Chien Cheng Liu

Effects of matrix microstructure and particle distribution on fracture of an aluminum metal matrix composite

Abstract This paper presents the results of a study on the effects of matrix microstructure and particle distribution on the fracture of an aluminum alloy metal matrix composite containing 20% by volume SiC particulate. The matrix microstructure was systematically varied by heat treating to either an under- or over-aged condition of equivalent strength, and was characterized using a combination of techniques. Quantitative metallographic techniques were utilized to characterize the material with respect to size, size distribution, and particle clustering, while transmission electron microscopy was utilized to characterize the details of the matrix microstructure in addition to the effects of aging on the character of the particle/matrix interfaces. Fracture experiments were conducted on smooth tensile, notched bend, shortrod toughness, and on specimens designed to permit controlled crack propagation, in an attempt to determine the effects of matrix microstructure and clustered regions on the details of damage accumulation. Large effects of microstructure on the notched properties were obtained with little effect of microstructure on tensile ductility. It is shown that the micromechanisms of fracture are significantly affected by the details of the matrix microstructure, interface character, and degree of clustering in the material. Fracture of the SiC was predominant in the underaged materials, with a preference for failure in the matrix and near the interface in the overaged material. Metallographic and fractographic analyses revealed that clustered regions were preferred sites for damage initiation in both the aging conditions tested, while preliminary results additionally indicate that damage accumulation ahead of a propagating crack also tended to occur in clustered regions.

Effect of the electrical discharge machining on strength and reliability of TiN/Si3N4 composites

Conductive TiN/Si3N4 hot pressed composites were processed by electrical discharge machining (EDM) and their microstructure and conductivity investigated. The dependence of surface texture, surface roughness, and materials removal rate on electrical discharge machining conditions including working voltage and feed rate were also analyzed. The flexural strength and strength reliability in terms of Weibull modulus of TiN/ Si3N4 processed by EDM and conventional cutting and polishing are compared. Higher working voltage and current, as well as higher content of TiN result in greater material removal rate. Comparison of the flexural strength and Weibull modulus of the composites processed by EDM with conventional polished samples revealed that the surface with low roughness lead to an increase in strength and reliability for electrical discharge machining.

Microstructure and tool electrode erosion in EDMed of TiN/Si3N4 composites

Abstract Conductive TiN/Si3N4 ceramic composites were processed by electrical discharge machining (EDM) and their microstructure and conductivity were investigated. The whole process of tool electrode wear is evaluated by sinker-EDM. The machined surfaces of TiN/Si3N4 ceramic composites were examined by scanning electron microscopy (SEM) and profilometry to determine the surface finish. The electrode wear rate of brass is higher than copper electrode for all EDMed tests. The surface texture was found to have greater dependence on pulse energy. It was observed that the sinker-EDM at higher pulse energy caused severe microdamage in the surface. The surface roughness (Ra) values also increase with increasing pulse energy.

MICROSTRUCTURAL EFFECTS ON FRACTURE MICROMECHANISMS IN LIGHTWEIGHT METAL MATRIX COMPOSITES

ABSTRACT Microstructural effects on the deformation and fracture behavior of an aluminum alloy metal matrix composite has been studied. The matrix microstructure was systematically varied via both heat treatment and changes in the SiC particle size. Testing included smooth tensile and smooth bend specimens, in addition to notch toughness specimens. It is shown that both the matrix microstructure and the SiC particle size affect the failure micromechanisms. SiC particle fracture predominates in underaged (UA) specimens containing large (i.e. average size 13 μm) SiC particles while matrix and “interface” failure predominate in UA specimens containing smaller (i.e. average size 5 μm) SiC. Overaged (OA) microstructures exhibited a preference for fracture in the matrix and near the SiC/ matrix interface, regardless of the SiC particle size. Analyses were performed using a combination of scanning and transmission electron microscopy. The fracture results are discussed in light of recent work on fracture of composite materials.

