Advanced Materials Research Vols. 47-50

Abstract: In this work, we derive a general piezoelectric interface model by using a coordinate-free asymptotic approach. Next, this interface model is applied to the homogenization of fibrous piezoelectric composites. The overall piezoelectric properties are calculated and compared to the ones obtained by using the three-phase model.

Abstract: Sputter-deposited FePt films exhibit an in-plane magnetic anisotropy when they use MgO as capped layer. The perpendicular magnetic anisotropy of FePt films are enhanced by introducing Ag capped layer instead of MgO capped layer. Although the in-plane coercivity (Hc⊥ ) of FePt films decreases slightly after introducing an Ag capper layer instead of a MgO capped layer, the perpendicular coercivity (Hc⊥ ) is increased significantly from 3169 Oe to 6726 Oe. The Auger electron spectroscopy analysis confirms that the Ag atoms diffuse from capped layer into the FePt magnetic layer and the Ag atoms mainly distribute at the grain boundary of FePt. This phenomenon results in the grain boundary energy enhancement and the grain growth inhibition and therefore increases the perpendicular coercivity and decrease the grain size of the FePt film.

Abstract: Co3Pt films were deposited on Pt underlayers with various thicknesses by conventional sputtering in order to investigate the effect of Pt underlayers and annealing temperatures on their microstructure and the magnetic properties. From XRD and HRTEM analysises, as annealing at 300°C, a well epitaxial growth of Co3Pt (002) on Pt (111) underlayer that leads the film to present perpendicular magnetic anisotropy. However, Pt atoms in the Pt underlayer will diffuse seriously into Co3Pt layer as the annealing temperature is increased to 375°C that changes the compositions to approach equiatomic CoPt, and showing in-plane magnetic anisotropy with soft magnetic properties.

Abstract: Intensity of the (200) peak in the X-ray diffraction pattern of the MgO film increases as N2 is added to Ar gas during MgO deposition. The optimum flow rate ratio of N2 to Ar in order to obtain maximum intensity of the MgO (200) peak is 2 : 5. As introducing N2 gas, no residual nitrogen atoms are found in the MgO films, which are confirmed by AES and ESCA analysis. On the other hand, the TEM dark field image shows that the average grain size of MgO film increases with increasing the flow rate ratio of N2 to Ar. This is due to that the deposition rate of MgO film is decreased with increasing the flow rate ratio of N2 to Ar.

Abstract: To deal with the stringent operational demands the aerospace structural materials of light weight Aluminum alloy 2024 sheets and plies of carbon fibers reinforced thermoplastic matrix PEEK were used to sustain at least 80% of their mechanical properties at elevated temperature. The addition of nanoparticles SiO2 can enhance the composite laminate strength and stiffness. Also, Al 2024 sheets were treated by an anodic method of electroplating to increase surface roughness to achieve perfectly bonding with matrix PEEK. Then, the modified diaphragm curing process was adopted to make the innovative hybrid Al/APC-2 hybrid nanocomposite laminates. Next, both static tensile and fatigue tests were conducted at elevated temperature to obtain the mechanical properties, lives and failure mechanisms to verify the improved features of hybrid specimens. From tensile tests the mechanical properties of Al/APC-2 [4Al/0/±45/90/2Al]s hybrid laminates at elevated temperature were obtained. Although there is a big drop at 150°C, the reduction in strength from RT to 125°C is generally not significant. The longitudinal stiffness is almost unchanged at elevated temperature. After cyclic tension-tension (T-T) tests, the positions of received S-N curves go downwards as temperature rising. No delaminations were found in both tests. If the applied stress normalized by the ultimate strength at corresponding temperature, the normalized S-N curves are closer with some curve positions reversed. Significant improvement of manufacturing and enhancement of mechanical properties in hybrid laminates were achieved finally.

