The Determining Influence of the Phase Composition on the Mechanical Properties of Titanium-Iron Alloys after High-Pressure Torsion.

Three titanium alloys with 0.5, 6, and 9 wt.% iron were investigated, and the samples were pre-annealed in three different regions of the Ti-Fe phase diagram, namely ß, α+ß, and α+FeTi. After annealing, five samples of different phases and structural compositions were studied. They were then subjected to the high-pressure torsion (HPT). The microstructure of the samples before and after HPT treatment was studied using transmission and scanning electron microscopy. The microstructure of the samples obtained during heat treatment before HPT treatment had a fundamental effect on the microstructure after HPT. Grain boundary layers and chains of particles formed during the annealing process made it difficult to mix the material during HPT, which led to the formation of areas with non-uniform mixing of components. Thus, the grain boundary layers of the α-phase formed in the Ti-6wt % Fe alloy after annealing at 670 °C significantly decreased the mixing of the components during HPT. Despite the fact that the microstructure and phase composition of Ti-6wt % Fe alloys pre-annealed in three different regions of the Ti-Fe phase diagram had significant differences, after HPT treatment, the phase compositions of the studied samples were quite similar. Moreover, the measured micro- and nanohardness as well as the Young's modulus of Ti-6wt % Fe alloy had similar values. It was shown that the microhardness of the studied samples increased with the iron content. The values of nanohardness and Young's modulus correlated well with the fractions of ß- and ω-phases in the studied alloys.

Electrospun Zr-Doped CaO Sorbent for CO2 Capture.

A Zr-doped CaO sorbent for high-temperature CO2 capture was fabricated using electrospinning. The nanofiber sorbent with an average filament diameter of about 160 nm is characterized by an initial CO2 uptake capacity of 12.1 mmol/g, a specific surface area of 79 m2/g, an indentation Young's modulus of 520 MPa, and a hardness of 1.6 MPa. After 50 carbonation/decarbonation cycles, the sorbent has a decent CO2 uptake capacity of 9.7 mmol/g due to the uniform distribution of CaZrO3 in the CaO nanofibers to prevent CaO grain growth caused by CaCO3 sintering. It is revealed that the sorbent CO2 uptake capacity decreases both with an increase in the decarbonation temperature and with an increase in the CO2 concentration in the gas flow upon carbonation, where the sorbent CO2 uptake capacity is more sensitive to the decarbonation temperature than to the CO2 concentration in the gaseous stream during carbonation. It is assumed that the electrospun regenerable Zr-doped CaO sorbent is effective for removing CO2 from flue gases.

Phase Transformations Caused by Heat Treatment and High-Pressure Torsion in TiZrHfMoCrCo Alloy.

In this work the high-entropy alloy studied contained six components, Ti/Zr/Hf/Mo/Cr/Co, and three phases, namely one phase with body-centered cubic lattice (BCC) and two Laves phases C14 and C15. A series of annealings in the temperature range from 600 to 1000 °C demonstrated not only a change in the microstructure of the TiZrHfMoCrCo alloy, but also the modification of phase composition. After annealing at 1000 °C the BCC phase almost fully disappeared. The annealing at 600 and 800 °C leads to the formation of new Laves phases. After high-pressure torsion (HPT) of the as-cast TiZrHfMoCrCo alloy, the grains become very small, the BCC phase prevails, and C14 Laves phase completely disappears. This state is similar to the state after annealing at high effective temperature Teff. The additional annealing at 1000 °C after HPT returns the phase composition back to the state similar to that of the as-cast alloy after annealing at 1000 °C. At 1000 °C the BCC phase completely wets the C15/C15 grain boundaries (GBs). At 600 and 800 °C the GB wetting is incomplete. The big spread of nanohardness and Young's modulus for the BCC phase and (C15 + C14) Laves phases is observed.

The Nanofibrous CaO Sorbent for CO2 Capture.

The nanofibrous CaO sorbent for high-temperature CO2 capture was fabricated by the calcination of electrospun composite filaments containing calcium acetylacetonate and polyacrylonitrile as a calcium-oxide precursor and a binder polymer, respectively. The calcination was carried out in air to prevent PAN carbonization and to obtain pure CaO nanofibers. The resulting mats of CaO nanofibers with the average diameter of 130 nm were characterized by a specific surface area of 31 m2/g, a CO2-uptake capacity of 16.4 mmol/g at the carbonation temperature of 618 °C, a hardness of 1.87 MPa, and the indentation Young's modulus of 786 MPa. The low decarbonation temperature makes the fabricated sorbent promising, for example, for the calcium-looping technology of CO2 removal from the hot exhaust gases of fossil-fueled power plants.

Relationship between Thermal Diffusivity and Mechanical Properties of Wood.

