Free vibration of functionally graded material beams with surface-bonded piezoelectric layers in thermal environment

Free vibration of statically thermal postbuckled functionally graded material （FGM） beams with surface-bonded piezoelectric layers subject to both temperature rise and voltage is studied. By accurately considering the axial extension and based on the Euler-Bernoulli beam theory, geometrically nonlinear dynamic governing equations for FGM beams with surface-bonded piezoelectric layers subject to thermo-electro- mechanical loadings are formulated. It is assumed that the material properties of the middle FGM layer vary continuously as a power law function of the thickness coordinate, and the piezoelectric layers are isotropic and homogenous. By assuming that the amplitude of the beam vibration is small and its response is harmonic, the above mentioned non-linear partial differential equations are reduced to two sets of coupled ordinary differential equations. One is for the postbuckling, and the other is for the linear vibration of the beam superimposed upon the postbuckled configuration. Using a shooting method to solve the two sets of ordinary differential equations with fixed-fixed boundary conditions numerically, the response of postbuckling and free vibration in the vicinity of the postbuckled configuration of the beam with fixed-fixed ends and subject to transversely nonuniform heating and uniform electric field is obtained. Thermo-electric postbuckling equilibrium paths and characteristic curves of the first three natural frequencies versus the temperature, the electricity, and the material gradient parameters are plotted. It is found that the three lowest frequencies of the prebuckled beam decrease with the increase of the temperature, but those of a buckled beam increase monotonically with the temperature rise. The results also show that the tensional force produced in the piezoelectric layers by the voltage can efficiently increase the critical buckling temperature and the natural frequency.

Y2O3-CeO2-ZrO2 Powder Prepared by Co-Precipitation and As-Plasma-Sprayed Coating

The characteristic of the bond zone between Ni-based alloy light beam surfacing layer (SL) and base metal (BM) was investigated by scanning electron microscope, energy dispersive spectrometer and X-ray diffraction. The results show that the bond zone, which consists of γ-Ni or γ-(Fe, Ni) planar crystal band close to SL and α-Fe bright band close to heat affected zone (HAZ), is actually the transition zone of composition and microstructure between SL and HAZ, and the metallurgical bond interface lies between the α-Fe bright band and HAZ. With the increase of light beam heat input from 2 kJ/mm to 4 kJ/mm, the width of the bond zone increases from 4 μm to 15 μm, and the morphology of bond interface changes from zigzag to straight. The formation of bond interface indicates the formation of reliable metallurgical bond between SL and BM.

Characteristic of Bond Zone between Powder Surfacing Layer and Base Metal

The characteristic of the bond zone between Ni-based alloy light beam surfacing layer(SL)and base metal(BM)was investigated by scanning electron microscope,energy dispersive spectrometer and X-ray diffraction.The results show that the bond zone,which consists ofγ-Ni orγ-(Fe,Ni)planar crystal band close to SL andα-Fe bright band close to heat affected zone(HAZ),is actually the transition zone of composition and microstructure between SL and HAZ,and the metallurgical bond interface lies between theα-Fe bright band and HAZ.With the increase of light beam heat input from 2kJ/mm to 4kJ/mm,the width of the bond zone increases from 4μm to 15μm,and the morphology of bond interface changes from zigzag to straight.The formation of bond interface indicates the formation of reliable metallurgical bond between SL and BM.

Surface alloying of Al films/Ti substrate based on high-current pulsed electron beams irradiation

Ti–Al surface alloy was fabricated using a cyclic pulsed liquid-phase mixing of predeposited 100 nm Al film with a-Ti substrate by low-energy high-current electron beam. Electron probe micro-analysis（EPMA）,grazing incidence X-ray diffraction analysis（GIXRD）,transmission electron microscopy（TEM）, and nanoindentation were used to investigate the characterization of Ti–Al surface alloy. The experimental results show that the thickness of alloy layer is ＊3 lm, and the content of Al in the ＊1 lm thickness surface layer is ＊60 at%. The tetragonal TiAl and TiAl2intermetallics were synthesized at the top surface, which have nanocrystalline structure.The main phase formed in the ＊2.5 lm thick surface is TiAl, and there are few TiAl2and Ti3Al phase for the alloy.Dislocation is enhanced in the alloyed layer. The nanohardness of Ti–Al surface alloy increased significantly compared with a-Ti substrate due to the nanostructure and enhanced dislocation. Since the e-beam remelted repeatedly, the Ti–Al surface alloy mixed sufficiently with Ti substrate. Moreover, there is no obvious boundary between the alloyed layer and substrate.