Abstract: Vacuum brazing of Cemented Tungsten Carbide (WC-Co) and JIS SCM440 steel using Cu-Sn braze alloy has been studied. The effect of Sn content in the filler metals on the properties of brazed joints was investigated. The specimens were brazed under 1050°C to 1110°C for 5 to 15 minutes. The experimental results show that the maximum shear strength is 341±15MPa for the joints brazed at 1080°C for 10 min by using Cu-9Sn filler. Shear strength of the joints brazed at 1050°C and 1080°C increased as Sn content added to the braze alloy. However, joints brazed at 1110°C showed a decline in shear strength as the increase of Sn content. From SEM micrographs, a Fe-Co-Cu alloy layer was formed at WC-Co/Cu-Sn interface and the property of the layer was affected by brazing temperature and Sn content.

Abstract: A series of Zn0.95-xCo0.05AlxO (x=0, 0.01, 0.02, 0.05, 0.08, 0.10) powders with different percentages of aluminum was fabricated using the sol-gel method. X-ray diffraction (XRD) revealed that the Co ions and Al ions substitute for Zn2+ ions without changing the wurtzite structure. No impurity phases were found. No clusters or precipitates of cobalt or aluminum were found using scanning electron microscope analysis. Fourier transform-infrared reflection (FT-IR) spectrometry was used to examine the infrared transmission properties and revealed that Co ions were incorporated into the lattice as Co2+ substituting for Zn2+. Ferromagnetic behavior in the samples was obtained at room temperature. As the Al content x increased, the room temperature ferromagnetism of the samples was reduced, and when x increased to 0.08, the room temperature ferromagnetism disappeared.

Abstract: Resorbable metallic implant of magnesium and its alloys had been studied since the 1900s. However, the excessive gas production resulted in its unpopularity after CoCr alloys and stainless steel were developed. With the advancement of alloying technologies, its use as a resorbable implant has re-emerged recently. Foreign researchers focused on the use of AZ-series and magnesium-rare earth metal alloys. However, the corrosion property of AZ-series alloys is unsatisfactory, and the effect of rare-earth metals on human is poorly studied. Therefore, we have investigated on the feasibility of using commercially available AM-series magnesium alloys. Previous researchers avoided this alloy series presumably because of the potential health effect of manganese, however our toxicological risk assessment revealed that the exposure level would be lower than the NOAEL (No Observable Adverse Effect Level), thus it is unlikely to cause any observable health effect on healthy individuals. Subcutaneous implantation of AM-series magnesium alloys into a mouse model for six months confirmed that, while all alloys tested showed slow corrosion and no observable in vivo toxicity, pitting corrosion did not occur for AM-series alloys but was frequent for AZ91D. This suggests that AM-series magnesium alloys are good candidates of resorbable metallic implants.

Abstract: In this paper the response of circular cylindrical shell made of Functionally Graded Material (FGM) subjected to lateral impulse load was investigated. The effective material properties are assumed to vary continuously along the thickness direction according to a volume fraction power law distribution. First order shear deformation theory (FSDT) and Love's first approximation theory were utilized in the equilibrium equations. The boundary condition was considered to be simply supported. Displacement components are product of functions of position and time. Equilibrium equations for free and forced vibrations were solved using the Galerkin method. The impulse load in the form of time varying uniform pressure was applied onto a small rectangular area of the shell surface. The function of time for displacement components is obtained using the results of free vibration and convolution integral. Finally time response of displacement components is derived using mode superposition method. The influence of material composition (power law exponent), geometrical parameters (length to radius and radius to thickness ratios) and load parameters (position and size of the area of the applied load and peak pressure value for different pulse type) on the dynamic response was investigated.

Abstract: In this paper, the impact behavior of repaired cracked plates was investigated experimentally. single edge cracked aluminum plate having crack length to width ratios of 0.1, 0.3 and 0.5 was repaired with four different patch configurations namely: 3 layer GRP, 5 layer GRP patch, 2/1 FML patch and 3/2 FML patches tested in Charpy impact and the energy absorbed by specimens were compared together and compared with the unrepaired cracked plate. FML patches were made of thin layers of glass/epoxy composites of 0.2 mm thickness with phosphor bronze sheets of 0.2 mm thickness. The patching was single side. The composite and FML patching was more effective in repairing the specimens with greater crack length. Placing 3 GRP and 5 GRP patches increased the absorbed energy by only 3 to 4 joules respectively as compared to unrepaired plate. The use of 2/1 and 3/2 FML patches could increase the absorbed energy two to four times depend on crack length.