Magnetron Sputtering of Tantalum Oxide Thin Electrolyte Film for Electrochromic Applications

Electrochromism have been widely investigated due to their potential applications such as automobile and building window. In this study, tantalum oxide thin films used as ion conducting layer were deposited on WO3/ITO at room temperature by magnetron sputtering. The thickness of tantalum oxide films were varied to investigate their effects on composition, microstructure, optical properties, and electrochromic properties determined by X-ray diffraction, UV-visible spectrometer, Atomic force microscope (AFM), and field-emission scanning electron microscope (FE-SEM). Experimental results indicated Ta2O5 at thickness of 300 nm with low packing density were favorable for ions transmission deposited on WO3/ITO had better electrochromic property.

Fabrication and Analysis of Nano-Aluminum-Induced Low-Temperature Polycrystalline Silicon Film

In this paper, we successfully fabricate polycrystalline silicon films with very large and uniform-size grains by the method of nanometer thick aluminum induced crystallization (nano-AIC) on the a-Si:H film deposited by plasma enhanced chemical vapor deposition (PECVD). The effect of annealing ramp-up time is discussed. Four different annealing ramp-up time, 1,5,10,20 hours, are tested. The results show the maximum average grain size obtained in this paper is about 60 μm under the condition of 20-hour annealing ramp-up time. The nano-AIC specimens show a much better leakage current characteristics than the AIC specimens since the Al layer in AIC process is much thicker and was not removed completely from the polycrystalline silicon film during Al wet selective etching process.

An Investigation of Structure and Wear Properties of TiN/NbN Films Deposited by Reactive Magnetron Sputtering

TiN/NbN multilayers on steel substrates (SKD11) are produced using DC magnetron sputtering process. The multilayer obtained are characterized in composition by means of X-ray diffraction techniques, Microhardness and adhesion to the substrate were studied by atomic force microscopy and scratch tests. The morphological analysis and coating structure are studied using scanning electron microscopy, and atomic force microscopy. The film thickness is measured by a stylus profiler (XP-2 stylus profiler). Wear tests were performed on pin-on-disk configuration and dry sliding conditions, at 5N load by using hardened steel ball. On mechanical properties, higher Young’s modulus and hardness values follow to increase the TiN/NbN layers number. The multilayer films of 64 layers at 500°C 1h annealing indicated that the microhardness and Young’s modulus had the highest values.

Microstructure and Electrode Discharge Machining of TiN/Si3N4 Composites

Conductive TiN/Si3N4 ceramic composites were processed by electrical discharge machining (EDM) and their microstructure and conductivity investigated. A low electrical resistivity of 1.25×10-3Ω.cm was obtained in 40vol%TiN/Si3N4 composite. The whole process of tool electrode wear is evaluated by sinker-EDM. The machined surfaces of TiN/Si3N4 ceramic composites were examined by scanning electron microscopy (SEM) and profilometry to determine the surface finish. Micropores of 700µm in depth and 70µm in diameter were successfully machined in TiN/ Si3N4 composites by the micro-EDM method.

Tribological Properties of the ZrN Coatings by DC Magnetron Sputtering

ZrN thin films were successfully deposited by DC magnetron sputtering on die steel substrates. The objective of this study was to investigate heat treatment on the microstructure, morphology, nanohardness properties determined by X-ray diffraction, field-emission scanning electron microscope (FE-SEM), nanoindentation, and pin-on-disk, respectively. The XRD result shows that ZrN has intensity of (111) and (200) peak after 400 °C for 1 h at lower nitrogen flow rates. The surface of coatings revealed smaller grains and smooth surface under heat treatment. ZrN coatings consisted of lower nitrogen flow rate had much lower friction coefficient, better mechanical properties by annealing treatment process.

A New Method for the Preparation of the Copper Bonding on Alumina Substrate

A novel method to prepare the copper bonding on alumina substrate was presented. The cuprous Cu2O on the surface of Cu foil was prepared by covering cupric oxide (CuO) powder on Cu foil and treating at 600°C in N2 atmosphere. Then eutectic process was executed at 1075°C in N2 atmosphere to bond the Cu and alumina substrate. The cuprous grew on copper foil and bonding between Cu foil-alumina substrate were identified by XRD spectrum and SEM micrographs.