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The effects of the electron beam (EB) continuity on the microstructures and mechanical properties of titanium lattice structures with produced by EB additive manufacturing were studied. Continuous line and discontinuous spot scans were applied for the EB continuity. The porous structures produced with the continuous line scans had lower defect densities than those produced with discontinuous spot scans. Most defects of the continuous line scans had spherical morphologies, whereas non-spherical defects formed in the porous structure produced with discontinuous spot scans because of the availability of sufficient heat for melting the powder. The microstructures were composed of an α-titanium matrix, martensitic α′ phases, and elongated FeTi4 phases on the grain boundaries. Furthermore, the atom probe tomography results showed that the FeTi4 phase had a network structure with a diameter of 5 nm after the continuous line scan, which enhanced the compressive strength. The compressive strength and elastic modulus of the porous structures produced with the continuous line scan were more than 400 MPa and 11 GPa, respectively. Despite the high porosity, continuous line scans are preferable for achieving high compressive strengths with low elastic moduli for biomedical devices.

Pure titanium components fabricated by casting have a coarse grain microstructure. To improve the mechanical strength of pure titanium components by refining the grain size, the cast samples were r...

Chemical composition of pure titanium, particularly oxygen, severely affects mechanical properties of product. Oxygen refining during electron-beam additive manufacturing (EBAM) of pure titanium products was thermodynamically analyzed. The oxygen concentration of the titanium sample fabricated by EBAM was 0.172%, which was lower than that of the initial titanium powders (0.228%). This was mainly because the TiO2 native oxide layer formed on the initial powders reduced during EBAM, thereby decreasing the oxygen concentration. Analysis of temperature and oxygen partial pressure in the EBAM building chamber confirmed the occurrence of reduction and hence the oxygen refining effect.

The refining effect of electron beam melting (EBM) during the additive manufacturing of Ti products was studied by comparing unused Grade-2 commercially pure (CP) Ti powder to an equivalent powder that had been recycled 50 times. The pre-heating and blasting processes that occur during recycling were found to degrade the perfectly spherical morphology of the powder, and the concentration of O and N were also increased by about 15%. This resulted in it changing to a Grade-3 CP Ti powder; however, the purity of the final product was improved to Grade-1 CP Ti by the slight refining effect of the EBM process.

Collective behavior of strain induced martensitic transformation (SIMT) in biomedical Co–Cr–Mo–N alloy polycrystal has been investigated by ex-situ electron backscattering diffraction (EBSD) analysis during tensile deformation. The formation of SIMTed e-hcp phase depends on the crystal orientation, and the SIMT behavior is basically understood by the motion of isolated Shockley partial dislocation associated with the negative stacking fault energy (SFE) of this alloy. However, their variant selection is not governed by Schmid׳s law. Most of SIMT occurred in grains with loading axes near and between 〈1 1 1〉 and 〈0 1 1〉 directions because of the low effective SFE, which is determined by the difference in the Schmid factors for leading and trailing Shockley partial dislocations. In grains with loading axes near the 〈0 0 1〉 direction, the SIMT did not occur due to the high value of the effective SFE. These findings are very important to improve the strength and wear resistance of this alloy without sacrificing the ductility by controlling the crystal texture.

Surface relief formation of a biomedical Co–Cr–Mo–N (CCMN) alloy under tension/compression cyclic deformation has been investigated by in situ optical microscopy, atomic force microscopy and electron backscattering diffraction analysis. The formation of slip traces exhibited tension/compression asymmetry, resulting in unique surface reliefs. This is attributed to the motion of isolated Shockley partial dislocations in the metastable γ-face-centered cubic phase, in which the stacking fault energy is negative.

The deformation mode of polycrystalline Co–27Cr–5Mo (in mass%) alloy consisting of the hexagonal close-packed e phase was examined. Basal 〈a〉 and prismatic 〈a〉 slips were the dominant deformation modes. The activation of these 〈a〉 slips is strongly dependent on Schmid factor, which indicates that the values of critical resolved shear stress for basal 〈a〉 slip and prismatic 〈a〉 slip are similar. For tensile strains up to 10%, the frequent occurrence of deformation twins could not be confirmed by electron backscattered diffraction analysis.

Energy requirement and yield for production of aluminum wirerods manufactured by continuous casting process were investigated to enhance yield of aluminum wiredrods. Also, it was compared with conventional process including extrusion process. The enhancement of yield more than 30% could be accomplished through the continuous casting process. The conventional process including extrusion process for production of wirerods consumes more energy compared to continuous casting. In addition, a number of intermediate annealing may be introduced during wiredrawing process of wirerods manufactured by conventional process including extrusion process. It can be mentioned that continuous casting process is suitable process for wiredrawing process because it can save energy requirement not only during manufacturing process of wirerods but also during following wiredrawing process.

Eco-friendly grain refinement of A3003 alloy was studied by addition of non-toxic Al-Ti alloy because of toxic-fluorine in Al-Ti-B alloys which used as a representative grain refiner for aluminum and its alloys. TiAl3 phase in Al-Ti alloy bring to decrease grain size of A3003 alloy. But, grain growth occurred with prolonged holding time due to the solution of Ti into aluminum matrix. In contrast, lasting grain refinement of A3003 alloy was occurred in graphite crucible. It can be mentioned that carbon comes from graphite crucible was combined with Ti solute in aluminum melt and then TiC acts as a heterogeneous nucleation for A3003 alloy.

