Papers by Author: J.C. Huang

Abstract: The (Zr53Cu30Ni9Al8)99.5Si0.5 bulk metallic glass (BMG) rods, 3 mm in diameter, with different crystallization fraction for compression test were prepared by isothermal annealing the as-cast BMG rods at the temperature in the middle of supercooled temperature region for different time period in vacuum, respectively. The result of compression test revealed that the fracture strength of these samples increases with the crystallization ratio at the beginning, then decreases rapidly at 40 vol.% crystallization fraction. In addition, the best mechanical performance with 1970MPa yield strength and 3 % plastic strain occurs at the sample with 30 vol.% nanocrystalline phase (with an average size about 50 nm). This was suggested these homogeneous distributed nanocrystals which embedded in the matrix may act as obstacles to branch the primary shear band into multiple shear band and result in improving the ductility.

Abstract: Based on the thermodynamic calculation, two phase separated Zr-based BMGs (Zr63.8Ni16.2Cu15Al5 and Zr66Cu15.3Ni8.7Al10) which developed by the authors previous study were selected for investigating their crystallization behavior and thermal stabilities by means of differential scanning calorimetry (DSC), and X-ray diffractometry. The results show that the Zr66Cu15.3Ni8.7Al10 amorphous alloy exhibits higher GFA than the Zr63.8Ni16.2Cu15Al5 amorphous alloy. But the Zr63.8Ni16.2Cu15Al5 amorphous alloy presents higher activation energy of crystallization (227 kJ/mole and 188 kJ/mole for Zr63.8Ni16.2Cu15Al5 and Zr66Cu15.3Ni8.7Al10 BMGs, respectively). However, Zr66Cu15.3Ni8.7Al10 amorphous alloy contains less atomic percentage of Cu and Ni elements (with positive heat of mixing) may result in forming less volume phase separation as well less interface area between these separated amorphous phase. Overall, the Zr66Cu15.3Ni8.7Al10 amorphous alloy exhibits longer incubation time at higher annealing temperature in comparison with the Zr63.8Ni16.2Cu15Al5 amorphous alloy, suggesting that the amorphous alloy which contains fewer amounts of Cu and Ni elements would have better thermal stability.

Abstract: This study presents the hot embossing micro-forming of the V-groove and micro-lens array on the Au-based bulk metallic glasses (BMGs). The thermal and thermomechanical properties were firstly investigated by using thermomechanical analysis (TMA). Based on the results, the temperature of the hot embossing experiment was set at 177oC. The formability of the Au-based BMGs were evaluated under different embossing pressures and time durations, and the results showed the increasing trend of the forming quality with increasing forming pressure and time. The Au-based BMGs are considered to be promising for micro-electro-mechanical system applications.

Abstract: 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 investigated. The clustering size of nano-ZrO2 and nano-SiO2 particles, measuring average ~200 nm was relatively uniformly dispersed, and the average grain size of the both Mg alloy of the composites varied within 1.0~2.0 μm after four FSP passes. No evident interfacial product between ZrO2 particles and Mg matrix was found during the FSP mixing in AZ31-Mg/ZrO2. However, significant chemical reactions at the AZ31-Mg/SiO2 interface occurred to form the Mg2Si phase. The mechanical responses of the nano-composites in terms of hardness and tensile properties are examined and compared.

Abstract: Mg65Cu20Y10Ag5 Amorphous/ nano ZrO2 composites alloy powder were fabricated through the combination method of melt spinning and mechanical alloying (MA). The melt spun amorphous matrix ribbons are ground into powders and mixed with 3 vol.% ZrO2 nano particles in the planetary mill. After then formed by hot pressing in Ar atmosphere under the pressure of 700 MPa at the temperature of soft point which measured by TMA (Thermal mechanical Analysis). The hot-pressed bulk composite specimens are compression tested at different temperature within the supercooled temperature region. The flow stress was found decrease with increasing temperature dramatically when the temperature exceeds the middle temperature of supercooled region. The specimens after compression test were examined by X-ray diffractometry and SEM to investigate its crystallinity and fracture mechanism.

