Papers by Keyword: Silicon

Abstract: Optimizing the performance and reliability of welding techniques for dissimilar aluminum (Al) to titanium (Ti) is a promising way to establish new applications in aerospace industry. Due to structural weight reduction, lightweight materials can help to minimize fuel consumption and save emissions. Solid-state welding technologies allow short joining cycles and metallurgical changes, residual stresses and severe intermetallic compound formation can be reduced by limited thermal exposure. Besides temperature and plastic deformation, intimate contact plays an important role for diffusion. In this work, AlMgSi alloys with systematic variations of Mg and Si alloying elements, were welded to Ti6Al4V (Ti64) by refill Friction Stir Spot Welding. The focus lays on the effect of Ti64 sheet surface roughness, varied by different surface preparations. Additionally, the influence of the plunge depth, the distance between the tool and the Ti64 sheet surface is analyzed. It was found that a reduced tool to interface spacing has a beneficial influence on joint integrity. Grinding trenches allowed better bonding compared to the pit-like surface structure generated by sandblasting, which led to an increase in mechanical lap-shear properties. Knurling the grinded surfaces resulted in high standard deviation, as most likely not the whole interface area was bonded. However, the partially outstanding properties showed that a beneficial effect can be expected due to mechanical interlocking mechanisms, when sufficient diffusion is ensured.

Abstract: Preliminary mechanical loading at a temperature close to the ductile-brittle transition temperature leads to stress relaxation near cracks in brittle materials due to local plastic deformation at microcrack tips. As a result, such preloading increases the physical and mechanical properties of ceramic materials when tested at room temperature. In the present work, this phenomenon is investigated for silicon and silicon-based ceramics. A thermomechanical treatment (TMT) method of the mentioned materials has been developed to increase their strength and fracture toughness.

Abstract: Optimizing the mechanical properties of aluminum to titanium welds is crucial to establish applications for dissimilar lightweight structures in the aerospace industry. In this context, solid-state welding technologies have proven effective in terms of short joining cycles, allowing the combination of cost-effective production and structural weight optimization. However, metallurgical effects between aluminum and titanium in the joint interface are still not completely understood due to differences in physical as well as chemical characteristics. In this study, aluminum alloy 6013 was welded to Ti6Al4V by refill Friction Stir Spot Wel ding, including systematic variations of Mg and Si alloying element content in the used AA6013 sheets. In total five different Al alloys were welded to the titanium to investigate the influence of Mg and Si during processing. Apart from the material selection, the weld strength is mainly influenced by the intermetallic compound thickness at the interface, which in turn primarily depends on the exposed temperature cycle. Consequently, major interest during this study was given on the temperature evolution, interfacial features and the global mechanical properties.

Abstract: The impact of Si on Zn-induced liquid metal embrittlement (LME) in 3^rd generation advanced high strength steels (AHSS) during resistance spot welding has been widely studied, but the effect of Al is rather unknown. This study investigates the substitution of Al for Si by analyzing two steels with the fixed C and Mn-contents of 0.2 and 3 wt.-% respectively. Si and Al-contents are both set to 1.4 wt.-%. To minimize microstructural effects, all steels were quenched and tempered before electro-galvanizing. The effects of Si and Al were examined using hot tensile testing (600 – 900 °C, in 50 K steps) on a Gleeble 3800, resistance spot welding with prolonged welding times, thermodynamic calculations with Thermo-calc® and dilatometry. Results indicate that the use of either Si or Al increases the LME-susceptibility but substituting Al for Si significantly reduces Zn-induced LME-cracking. In hot tensile testing, higher testing temperatures generally increase the steel’s vulnerability to LME. But comparing both alloying elements to one another, Si causes a higher LME-susceptibility.

Abstract: Paper investigates the possibility of producing silicon from silica contained in Shoda-Kedela (Oni-Gebi district, Georgia) quartz deposition. Characterization of silica from Shoda-Kedela quartz rock is carried by its crushing, grinding, thermal analysis, studying composition and density. Metallurgical grade silicon (MG-Si) is obtained by reducing Shoda-Kedela quartz in its reaction with coke in an electric arc furnace at temperature of ~1800°C. The obtained in this way material reveals that Shoda-Kedela silica containing of 99.58% SiO₂ would be useful for developing the silicon high-technology production.

