Chang-Pin Chou

The effect of pulsed GTA welding on the residual stress of a stainless steel weldment

Abstract The objective of this study was to investigate the effect of pulsed GTA welding parameters on the residual stress of the weldment. Autogenous gas tungsten arc welding was applied on SUS 304 and SUS 310 stainless steels to produce a bead-on-plate weld. The residual stress was determined by using the hole-drilling strain-gage method of ASTM standard E837. The experimental results show that a greater pulse frequency, a larger pulse spacing, a greater amplitude ratio, and a greater duration ratio can reduce the magnitude of the residual stress in the austenitic stainless steel weldment. The residual stress of the 310 stainless steel weldment is greater than that of the 304 stainless steel weldment under the same welding conditions because of its lower thermal conductivity and thermal diffusivity. The experimental results also showed that pulsed current welding has a smaller range of the tensile residual stress zone as compared to that of constant current welding because of its lesser amount of heat input.

Observation of Growth of Human Fibroblasts on Silver Nanoparticles

Silver nanoparticles have drawn extensive attention as biomaterial components. Human fibroblasts were grown on various concentrations of silver nanoparticles during the period observation. Normal viability (0% silver particles) was increased from 6 to 72 hours, increasing the amount of human fibroblasts (1.5 × 104 to 7 × 106 cells/well) normally. Nevertheless, at higher concentrations of silver nanoparticles (50%) 1.11 × 105 cells/well remained after 72 hours. Results indicated that the increase in the concentration of silver nanoparticles reduced the number of fibroblasts and affected their fission. Silver nanoparticles were found under the membranes of fibroblast following dry treatment. The number of tissues declined because the silver nanoparticles interrupted the fission mechanism during their development in vivo.

The study of nitrogen in argon gas on the angular distortion of austenitic stainless steel weldments

Abstract The objective of this study was to investigate the effect of nitrogen added in argon shielding gas on the angular distortion of austenitic stainless steels. An autogenous gas tungsten arc welding was conducted on austenitic stainless steels 304 and 310 to produce a bead-on-plate weld. The delta-ferrite content of welds was measured by using Ferritscope. The angular distortion of weldments was determined by using the mean vertical displacement method (MVDM). The present results indicate that the retained ferrite content in Type 304 stainless steel weld metals was rapidly reduced as the nitrogen addition in argon shielding gas was increased. The welding angular distortion was raised with the increase of the amount of nitrogen added in the shielding gas. This experimental result also found that the existence of retained ferrite microstructure within the austenitic matrix has a beneficial effect in reducing welding distortion tendency of austenitic stainless steel weldment.

Effect of pulsed gas tungsten arc welding on angular distortion in austenitic stainless steel weldments

Abstract The effect of the parameters of the pulsed gas tungsten arc welding (GTAW) process on the angular distortion in austenitic stainless steel weldments was investigated. Autogenous GTAW was conducted on types 304 and 310 stainless steels to produce a bead on plate weld. The weldment thermal cycle was recorded during pulsed GTAW to investigate the influence of thermal stress. Angular distortion was determined by using the mean vertical displacement method. The experimental results indicate that higher pulse frequency, smaller pulse spacing, greater amplitude ratio, and greater duration ratio can reduce the angular distortion. The angular distortion of type 310 stainless steel weldments was greater than that of type 304 weldments under the same welding conditions because of the lower thermal conductivity and thermal diffusivity of type 310.

Fabrication of a double-sided micro-lens array by a glass molding technique

In recent years, micro-lens arrays (MLAs) have become important elements of optical systems. One function of MLAs is to create a uniform intensity of light. Compared with one-sided MLAs, the uniformity of light intensity increases with double-sided MLAs. MLAs fabricated by glass can be used in higher temperature environments or in high-energy systems. Glass-based MLAs can be fabricated by laser machining, photolithography, precision diamond grinding process and precision glass molding (PGM) technologies, but laser machining, photolithography and precision diamond grinding process technologies are not the perfect approach for mass production. Therefore, this paper proposes a method to fabricate a mold by laser micro-machining and a double-sided MLA by a PGM process. First, a micro-hole array was fabricated on the surface of a silicon carbide mold. A double-sided MLA using two molds was then formed by a PGM process. In this paper, the PGM process parameters including molding temperature and molding force are discussed. Moreover, the profile of a double-sided MLA is discussed. Finally, a double-sided MLA with a diameter of 20 mm, and lenses with a height of 52 µm, a radius of 851 µm and a pitch of 700 µm were formed on glass.

