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To analyze the failure mechanism and energy-absorbing characteristics of composite thin-walled C-channels subject to the low-speed axial compression, 12 groups of T700/MTM28 specimens with three di...

CF/PEEK composites were welded assisted by ultrasonic. The influence of vibration time and using of energy director (ED) to the joints were investigated in details. The joints had defect of incomplete fusion at the interface under short welding time without ED, and defects of cracks and voids appeared at the interface of carbon fiber and PEEK resin, which attributed to too much heat accumulation at the heat affected zone (HAZ). By using flat ED, joint with sound bonding was realized under vibration time of 0.9 s. The lap shear strength of joint can reach 28 MPa, and the joint fractured at the HAZ. The real-time temperature at interfaces were monitored. It is found that the heating rate can be accelerated by using flat ED, and the peak temperature was lowered. At last, the influence mechanism of processing parameter to the joint were discussed in details.

Y2O3 has a great application potential at reaction barrier coating of high-temperature composites due to its high thermodynamic stability and high melting point, and the phase structure stability at high temperature and structure dependent mechanical property are key parameters for this application. Y2O3 thin films were deposited on silicon (100) wafers by DC magnetron sputtering with various oxygen partial pressure and substrate bias, and then vacuum annealing at 1000°C was performed to investigate the phase structure stability. The microstructure, stress and hardness of as-deposited and annealed Y2O3 thin films were explored by X-ray diffraction, transmission electron microscope, and nanoindenter. The result showed that as-60 bias voltage was applied to substrate, cubic-c phase formed regardless of variation of oxygen partial pressure, and the cubic-c phase remains stability and crystallinity became better after annealing at 1000 °C.In addition, the hardness and modulus also just had minor changes as a function of oxygen partial pressure. As oxygen partial pressure was kept at 0.043 Pa, phase transition from cubic-c to monoclinic-b phase took place with increasing substrate bias, accompanying by the increment of hardness and modulus, and 1000 °Chigh-temperature annealing resulted in that as-deposited monoclinic-b phase transforms to cubic-c phase.

Niobium carbide films was deposited by direct current reactive magnetron sputtering on Si (001) substrates in discharging a mixture of CH4/Ar gas. The effects of growth temperature (Ts) and methane flow rate (FCH4) on the phase structure, composition, mechanical and tribological properties for NbCx films were explored. For the film grown at FCH4=6 sccm, a phase transition from cubic-NbC phase to hexagonal-Nb2C phases occurred with increasing the Ts; In contrast, when the film deposited at FCH4=16 sccm, only the cubic-NbC phase was observed at different Ts. The surface of all the films became rough with increasing the Ts. In addition, when the Ts increased from RT to 600 °C, the films exhibited the compressive stress and kept rising. While as the Ts > 600 °C, the stress partially relaxed both at FCH4=6 sccm and FCH4=16 sccm. The hardness (H) for sample grown at FCH4=6 sccm first increased up to a maximum value, and then decreased with increasing the Ts. And the films grown at FCH4=16 sccm kept decreasing with the maximum super-hard value of the filmsof 40.5 GPa at FCH4=6 sccm and 600 °C. The friction coefficient for the film obtained at FCH4=16 sccm was lower than that at FCH4=6 sccm, which might be due to the presence more carbon in the film grown at FCH4=16 sccm.

Tungsten carbide thin films were deposited on silicon (100) substrates by DC reactive magnetron sputtering using CH4 as a carbon source. The microstructure, compressive stress, hardness and tribological behaviors showed great dependences on the rates of CH4 flow (FCH4). Increasing the FCH4 from 2 to 5 sccm, the film exhibited a phase transition from hexagonal-W2C to cubic-WC1-x. Further increasing the FCH4 larger than 10sccm, the film presented amorphous state. As the FCH4 increased, the Raman revealed that the films showed a graphitization trend, meanwhile, the surface of the films became smoother and smoother. The hardness of tungsten carbide films first increased, and then decreased after reaching the maximum 38.5GPa (FCH4=10 sccm). While the sample deposited at 15 sccm obtained the lowest wear rate (2.17×10-6 mm3/Nm) and low coefficient of friction (CoF, 0.24) and still maintained a high hardness of 32.1 GPa. The lowest wear rate could be ascribed to the highest ratio of H3/E2.

