Thermophysical Properties of Cold- and Vacuum Plasma-Sprayed Cu-Cr-X Alloys, NiAl and NiCrAlY Coatings II: Specific Heat
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JMEPEG DOI: 10.1007/s11665-017-3015-x
Thermophysical Properties of Cold- and Vacuum Plasma-Sprayed Cu-Cr-X Alloys, NiAl and NiCrAlY Coatings II: Specific Heat Capacity S.V. Raj (Submitted September 8, 2017) Part I of the paper discussed the temperature dependencies of the electrical resistivities, thermal conductivities, thermal diffusivities and total hemispherical emissivities of several vacuum plasma-sprayed (VPS) and cold-sprayed (CS) copper alloy monolithic coatings, VPS NiAl, VPS NiCrAlY, extruded GRCop-84 and as-cast Cu-17(wt.%)Cr-5%Al. Part II discusses the temperature dependencies of the constant-pressure specific heat capacities, CP, of these coatings. The data were empirically regression-fitted with the equation: C P ¼ AT4 þ BT3 þ CT2 þ DT þ E where T is the absolute temperature and A, B, C, D and E are regression constants. The temperature dependencies of the molar enthalpy, molar entropy and Gibbs molar free energy determined from experimental values of molar specific heat capacity are reported. Calculated values of CP using the Neumann– Kopp (NK) rule were in poor agreement with experimental data. Instead, a modification of the NK rule was found to predict values closer to the experimental data with an absolute deviation less than 6.5%. The specific molar heat capacities for all the alloys did not agree with the Dulong–Petit law, and CP > 3R, where R is the universal gas constant, were measured for all the alloys except NiAl for which CP < 3R at all temperatures. Keywords
aerospace, cold- and vacuum plasma-sprayed coatings, copper alloys, Neumann–Kopp rule, NiAl and NiCrAlY, specific heat capacity, thermodynamic functions
coatings, VPS NiAl, VPS NiCrAlY, extruded GRCop-84 and as-cast Cu-17(wt.%)Cr-5%Al. The objective of Part II is to report the constant-pressure specific heat capacities, CP, of these materials as a function of absolute temperature, T.
2. Experimental Procedures 1. Introduction As noted in Part I (Ref 1), an evaluation of the thermophysical properties of materials is important both for gaining a fundamental understanding of material behavior, as well as in engineering applications, such as structural design of components and systems. Environmental and thermal barrier protective metallic coatings designed for aerospace applications, such as reusable launch vehicle (RLV) combustion liners, turbine blades and vanes, are commonly deposited by conventional cold and vacuum plasma spray processes. The deposition of these coatings on the substrates results in the development of residual stresses which can affect the performance and durability of the coating-substrate system. In the case of aerospace applications, modeling the heat transfer behavior and stress analyses of the coating-substrate system is crucial for predicting component performance and life. Part 1 discussed the microstructures, densities and temperature dependencies of electrical resistivity, thermal conductivity, thermal diffusivity and total hemispherical emissivity of several vacuum plasmasprayed (VPS) and cold-sprayed (CS) cop
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