A new technique for reducing the residual stress induced by welding in type 304 stainless steel

Abstract A new Technique named as “parallel heat welding” (PHW) is developed for the reduction of residual stress. It is performed by a pair of parallel heating torches attached to the welding torch on both sides as a movable heat source during welding. Autogenous gas tungsten are welding process was used in type 304 stainless steel. The experimental results showed that the maximum principal residual stress and parallel welding direction stress can be reduced by 21–32% when the conventional welding(CW) process is replaced by the parallel heat welding process. The elevation of equilibrium temperature during welding process is a main mechanism for the reduction of residual stress in PHW process.

Nanoscratch Characterization of GaN Epilayers on c- and a-Axis Sapphire Substrates

In this study, we used metal organic chemical vapor deposition to form gallium nitride (GaN) epilayers on c- and a-axis sapphire substrates and then used the nanoscratch technique and atomic force microscopy (AFM) to determine the nanotribological behavior and deformation characteristics of the GaN epilayers, respectively. The AFM morphological studies revealed that pile-up phenomena occurred on both sides of the scratches formed on the GaN epilayers. It is suggested that cracking dominates in the case of GaN epilayers while ploughing during the process of scratching; the appearances of the scratched surfaces were significantly different for the GaN epilayers on the c- and a-axis sapphire substrates. In addition, compared to the c-axis substrate, we obtained higher values of the coefficient of friction (μ) and deeper penetration of the scratches on the GaN a-axis sapphire sample when we set the ramped force at 4,000 μN. This discrepancy suggests that GaN epilayers grown on c-axis sapphire have higher shear resistances than those formed on a-axis sapphire. The occurrence of pile-up events indicates that the generation and motion of individual dislocation, which we measured under the sites of critical brittle transitions of the scratch track, resulted in ductile and/or brittle properties as a result of the deformed and strain-hardened lattice structure.

Effect of annealing treatment and nanomechanical properties for multilayer Si0.8Ge0.2–Si films

Multilayered silicon–germanium (SiGe) films consisting of alternating sublayers with different mechanical properties have been epitaxially deposited by an ultra-high vacuum chemical vapor deposition (UHV/ CVD) system. We report engineering of the mechanical properties of SiGe multilayer films by a commercial nanoindenter. From annealing treatment, it consists of an ex situ thermal treatments in furnace (600 C) and rapid thermal annealing (800 C) system. Subsequent roughness and microstructure of SiGe multilayer films were characterized by means of atomic force microscope (AFM) and transmission electron microscopy (TEM). The annealing treatment not only produced misfit dislocations as a significant role in the critical pileup event but also promoted hardness. The hardness of the films increased slightly and then gradually achieved a maximum value (from 12.6 ± 0.4 GPa to 14.2 ± 0.7 GPa) with increasing annealing temperature. This may be due to the relaxation effect from thermal annealing and is potential to provide the reliability behaviours to design periodical SiGe multilayer structure in further. 2010 Published by Elsevier Ltd.

Effect of post-weld heat treatments on microstructure and mechanical properties of electron beam welded flow formed maraging steel weldment

Abstract Seamless tubing of C-250 maraging steel manufactured by the flow forming technique was joined by the electron beam welding process. Various post-welding heat treatments were conducted to improve the overall mechanical properties of the welded tubing. For the 480°C/6 h/air cooling post-weld aging treated maraging steel, a significant increment of 11% reversion austenite was present in the weld metal. Only the tensile strength of this aging treated metal met the required specification while its percentage elongation reached only 50% of the specification, attaining only 35% of the strength of the parent metal. For the post-welded solution + aging treated maraging steel, only the yield strength met the specification. Moreover, a significant amount of reversion austenite pools was also present at the grain boundaries of the material located at the weld metal. Although the homogenisation treatment could improve the hardness of the weld metal, it failed to have the tensile strength of the steel met the specification.

Effect of aging treatment on the mechanical properties of C-250 maraging steel by flow forming

The technique of forward flow forming has been used to produce a long, thin walled tube made of C-250 maraging steel. The forward flow forming can save raw material, increase strength, and reduce the production process time. Because the work hardening effect on solution-treated C-250 using flow forming is minimal, the flow-formed tube requires an additional heat treatment to obtain higher hardness and strength. With the direct aging treatment, low elongation values are obtained, making this treatment unsuitable for the engineering design. It was found that the 540 °C/6 h/AC over-aging treatment results in better strength and elongation values. The strengthening phase of the flow-formed C-250 maraging steel was found to be the intermetallic compound of Fe3Mo.