Dynamic Light Scattering by Foamed Polymers during Preparation of Scaffold Prototypes: Events Statistics Analysis versus Evaluation of Correlation Time in Data Interpretation

Polylactide foaming as the key stage in laboratory preparation of highly porous biocompatible matrices used as scaffold prototypes was monitored based the effect of dynamic light scattering in expanding polylactide foams. Intensity fluctuations of scattered laser radiation in the course of foam expansion were analyzed using ensemble-averaged estimates of the speckle lifetime within a running window in the time domain. It was found that, in contrast to the commonly used correlation time of intensity fluctuations, the values of the average speckle lifetime are invariant with respect to the type of dynamics of phase fluctuations of partial components in scattered radiation. This makes it possible to relate this parameter to microscopic mobility of interphase boundaries in the foam in the absence of a priori information on the law of motion relating these boundaries at the microscopic level. The proposed approach in combination with the developed phenomenological model describing the relationship between the average speckle lifetime and the current values of the foam volume, as well as its first-time derivative made it possible to interpret the features of foam structure formation.

The Influence of the Microstructure of Ceramic-Elastomer Composites on Their Energy Absorption Capability

The paper presents the experimental results of static and dynamic compressive tests conducted on ceramic-elastomer composites. The alumina ceramic preforms were fabricated by the four-step method: ceramic mixture preparation, consolidation under pressure, presintering, and sintering under pressure, respectively. To obtain ceramic preforms with a similar volume fraction of open pores, but with different pore sizes, alumina powder with different particle size and a ceramic binder were used, as well as pore-forming agents that were evenly distributed throughout the volume of the molding mass. The composites were obtained using vacuum pressure infiltration of porous alumina ceramic by urea-urethane elastomer in liquid form. As a result, the obtained composites were characterized by two phases that interpenetrated three-dimensionally and topologically throughout the microstructure. The microstructure of the ceramic preforms was revealed by X-ray tomography, which indicated that the alumina preforms had similar porosity of approximately 40% vol. but different pore diameter in the range of 6 to 34 µm. After composite fabrication, image analysis was carried out. Due to the microstructure of the ceramic preforms, the composites differed in the specific surface fraction of the interphase boundaries (Sv). The highest value of the Sv parameter was achieved for composite fabricated by infiltration method of using ceramic preform with the smallest pore size. Static and dynamic tests were carried out using different strain rate: 1.4·10−3, 7·10−2, 1.4·10−1, and 3·103 s−1. Compressive strength, stress at plateau zone, and absorbed energy were determined. It was found that the ceramic-elastomer composites’ ability to absorb energy depended on the specific surface fraction of the interphase boundaries and achieved a value between 15.3 MJ/m3 in static test and 51.1 MJ/m3 for dynamic strain rate.

The Spectrum of Crystallographic Misorientations of Intercrystalline Boundaries for BCC-HCP Phase Transformation in Additively Manufactured Ti-6Al-4V

Electron backscatter diffraction is a modern experimental method for local structure and texture investigation, which makes it possible to establish the presence and types of the various boundaries between the elements of the mesostructure such as low or high angle, special and interphase boundaries. Moreover, this technique can demonstrate the migration of boundaries during structural and phase transformations. This study estimated the possible spectrum of crystallographic misorientations of intercrystalline boundaries in additively manufactured titanium alloy Ti-6Al-4V using orientation microscopy and crystallographic calculations based on Burgers orientation relationship during β→α-transformation. The study has established that the boundaries between grains of α-phase are characterized by the misorientation angles of 11±2 °, 61±5 °, 89±3 °. The majority of high-angle boundaries are characterized by misorientation angles in the range of 57-65 °. The study also ascertained that the experimental spectrum of intercrystalline boundaries in the α-phase reveals the displacive nature of β→α-transformation in titanium alloys.

Al2O3/ZrO2 Materials as an Environmentally Friendly Solution for Linear Infrastructure Applications

The present work deals with the evaluation of the effect of ZrO2 on the structure and selected properties of shapes obtained using the centrifugal slip casting method. The samples were made of alumina and zirconia. The applied technology made it possible to produce tubes with a high density reaching 99–100% after sintering. Very good bonding was obtained at the Al2O3/ZrO2 interphase boundaries with no discernible delamination or cracks, which was confirmed by STEM observations. In the case of Al2O3/ZrO2 composites containing 5 vol.% and 10 vol.% ZrO2, the presence of equiaxial ZrO2 grains with an average size of 0.25 µm was observed, which are distributed along the grain boundaries of Al2O3. At the same time, the composites exhibited a very high hardness of 22–23 GPa. Moreover, the environmental influences accompanying the sintering process were quantified. The impacts were determined using the life cycle analysis method, in the phase related to the extraction and processing of raw materials and the process of producing Al2O3/ZrO2 composites. The results obtained show that the production of 1 kg of sintered composite results in greenhouse gas emissions of 2.24–2.9 kg CO2 eq. which is comparable to the amount of emissions accompanying the production of 1 kg of Polyvinyl Chloride (PVC), Polypropylene (PP), or hot-rolled steel products.

Behavior of Inelastic and Plastic Strains in Coarse-Grained Ti49.3Ni50.7(at%) Alloy Deformed in B2 States

The regularities of the change in inelastic strain in coarse-grained samples of the Ti49.3Ni50.7 (at%) alloy are studied when the samples are given torsional strain in the state of the high-temperature B2 phase. During cooling and heating, the investigated samples underwent the B2–B19′ martensite transformation (MT); the temperature of the end of the reverse MT was Af = 273 K. It was found that at the temperature of isothermal cycles “loading-unloading” Af + 8 K, when the specimen is assigned a strain of 4%, the effect of superelasticity is observed. With an increase in the torsional strain, the shape memory effect is clearly manifested. It is assumed that the stabilization of the B19′ phase in unloaded samples is due to the appearance of dislocations during deformation due to high internal stresses at the interphase boundaries of the B2 phase and the martensite phase during MT. The appearance of dislocations during the loading of samples near the temperatures of forward and reverse MT can also be facilitated by the “softening” of the elastic moduli of the alloy in this temperature range. At a test temperature above Af + 26 K, the superelasticity effect dominates in the studied samples.

Non-metallic inclusions in different zones of crystallization of E90KhAF rail steel

Metallographic and X-ray studies of continuously cast billets of E90KhAF rail steel have been carried out. We have established the regularities of non-metallic inclusions distribution over the crystallization zones before and after billets deformation. It was revealed that in crustal zone the main non-metallic inclusions are point oxides, aluminum nitrides, iron silicates (FeO·SiO2) and alumosilicates (Al2O3·SiO2). They were identified in the zone of columnar crystals. In central zone of the billet, manganese sulfides (MnS), manganese silicates (MnO·SiO2), alumosilicates (Al2O3·SiO2), iron silicates (FeO·SiO2), and point oxides were found. It has been determined that concentration and size of nonmetallic inclusions tend to increase from the surface to central zone of continuously cast billets, which is consistent with generally accepted ideas about mechanisms of billet formation during crystallization. The mechanism of deformation of two-phase silicate non-metallic inclusions and their influence on quality of rail products was disclosed. It is shown that inhomogeneous deformability of complex silicate inclusions aggravates their harmful effect on rail products quality. In this case, additional stresses appear in addition to inclusion-matrix deformation and contact stresses existing at interphase boundaries. This pattern also holds for non-deformed silicate inclusions. Such a distribution of inclusions in the billets volume somewhat reduces their negative effect on rails quality, since near-contact layers of the billet undergo more intense deformation during rolling, and as the axial zone of a billet is approached, deformation rate decreases.