Fractal analysis of fracture surfaces in aluminum borate whisker-reinforced aluminum alloy 6061 composite

The effect of interface reaction on the fractal dimensions of fracture surface in aluminum borate whisker-reinforced aluminum alloy 6061 composite was investigated. The composite was fabricated by squeeze-casting technique. The fracture surfaces created in tensile test were measured by vertical sectioning method. Fractal phenomena were found in two plots, in which the measuring units were from 3 to 15 μm and 1 to 5 μm, respectively. The relation was established between the tensile properties and fractal dimension with measuring units of 3-15 μm. The results show that the ultimate tensile strength increases while the fracture surface roughness increases with fractal dimension increasing due to the change in fracture mode depending on the degree of interface reaction status induced by heat treatment. But when the measuring units are 1-5 μm, fractal dimension does not change with heat treatment.

Microstructure,mechanical and wear properties of aluminum borate whisker reinforced aluminum matrix composites

The microstructural features and the consequent mechanical properties were characterized in aluminium borate whisker(ABOw)(5, 10 and 15 wt.%) reinforced commercially-pure aluminium composites fabricated by conventional powder metallurgy technique. The aluminium powder and the whisker were effectively blended by a semi-powder metallurgy method. The blended powder mixtures were cold compacted and sintered at 600 ℃. The sintered composites were characterized for microstructural features by optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), transmission electron microscopy(TEM) and X-ray diffraction(XRD) analysis. Porosity in the composites with variation in ABOw contents was determined. The effect of variation in content of ABOw on mechanical properties, viz. hardness, bending strength and compressive strength of the composites was evaluated. The dry sliding wear behaviour was evaluated at varying sliding distance at constant loads. Maximum flexural strength of 172 MPa and compressive strength of 324 MPa with improved hardness around HV 40.2 are obtained in composite with 10 wt.% ABOw. Further increase in ABOw content deteriorates the properties. A substantial increase in wear resistance is also observed with 10 wt.% ABOw. The excellent combination of mechanical properties of Al-10 wt.%ABOw composites is attributed to good interfacial bonds, less porosity and uniformity in the microstructure.

Effect of aluminum borate whisker coating on interface and mechanical properties of 6061Al matrix composites

Copper coating was deposited on the surface of aluminum borate whisker by an electroless plating method.This method was used to modify the interfacial property of squeeze-casting aluminum borate whisker reinforced 6061Al matrix composite.Interface observation indicates that the spinel reaction(MgAl2O4) is hindered by the copper coating,and the difference in interfacial reaction degree affects the tensile property and aging behavior of the composite.For the composite with less spinel reaction(MgAl2O4),its peak-aging process are postponed due to less depletion of magnesium.On the fracture surface of copper-coated composite dimples and fractures of whiskers are more,but on the fracture surface of uncoated composite pull-out of whiskers are more than that on the coated one.In uncoated composite the fracture generally originates from the near-interface-region.

Preparation of Chromium Oxide Coatings on Aluminum Borate Whiskers by a Hydrothermal Deposition Process

Aluminum borate whiskers (9Al 2O 3·2B 2O 3) can be used to reinforce aluminum alloys to produce light and strong composites. However, the adverse interfacial reactions between the whiskers and the aluminum alloys inhibit their practical uses; therefore, a protective coating is needed on whiskers. In this work, aluminum borate whiskers were coated with chromium coating deposits in a hydrothermal solution containing CrCl 3, Na 2C 4H 4O 6, NaPH 2O 2, and H 3BO 3. The presence of the impurity P in the hydrothermal deposits can be avoided by reducing the amount of NaPH 2O 2 in the coating solution. Thermodynamic analysis was used to discuss the behavior of ions in the coating process. The subsequent heating of the hydrothermal products in air at 800 ℃ yielded smooth Cr 2O 3 films with a thickness of 0.060.07 μm.

Raman Spectrum of Rhombohedral Neodymium-Aluminum Borate

The Raman spectrum of rhombohedral NdAl 3 (BO 3) 4 (NAB) is recorded and interpreted. A factor group analysis of the NAB space group shows that there are 21A 1 and 59E Raman active modes. A discussion of the assignment of the individual Raman lines is given. The splitting predicted by factor group for the internal modes of (BO 3) 3+ anion are observed and interpreted.

Effects of whisker surface treatment on microstructure and properties of Al_(18)B_4O_(33w)/6061Al composites

6061Al matrix composites reinforced by ZnO-coated Al18B4O33 whiskers were fabricated by a semi-solid mechanical stirring technique.The effects of ZnO coating on interfacial reaction between whiskers and matrix and the tensile properties of the composites were investigated.Tensile tests on composites were performed at room temperature,and microstructures were observed by scanning electron microscopy(SEM).The results show that the surface treatment of whiskers could reduce interfacial reaction effectively,improve the wettability between whiskers and matrix and enhance the tensile properties of the composites obviously.In addition,semi-solid stirring parameters were also under preliminary study.The stirring parameters were determined by the distribution of whiskers in the composites.The composites with homogeneously distributed whiskers were fabricated by semi-solid stirring at 610 ℃ for 30 min.

Interface modification of Al_(18)B_4O_(33)w/6061Al composite by CuO coating on whisker surface

Copper coating was deposited on the surface of aluminum borate whisker(denoted by Al18B4O33w) by an electroless plating method.The result of X-ray diffraction(XRD) of whisker sintered at 850 ℃ indicates that CuO peaks can be found clearly.This method was used to modify the interface properties of the Al18B4O33w reinforced 6061Al matrix composite.Scanning electron microscope(SEM) observation indicates that the uniform coating can be obtained on the whisker surface.Transmission electron microscope(TEM) observation indicates the brittle spinel product(MgAl2O4) between Al18B4O33w and 6061Al matrix,the structure continuity of the whisker are greatly destroyed after the squeeze-casting process and heat treatment.Although copper coating can not totally hinder the spinel reaction,it effectively constrains the spinel reaction and preserves the structure integrity of the Al18B4O33w.

Recent progress in ultraviolet and deep-ultraviolet nonlinear optical aluminoborates

Aluminoborates(ABOs)show wide ultraviolet(UV)transmittance,and are one of the important types of UV and deep-UV nonlinear optical(NLO)materials.In recent years,the combination of AlO_(n)(n=4,5,6)polyhedra or their fluorinated analogues with different polyborate anions leads to a rich variety of crystalline ABOs.In this review,we summarize the recent developments of UV and deep-UV NLO inorganic ABOs.These ABOs can be grouped into three types in terms of their compositions:(i)aluminum oxyborates,(ii)alkali/alkaline earth metal aluminoborates,and(iii)alkali/alkaline earth metal aluminoborate fluorides and fluoroaluminoborates.We discuss the synthesis,structural features,NLO properties,as well as related structure-performance relationships of these non-centrosymmetric ABOs.Finally,the future perspectives in this field are discussed.