Papers by Keyword: Powder

Abstract: Production of the honeycomb or thin walled structures by the selective laser melting of powder is of a great scientific and practical interest. It’s because that such approach allows producing structures practically of any configuration and thickness, unobtainable or very hard to produce by traditional methods. Using the additive technology, the principal difference from the traditional is that the honeycomb structures can be produced practically of any shape, and the method itself is 100% waste-free, because there is no need in supporting structures. The results of the structure investigation of the honeycomb structures with the wall thickness of 80-170 μm and 44 mm height are presented along with the correlation dependencies between samples mass, wall thickness, activation and compression loads.

Abstract: The Bi–Te thermoelectric system shows an excellent figure of merit (ZT) near room temperature. Research on increasing the ZT value for n‑type Bi–Te is imperative because the thermoelectric properties of this compound are inferior to those of the p-type material. For this purpose, n-type Bi₂Te_3-ySe_y powders with various amounts of Se dopant (0.3 ≤ y ≤ 0.6) were synthesized by a vacuum melting-grinding process to improve the physical properties. The ZT value of the sintered bodies was investigated in the temperature range of 298–423 K with regard to the electrical and thermal characteristics. As the Se content increased, the electrical conductivity decreased owing to a reduction in the carrier concentration, which improved the overall value of ZT. The thermal conductivity clearly decreased as the Se content increased in the temperature range of 298–373 K due to increased alloy scattering, as well as a reduction in the lattice thermal conductivity caused by crystal grain boundary scattering. At room temperature, Bi₂Te_2.7Se_0.3 (y = 0.3) exhibited the highest ZT of 0.85. At increased temperatures, the ZT value was highest for Bi₂Te_2.55Se_0.45 (y = 0.45), indicating that the optimal effect of the Se dopants varies depending on the temperature range.

Abstract: The use and application of alloys as biomedical alloys have increased over the past few years owing to their excellent biocompatibility, corrosion resistance, high mechanical and fatigue resistance, low density, adequate wear resistance, and low elastic modulus. Orthopedic implant materials are exposed to high mechanical loading. Conventional materials based on Ti-6Al-4V, stainless steel or cobalt-chromium alloys demonstrate good mechanical strength, but also some toxicological concerns due to release of toxic elements which may result in inflammatory reactions. Metal alloys based on titanium, zirconium, tantalum and niobium represent higher biocompatibility with appropriate mechanical properties for avoiding stress-shielding and consecutive implant loosening. Application of specifically designed spherical β-titanium alloy powders in additive manufacturing, such as selective laser melting (SLM) or electron beam melting (EBM); enable the production of components with a high degree in freedom of design. Accordingly, SLM or EBM of Ti/Nb (/Ta) alloys offer the possibility to fabricate patient-specific orthopedic implants. The present paper describes development of β-titanium alloys powders designed for application in additive manufacturing technologies. TiNbZrTa (TNZT)-based 3D structures were successfully manufactured and mechanically tested.

Abstract: Microstructure of Ti-28Ta powders produced by plasma rotating electrode process (PREP) was investigated by using scanning electron microscopy (SEM), optical microscopy (OM), and transmission electronic microscopy (TEM). Phase constituent of the PREP Ti-28Ta powders was analyzed by X-ray diffraction (XRD). It was found that microstructure of the PREP Ti-28Ta powders was dependent on the powder particle sizes. Predominant martensitic α”, some metastable β and trace athermal ω phases were observed in the powders with the small diameter. While, phase constituent of the PREP Ti-28Ta powders with the large particle size was predominant metastable β, some martensitic α” and trace athermal ω. With the reduction of the powder particle size, the amount of martensitic α” increased and the metastable β decreased. The martensitic α” was formed preferentially on the metastable β grain boundaries of the PREP Ti-28Ta powders. The increase of α” phase and decrease of β with reduction of the powder particle size is attributed to the increase of the volume of the grain boundaries due to the grain refinement.

Abstract: In this paper, the processes of forming the samples of powder materials based on the titanium – nickel and nickel – aluminium systems were investigated. The possibility of conducting self-propagating high-temperature synthesis (SHS) in the nickel – aluminium system without protective atmosphere is shown. The initial heating temperature of the starting mixture is the main factor determining the flow of this process. Its growth leads to an increase of the synthesis speed. The number of the oxides decreases at the same time. Thermodynamic calculations of the combustion reactions were performed under different conditions. Phase analysis has shown the presence of the intermetallic compounds, which correspond to the phase diagram of the nickel – aluminium system. Thermodynamic calculations confirmed the assumption of preferential oxidation of metallic sodium when it was added to the mixture of powders in the titanium – nickel system. Technological features of obtaining products of various functional purposes are justified. The performed research confirms the effectiveness and promising use of self-propagating high-temperature synthesis for the products fabrication by powder metallurgy methods.

