni60 coating (611.1HV and 34.89 MPa, respectively). After the mechanical impact test, the cracks in these two kinds of coatings were basically the same (surface arc crack and transverse crack), and their failure mechanisms were plastic deformation and fracture of the coating caused by high load impact. When the arc crack and transverse crack were connected, spalling failure occurred. From the perspective of coating peeling, the interface between Ni60 coating and matrix produced a lot of cracking, and a large chunk of coating directly peeled off from the matrix, indicating that the failure mechanism of Ni60 coating was the failure of binding force, while the impact surface of NiCr-Cr3C2 coating had only a few peeling holes, indicating that the failure mechanism of NiCr-Cr3C2 coating was cohesion failure. This was mainly due to the presence of a large amount of Cr3C2 brittle phase in 20% NiCr-80% Cr3C2 coating, which caused secondary brittle fracture simultaneously. After 100 cycles of thermal shock experiment, neither of these two coatings peeled off. The oxide layer was generated at the interface between the Ni60 coating and the matrix. Although the oxide layer replaced the microcrack at the interface between the Ni60 coating and the matrix, the bonding between the coating and the matrix was not improved, and it could be found that there were microcracks in the oxide layer. The NiCr-Cr3C2 coating and matrix interface also showed an oxide layer after 100 thermal shock cycle tests, but the oxide layer was continuous and compacted, and combined well with both the matrix and coating, which showed better thermal shock resistance. It was also found that the surface of Ni60 coating was black blue and uneven, which also indicated that NiCr-Cr3C2 coating had better thermal shock resistance. Thus, the 20%NiCr-80%Cr3C2 coating has better microstructure, mechanical properties, mechanical impact and thermal shock properties. |
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