双金属涂层SiC纤维强化Ti-15-3基复合材料的疲劳特性

不久的未来,用SiC(SCS-6)纤维强化的钛合金基复材料可以成为航空航天结构材料,复合材料通常处于周期负荷状态,因此这些材料必须通常处于周期负荷状态,因此这些材料必须具有良好的抗疲劳性能。

Effect of solid carburization on surface microstructure and hardness of Ti-6Al-4V alloy and(TiB+La_2O_3)/Ti-6Al-4V composite

Solid carburization was employed to improve the hardness of Ti-6Al-4V alloy and （TiB＋La2O3）/Ti composite. The samples wrapped in graphite powder were placed in sealed quartz tubes, followed by solid carburization at 1227 K for 24 h. Microstructure and phase analysis indicated that TiC reinforcements and Ti-C solid solutions were introduced after solid carburization. Moreover, the volume fraction of equiaxedα-Ti phase in diffusion layer decreased obviously with increasing sample depth. Hardness testing results indicated that both the carburized surfaces performed significant improvement of about 100% in micro-hardness compared with untreated materials. The variation of carbon contents with increasing sample depth resulted in a hardened layer of 300 μm in the carburized samples. Meanwhile, slight influence on the internal microstructure and hardness indicated that solid carburization was an effective method in strengthening the surface of titanium alloy and titanium matrix composite.

Microstructure and interface thermal stability of C/Mo double-coated SiC fiber reinforced γ-TiAl matrix composites

C/Mo duplex coating interfacially modified SiC fiber-reinforced γ-TiAl matrix composite （SiCf/C/Mo/γ-TiA1） was prepared by foil-fiber-foil method to investigate its interfacial modification effect. SiCf/C/TiAl composites were also prepared under the same processing condition for comparision. Both kinds of the composites were thermally exposed in vacuum at 800 and 900℃ for different durations in order to study thermal stability of the interfacial zone. With the aids of scanning electron microscope （SEM） and energy dispersive spectrometer （EDS）, the interracial microstructures of the composites were investigated. The results reveal that, although adding the Mo coating, the interfacial reaction product of the SiCf/C/Mo/TiAl composite is the same with that of the SiCf/C/TiA1 composite, which is TiC/Ti2AlC between the coating and the matrix. However, C/Mo duplex coating is more efficient in hindering interfacial reaction than C single coating at 900 ℃ and below. In addition, a new layer of interfacial reaction product was found between Ti2AlC and the matrix after 900 ℃, 200 h thermal exposure, which is rich in V and close to the chemical composition of B2 phase.

Damping capacity of BaTiO_3/Al composites fabricated by hot extrusion

To develop new type of high damping metal matrix composites, large grain size barium titanate （BaTiO3） ceramic was sintered and added into Al powder to fabricate BaTiO3/Al composites through the powder metallurgy method and hot extrusion. The damping properties of BaTiO3 ceramic, Al matrix and BaTiO3/Al composites were examined by dynamic mechanical analysis in the temperature range from 273 K to 573 K. The results show that although BaTiO3 exhibits high damping （tan δ=0.12） below 400 K, the damping capacity of 10%BaTiO3/Al （mass fraction） composites below 400 K is not increased as compared to the Al matrix. On the other hand, the damping capacity above 450 K is greatly enhanced due to the motion of dislocations at the interfaces between ceramic particles and Al matrix. The failure of exerting the intrinsic damping of BaTiO3 particles in the composites is attributed to the poor interface bonding between the particles and the matrix. The tensile strength of the composite is 42% higher than that of the Al matrix, which indicates the possibility of obtaining high strength and high damping composites via interface improvement and the addition of high volume fraction of large grain BaTiO3 particles.

Influence of rutile(TiO_2) content on wear and microhardness characteristics of aluminium-based hybrid composites synthesized by powder metallurgy

The effect of rutile（TiO_2） content on the wear and microhardness properties of aluminium（Al）-based hybrid composites was explored. The proposed content of TiO_2（0, 4%, 8%, 12%, mass fraction） was blended to Al-15% SiC composites through powder metallurgy（P/M） process. Wear test was conducted using pin-on-disc apparatus under dry sliding conditions. Fabricated preforms were characterized using X-ray diffractometer（XRD）, scanning electron microscope（SEM） and energy-dispersive X-ray spectrometer（EDS）. Optical micrographs of the composite preforms display uniform distribution of TiO_2 throughout the matrix. Quantitative results indicate that wear resistance and microhardness increase with the increase of TiO_2 content. SEM images unveil that high wear resistance is attributed to high dislocation density of deformed planes and high hardness of TiO_2. SEM images of wear debris display gradual reduction in mean size of debris when TiO_2 content increases. EDS spectra confirm the presence of oxide layer which obviously reduces the effective area of contact between the sliding surfaces thereby lowers the wear loss of composites. The observation concludes that delamination and adhesive wear are the predominant mechanisms.