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A study has been made to investigate the fatigue properties of a high-strength spring steel in relation to the microstructural variation via different heat treatments. Rotating–bending fatigue and fatigue crack growth (FCG) tests were conducted to evaluate the fatigue properties, and a transmission electron microscope (TEM) equipped with an energy dispersive X-ray (EDX) unit was used to characterize the tempered microstructure. The results indicate that the fatigue endurance σf increases with increasing tempering temperature, reaching a maximum at 450°C, then decreases. The increase of σf is mainly attributed to the refined distribution of precipitation, together with the structural uniformity of tempered martensite. The softening of tempered martensite due to excessive precipitation accounts for the decrease of σf. By contrast, the FCG results show an insensitivity of the stage-II growth behavior to the microstructural changes for the whole range of tempering temperature tested. The insensitivity is interpreted in terms of the counterbalancing microstructure-dependent contributions to the FCG behavior.

An investigation was carried out to study the microstructural influence on the acoustic emission (AE) behavior during the tensile and fracture tests of an Al Li 8090 alloy, and to correlate it with the deformation mechanisms of two different microstructures (the δ ′ microstructure and the S ′ + δ ′ microstructure), and of two different orientations ( L and S ). For the L -oriented specimens, continuous emissions were mostly produced in the δ ′ microstructure due to the shearing of coherent δ ′ precipitates, while in the S ′ + δ ′ microstructure the burst type emissions were dominant mainly due to the shearing or microcracking of large incoherent S ′ precipitates as well as the intergranular failure. The S -oriented specimens of both microstructures showed more burst emissions than the L -oriented ones, which resulted from the frequent occurrence of intergranular delamination in the S -oriented specimens. The K AE values measured by AE method were well agreed with the K IC values, implying that the K AE could be considered as a quantitative and reliable parameter to evaluate the fracture toughness of a material.

The effect of high temperature deformation on the low thermal expansion property of Fe-29Ni-17Co alloy was investigated in the compressive temperature range of 900~1300°C at a strain rate range of 25 ~ 0.01 sec.-1. The thermal expansion coefficient (α30~400) generally increased with increasing compressive temperature. In particular, α30~400 increased remarkably as the strain rate decreased at temperatures above 1100°C. Note, however, that α30~400 at low compressive temperatures (900°C and 1000°C) increased abnormally at high strain rates. Based on the investigation of various possibilities of change in low thermal expansion behavior, the experimental results indicated that both the appearance of the α phase and evolution of grain size due to hot compression clearly influenced the low thermal expansion behavior of this invar-type alloy. The correlation between the microstructural cause and invar phenomena and theoretical explanation for the low thermal expansion behavior of Fe-29%Ni-17%Co were also suggested.

We propose a self-consistent analytic scattering theory for apertureless THz near-field microscope (NFM) which is based on an exact image theory. In this new scattering theory, a quasi-electrostatic image theory is adopted to include the effects of the specular reflection of the incident field and the exact image dipoles induced in the probe tip and the sample substrate. The analytic results from our self-consistent theory are in good agreement with the simulation results obtained by using HFSS, a commercial software based on finite element method.

We present a numerical analysis of apertureless terahertz near-field microscopy (THz NFM), and successfully demonstrate that the THz NFM can have nanometer-scale resolution. For the numerical analysis we used HFSS based on finite element method (FEM). It is found that the THz near-field is strongly localized between two particles.

The spatial resolutions of conventional THz TDS systems are limited by diffraction. In this work, we present a numerical analysis of apertureless THz pulse near-field microscopy (NFM), and successfully demonstrate that the THz NFM can have nanometer-scale resolution. For the numerical analysis we used CST MWS, a commercial software based on finite integral time domain (FITD) method. It is found that the THz near field is strongly localized around the probe tip as expected, which is of importance for nanometer resolution.

Cu-based amorphous (Cu54Zr22Ti18Ni6) coating was produced through cold spraying as a new fabrication process. The microstructure and macroscopic properties of the amorphous coating layer were investigated and compared with those of the cold-sprayed, pure Cu coating. Amorphous powder was prepared via gas atomization, and Al 6061 was used as the substrate plate. The X-ray diffraction results showed that Cu-based amorphous powder could be successfully deposited through cold spraying sans any crystallization. The Cu-based amorphous coating layer (300-400 μm thick) had 4.87% porosity. The hardness of the Cu-based amorphous coating was 412.8 Hv or 68% of the hardness of the injection-casted bulk amorphous material. The wear resistance of the Cu-based amorphous coating was found to be three times higher than that of the pure Cu coating. The results of the 3-point bending test showed that the adhesion strength of the Cu-based amorphous coating layer was higher than the pure Cu coating. The hard Cu-based amorphous particle was also observed to be able to deform soft substrate easily through particle collisions; thus generating strong adhesion between the coating and substrate. Note, however, that the amorphous coating layer unexpectedly showed lower corrosion resistance than the pure Cu coating, possibly due to the higher porosity of the cold-sprayed amorphous coating.

The effects of nozzle-wheel gap size and annealing temperature on magnetic properties of FeSiB amorphous alloy strips fabricated by the PFC method were investigated. 50mm wide amorphous alloy strips were prepared by single-roll PFC equipment with various nozzle-wheel gap sizes and annealing temperatures. The decreasing nozzle-wheel gap size improved the magnetic properties of amorphous alloy strips by decreasing the eddy current losses and the easy magnetization. In addition, magnetic properties of annealed amorphous alloy strips primarily depended on size and volume fraction of nano-sized crystallites, which were closely related to annealing temperature.

The effect of casting defects on the high cycle fatigue property of magnesium alloy was investigated in this study. Two AM60B magnesium alloys were manufactured by high pressure die casting with different processing parameters such as die morphology, melt and die temperatures. One of AM60B alloys with relatively high porosity was called C1 (4.06%) and the other was called C2 (0.07%). Microstructures of both C1 and C2 were composed of primary dendrite α-Mg, Al rich α-Mg, AlMn particles and Mg17Al12 phases. The tensile properties of both alloys were showed that C2 had superior strength and elongation. High cycle fatigue properties were also showed differently: fatigue limit of C1 exhibited 32 MPa at 107 cycles beside that of C2 showed 82 MPa at same cycles. Thus, C1 had significantly lower fatigue life than that of C2. Fractographical observations performed to explain the differences of fatigue properties by using SEM. From the observation of the differences in porosities and fractography of two AM60B magnesium alloys, an attempt to explain the high cycle fatigue fracture behavior of casted magnesium alloys was made by using the amplitude of stress intensity factor, Δ K .