Search

Studies of the microstructure, phase composition and mechanical characteristics, namely the microhardness of metal–ceramic composites made of Fe 90 wt.%–Cu 10 wt.% powder and hydroxyapatite (Fe-Cu-HA), are presented in the manuscript. The composite material was obtained using additive manufacturing based on the 3D-printing method, with different content levels of powder (40, 45 and 50%) and polymer parts (60, 55 and 50%). It is shown that varying the proportion of Fe-Cu-HA powder does not significantly affect the elemental and phase compositions of the material. The X-ray phase analysis showed the presence of three phases in the material: alpha iron, copper and hydroxyapatite. It is shown in the experiment that an increase in the polymer component of the composite leads to an increase in the defectiveness of the structure, as well as an increase in microstresses. An increase in the mechanical properties of the composite (Vickers microhardness), along with a decrease in the percentage of Fe-Cu-HA powder from 50 to 40%, was established. At the same time, the composite containing 45% Fe-Cu-HA powder demonstrated the maximum increase in the microhardness of the composite by ~26% compared to the composite containing 50% Fe-Cu-HA powder, which is due to the more uniform distribution of components.

Functionalization of titanium (Ti)-based alloy implant surfaces by deposition of calcium phosphates (CaP) has been widely recognized. Substituted hydroxyapatites (HA) allow the coating properties to be tailored based on the use of different Ca substitutes. The formation of antibacterial CaP coatings with the incorporation of Zn or Cu by an RF magnetron sputtering is proposed. The influence of RF magnetron targets elemental composition and structure in the case of Zn-HA and Cu-HA, and the influence of substrate’s grain size, the substrate’s temperature during the deposition, and post-deposition heat treatment (HT) on the resulting coatings are represented. Sintering the targets at 1150 °C resulted in a noticeable structural change with an increase in cell volume and lattice parameters for substituted HA. The deposition rate of Cu-HA and Zn-HA was notably higher compared to stochiometric HA (10.5 and 10) nm/min vs. 9 ± 0.5 nm/min, respectively. At the substrate temperature below 100 °C, all deposited coatings were found to be amorphous with an atomic short-range order corresponding to the {300} plane of crystalline HA. All deposited coatings were found to be hyper-stochiometric with Ca/P ratios varying from 1.9 to 2.5. An increase in the substrate temperature to 200 °C resulted in the formation of equiaxed grain structure on both coarse-grained (CG) and nanostructured (NS) Ti. The use of NS Ti notably increased the scratch resistance of the deposited coatings from18 ± 1 N to 22 ± 2 N. Influence of HT in air or Ar atmosphere is also discussed. Thus, the deposition of Zn- or Cu-containing CaP is a complex process that could be fine-tuned using the obtained research results.

Heat resistant cobalt-based alloys have found a specific niche in the present-day mechanical engineering due to their unique properties. To begin with, cobalt-based alloys are used as corrosion, heat and wear resistant materials intended for aggressive environments and operation at extreme temperatures, e.g. blades, nozzles, swirlers, rings and other elements of turbines and internal combustion engines. Traditional molding methods applied in the mechanical engineering fail to provide necessary operational and technological characteristics of aforementioned machine parts. Owing to selective laser melting it is possible to reduce a production time and manufacturing costs for machine elements with a complex physical configuration and generate an alloy with an extraordinary structure, which is not found in traditionally combined compounds. A structure of cobalt exists in two crystal modifications: a hexagonal close-packed epsilon phase, a low-temperature phase and a face-centered cubic lattice gamma phase, a high-temperature phase. The alloy hardness is directly related to an amount of a low-temperature phase. The laser melting shortens a laser beam impact time on a powder composition due to a higher power and laser travelling speed. A high value of heat conductivity seems to be the reason for rapid solidification and cooling, which, in their turn, increase a percent of an alpha-martensite phase in an alloy and improve the hardness and wear resistance of machine parts. The reported paper summarizes studies aimed at the development of a stable phase structure three-component alloy (Сo-66 mass % Cr-6 mass % Mo) based on the cobalt-chromium-molybdenum system and mixed up via selective laser melting.

