PSI - Issue 25

Sergey Smirnov et al. / Procedia Structural Integrity 25 (2020) 209–213 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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frequently added, which improve mechanical, physical, thermal, electrical, etc. properties (Kickelbick G., 2003, Rahman A. et al., 2011, Pinto D. et al., 2015). Herewith, the final properties of the resulting heterogeneous material depend on a number of factors, namely the type and mass concentration of the dope, the size and distribution of the filler particles in the polymer matrix, the nature of the interaction of the matrix material and the filler (Ali Allahverdi et al., 2012, Wichmann M. et al., 2006, Starkova O. et al., 2012, Yu Jia et al., 2011). Besides, it is necessary to take into account what effect the dopes will have on the performance characteristics of the material. Coatings have lately been actively studied, with the determination of their local properties by indentation methods (Ana M. Díez -Pascual et al., 2015,. Oliveira G.L. et al., 2014). Our earlier studies (Smirnov S.V. et al., 2019, Smirnov S.V. et al., 2017) have shown that this technique enables one to estimate effectively the mechanical properties (the elastic modulus, hardness, and creep) of coatings. It is well known that the properties of coatings, including protective ones, may change under operating conditions (e.g. the effect of temperature, acids and alkali, mechanical factors, etc.) ( João M. Sousa et al., 2018). The aim of this paper is to study the effect of nanosized oxides, namely TiO 2 , SiO 2 , and ZnO, used as modifiers of epoxy lacquer based on ED-20 epoxy resin, on the elastic modulus, microhardness, and creep of the resulting coating after multiple temperature differences. Due to the difference between the linear thermal expansion coefficient of the substrate and that of the coating material, the system experiences internal stress fluctuations, and this may eventually change the mechanical properties. 2. Materials and methods In this study, we used ED-20 epoxy-diane resin (Sverdlov Plant, Dzerzhinsk, Russia) with the epoxy number equal to 21.1%. Commercial titanium(IV) oxide (99.5% purity, 21 nm particle size), silicon(IV) oxide (99.5% purity, 10 – 20 nm particle size), and zinc(II) oxide (99.5% purity, <100 nm particle size) produced by Sigma-Aldrich were used as the modifiers. To produce the compositions, we prepared a solution of ED-20 epoxy resin in tetrahydrofuran (THF), and dispersed the oxides therein with the use of a ball mill, with a content of 10 wt%. AMg6 aluminum-magnesium alloy plates were used as the coating base. The coating thickness was 123 µm for the sample with pure lacquer, 112 µm for the sample filled with TiO 2 , 98 µm for the one filled with ZnO, and 216 µm for the sample doped with SiO 2 . Instrumented indentation in accordance with ISO 14577-1:2002 was performed with the use of a Fisherscope HM2000 XYm device. A Vickers tetrahedral diamond pyramid was used as an indenter. The indentation was performed at 22±2 C. Martens hardness HM and reduced (contact) normal elastic modulus, determined according to ISO 14577-1:2002, were chosen as the characterizing parameters. The relative change of the indentation depth was used as the characteristic of the creep of the coating material at given holding time and value of constant test load,

h h 

1 2 1 h

(1)

100%

C IT



where h 1 is the indentation depth at the attainment of the test load kept constant from the moment t 1 , mm, and h 2 is the indentation depth at the moment t 2 after holding under loading, mm. Thermocycling was performed according to GOST 27037-86. Paints and varnishes. The samples were placed in a drying oven and held at 60 ± 2 °С for 1 h; they were then transferred into a cold chamber, with a transfer time of at most 2 min, and held at − 40 ± 2 °С for 1 h. Thereafter, the samples were taken out of the cold chamber and held at 20 ± 5 °С for 15 min. The cycle was repeated 5 and 10 times. The parameters HM , E IT , and IT C were measured after 5 and 10 cycles.