Chih-I Chang

National Tsing Hua University | NTHU · Department of Chemical Engineering

The relationship between the resulting grain size and the applied working strain rate and temperature for the friction stir processing in AZ31 Mg is systemically examined. The Zener–Holloman parameter is utilized in rationalizing the relationship. The grain orientation distribution is also studied using the X-ray diffraction.

Ultrafine-grained (UFG) microstructures with an average grain size of 100–300 nm are achieved in solution-hardened AZ31 Mg–Al–Zn alloy prepared by friction stir processing equipped with a rapid heat sink. The mean hardness of the UFG region reaches ∼120Hv, which is more than twice as high as that of the AZ31 matrix. The grain refinement kinetics ar...

Nanograined structures with an average grain size of similar to 85 nm have been achieved in solution hardened AZ31 magnesium alloy by two-pass friction stir processing under rapid heat sink in which the second pass has a lower heat input. The mean hardness of the nanograined region reaches similar to 1.5 GPa (or 150 H(v)), about three times that of...

This study proposes a novel two-step strategy to prepare single-phase unitary/binary oxides-graphene composites: precipitating hydroxides followed by microwave-assisted hydrothermal or solvothermal annealing.

Crystalline tungsten oxide mixtures, WO3–WO3·0.5H2O, prepared by microwave-assisted hydrothermal (MAH) synthesis at 180°C for various periods, show capacitive-like behavior at 200mVs−1 and CS≈290Fg−1 at 25mVs−1 in 0.5M H2SO4 between −0.6 and 0.2V. Oxide rods can be obtained via the MAH process even when the synthesis time is only 0.75h while WO3·0....

A unique two-step modified Hummers method is developed to unzip and exfoliate multiwalled carbon nanotubes (MWCNTs) into low-defect graphene oxide nanoribbons (GONRs). From the X-ray diffraction (XRD), Raman spectroscopic (RS), X-ray photoelectron spectroscopic (XPS), Fourier transform infrared spectroscopic (FTIR), and transmission electron micros...

The thermomechanical properties and viscous flow behaviors of the Mg65Cu25-xAgxGd10 (x = 0, 3, 10at%, namely, Mg65Cu25Gd10, Mg65Cu22Ag3Gd10, and Mg65Cu15Ag10Gd10) bulk metallic glasses in the supercooled viscous region under the loading condition were investigated using the thermomechanical analyzer. In this study, the supercooled viscous temperatu...

Micropillars with diameters of 3.8, 1 and 0.7 mu m were fabricated from a two-phase Zr-based metallic glass using focus ion beam (FIB), and then tested in compression at strain rates from 1 X 10(-4) to 1 X 10(-2) s(-1). The apparent yield strength of the micropillars ranges from 1992 to 2972 MPa, or 25-86% increase over that of the bulk specimens....

Friction stir processing (FSP) has been applied to fabricate 10~20 vol% nano-sized ZrO2 and 5~10 vol% nano-sized SiO2 particles into an Mg-AZ31 alloy to form bulk composites under the FSP parameters of advancing speed of 800 rpm and pin rotation of 45 min/min. The microstructures and mechanical properties of the resulting composites were investigat...

The characterizations on the microstructural and mechanical properties of the Mg-Al-Zn multi-element intermetallic alloys fabricated by friction stir processing (FSP) are presented. The composites of the alloys vary within Mg 35-70 Al 5-25 Zn 25-45 . The maximum working temperature can reach 550 o C. The current process applies the FSP on verticall...

Mg-AZ31 based composites with 10-20 vol% nano-sized ZrO2 and 5-10 vol% nano-sized SiO2 particles were fabricated by friction stir processing (FSP). The clusters of the nano-ZrO2 and nano-SiO2 particles, measuring 180-300 nm in average, were relatively uniformly dispersed. The average grain size of the Mg matrixes of the composites varied within 2-4...

The Mg–Zn–Al alloy processed by hot extrusion typically exhibits strong grain size dependence of yield stress. However, the same friction stir processed Mg–Zn–Al alloy samples exhibited much weaker grain size dependence. The high Schmid factor of around 0.3 of the friction stir processed samples is responsible for the low parameters in the Hall–Pet...