The cubic-NbN/NbCN multilayers with modulation periodicity (Λ) ranging from 4.2 to 39.1 nm were deposited on Si (100) substrate by reactive magnetron sputtering in a mixture of Ar and N2 gases. The Λ dependent structural, mechanical and tribological properties for resulting c-NbN/NbCN multilayers were explored. As Λ varied from 4.2 to 39.1 nm, all the films exhibited an obvious modulated structure. Increasing the Λ, the Nb (C,N)(111) peak in XRD gradually shifted to bigger angles and the peak intensity of NbN(111) became stronger. The stress for all multilayers was compressive ranging in between the stress for both NbN and NbCN single layers, and the stress value was stable with increasing Λ. The NbN layer was beneficial to relaxing the compressive stress which induced by NbCN layer. In addition, as Λ increases, the hardness (H) first increased, and then decreased after reaching a maximum value. The obvious enhancement in hardness for multilayers was observed, whose maximum value approaches 43.3 GPa when Λ = 8.4 nm, 37% larger than that obtained by the rule of mixture value. The friction coefficient values of NbN/NbCNmultilayers ranging between 0.34 and 0.4 were much lower than that of NbN monolayer but higher than that of NbCN monolayer were.

TC4 coating was successfully prepared on the surface of carbon fiber reinforced thermoplastics (CFRP) via laser cladding technology. The microstructure of the TC4 coating/CFRP substrate interface was analyzed. The results indicated that the molten TC4 infiltrated into the CFRP substrate and reliable bonding of TC4 coating and CFRP substrate was obtained. TiC and a small amount of TiS2 phases were formed at the interface between TC4 coating and CFRP substrate. In addition, the process for preparing TC4 coating on the surface of CFRP substrate and the bonding mechanism at the interface was put forward based on the basis of experimental observation and theoretical analysis.

In this paper, thick-section TC4 alloy was welded to itself by laser-MIG hybrid (LAMIG) welding. The microstructure of the welded joints was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results revealed that &alpha, &rsquo, and &beta, phases were formed in the weld seam. The effects of heat input (E) on the microstructure and tensile strength of the joints were investigated. With the increase of heat input, the residence time of platelet &alpha, martensite in the high-temperature phase changing zone became longer and the thickness of platelet &alpha, martensite increased. Furthermore, the &beta, thickness became large, and tangling dislocations were found to exist in platelet &alpha, In addition, the increasing heat input could cause a decrease in the tensile strength. The failed dimple pattern experienced a change from equiaxed to tearing, which was harmful to the property of the joint.

Based on previous work on lubricant hard HfCxfilm, the HfCxNyfilmswere deposited by sputtering from theHf target in a mixture of discharging N2,Ar and CH4, and the N content in films was accurately controlled by changing the N2flow rate.Theintroduction of N into the films contributed to the presence of solid solution FCC-HfC(N) and FCC-HfNphase appeared at high N content in films. In addition, the a-C content in the filmsdecreasedwith increment ofN content in the films. In comparison with HfCxfilm, hardness of HfCxNyfilms were enhanced from 21 GPa to 25 GPa with N content rising to 6.8 at.% but then surplus N in the films impaired the hardness. The coefficient of friction and surface roughness for HfCxNyfilms increasedfrom 0.10 to 0.23 and 3.13 nm to 12.4 nm, respectively, with decreasing a-C content from 52.9 at.% to 46.3 at.%. However, the introduction of N into HfCxFilm improvedthe wear resistance of filmseffectively, and the specific friction rate for this HfCxNyfilm deposited at 8 sccm N2was only 6.17×10-7mm3/Nm about half of that of HfCxfilm (1.09×10-6mm3/Nm).

In order to understand well the different ferroelectric behaviour of quantum paraelectrics and ferroelectrics and the origin of the ferroelectricity of the solid solution KTa0.5Nb0.5O3(KTN), we calculated the electronic structure of CaTiO3, BaTiO3 and KTN by first principles calculation. From total energy analysis, it is shown that, with increasing cell volume, the crystals (CaTiO3, SrTiO3) will have a ferroelectric instability. For BaTiO3, the ferroelectricity will disappear as the cell volume is decreased. From the density of states analysis, it is shown that the hybridization between B d and O p is very important for the ferroelectric stability of ABO3 perovskite ferroelectrics. This is consistent with the analysis of band structure.