Silica coatings on bismaleimide substrates

Neat (unreinforced) BMI specimens were coated with a thin, protective layer of a dense silicate ceramic material. Vickers indentation testing on the coated and uncoated BMI specimens was carried out to get an idea of point contact damage to a first approximation. Amount of silica coating spalled off from an indentation was measured as a function of indentation load and for different curing temperatures. Spalling for BMI specimens having coatings cured at 175°C for one hour (0.5% to 5%) was considerably less compared to spalling for BMI specimens (15% to 25%) with coatings cured at 150°C for 20 minutes. Crack spacings were characterized at constant loads for unabraded and d abraded coatings, and their distribution studied. Mean crack spacings were independent of the abraded coatings, and their distribution studied. Mean crack spacings were independent of the indentation load for BMI specimens with coatings cured at 150°C for twenty minutes. However for BMI specimens with coatings cured at 175°C for one hour, the mean crack spacing increased 47% over a load range of 2.94 N to 196 N. The mean crack spacing normalized with respect to half the total crack dimension when plotted against indentation load is consistent with the power law relationship, mu/a = ϕP epsilon.; In addition, the silica coating slowed the uptake of water during water-immersion testing 1.7 times. An expression for the mass change as a function of time due to the he diffusion of water into the BMI specimens was developed in Section 3.6. diffusion of water into the BMI specimens was developed in Section 3.6.