Papers by Keyword: Amorphous Structure

Abstract: Experimental studies of bending deformation of carbon - and fiberglass samples after 8-month exposure in full-scale conditions were performed and the modulus of transverse elasticity was determined. It was found that the influence of the external environment on fiberglass samples is more significant. For carbon fiber, there was an average decrease of 7.1%, and for fiberglass-by 14%. Modification of samples in ultrahigh frequencies (UHF) electromagnetic field reduces the negative influence of the environment: the values of the transverse elastic modulus of carbon fiber and fiberglass samples are reduced by 5% and 11%, respectively. It is shown that the UHF electromagnetic field in rational modes can increase the modulus of transverse elasticity of carbon fiber by (27-30)%, fiberglass – by (20.8-25.6)% with a significant increase in the uniformity of this parameter. Experimental studies of the bending deformation of carbon-and fiberglass specimens after 8-month exposure in natural conditions have been carried out, and the shear elastic modulus has been determined. It has been established that the influence of the external environment on fiberglass samples is more significant. For carbon fiber reinforced plastic, a decrease was noted on average by 7.1%, for fiberglass - by 14%. Modification of samples in a microwave electromagnetic field helps to reduce the negative influence of the external environment: the values ​​of the shear modulus of the prototypes of carbon fiber reinforced plastic and fiberglass are reduced by 5% and 11%, respectively. It is shown that the microwave electromagnetic field in rational modes allows increasing the transverse elastic modulus of carbon fiber reinforced plastic by (27-30)%, fiberglass - by (20.8-25.6)% with a significant increase in the uniformity of this parameter.

Abstract: An algorithm for generating the representative structures of covalent triazine-based frameworks (CTFs) is proposed, and examined by being applied to the framework synthesized by the trimerization of dicyanobenzene. The algorithm is validated by the comparison between the calculated and experimental results of the structural properties such as surface areas and pore size distributions, which shows acceptable consistency. Moreover, the presented modeling approach can be expected for more extensive use for other CTFs. Thus the simulated atomistic strucutures produced from the modeling method can improve the understanding for amorphous structures of the CTFs which have already been developed, as well as predict the theoretical model of new CTFs, and provide useful design strategies for the future experimental efforts.

Abstract: The alloys Al₈₈Co₄Y₈, Al₈₈Ni₄Y₈, Al₈₇Ni₁₀Ce₃ and Al₈₅Ni₁₀Ce₅ were heated and mixed by using intermediate frequency furnace. By controlling different melt superheat tempratures, a series of thin strip alloy samples were prepared by single roller spinning quenching method. The X-ray diffraction (XRD) results show that melt temperatures have different effects on the amorphous structure formation of Al-(Co,Ni)-(Y,Ce) alloy. In addition The glass forming ability of Al-based amorphous alloy prepared by thermal analysis was analyzed. Experiments results indicate that the higher the melt temperature of Al₈₈Co₄Y₈ alloy, the easier the formation of the crystallization phase.

Abstract: TiCN thin coatings with various different carbon contents were deposited using cathode arc evaporation of pure titanium in a mixture of N₂ and C₂H₂ gasses at a constant pressure of 1.5 Pa. The analyses show a transition from a stoichiometric to a non-stoichiometric coating structure with an increasing C₂H₂ content. Moreover, the increase in the acetylene in the gas mixture leads to a decrease in the crystal phase from pure polycrystalline to pure amorphous. Nanohardness changes from 30.4 to 4.4 GPa and the cohesive failure of the coatings is in the range of 61 - 72 N. The tribology is estimated by the Ball-on-Disc method and an Si₃N₄ ball as the counterpart. The measured coefficient of friction is in the range of 0.2 - 0.56.

Abstract: The effect of Ni or Zr addition to Ti-Cu alloy was studied on the microstructure evolution during mechanical milling regarding to dependence of the amorphous transformation on the various composition elements. The microstructure of initial crystalline alloys and the remained phases after few hours of milling were investigated. The milling process lasted to the full amorphization of the powders. The results show that amorphous Ti₄₈Cu₄₂Ni₁₀ and Ti₄₈Cu₄₂Zr₁₀ powders are obtained after 13 h and 14 h of milling.

Abstract: The Al-based amorphous ribbons were prepared by the copper roller melt spinning method, and then the laser brazing was carried out between aluminum alloy and aluminum alloy. Subsequently, the Micro Vickers Hardness Tester, Metallographic Microscope, Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) were used to characterize the hardness, morphology, micro structure and composition distribution of the welded joints respectively, so as to analyze the structural characteristic, performance characteristic and binding effect of the matrix metal joints. The results indicate that the prepared Al-based amorphous ribbon is of amorphous structure, the soldering point between aluminum alloy and aluminum alloy is well-connected and the joint’s hardness is identical to that of the base metal. The connection between the metal sheets can be achieved by using Al-based amorphous ribbon as solder, which could provide concrete references for the development and application of amorphous brazing in various fields.

Abstract: In situ TiC_p/Al-4.5wt.%Cu composites have been coated using an electro-less Ni-P plating technique. The morphology and composition of the plating coating have been examined by scanning electron microscopy, optical microscopy, and X-ray diffraction. The results indicated that the coating had a high-phosphorus amorphous microstructure. The coatings microstructures showed significantly changes when the citric acid concentration in the chemical bath was varied in the range 16-20g/L.

Abstract: Different cooling process, annealing temperature and addition of B₂O₃ were experimented on the CaO-MgO-SiO₂-Al₂O₃-Cr₂O₃-Fe₂O₃ slag system with an aim to investigate the chromium precipitation behaviour. The solidified slags were characterized by XRD, SEM, EDX and EPMA. It was shown that, under melt-quenching process, chromium was immobilized in amorphous structure in the slag with basicity lower than 1.0 and Cr₂O₃ content less than 4.0 wt%. It was also found that addition of B₂O₃ and higher annealing temperature would be helpful for the precipitation of chromium into spinel solid solution in slag with basicity of 1.5.

Abstract: This article reviews the synthesis of Si-B-C-N ceramics, and the characteristics and principle of fabricating Si-B-C-N ceramics by using different precursors. So far, there only have two reports on preparation of Si-B-C-N ceramics, which are precursor pyrolysis and mechanical alloying. Therefore, this paper mainly discusses precursor pyrolysis and mechanical alloying. In addition, this paper proposed some prospects on the development and applications of Si-B-C-N ceramics in material science.

Abstract: Transmission electron microscopy and X-ray diffraction were used to study structural changes in the Ti-50.5 at. % Ni alloy upon severe plastic deformation by shear under pressure and subsequent heating. An increase in the degree of deformation leads sequentially to a martensite transformation, twinning of martensite crystals, formation of reorientation bands, development of rotational modes of deformation, formation of a nanocrystalline structure, and finally amorphization. A scheme of the formation of amorphous structure of the alloy during deformation is suggested based on the observed structural changes. It has been found that a reverse martensitic transformation might be one of mechanisms of plastic deformation of the alloy. Therefore, as the degree of deformation increases, first forward and subsequently reverse martensitic transformations can occur. The formation of an amorphous structure starts as the degree of deformation reaches 4.2 (one revolution of Bridgman anvils); at a degree of deformation of 6.8 (5 revolutions of the anvils), the process is virtually completed. The crystallization of the amorphous alloy upon heating starts even at 200°C. However, upon heating up to 300°C (for 0.5-h holdings), the kinetics of crystallization is slow. After annealing at 350°C, the complete crystallization with the formation of a nanocrystalline structure with a grain size of 20-70 nm takes place