Analysis of Shear Bond Strength of Plasma-Sprayed Alumina Coatings on Stainless Steel
NASA technical note
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CENTER
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The effects of various surface roughness conditions and spray powders on the shear bond strength of plasma-sprayed alumina coatings on AISI 304 stainless steel were investigated. Substrate root-mean-square surface roughness values examined ranged from near 0 to 280 microinches with intermediate values at 115 and 225 microinches. Spray powders varied in particle size range, size distribution, median particle size, and purity. Coatings on polished surfaces showed zero bond strength, which indicated that the coating-substrate bond was predominantly mechanical. Increased surface roughness resulted in increased bond strengths for all coatings. Increased median spray powder particle size and uniformity also contributed to higher bond strengths. The highest median bond strengths 380, 540, and 600 lbsq in. at surface roughnesses of 115, 225, and 280 microinches. on 0. 301-sq in. specimens were obtained with the highest purity spray powder and particle sizes ranging from 3.4 to 37. 9 microns, a uniform particle size distribution, and a median particle size of 15.9 microns. For this material, as for the others, the highest bond strengths were obtained on 280-microinch surfaces. data were analyzed by Weibull statistical methods. The measured bond strengths decreased with increasing test areas over the range from 0. OS to 0. 43 sq in.. This decrease was approximated by curves based on probability theory calculations.
- Coatings, Colorants and Finishes
- Metallurgy and Metallography