Four various methods of powder feedstock preparation for laser powder bed fusion are compared. Application of commercial spherical powder leads to the formation of single-phased state. Powder mechanically alloyed during 14 minutes in air atmosphere provides conditions for the formation of double-phased state with nonuniform distribution of components in the samples. Mechanical alloying in Ar-atmosphere during 30 minutes leads to the formation of double-phased state with more uniform distribution of components and precipitations of Cr2O3. Preliminary mechanical sieving of the powder allows to produce double-phased samples with nonuniform distribution of components comparable with that in samples produced from powder mechanically alloyed during 14 minutes in air atmosphere. Microhardness of all the studied samples produced from all the studied powders was comparable. All the proposed methods of powder feedstock preparation are applicable in laser powder bed fusion depending on the required properties, elemental and phase composition of the final product.

The results for thermal stability of the microstructure and mechanical properties of ultrafine-grained alloys Zr-1 wt. % Nb and Ti-45 wt. % Nb alloys after long-term thermal annealing at temperature of 400°C are presented. It is shown that in the Zr-1 wt.%Nb alloy in the ultrafine-grained state, increase in the annealing duration from 5 to 360 hours leads to growth of the structural elements (grains, sub-grains, fragments) of the matrix phase a - Zr and the particles β-Nb. This fact is due to the processes of recrystallization. It leads to softening of the alloy and decrease of microhardness and yield stress. It was also found that annealing up to 360 hours does not affect the size of the structural elements of the matrix β-phase in the Ti-45 wt. % Nb alloy, but contributes to the noticeable growth of the α-phase and ω-phase grains. According to our results, softening of the Ti-45 wt. % Nb alloy and decrease in its mechanical characteristics are associated with the processes of return at the grain boundaries, as well as with growth of the nanoscale grains of α-phase and ω-phase and decrease in their contribution to dispersion hardening.

Biodegradable materials are currently attracting the attention of scientists as materials for implants in reconstructive medicine. At the same time, ceramics based on calcium silicates are promising materials for bone recovery, because Ca2+ and Si2+ ions are necessary for the mineralization process, and they take an active part in the formation of apatite. In the presented research, the protective silicate biocoatings on a Mg0.8Ca alloy were formed by means of the micro-arc oxidation method, and the study of their morphology, structure, phase composition, corrosion, and biological properties was carried out. Elongated crystals and pores were uniformly distributed over the surface of the coatings. The coated samples exhibited remarkable anti-corrosion properties in comparison with bare magnesium alloy because their corrosion current decreased 10 times, and their corrosion resistance increased almost 100 times. The coatings did not significantly affect the viability of the cells, even without the additional dilution of the extract, and were non-toxic according to ISO 10993-5: 2009. In this case, there was a significant difference in toxicity of the pure Mg0.8Ca alloy and the coated samples. Thus, the results demonstrated that the applied coatings significantly reduced the toxicity of the alloy.

A comparative analysis of the structure, properties and the corrosion behavior of the micro-arc coatings based on Sr-substituted hydroxyapatite (Sr-HA) and Sr-substituted tricalcium phosphate (Sr-TCP) deposited on Mg0.8Ca alloy substrates was performed. The current density during the formation of the Sr-HA coatings was higher than that for the Sr-TCP coatings. As a result, the Sr-HA coatings were thicker and had a greater surface roughness Ra than the Sr-TCP coatings. In addition, pore sizes of the Sr-HA were almost two times larger. The ratio (Ca + Sr + Mg)/P were equal 1.64 and 1.47 for Sr-HA and Sr-TCP coatings, respectively. Thus, it can be assumed that the composition of Sr-HA and Sr-TCP coatings was predominantly presented by (Sr,Mg)-substituted hydroxyapatite and (Sr,Mg)-substituted tricalcium phosphate. However, the average content of Sr was approximately the same for both types of the coatings and was equal to 1.8 at.%. The Sr-HA coatings were less soluble and had higher corrosion resistance than the Sr-TCP coatings. Cytotoxic tests in vitro demonstrated a higher cell viability after cultivation with extracts of the Sr-HA coatings.

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.

