Comparison of two NiCoCrAl/YSZ microlaminates deposited on substrates with different surface roughness by EB-PVD
(Center for Composite Materials, Harbin Institute of Technology, Harbin 150001, China)
Abstract: Two substrates with surface roughness (Ra) of about 1.6 and 0.8, respectively, were employed to fabricate two NiCoCrAl/YSZ microlaminates by using EB-PVD method. The average ceramic-layer thicknesses of the two NiCoCrAl/YSZ microlaminates are different, about 0.9 μm and 1.2 μm, respectively, but their average metal-layer thicknesses are equal, about 5 μm. The microstructures and fractographs were examined by SEM. Uniaxial tensile testing was performed to determine the mechanical properties. The results show that the microlaminate deposited on the relatively coarse substrate (MDCS) contains wavy layer interfaces and larger flaws, while the microlaminate deposited on the relatively smooth substrate (MDSS) has relatively flat layer interfaces and no larger flaws. The tensile specimens of the two microlaminates display obvious difference in tensile strengths and fracture modes. The ratio of strength of MDCS to that of MDSS is 0.5 at room temperature, 0.67 at 700 ℃ and 1.33 at 1 000 ℃, increasing with increasing temperature. The factors which caused the variation of the strength ratio were discussed. It is found that the larger flaws in MDCS result in the relatively low strength ratio at room temperature and 700 ℃, and the wavy layer interface in MDCS is responsible for the relatively great strength ratio at 1 000 ℃.
Key words: NiCoCrAl/YSZ; microlaminate; EB-PVD; flaw; layer interface; tensile property