Abstract
One of the main requirements for powders for additive 3D technologies is the spherical shape of particles. Such particles are most densely fit into a certain space and provide the ‘fluidity’ of powder compositions in the systems of material supply with minimal resistance. In addition, the powder should contain a minimum amount of dissolved gas. The microstructure of the powder should be homogeneous and finely dispersed (with a uniform distribution of phase constituents). Based on the peculiarities of the methods of producing spherical powders in order to obtain spherical granules of regulated granularity, the electroerosion dispersion (EED) technology, which is characterized by relatively low energy costs and environmentally sound process, is proposed. The main advantage of the proposed technology is the use of waste materials as raw stuff which are much cheaper than the pure constituents used in traditional technology. In addition, this technology allows varying the granulometric composition of the resulting powder by changing electrical parameters. The objective of this work is to study the porosity of sintered samples of cobalt-chromium powders obtained for additive technologies by means of electroerosion dispersion. To implement the proposed research, wastes of the cobalt-chromium alloy of KHMS "CELLIT" grade were chosen. Distilled water and isobutyl alcohol were used as the working fluid. Electrical discharge machine to disperse conductive materials was used to produce cobalt-chromium powders. The powders are consolidated by the method of spark plasma sintering using the spark plasma sintering system SPS 25-10 (Thermal Technology, USA). The initial material was put in a graphite matrix placed under a press in a vacuum chamber. Electrodes integrated into the mechanical part of the press feed electric current to the matrix and create spark discharges between the sintered particles of the material, providing intensive interaction. The porosity was determined using Olympus GX51 optical inverted microscope with a software for quantitative image analysis. Prepared samples had no traces of structural components grinding, polishing or dying. The microsection metalographic specimen was made by the cross section (fracture) of the whole product. Based on the results of the conducted experiment aimed at studying the porosity of sintered samples from cobalt-chromium powders obtained for additive technologies by electroerosion dispersion in isobutyl alcohol, it was found that the porosity ranges from 3.19 to 6.15 %.
Highlights
Консолидация порошков проведена методом искрового плазменного спекания с использованием системы искрового плазменного спекания SPS 25-10 (Thermal Technology, США)
The objective of this work is to study the porosity of sintered samples of cobalt-chromium powders obtained for additive technologies by means of electroerosion dispersion
Based on the results of the conducted experiment aimed at studying the porosity of sintered samples from cobalt-chromium powders obtained for additive technologies by electroerosion dispersion in isobutyl alcohol, it was found that the porosity ranges from 3.19 to 6.15 %
Summary
Для выполнения намеченных исследований выбраны отходы кобальтохромового сплава марки КХМС «ЦЕЛЛИТ». Одним из основных методов определения пористости является металлографический метод с элементами качественного и количественного анализов геометрии пор (стереоскопическая металлография) [16]. Металлографический метод охватывает широкий диапазон измерения размеров пор, соответствующей разрешающей способности оптической способности (для оптического инвертированного микроскопа Olympus GX51 – 500 нм). При использовании микроскопа основным недостатком является отсутствие четкого распределения пор, так как их границы не всегда попадают в плоскость шлифа в связи со случайным сечением при его изготовлении. Метод дает распределение пор в одной плоскости образца, куда попадают и узкие, и широкие их сечения, в то время как по методу гидростатического взвешивания и ртутной порометрии фиксируются размеры пор по их самому узкому сечению. Для того чтобы обеспечить достоверность результатов анализа, ПО обладает элементами экспертной системы: в интерактивном режиме оператору предлагается выбрать те из автоматически выделенных объектов, которые, по его мнению, представляют собой дефекты микроструктуры. Результаты исследования пористости образцов металлографическим методом приведены в таблице и на рисунках 3 и 4
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