Mg-based alloys became a material of interest for biomedical applications. The major difficulty in the Mg-based alloy application is its rapid corrosion rate. Various coating methods are used to form a barrier layer onto Mg-based materials. In this work, a thin film of calcium phosphate was deposited on an Mg–0.8 at % Ca alloy using RF magnetron sputtering. As-deposited coatings were in an X-ray amorphous state. Post-deposition heat treatment resulted in the coating crystallization, exhibiting the pure HA phase. Heat-treatment at 450°C for 3 hours did not significantly change the coating integrity and adhesion strength to the Mg–0.8 at % Ca substrate. The Ca/P ratio, however, was changed from 1.85 for as-deposited to 2.00 for heat-treated samples. Both coating and substrate material after heat treatment exhibit preferential crystallographic growth in (002) direction with Tc(002) = 2.86 and 5.79, correspondingly.

Experimental data of thermal stability of the microstructure and mechanical properties (exemplified by the microhardness tests) of the ultrafine grained (UFG) Ti–45 wt % Nb alloy after long-term thermal influence were presented in the paper. UFG structure in the alloy was formed with the severe plastic deformation (SPD) method. It was proved that the SPD method including the multiple abc-pressing and multi-pass rolling and further pre-recrystallizing annealing enhances the formation of UFG structures with the mean element size of 0.25 µm. Samples of Ti–45 wt % Nb alloy in UFG state were annealed at 350 and 400°C during 1, 5, 10, 24, 120, 240 and 360 hours. It was shown that the UFG structure was stable after annealing at 350 and 400°C as a result of thermal influence within the time range up to 360 hours. Stability of mechanical properties depended on the temperature and duration of annealing, i.e. microhardness of 3200 MPa was remained during 120 hours of annealing at 350°C, while microhardness of 3000 MPa was remained during 10 hours of annealing at 400°C.

CoCrMo alloys are very prospective in aerospace, medicine and other applications. Powder bed laser fusion (PBLF) allows to form the structure, phase and elemental compositions, physical and mechanical properties, which could not be achieved with conventional production methods. PBLF specimens were produced from spherical commercial and mechanically alloyed powders. Results of structure, phase and elemental compositions studies and microhardness’ measurements are represented.

Cobalt-based heat-resistant alloys have unique properties that are used in corrosive environments and at high temperatures. The addition of chromium improves resistance to hot corrosion, while molybdenum improves corrosion resistance and strength. When machining a workpiece of a heat-resistant alloy, up to half of the material goes into chips and goes to processing. Modern trends in the development of additive technologies are aimed at saving material, introducing new materials and improving the physical and mechanical characteristics of the resulting products. Selective laser melting (SLM) is one of the additive methods for obtaining bulk metal products and is one of the most promising directions in the development of science and technology in recent years. This paper describes the porosity (the average value was 14 ± 5%), the structure and properties of alloy samples obtained by selective laser melting in the following modes: laser power - 100 W, scanning speed - 350 mm / s, thickness of the applied powder layer - 25 um, scanning step - 100 um, frequency of pulse-periodic laser action (modulations) - 2.5 kHz from a spherical powder of the CoCrMo alloy (66 wt% Co, 28 wt% Cr, 6 wt% Mo).

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.

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.

The changes of the phase composition, structure and physicomechanical properties of Ti‑40 mas % Nb after severe plastic deformation are investigated in this paper. By the methods of microstructural, X-ray diffraction analysis and scanning electron microscopy it is determined that phase and structural transformations occur simultaneously in the alloy after severe plastic deformation. The martensitic structure formed after tempering disappears. The inverse α'' → β transformation occurs. The structure consisting of oriented refined grains is formed. The alloy is hardened due to the cold working. The Young modulus is equal to 79 GPa and it is less than that of initial alloy and close to the value obtained after tempering. It is possible that Young modulus is reduced by additional annealing.

The phase transformations of the alloy Ti-40 mas % Nb after tempering and severe plastic deformation are studied. The phase transformations of the alloy according to the type and conditions of external influences are analyzed using methods of XRD, SEM and optical metallography. It is determined that inverse phase transformation of the metastable α''-phase to equilibrium β-phase is carried out after severe plastic deformation. Complete phase transformation α'' → β is typical for the mode, which consists of three pressing operation with the change of the loading axis in cramped conditions, followed by a multi-pass rolling in grooved rolls.

