Frontier Materials & TechnologiesFrontier Materials & TechnologiesFrontier Materials & Technologies2782-40392782-6074Togliatti State University80810.18323/2782-4039-2022-4-49-69ArticlesСтатьиDifferent-sized porosity and thermal conductivity of oxide layers formed by plasma-electrolytic oxidation on the AlSi12Mg siluminРазноразмерная пористость и теплопроводность оксидных слоев, сформированных плазменно-электролитическим оксидированием на силумине АК12ДIvashinPavel V.ИвашинПавел Валентинович
Russian Federation

PhD (Engineering), senior researcher

кандидат технических наук, старший научный сотрудник

ivashinpv@gmail.comhttps://orcid.org/0000-0001-7189-0002KrishtalMikhail M.КришталМихаил Михайлович
Russian Federation

Doctor of Sciences (Physics and Mathematics), Professor

доктор физико-математических наук, профессор

krishtal@tltsu.ruTverdokhlebovAndrey Ya.ТвердохлебовАндрей Яковлевич
Russian Federation

engineer

инженер

andr.tverd@gmail.comhttps://orcid.org/0000-0001-8484-2456PoluninAnton V.ПолунинАнтон Викторович
Russian Federation

PhD (Engineering), leading researcher

кандидат технических наук, ведущий научный сотрудник

anpol86@gmail.comhttps://orcid.org/0000-0003-2269-0498DudarevaNatalya Yu.ДудареваНаталья Юрьевна
Russian Federation

Doctor of Sciences (Engineering), Professor

доктор технических наук, профессор

dudareva.nyu@ugatu.suhttps://orcid.org/0000-0002-0530-0729KruglovAleksandr B.КругловАлександр Борисович
Russian Federation

PhD (Physics and Mathematics), Associate Professor

кандидат физико-математических наук, доцент

ABKruglov@mephi.ruTogliatti State University, TogliattiТольяттинский государственный университет, ТольяттиUfa University of Science and Technology, UfaУфимский университет науки и технологий, УфаNational Research Nuclear University MEPhI, MoscowНациональный исследовательский ядерный университет «МИФИ», Москва301220224496930122022https://vektornaukitech.ru/jour/article/view/808

Oxide layers formed by plasma-electrolytic oxidation (PEO) are characterized by a sufficiently high porosity, which influences almost the whole complex of service characteristics. However, the known data on the integral porosity of PEO-produced layers are rather contradictory, and the pore size distribution in these layers remains understudied.  Pore size distribution in the range of 10 nm to 10 µm (pore geometry was approximated by a spherical shape) was obtained by using analysis of scanning electron microscopy (SEM) images in a wide range of magnifications. Lognormal distribution function fits the shape of pore size distribution sufficiently well. Such distribution indicates the nature of pore formation, which can be related to the thermally activated process of gas emission from a liquid melt, the volume and average temperature of which, in turn, depend on the micro-arc discharge energy. The results of the oxide layer phase composition and crystallites sizes by the X-ray crystallography were described in the present paper. The amorphous component phase composition was estimated by the comparing of the of X-ray spectral microanalysis and X-ray crystallography methods. The thermal conductivity of the intact oxide layer and the polished layer (after the removal of its highly-porous outer part) was evaluated by using of the steady-state method and the laser flash method. The porosity values calculated based on the analysis of SEM-images, and the results of determining the phase composition, including amorphous phases, allowed evaluating the oxide layer thermal conductivity with use of four known analytical models. The results of calculating the thermal conductivity using the Loeb model demonstrate the good convergence with the experimental results obtained in this paper. Modeling results the size of crystallites effect on the oxide layer thermal conductivity significantly less than the porosity and amorphous phase.

Оксидные слои, сформированные плазменно-электролитическим оксидированием (ПЭО), характеризуются достаточно высокой пористостью, что влияет практически на весь комплекс служебных характеристик. Тем не менее известные данные об интегральной пористости слоев, получаемых ПЭО, достаточно противоречивы, а характер распределения пор по размерам в этих слоях остается малоизученным. В результате обработки полученных в широком диапазоне увеличений изображений поперечного сечения слоя (сканирующая электронная микроскопия – СЭМ, image-based анализ) получено распределение пор по размерам в диапазоне от 10 нм до 10 мкм, которое достаточно хорошо описывается функцией логарифмически нормального распределения (геометрия пор аппроксимировалась сферической формой). Такой характер распределения указывает на природу образования пор, которую можно связать с термически активируемым процессом выделения газа из расплава, объем и средняя температура которого, в свою очередь, определяются энергией микродуговых разрядов. В работе также представлены результаты определения методом рентгеноструктурного анализа (РСА) фазового состава оксидного слоя и размеров кристаллитов. Сравнением результатов рентгеноспектрального микроанализа (РСМА) и РСА оценен фазовый состав аморфной составляющей. Стационарным методом и методом импульсного лазерного нагрева определена теплопроводность исходного оксидного слоя и слоя после удаления его высокопористой наружной части. Полученные экспериментально-расчетным путем на основе анализа СЭМ-изображений значения пористости и результаты определения фазового состава, включая аморфные фазы, позволили оценить теплопроводность оксидного слоя с помощью четырех известных аналитических моделей. Результаты расчета теплопроводности по модели Loeb показали хорошую сходимость с экспериментальными результатами, полученными в настоящей работе. Путем моделирования показано, что на теплопроводность оксидного слоя размер кристаллитов влияет существенно меньше пористости и аморфной фазы.

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