Evaluation of Oxidation-Resistant Coatings in a Water-Stabilized Electric Arc at Temperatures to 2325c (4215f)

摘要

Twelve oxidation-resistant coatings on molybdenum and graphite pressure sensing probe models were evaluated. These evaluations were made in an atmosphere simulating re-entry trajectory heating conditions experienced at a Mach. No. of 8.5. A water-stabilized electric arc was used to simulate heat input of 450 BTU/sq ft-sec. to be reached in 25 seconds. Duration of test was 60 seconds. Under conditions of equal heat input, the surface temperatures of the probes, as observed with a calibrated optical pyrometer, varied due to differences in the physical and thermodynamic properties of the coatings. The highest surface temperature, 2325C (4215F), was attained by a molybdenum probe with a zirconium diboride coating. Out of nine coatings tested on molybdenum, a flame-sprayed coating of 90% W and 10% ZrB2 exhibited the least damage. Other coatings, Al-Cr-Si, MoSi2, gradated Zr02 and ZrB2 protected the molybdenum against catastrophic oxidation. Out of three coatings tested on graphite, a vapor-deposited, silicon carbide coating showed the least damage. American Lava Corp proprietary coating and a 90% W and 10% Zr02, flame-sprayed coating eroded but still protected the graphite against catastrophic oxidation. (Author)