Abstract: To understand the kinetics of changes in the majority current carriers Hall mobility temperature-dependency (in the temperature range of 77–300 K) in n- and p-type silicon crystals irradiated with high doses of high-energy particles during isochronous annealing, there are investigated P-doped n-Si samples irradiated with 25 MeV protons with dose of 8.1·10¹² cm^–2 at flux density of 1.5∙10¹¹ cm^–2·s^–1 and B-doped p-Si samples irradiated with 8 MeV electrons with dose of 1.0·10¹⁵ cm^–2 at flux density of 5.0·10¹² cm^–2·s^–1 at room temperature. Their isochronous annealing is performed in the temperature range of 80–500°C. The oscillatory character of the change in the majority current carriers Hall mobility in process of isochronous annealing of irradiated silicon samples is explained by the formation of disordered regions and the changes in degree of screening of their electric field potential barriers depending on charge states of nonequilibrium vacancies induced by irradiation.

Abstract: Unidirectional composite structures are increasingly utilized in structural design due to their excellent compressive strength. The present study provides an evaluation of the fatigue performance of materials commonly used in hip prostheses such as Ti-6Al-4V, Co-Cr alloys, UHMWPE, and a silicon matrix composite reinforced with unidirectional carbon fibers in three different fiber volume fractions. Using Bergmann's loading factors, stress calculations were conducted for an 80 kg individual. The Goodman criterion and S-N curves were applied to assess fatigue life. Results show the unidirectional composite with 70% fiber volume fraction has the highest fatigue resistance, making it most suitable for high-stress applications. In contrast, Ti-6Al-4V and Co-Cr alloys showed moderate performance, while UHMWPE was found to be suitable for low-stress applications. These results underscore the necessity of selecting the ideal composition to maximize durability and fatigue resistance in essential mechanical applications. This finding suggests a promising alternative for improving the design and performance of femoral neck implants. This suggests a promising alternative for improving the design and performance of femoral neck implants.

Abstract: The centers of bismuth (Bi) in silicon are being scrutinized as the defect qubits for mostly developed integrated electronics including its photonic component and we have applied the positron annihilation lifetime spectroscopy (PALS) to gain deeper insight into symmetry of the Bi impurity center whose configuration was modified by 15 MeV proton irradiation. It was revealed that hyperfine (hf) and super-hyperfine (shf) interactions of the nuclear and electron spin systems of the bismuth impurity center, ²⁰⁹Bi (J = 9/2), with the regular ²⁹Si (J = 1/2) atoms of silicon delay the essentially local event of emitting of a couple of annihilation gamma–quanta from within the crystal cell which comprises Bi impurity atom (J is the nuclear spin). This phenomenon is observed under increasing occupancy of Bi donor ground and excited states, in contrast to a profoundly enriched ²⁸Si (J = 0) material (so-called “semiconductor vacuum”) where content of ²⁹Si (J = 1/2) isotope was suppressed up to the value of ≈ 50 ppm. The many-body exciton-like states comprising a polyelectronic exciton {e⁻e⁺e⁻h} at Bi donor center are suggested for interpreting the data. The proton irradiation leads to acquiring by Bi impurity atom of an open volume ( V_op ) which is splitted in [V_op – Bi] complex. This defect possessing of D_3d symmetry dominates in the irradiated material. Being thermally stable up to ≈ 370 °C, [V_op – Bi] complex is annealed at ~ 470 – 500 °C. These data agree well with the results of ab intio cluster calculations performed on the basis of LDA-KKR formalism for exploring both the energy gain and symmetry of Bi–vacancy complex.

Abstract: Initially, this work briefly outlines how ultrasound can modify and characterize the defect system in semiconductors. Then, the study experimentally examines the effect of different types of acoustic waves on the association of FeB pairs in monocrystalline silicon. The results reveal that as the frequency of longitudinal waves increases, the ultrasound's effectiveness in accelerating the association rate decreases. Conversely, exciting transverse waves show the opposite trend. The study also assesses the potential to obtain a positron-annihilation response from the FeB complex in silicon, highlighting the advantages of conducting such measurements under ultrasound loading of the crystal.

Abstract: LiFe(P,Si)O₄ is a material that belong to parent compound of LiFePO₄ widely known as cathode material for lithium-ion battery (LIB). Previous study reports that electrochemical performance of LiFePO₄ can be improved by silicon (Si) substitution to the phosphorus (P) site. The sample was obtained via a solid-state synthesis route with the amount of Si doping to the P site is ∼3%. The electrochemical performance of silicon substituted LiFePO₄ has been widely studied in other report whilst the magnetic properties is still less explored. Here we investigate the magnetic properties of LiFe(P,Si)O₄ using superconducting quantum interference device (SQUID) and muon spin relaxation (µSR). The two measurements display a good agreement result showing two anomalies at the temperature of ∼27 K and ∼52 K that represent the Neel Temperature (Τ_N) of Li₂FeSiO₄ and LiFePO₄, respectively. The presence of Li₂FeSiO₄ that is also a candidate of cathode of LIB has been confirmed by X-ray Diffraction (XRD). Based on the current study, there is no alteration of Τ_N on LiFePO₄ phase due to Si doping.