Abstract: Magnesium powder in micron scale and various volume fractions of SiC particles with an average diameter of 50 nm were co-milled by a high energy planetary ball mill for up to 25 h to produce Mg-SiC nanocomposite powders. The milled Mg-SiC nanocomposite powders were characterized by scanning electron microscopy (SEM) and laser particle size analysis (PSA) to study morphological evolutions. Furthermore, XRD, TEM, EDAX and SEM analyses were performed to investigate the microstructure of the magnesium matrix and distribution of SiC-reinforcement. It was shown that with addition of and increase in SiC nanoparticle content, finer particles with narrower size distribution are obtained after mechanical milling. The morphology of these particles also became more equiaxed at shorter milling times. The microstructural observation revealed that the milling process ensured uniform distribution of SiC nanoparticles in the magnesium matrix even with a high volume fraction, up to 10 vol%.

Abstract: The increasing demand for lightweight materials capable to absorb impact energy has driven the growth of scientific research in the metallic foams field. This paper aims to investigate the possibility to obtain Al foams from recycled aluminium alloy through the sintering dissolution process (SDP) with sodium chloride (NaCl) as space holder. Aluminium scraps from AA 3104 alloy were powdered by high energy ball milling. Alloy powder was mixed with variable weight fraction of NaCl. The mixtures were die-pressed at room temperature and then sintered at 680°C. In the following step sintered parts were immersed in boiling water to obtain the aluminium foam. Foam microstructure was characterized by scanning electron microscopy and chemical composition was analyzed by energy dispersive spectroscopy. In addition, the residual NaCl was quantified and the foam density was determined by hydrostatic method. Best result was obtained with 60 wt% of NaCl, given a relative foam density of 30%, which in turn justifies further studies with metallic foams from aluminium scraps.

Abstract: Combustion synthesis (CS) of β-SiAlON was conducted using a 3D ball mill, with a focus on the effect of the 2D/3D ball mill premixing conditions on the CS raw material particle size as well as on the yield and grain shape of the final products. The results showed that the particle size distribution of the raw materials was significantly affected by the premixing conditions. Various particle sizes and particle size distributions could easily be obtained by using a 3D mill instead of a 2D mill due to the complex biaxial rotation movement of 3D milling. The particle size was more sensitive to the rotation ratio (vertical spin/horizontal spin, V_v/V_h) than the rotation rate when using 3D milling. Finally, β-SiAlON with less than 5 mass% unreacted Si was obtained using premix milling conditions of 135×200 [vertical spin (rpm) × horizontal spin (rpm)]. The grain shapes of the final products were clearly influenced by the particle size distribution of the raw mixtures.

Abstract: Free Ti/Si/C powder mixtures with or without molten salt were heated under vacuum with various schedules. The effect of molten salt during synthesis on the morphology and phase composition of Ti₃SiC₂ powders were investigated. The combustion powders were analyzed by DSC, XRD, SEM and EDS. The results indicated that the existence of molten salt could promote the reaction process and decrease the synthesis temperature. The Ti₃SiC₂ powders obtained by molten salt method were uniform and well dispersive. The content of Ti₃SiC₂ phase was influenced by salt/powders ratio and molding pressure. The appropriate salt/powders ratio and pre-press pressure were 1:1and 100 MPa, respectively.

Abstract: The paper describes the study of mechanical activation of multi-component ceramic powder materials based on boron nitride. The mechanical activation of the powders was carried out according to the best optimal parameters in a ball mill AGO-2U. Increasing the time of mechanical activation leads to more fine-grained powders. We described the technique of mechanical activation of ceramic powder materials. We introduced the results of X-ray diffraction analysis of the ceramic powder cBN, cBN-Co, hBN-Co before and after mechanical activation. We generated mathematical equations of dependence of an average powder particle size on the average mechanical activation time. We described how the crystal lattice "a" parameters and unit cell volume "V" of cBN and hBN powders depend on mechanical activation time. We studied the chemical composition of powder materials. We also studied the structural parameters of ceramic powders.