Metallic Cu-8%Cr, Cu-26%Cr, Cu-8%Cr-1%Al, NiAI and NiCrAlY monolithic coatings were fabricated by vacuum plasma spray deposition processes for thermal expansion property measurements between 293 and 1223 K. The corrected thermal expansion, (AL/Lo)therma1, Varies with the absolute temperature, T, as (AL/L.o)the.a1= A(T – 293) 3 + B(T – 293)2 + C(T – 293) + D where, A, B, C and D are regression constants. Excellent reproducibility was observed for all the coatings except for data obtained on the Cu-8%Cr and Cu-26%Cr coatings in the first heat-up cycle, which deviated from those determined in the subsequent cycles. This deviation is attributed to the presence of residual stresses developed during the spraying of the coatings, which are relieved after the first heat-up cycle. In the cases of Cu-8%Cr and NiAl, the thermal expansion data were observed to be reproducible for three specimens. The linear expansion data for Cu-8%Cr and Cu-26%Cr agree extremely well with rule of mixture (ROM) predictions. Comparison of the data for the Cu-8%Cr coating with literature data for Cr and Cu revealed that the thermal expansion behavior of this alloy is determined by the Cu-rich matrix. The data for NiAI and NiCrAlY are in excellent agreement with published results irrespective of composition and the methods used for processing the materials. The implications of these results on coating GRCop-84 copper alloy combustor liners for reusable launch vehicles are discussed. 1.0 Introduction Many engineering components experience temperature variations during service, which often require the availability of good quality data to ensure that they can be designed reliably and safely to meet the required design objectives. The necessity for generating high quality data is more critical for aerospace components especially those where two or more different materials are bonded to each other to fabricate components with optimized design properties. For example, differences between the thermophysical and mechanical properties of coating materials and the substrate can lead to the development of large residual stresses, which can either distort or debond the coating from the substrate during thermal cycling of a coated component during service. The National Aeronautics and Space Administration (NASA) has been developing technologies for a new generation of advanced reusable launch vehicles (RLVs) in its efforts to increase its future heavy lift capacity in a more reliable and economical manner compared to the Space Shuttle. Combustion chamber liners in liquid hydrogen (LHZ) fueled-rocket engines experience extreme conditions due to a combination of environmental and thermo-mechanical effects. The combustion flame temperatures in the chamber interior are about 3600 K whereas the backside of the approximately 1 mm thick liner wall experiences cryogenic temperatures of 20 K (Refs. 1 to 6). Uncoated copper and its alloys have been used as combustor liner materials in these regenerative rocket engines because their high thermal conductivities enable efficient heat transfer from the combustion flame to preheat the cryogenic LH2 flowing in the cooling channels. However, uncoated copper alloy liners undergo environmental degradation due to a combination of the spallation of the locally formed copper oxide scales and "blanching," which consists of repeated oxidation of the copper matrix and subsequent reduction of the oxide scale (Ref. 6).

Polymerization of di- and tri-isocyanates can be templated onto the mesoporous surface of a preformed network of sol–gel-derived silica nanoparticles, resulting in a conformal ‘crosslinked’ coating that renders the interparticle neck zone wider. Upon drying, these crosslinked networks yield aerogels which are up to ∼3× more dense than native aerogels based on the underlying silica framework, but also up to 10× less hygroscopic and they may take more than 300× the force to break. These results have been obtained with one-step based-catalyzed sol–gel silica networks, as well as with gels derived through a two-step process involving an acid-catalyzed sol and a based-catalyzed gel. Furthermore, it has been also found that crosslinking increases the dielectric constant only by ∼35% relative to values reported in the literature for native silica aerogels of about the same porosity. Chemical investigations into the polymerization reaction have shown that the process of crosslinking involves reaction of the isocyanate with: (a) OH groups at the surface of silica to form carbamate; and (b) adsorbed water, to form an amine and carbon dioxide. This amine then reacts with additional isocyanates resulting in polymer chain extension and bridging of particles with urethane-terminated polyurea.