Microstructure and Properties of 3Y-TZP/LZAS Glass-ceramic Functionally Gradient Coatings

doi:10.15541/jim20160206

Abstract

Abstract:

In order to improve toughness of glass-ceramic coatings, 3mol% yattria-tetragonal zirconia polycrystal/Li₂O-ZnO-Al₂O₃-SiO₂(3Y-TZP/LZAS) glass-ceramic functionally gradient coatings on Q235 steel substrate were prepared by slurry method. Phase constitution and microstructure of samples were examined by XRD and SEM, respectively. Their micro-hardness and fracture toughness were measured by indentation method. And their bonding strength of the coatings was also investigated by pulling test. Resulting data indicate that the seamless interfaces among toughening coatings, LZAS transition layer and substrate are obtained. SiO₂ in the LZAS glass reacts with iron oxides at interfacial region forming Fe₂SiO₄ and FeSiO₃, which causes tight interface bind between gradient coatings and steel substrate. Micro-hardness and fracture toughness from inner substrate to top surface on the section of the coatings increase gradually. Residual compressive stress toughening, 3Y-TZP particles toughening and 3Y-TZP transformation toughening are the dominant factors for improving fracture toughness of the gradient coatings. Bonding strength of the coatings is up to 16.3 MPa. The gradient coatings withstand more than 30 thermal cycles at 300℃, demonstrating their excellent thermal sock resistance.

Key words: functionally gradient coating, glass-ceramic, slurry method, microstructure

CLC Number:

TG174

GONG Wei, LI Hua, ZHOU Li-Ming, BAI Cao-Zhong, WANG En-Ze. Microstructure and Properties of 3Y-TZP/LZAS Glass-ceramic Functionally Gradient Coatings[J]. Journal of Inorganic Materials, 2017, 32(1): 63-68.

Figures/Tables 10

Fig. 1 Flow chart for preparing 3Y-TZP/LZAS gradient coatings by slurry method

Fig. 2 Relationship between viscosity of LZAS glass ceramic and temperature

Fig. 3 Wettability of LZAS glass ceramic with Q235 steel at different temperatures(a) 690℃, 88.9°; (b) 720℃, 68.3°; (c) 750℃, 35.6°; (d) 780℃, 15.9°

Fig. 4 Firing schedule for the 3Y-TZP/LZAS gradient coatings

Fig. 5 XRD pattern of the top surface of 3Y-TZP/LZAS gradient coatings

Fig. 6 Section morphology of the 3Y-TZP/LZAS gradient coatings

Fig. 7 Interface morphology of Q235-LZAS glass-ceramic

Fig. 8 XRD pattern of the interface between LZAS glass ceramic and Q235 steel

Table 1 Micro-hardness and fracture toughness of different layer for the 3Y-TZP/LZAS gradient coatings

Layer	Micro-hardness H_v/GPa	Fracture toughness K_IC/(MPa•m^1/2)
Transition layer	2.43	0.62
1st toughening layer	3.24	1.32
2nd toughening layer	3.78	1.94
3rd toughening layer	4.53	2.12
4th toughening layer	5.11	2.83

Fig. 9 Optical images of Vickers indentation on the section of coatings(a) Transition layer; (b) The 1st toughening layer; (c) The 2nd toughening layer; (d) The 3rd toughening layer; (e) The 4th toughening layer

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