Abstract
In the process of low-cycle fatigue testing of blanks of turbine disks of turbojet engines made of granular EP741NP nickel alloy, fracture samples were obtained. The fracture area was examined by various electron microscopy methods. Accumulation of rounded high-hafnium micro-particles was detected in the center of the fracture according to the data of energy-dispersive X-ray microanalysis. Such clusters are observed in about half the instances of fractures in similar blanks. Hafnium is an alloying element, but its content is strictly limited and should not exceed 0.4 mass %. Elucidation of the nature of the formation of this type of defects is a subject of scientific and practical interest. Using high-resolution transmission electron microscopy, energy-dispersive X-ray microanalysis and electron diffraction, it was determined that these particles are monoclinic single crystal HfO2 structures. Some particles contain nuclei that differ in their elemental composition and structure. Some of the nuclei contain C, O, S, F, etc. that may be indicators of organic contamination of the sample. A high-carbon amorphous shell was found around some HfO2 particles. The data obtained indicate that the formation of these particles is associated with organic contaminations. To prevent the formation of such centers of destruction, it is necessary to improve the purity of the technological processes of production.
Highlights
В ходе испытания на малоцикловую усталость заготовок турбинных дисков турбореактивных двигателей, изготовленных из гранулируемого никелевого сплава ЭП741НП, были получены образцы изломов
Accumulation of rounded high-hafnium micro-particles was detected in the center of the fracture according to the data of energy-dispersive X-ray microanalysis
Using high-resolution transmission electron microscopy, energy-dispersive X-ray microanalysis and electron diffraction, it was determined that these particles are monoclinic single crystal HfO2 structures
Summary
Установлено, что зарождение усталостных трещин может происходить от дефектов, находящихся в объёме материала. При рабочей температуре 650°С и испытаниях по мягкому циклу с коэффициентом асимметрии R 0,1 с максимальным уровнем напряжения цикла около 980 МПа (данные условия испытания прописаны в технических условиях (ТУ) к заготовкам дисков и валов из гранул жаропрочного никелевого сплава ЭП741НП) зарождение усталостных трещин от внутренних дефектов происходит примерно в 80 % от общего количества разрушений. В половине случаев дефектная область (ДО) представляет собой керамическое включение (например оксид Ti) Однако в остальных случаях ДО представляет собой кластер множества частиц округлой формы Повышение чистоты материала приведёт к уменьшению образования ДО и, как следствие, к улучшению усталостных характеристик деталей. Наблюдаемых в сплаве ЭП-741НП: а – керамическое включение (оксид титана); б – кластер из частиц, содержащих гафний
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