Jaeho Jang

Effect of solution treatment and artificial aging on microstructure and mechanical properties of Al−Cu alloy

Abstract In order to achieve good mechanical properties of Al-Cu alloys such as high strength and good toughness, precipitation hardening and artificial aging treatment were applied. As defined by the T6 heat treatment, the standard artificial aging treatment for Al-Cu alloy followed heat treatments of solution treatment at 510–530 °C for 2 h, quenching in water at 60 °C and then artificial aging at 160–190 °C for 2–8 h. The effects of solution treatment and artificial aging on the microstructure and mechanical properties of Al-Cu alloy were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and tensile test. The results of solution treatment indicate that the mechanical properties of Al-Cu alloy increase and then decrease with the increase of solution temperature. This is because the residual phases dissolve gradually into the matrix, and the fraction of the precipitation and the size of the re-crystallized grain increased. Compared to the solution temperature, the solution holding time has less effect on the microstructure and the mechanical properties of Al-Cu alloy. The artificial aging treatments were conducted at 160–180 °C for 2–8 h. The results show that the ultimate tensile strength can be obtained at 180 °C for 8 h. Ultimate tensile strength increased with increasing time or temperature. Yield strength was found as the same as the ultimate tensile strength result.

Microstructure and mechanical properties of Ti-B-C-N-Si nanocomposite films deposited by unbalanced magnetron sputtering

Quinary Ti–B–C–N–Si nanocomposite thin films were deposited on AISI 304 stainless steel substrates by d.c. unbalanced magnetron sputtering from a TiB2–TiC compound target and a pure Si target. The relationship between microstructure and mechanical properties of the films was investigated in terms of the nanosized crystallites/amorphous system. The synthesized Ti–B–C–N–Si films were characterized using x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and high resolution transmission electron microscopy. The results showed that the Ti–B–C–N–Si films were nanocomposites composed of nanosized TiB2, TiC, and TiSi2 crystallites (2-3 nm in size) embedded in an amorphous matrix. The addition of Si to the Ti–B–C–N film led to precipitation of nanosized crystalline TiSi2 and percolation of amorphous SiC phases. The Ti–B–C–N–Si films with up to 7 at. % Si content presented high hardness (≥35 GPa), H/E (≥0.0095), and We (>50%) with compressive residual stress (∼0.5 GPa). A systematic inve...

Microstructure, Mechanical, Oxidation and Corrosion Properties of Zr-Al-N Coatings Synthesized by the Hybrid Coating System

Korea Institute of Industrial Technology (KITECH), Busan 618-230, Korea(Received December 2, 2013 ; revised December 12, 2013 ; accepted December 20, 2013)AbstractZr-Al-N coatings were synthesized by the hybrid coating system combining arc ion plating and DC magnetronsputtering from a Zr and an Al target in argon-nitrogen atmosphere, respectively. By changing the powerapplied on the Al cathodes, the Zr-Al-N coatings with various Al contents were deposited. The microstructureand chemical compositions of the Zr-Al-N coatings were studied by X-ray diffraction (XRD), high-resolutiontransmission electron microscopy (HRTEM). With increasing of Al content in the coatings, the solid solution(Zr, Al)N crystallites were observed in the Zr-Al-N coatings. The nanohardness of the Zr-Al-N coatings exhib-ited a maximum value of 42 GPa for the Zr-Al (7.9 at.%)-N, and decreased with further increase in Alcontent in the coatings. The oxidation and corrosion behavior of the Zr-Al-N coatings revealed better propertiescompared than those of ZrN coatings due to the formation of a solid solution.

Analysis of Microstructure for Resistance Spot Welded TRIP Steels using Atomic Force Microscope

The spot welds of Transformation Induced Plasticity (TRIP) steels are prone to interfacial failure and narrow welding current range. Hard microstructures in weld metal and heat affected zone arenormally considered as one of the main reason to accelerate the interfacial failure mode. There fore, detailed observation of weld microstructure for TRIP steels should be made to ensure better weld quality. However, it is difficult to characterize the microstructure, which has similar color, size, and shape using the optical or electron microscopy. The atomic force microscope (AFM) can help to analyze microstructure by using different energy levels for different surface roughness. In this study, the microstructures of resistance spot welds for AHSS are analyzed by using AFM with measuring the differences in average surface roughness. It has been possible to identify the different phases and their topographic characteristics and to study their morphology using atomic force microscopy in resistance spot weld TRIP steels. The systematic topographic study for each region of weldments confirmed the presence of different microstructures with height of 350nm for martensite, 250nm for bainite, and 150nm for ferrite, respectively.

Oxidation and Tribological Behavior of Ti–B–C–N–Si Nanocomposite Films Deposited by Pulsed Unbalanced Magnetron Sputtering

Quinary Ti-B-C-N-Si nanocomposite films were deposited onto AISI 304 substrates using a pulsed d.c. magnetron sputtering system. The quinary Ti-B-C-N-Si (5 at.%) film showed excellent tribological and wear properties compared with those of the Ti-B-C-N films. The steady friction coefficient of 0.151 and a wear rate of 2 × 10-6 mm3N-1m-1 were measured for the Ti-B-C-N-Si films. The oxidation behavior of Ti-B-C-N-Si nanocomposite films was systematically investigated using X-ray diffraction (XRD), and thermal analyzer with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It is concluded that the addition of Si into the Ti-B-C-N film improved the tribological properties and oxidation resistance of the Ti-B-C-N-Si films. The improvements are due to the formation of an amorphous SiOx phase, which plays a major role in the self-lubricant tribo-layers and oxidation barrier on the film surface or in the grain boundaries, respectively.

Microstructure Analysis of Ni-P-rGO Electroless Composite Plating Layer for PEM Fuel Cell Separator

Department of Nano Science & Engineering, Inje University, Gimhae 621-749, Korea(Received September 14, 2015 ; revised October 28, 2015 ; accepted October 30, 2015)AbstractRecently, fuel cell is a good alternative for energy source. Separator is a important component for fuelcell. In this study, The surface of separator was modified for corrosion resistance and electric conductivity.Reduced graphene oxide (rGO) was made by Staudenmaier’s method. Nickel, phosphorus and rGO werecoated on 6061 aluminum alloy as a separator of proton exchange membrane fuel cell by composite electrolessplating. Scanning electron microscope, energy-dispersive X-ray spectroscopy and X-ray photoelectron spec-troscopy were used to examine the morphology of Ni-P-rGO. Surface images were shown that the rGO wasdispersed on the surface of Ni-P electroless plating, and nickel was combined with the un-reduced oxygenfunctional group of rGO.