Margarita A. Khimich

The Structure of Quaternary Iron-Based Alloy Obtained at High and Ultrahigh Cooling Rates

Influence of Fe-Si-Al-C alloy cooling rate on its phase composition, structure and microhardness is shown based on metallographic investigations, electron microscopy and x-ray diffraction analysis. It was determined that the structure will change from dendrite to grained, size of structure elements will decrease, quantity and size of secondary phases precipitations will decrease when cooling rate changes from 103 to 107 K/s. The metastable phases such as primary ferrite, austenite and complex carbides are formed in cooling rate range. The volume ratio of main phases changes in favor of primary ferrite with cooling rate increasing. Hardening of the material occurs more than twice. Hardening is due to the interaction of solid-solution hardening, grain boundary hardening and dispersive hardening by secondary phases particles. The maximum hardening is achieved during formation of the alloy in molten pool at electron-beam melting. The alloy in this case contains 80 vol. % of austenite with dendrite similar structure and precipitations of carbide and silicocarbide phases. It can be assumed than such structure will be formed from the alloy with investigated composition at additive manufacturing.

Evaluation of Physicomechanical Properties of Ti-45Nb Specimens Obtained by Selective Laser Melting

Porosity, values of nanohardness and Young’s modulus of the specimens obtained with the method of selective laser melting were measured with optical methods, scanning electron microscopy and Nano Hardness Tester NHT-S-AX-000X device for measuring physicomechanical properties. Ti-45wt%Nb powder obtained with mechanical alloying was used for selective laser melting. The results have shown that increased heat input due to the laser power growth up to 80 W and scanning speed decrease down to 40 mm/s decreases the porosity of the specimen. The nanohardness average value is not sensitive to the changes of scanning modes in the investigated range. The Young’s modulus decreases with energy input increase.

The investigation of the influence of formation conditions on the structure of Ti-40Nb alloy

It was determined that there is components segregation in Ti-Nb alloy under electro arc melting and selective laser melting. It leads to two phase formation. The β-phase forms in the areas enriched in Nb. α”-phase forms in the Nb-depleted areas. It is recommended to increase the Nb concentration in the alloy up to 45 wt. % to eliminate heterogeneity of phase and elemental composition.

APPLICATION OF SELECTIVE LASER MELTING TO PRODUCE LOW MODULUS ALLOYS OF THE TITANIUM-NIOBIUM

Сплав системы титан – ниобий широко используется при производстве имплантатов. В первую очередь это связано с низким модулем упругости и биоинертными свойствами сплава. Наибольшее распространение данные сплавы получили в зубном протезировании и ортопедии. На сегодняшний день сплав системы титан – ниобий в основном получают традиционными методами металлургии. При дальнейшем субтрактивном получении готового изделия образуется большое количество отходов. В связи с этим увеличивается стоимость конечного изделия. Противоположностью данным технологиям является аддитивное производство. Селективное лазерное сплавление (Selective Laser Melting) – технология, позволяющая печатать детали из порошков металлов и их смесей. Ее суть заключается в том, что слой материала в порошковой форме сплавляется лазером, затем поверх сплавленного слоя наносится следующий слой порошка и т.д. Технология используется для создания сложных изделий и рабочих прототипов. В данной работе рассмотрена возможность применения метода селективного лазерного сплавления для получения бинарного сплава из композитного порошка системы титан – ниобий. Получена панель образцов размером 10 × 10 мм при различных технологических параметрах. Образцы изготавливались на экспериментальной установке послойного лазерного синтеза «ВАРИСКАФ-100МВ». Данная установка позволяет управлять следующими технологическими параметрами: мощность лазерного излучения, скорость и шаг сканирования, температура подогрева порошка, толщина насыпаемого слоя, диаметр фокусировки пятна лазера. Все образцы получены в защитной среде аргона после предварительного вакуумирования. Построены зависимости изменения пористости и толщины сплавленного слоя от мощности лазерного излучения при разных скоростях сканирования. Установлено, что из всех контролируемых технологических параметров наибольшее влияние на формирование сплавленного слоя оказывает скорость сканирования и мощность лазерного излучения.

Features of the Ti-40Nb alloy prototype formation by 3D additive method

The structure of Ti-40Nb alloy prototype obtained by selective laser melting (SLM) on “VARISKAF 100MV” installation was considered by the methods of optical metallography, scanning and transmission electron microscopy. It was revealed that the most of the specimens’ surface is uniform flowed surface with typical banded structure formed by laying-on molten pools. The process of the individual layer formation was followed by drop formation. This leads to the porosity formation on the specimen’s surface. The structure of entire specimen is not homogeneous throughout the transverse section. The porosity of three kinds is observed. They are cavities of not full contact and melting of the layers, drawholes, gas pores. The porosity optimization requires more careful SLM modes selection. The alloy has a grain structure with anisotropy from small (2–8 µm) to medium (8–20 µm) grain size. The anisotropy of the specimen is formed in each layer and is retained during building of the specimen. The grains of microstruct...

Structural and phase transformations in iron-based alloy obtained in conditions of high cooling rate crystallization

The production of parts by selective electron beam melting (SEBM) is accompanied by the formation of nonequilibrium structures. This is caused by the crystallization of alloys with high cooling rates. To evaluate the influence of cooling rate on the process of structural and phase transformations in the Fe-8Si-5Al-2C alloy, the electron beam melting of plasma coating was carried out. The dendritic structure was formed in the molten pool. The distance between dendritic branches of the second order was 2–5 µm. This corresponds to the cooling rate of about 103 K/s. The electron microscopy has shown that dendrites were formed by α-phase, while γ-phase was localized between α-phase crystals in form of intercalations. The secondary phases (intermetallic, aluminum and iron carbosilicides, aluminates and iron carboaluminates) are of sub-micron size and located in the α- and γ-phase boundary intersections or within the grains of the main phase. The microhardness of the alloy increases twofold. This suggests that c...