Abstract: The nano-sized silica particulates reinforced poly(ether ether ketone) (PEEK) composites were fabricated by means of simple compression molding technique. The nano-sized silica, measuring 30 nm in size, was firstly modified by surface-pretreatment with stearic acid. The thermomechanical properties of the resulting PEEK/SiO2 nanocomposites were measured using dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA). The TMA results show that the coefficient of thermal expansion (CTE) becomes lowered when the content of the nanosilica increases. Furthermore, the CTE of the modified-silica filled PEEK nanocomposites shows higher CTE values, as compared with those of the unmodified counterparts. The dynamic modulus of the PEEK nanocomposites shows over 40% increment at elevated temperatures from 100-250oC, indicating the apparent improvement of elevated temperature mechanical properties.

Abstract: The microstructure characteristics of the spray-formed and melt-spun Al85Nd5Ni10 and Al89La6Ni5 alloys were studied. The spray forming process was demonstrated to produce a bulk scale hybrid composite consisting of amorphous and nanostructured phases directly without the need of an amorphous precursor. The spray-formed Al89La6Ni5 deposit (~1 mm in thickness) were partially amorphous, and the amorphous phase came from the undercooled liquid droplets upon deposition. The as-spray-formed Al85Nd5Ni10 deposit (~20 mm in thickness) was completely crystallized due to the devitrification of the retained amorphous phase to nano-scale secondary crystals upon deposition. Primary crystals (~1 μm) are dispersed uniformly in the bulk spray-formed amorphous/or partial amorphous composites and many distinctive deformation twins also are observed in the crystals, however, not twins found in the corresponding completely devitrified ribbon. This is mainly because of the stirring and impacting force offered by high velocity droplets during spray forming and the mismatch of thermal expansion coefficient between primary crystals and adjacent amorphous matrix.

Abstract: Ti3Al based alloys have been widely reported for their admirable superplasticity in the temperature range of 900-1000oC. However, the superplastic behavior of temperature lower than 900oC was seldom reported. Dual phase (α2+β) Ti3Al-10Nb alloy has shown superior superplastic elongation of 1500% at 960oC and 2x10-4 s-1. In this paper, it aims to investigate the superplastic behavior at lower temperature (700-900oC). The relationship of texture characteristics, phase transformation phenomena, and deformation mechanism at lower temperature (below 900oC) are studied. The optimum low-temperature superplastic condition with an elongation of 333% was occurred at 850oC and 5x10-4 s-1. With abundant hexagonal α2’ laths formed inside the β grains, the major accommodation process via dislocation slip across the β grains is impeded. It leads to premature failure and lower tensile elongations at lower temperature. Moreover, with the minor operating of grain rotations and grain boundary sliding, the texture intensity decreases significantly at temperature 850oC.

Abstract: The Mg65Cu25Gd10-xNdx (x=0 ~ 10) amorphous alloy rods with 3~6 mm in diameter were prepared by Cu-mold injection method. The thermal properties and mechanical properties of these amorphous alloys have been investigated by DSC, SEM with EDS capability, X-ray diffractometry (XRD) and Vickers hardness test. The XRD revealed that these entire as-quenched Mg65Cu25Gd10-xNdx alloy rods exhibit a broaden diffraction pattern of amorphous phase. A clear Tg (glass transition temperature) and supercooled region (about 30~60 K) were revealed for all of those Mg65Cu25Gd10-xNdx alloys. In addition, the single stage crystallization of the Mg65Cu25Gd10 alloy was found to change into two stages crystallization when the Nd element was added into this alloy. In parallel, the crystallization temperature (Tx) and supercooled region (
Tx) presents a decreasing trend with increasing Nd content. The lowest liquidus temperature (Tl, about 721 K) occurs at the Mg65Cu25Gd8Nd2 alloy. In addition, The Mg65Cu25Gd8Nd2 alloy exhibits the high γ value (0.416, defined as γ= Tx/Tg+Tl), a relatively high Trg (0.59, defined as Trg = Tg/Tl) and the highest hardness in these alloys.

Abstract: The thermal and mechanical characteristics of various Mg-Cu(Ni)-Y(Gd) metallic glassy alloys prepared by melt spinning are examined using differential scanning calorimetry (DSC), thermomechanical analyzer (TMA), and instrumental nanoindenter. The replacement of Y by Gd appears to benefit both the thermal and mechanical properties, while the replacement of Cu by Ni improves only the hardness and modulus, with the sacrifice of thermal characteristics. The amorphous Mg-Cu-Gd based alloys can be fabricated into rods with a diameter greater than 6 mm, with minimum porosity and reasonable toughness.