Enhancement in aerothermal shock survivability of lanthana-strengthened yttria windows and domes

Abstract

Experiments aimed at improving the physical properties of transparent polycrystalline lanthanastrengthened yttria (LSY) infrared windows and domes were conducted. The objective was to enhance the thermal shock resistance for aggressive aerothermal environments. The approach included improving the average equibiaxial flexure strength, Weibull modulus, and other relevant physical properties. Initial results of an extensive study on polishing and post-fabrication treatment along with improved powder processing showed an -30% strength improvement without sacrifice in optical properties, leading to an appreciable increase in the calculated survivability. LSY with a low lanthana content significantly enhanced predicted survivability.

Fabrication of transparent La-doped Y2O3 ceramics using different La2O3 precursors

“…Yttria is one of the most promising materials for use in 3-5 m infrared transmitting applications because of its long wavelength transmittance [1][2][3]. Owing to their low infrared emissivity at both ambient and elevated temperatures, Y 2 O 3 ceramics are considered as a candidate material for use in hypersonic guided-missile windows and domes [4][5][6][7].…”

Sintering Behavior and Optical Properties of Yttria

“…P olycrystalline , fully dense, pure and lanthana‐doped yttria‐based materials were developed in the 1980–1990s for optical applications like missile infrared‐domes 1–5 . Very high values of in‐line transmittance (IT) have been measured for electromagnetic radiations with wavelength in the range 0.2–10 μm 1,3,4 …”

“…The mechanical properties of such materials were consequently poor, e.g., the four‐point flexural strength was around 150–180 MPa at room temperature 6 . Because of such low strength, thermal shock resistance was also unsatisfactorily low 5 . The second obstacle to the emergence of fully dense yttria materials was linked to the robustness of optical properties.…”

“…P OLYCRYSTALLINE, fully dense, pure and lanthana-doped yttria-based materials were developed in the 1980-1990s for optical applications like missile infrared-domes. [1][2][3][4][5] Very high values of in-line transmittance (IT) have been measured for electromagnetic radiations with wavelength in the range 0.2-10 mm. 1,3,4 In spite of excellent optical properties, no extensive implementation of such polycrystalline yttria materials has become effective.…”

“…6 Because of such low strength, thermal shock resistance was also unsatisfactorily low. 5 The second obstacle to the emergence of fully dense yttria materials was linked to the robustness of optical properties. Because of variations of purity in the raw powder from batch to batch, optical properties of the final objects also fluctuated, in particular at wavelengths belonging to the visible range.…”