Enhanced Flexural Strength and Thermal Shock Resistance of Alumina Ceramics by Mullite/Alumina Pre-stressed Coating

doi:10.15541/jim20220238

Abstract

Abstract:

It is an effective strengthened technique to introduce a coating containing compressive stress on the surface of ceramic. In this work, the mixed slurry of alumina and quartz powder was coated on the pre-sintered alumina body, then the mullite-alumina coating with lower thermal expansion coefficient was synthesized in-situ after pressureless co-sintering. The pre-stressed strengthening of alumina was achieved by the residual compressive stress formed in the coating during the cooling process. The results indicate that, with the increase of the doping content of quartz in the coating, the flexural strength of pre-stressed alumina increases firstly and then decreases. The flexural strength of specimen realizes the highest value when the doping mass fraction of quartz is 15%, and the interface between the coating and the substrate bonds tightly. Under this condition, the flexural strength of the pre-stressed alumina ceramic is (549.44±27.2) MPa, which is 37.19% higher than that of the common alumina. When the doping mass fraction of quartz is higher than 15%, the flexural strength decreases due to the shrinkage stress mismatch in the sintering process. The effect of prestress enhancement weakens gradually with the increase of temperature. As the testing temperature reaches and exceeds 1000 ℃, pre-stressed alumina and common alumina possess approximately equal flexural strength. Pre-stressed alumina also exhibits better thermal shock resistance and damage tolerance due to the compressive stress formed in the coating

Key words: pre-stressed strengthening, alumina ceramics, low coefficient of thermal expansion, flexural strength, thermal shock resistance

CLC Number:

TQ174

HAO Hongjian, LI Haiyan, WAN Detian, BAO Yiwang, LI Yueming. Enhanced Flexural Strength and Thermal Shock Resistance of Alumina Ceramics by Mullite/Alumina Pre-stressed Coating[J]. Journal of Inorganic Materials, 2022, 37(12): 1295-1301.

Figures/Tables 12

Fig. 1 Schematic illustration of pre-stressed Al2O3

Fig. 2 Phase analyses of mullite-alumina coating materials fabricated with different mass fractions of quartz (a) XRD patterns after sintered at 1550 ℃; (b) Quantitative analysis by Rietveld method

Fig. 3 Flexural strength at room temperature of pre-stressed Al2O3 fabricated with different mass fractions of quartz

Fig. 4 Flexural strength of C15-A pre-stressed ceramics tested at different high temperatures

Fig. 5 Fracture section SEM images of pre-stressed alumina ((a) C10-A, (b) C25-A, (c) C15-A), (d) EDS analysis of C15-A

Fig. 6 Optical micrograph of the side of C30-A sample

Table 1 Calculation of residual stresses of coatings and substrates in pre-stressed Al2O3 fabricated with different mass fractions of quartz

Sample	E_c/GPa	E_s/GPa	α_c/(×10^-6, K^-1)	α_s/(×10^-6, K^-1)	h_c/μm	h_s/μm	ΔT	σ_c/MPa	σ_s/MPa
C5-A	91.36	380.11	6.69	7.58	50	1450	1000 ℃	-119.66	4.80
C10-A	80.18	380.11	6.06	7.58	50	1450	1000 ℃	-151.94	6.09
C15-A	73.33	380.11	5.33	7.58	50	1450	1000 ℃	-181.86	7.29
C20-A	67.71	380.11	5.04	7.58	50	1450	1000 ℃	-189.74	7.60
C25-A	62.14	380.11	4.72	7.58	50	1450	1000 ℃	-196.17	7.86
C30-A	58.31	380.11	4.41	7.58	50	1450	1000 ℃	-197.69	7.91

Fig. 7 Fracture section SEM images of C30-A sample

Fig. 8 Theoretical relationship between residual compressive stress and substrate-to-coating thickness ratio in different pre- stressed aluminas

Fig. 9 Residual flexural strength of C15-A pre-stressed alumina after thermal shock at different temperatures

Fig. 10 Surface optical micrographs of ceramics after thermal shock (a) Al2O3 at 260 ℃; (b) Al2O3 at 320 ℃; (c) C15-A at 320 ℃

Fig. 11 Cross section SEM images of ceramic after thermal shock at 320 ℃ (a) Al2O3; (b) C15-A

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