This paper describes an experimental study of the relationships between thermal diffusivity and mechanical characteristics including Brinell hardness, microhardness, and Young's modulus of common pine (Pinus sylvestris L.), pedunculate oak (Quercus robur L.), and small-leaf lime (Tilia cordata Mill.) wood. A dependence of Brinell hardness and thermal diffusivity tensor components upon humidity for common pine wood is found. The results of the measurement of Brinell hardness, microhardness, Young's modulus, and main components of thermal diffusivity tensor for three perpendicular cuts are found to be correlated. It is shown that the mechanical properties correlate better with the ratio of longitude to transversal thermal diffusivity coefficients than with the respective individual absolute values. The mechanical characteristics with the highest correlation with the abovementioned ratio are found to be the ratio of Young's moduli in longitude and transversal directions. Our technique allows a comparative express assessment of wood mechanical properties by means of a contactless non-destructive measurement of its thermal properties using dynamic thermal imaging instead of laborious and material-consuming destructive mechanical tests.

Effect of Zirconia Nanofibers Structure Evolution on the Hardness and Young's Modulus of Their Mats.

Zirconia nanofiber mats containing filaments with the average diameter of less than 100 nm were fabricated. It is found that the hardness and Young's modulus of the mats are sensitive to the microstructure, phase composition and average diameter of the zirconia nanofibers. The hardness and Young's modulus of the prepared zirconia nanofiber mats vary from 0.86 to 1.67 MPa and from 133 to 362 MPa, respectively, wherein an increase in hardness is accompanied by the rise in Young's modulus.

An Engineering Zirconia Ceramic Made of Baddeleyite.

Wet high-energy milling and uniaxial pressing are used to fabricate CaO-stabilized tetragonal zirconia polycrystalline ceramic (Ca-TZP) with decent mechanical characteristics, i.e., a hardness of 11.5 GPa, Young's modulus of 230 GPa, and fracture toughness of 13 MPa·m0.5. The effect of CaO concentration and the sintering temperature on phase composition and mechanical characteristics of CaO-stabilized zirconia ceramic made of baddeleyite is investigated.

Morphology and Mechanical Properties of 3Y-TZP Nanofiber Mats.

The mats of yttria-stabilized tetragonal zirconia nanofibers were prepared using electrospinning. The effect of calcination temperature in the range of 600-1200 °C on their microstructure, phase composition and mechanical properties was investigated. Phase composition of the nanofibers did not change in all ranges of the calcination temperatures, while the average grain size increased from 8 to 39 nm. Nanoindentation testing of the mats showed a decrease in the hysteresis loop energy in samples with higher calcination temperature. Hardness and the elastic modulus measured with the indentation technique were the highest for the mats calcined at 900 °C.

Comprehensive Characterization of Titania Nanotubes Fabricated on Ti-Nb Alloys: Surface Topography, Structure, Physicomechanical Behavior, and a Cell Culture Assay.

In this study, hybrid composites based on ß-alloy Ti-xNb and oxide nanotubes (NTs) have been successfully prepared. NTs of different sizes were grown on Ti-Nb substrates with different Nb contents (5, 25, and 50 wt %) via electrochemical anodization at 30 and 60 V. Scanning electron microscopy imaging revealed that vertically aligned nanotubular structures form on the surface of Ti-Nb alloy substrates and influence Nb content in alloys based on NT length. X-ray diffraction analysis confirmed the formation of the anodized TiO2 layer and revealed several phases as the Nb content increased, starting with α' for low Nb content (5 wt %), the martensite α″ for intermediate Nb content (25 wt %), and the ß phase for the highest Nb content (50 wt %). Nanoindentation testing was used to evaluate the changes in mechanical properties of oxide NTs grown on Ti-Nb alloys with different compositions. NT arrays showed wide variations in Young's modulus and hardness depending upon the anodization voltage and the Nb content. The hardness and Young's modulus strongly correlated with NT morphology and structure. The highly dense morphology formed at a lower anodization voltage results in increased elastic modulus and hardness values compared with the surfaces prepared at higher anodization voltages. The nanostructurization of Ti-Nb surface substrates favored improved surface properties for the enhanced adhesion and proliferation of human mesenchymal stem cells (hMSCs). In vitro adhesion, spreading, and proliferation of hMSCs revealed the improved surface properties of the NTs prepared at an anodization voltage of 30 V compared with the NTs prepared at 60 V. Thus it can be concluded that NTs with diameters of ∼50 nm (at 30 V) are more favorable for cell adhesion and growth compared with NTs with diameters of 80 ± 20 nm (at 60 V). The surfaces of Ti-25Nb substrates anodized at 30 V promoted enhanced cell growth, as the further increase in Nb content in Ti-Nb substrate (Ti-50Nb) led to reduced cell proliferation. The application of NTs on Ti-Nb substrates leads to significant reductions in mechanical properties compared with those on the Ti-Nb alloy and improves cell adhesion and proliferation, which is vitally important for successful application in regenerative medicine.