In this work, we study the effect of RF magnetron oblique angle deposition (OAD) on morphology, structure, and elemental composition of as-deposited and heat-treated Cu containing calcium phosphates. The control over the surface morphology and nano roughness provided by OAD is of great interest as both Mesenchymal Stem Cells and various types of bacteria respond strongly to nanoscale topography. A Cu substituted hydroxyapatite target was used to deposit coatings on the surface of titanium (Ti) and silicon (Si) substrates. The samples were placed at an oblique angle of 80° relative to the surface of the sample holder and in a normal configuration with respect to the flux direction and, therefore, parallel to the target. The dense homogeneous coatings with globular surface features deposited at normal flux incidence (NFI) configuration changed to elliptical, highly oriented structures with the direction dictated by the atomic shadowing effect when the substrate was deposited at an oblique angle. As-deposited thin films were subjected to post-deposition-heat-treatment at 700 °C in an Ar atmosphere. This led to a drastic change in the surface morphology and, namely, lost the directionality of the nanostructures. According to the X-ray diffraction data, the samples deposited obliquely showed preferential growth in the (002) plane and lower internal stress, than samples coated at NFI for both the Si and Ti substrates. The RMS roughness of the films deposited obliquely on Si was twice that of the films deposited at NFI (860 ± 80 pm and 408 ± 60 pm, respectively). However, it was not the case for the Ti substrate, the RMS roughness decreased from 42 ± 4 nm for coatings deposited at normal flux geometry to 33 ± 2 nm for coatings deposited obliquely. The heat-treatment of the samples deposited at 80° resulted in a significant increase in the surface roughness: 8 ± 0.7 nm for Si and 71 ± 4 nm for Ti substrates. The obtained results demonstrate that the oblique angle deposition can be used to fabricate nano-rough surface morphologies.

In present paper Ti-Nb alloys produced via high-energy powder metallurgy method were studied. Ti-Nb alloys were obtained in form of layers on Ti substrate. The energy source was an electron beam emitted to the atmosphere, penetrating into deep layers of the powder. Electron energy was 1.4 MeV. It is shown that it is possible to produce alloys with predictable elemental and phase compositions via relativistic electron beam. Depending on the content of Nb, such phases as α′, α″ or β are formed. Produced alloys are non-toxic for cells. Due to this, manufacturing of small medical implants from this material is possible.

The surface modification of implants became of vital importance for medical field. One of the promising techniques allowing to deposit biocoatings with tailored properties including antibacterial activity is an RF magnetron sputtering. The material of the sputtering target that is going to be deposited on the surface of an implant can be made from various calcium phosphates. Here we present the results of Zn- and Cu-substituted hydroxyapatites and pure hydroxyapatite materials synthesised by mechanochemical method that were sintered in the form of targets for subsequent RF magnetron sputtering. With a set of analytical methods and physico-mechanical testing including X-ray diffraction analysis, energy-dispersive spectroscopy, microhardness measurements and the texture analysis it was shown that the approaches and regimes described in the paper allowed us to produce targets with desired phase composition and good mechanical properties. We estimated the influence of specific surface area of initial calcium phosphate powder with various hydroxyapatite compositions on sintered targets’ microhardness. It is concluded that the use of powders with specific surface area in the range of 40-60 m2/g is beneficial for formation and sintering of targets with high physico-mechanical parameters.

The results of investigation of the structure, physical and mechanical properties of the Ti-Nb alloy ingots with different composition obtained by arc melting are presented. X-ray diffraction and microstructural analyses were used. Microhardness was measured and the Young’s modulus of the alloys was evaluated. When the content of niobium in the alloy changes from 10 to 40 mass.%, phase composition of the alloy varies from α-and α'-phase (10 mass.% of Nb) to α'-, α''- and β-phases (25 mass.% of Nb), to the β-phase (40 mass.% of Nb). The alloy containing 40 mass.% Nb has the lowest Young’s modulus.

By the results of X-ray analysis, microstructural analysis, nanohardness and elastic modulus measurements it was defined that non-equilibrium phases during the process of crystallization are formed in the titanium-niobium alloy with 40wt.% of Nb. The minimum of non-equilibrium phases is formed at the Ti-40wt.% Nb alloy. The uniform grain structure, which consists of β-phase grains with the minimum of elastic modulus, is formed in the alloy ingot. Such structure and complex of properties allows using this alloy for severe plastic deformation.

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 [beta]-phase forms in the areas enriched in Nb. [alpha]”-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.

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...

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...