The influence of extrusion temperature and Ti content was investigated by observing the microstructure and determining the mechanical strength of A3003 alloy tube. The A3003 alloy was modified by inoculation in terms of addition of Ti and then extruded at the various extrusion temperatures. In case of A3003 alloy tube without addition of Ti, the yield strength was slightly improved with decreasing extrusion temperature. On the other hand, the yield strength was improved markedly in A3003 alloy tube with small addition of Ti, and also ductility was slightly reduced. Grain size distribution from observing the microstructure was different with addition of Ti. Coarse grains were formed on the outer and inner parts of the alloy tube without addition of Ti, whereas the finer grains were uniformly distributed in the alloy tube with addition of Ti. Thus the microstructure and mechanical strength of A3003 alloy tube could be controlled by addition of Ti. Threefore, optimum Ti content and extrusion temperature to fabricate high yield strength and ductility A3003 alloy tube (σy=60 MPa, ε=30%) for eco-friendly refrigerant application are above 0.05wt.Ti and below 480 °C, respectively. Introduction

The microstructures and mechanical properties of unidirectional deformation structured Al alloy during ECAP with various deformation routes were investigated. In order to fabricate unidirectional deformation structure for Al alloy, hot extrusion was carried out. It was found that the deformation route A in ECAP routes is the dominant route for the grain refinement and strengthening. In deformation route A, the high strength ultra-fine grained Al alloy with a grain size of ~ 200 nm was obtained due to the accumulation of consecutive strain process. In contrast, the strength of ECAP’ed Al alloy produced via deformation route C was greatly increased after one pass because the grains were strained and cancelled each pass. By contrast, the equiaxed grains were obtained in deformation route BC because the sample was rotated 90 O in the same sense in each pass. The deformation route BC was superior to the deformation route C because the deformation route BC was more favorable than the deformation route C in the accumulation of consecutive strain. It is also found that unidirectional deformation structured Al alloy via hot extrusion shows similar grain refinement tendency with equiaxed structured Al alloy during ECAP processing.

Free-cutting phosphor bronze alloy (ASTM C54400) was used as a material for automotive parts and industrial valve parts for its high strength, machinability and excellent corrosion resistance. To obtain desired mechanical strength of the alloy, the process parameters including continuous casting speed, reduction in area and annealing temperature have to be controlled. In this study, we investigated the effect of annealing on the mechanical property and machinability of free-cutting phosphor bronze alloy fabricated by continuous casting with different casting speeds of 80, 100, and 120 m/min, respectively. After annealing, the tensile strength of the alloy decreased with increasing annealing time owing to the occurrence of recrystallization and grain growth. In the cast and swaged alloy produced at casting speed of 120 m/min, the grain growth occurred rapidly. In contrast, in the alloy produced at the casting speed of 80 m/min, the grains growth rate was low. Furthermore, the effect of Pb particle in the alloy on machinability was also investigated by using a tool dynamometer installed force sensor.

The strength of aluminum alloys was improved by a severe deformation process while the decrease of elongation leads to the defect. Modification of A3003 alloy was attempted in order to develop a high strength and high formability Al alloy tube for the application of air-conditioning systems in transportation, such as passenger planes and automobiles. An A3003 alloy was modified by Ti addition, grain refiner. As a result of modification, the modified A3003 alloy was able to suitably satisfy the mechanical strength requirements, including elongation. Grain size and secondary dendrite arm spacing of A3003 alloy decreased by as much as 50 % by Ti addition. The finer grains were uniformly distributed in the modified A3003 alloy billet. The yield strength of the modified A3003 alloy was improved by 30 % without decreasing elongation.

Melt extrusion is a new fabrication process with the characteristics of both casting and extrusion. In this process, a metallic melt which is poured and solidified up to semisolid state in the container can be directly extruded through the die exit to form a product of bar shape without other intermediate processes. The effects of various process parameters, such as melt temperature and extrusion ratio, on the extrusion behavior of Al-Cu alloys in the semisolid state were investigated. Mechanical properties of the melt extruded Al-Cu alloy were measured and its characteristics are compared with the microstructure and copper contents in the alloy. Al-Cu alloys were successfully extruded after squeezing out of liquid during the melt extrusion with smaller force (60 Mpa) compared to the solid extrusion. Al-Cu alloys bar with the mean grain size of 200 μm was fabricated by melt extrusion; however, the mechanical properties have nothing to do with the extrusion ratio. The squeezing out of liquid was get lead to the segregation of the alloys and was affect on the mechanical properties.

Melt extrusion is a new fabrication process with the characteristics of both casting and extrusion. In this process, a metallic melt which is poured and solidified up to semisolid state in the container can be directly extruded through the die exit to form a product of bar shape without other intermediate processes. The aging behavior of Al-Cu alloys in the semisolid state was investigated. And the microstructure and mechanical properties of the melt extruded Al-Cu alloy bar were measured and its characteristics are compared with those of a hot extruded Al-Cu alloy bar. Al-Cu alloys were successfully extruded after squeezing out of liquid during melt extrusion with smaller force compared to the solid extrusion. Al-Cu alloys bar with the mean grain size of up to 200 μm was fabricated by melt extrusion process. And the mechanical properties of the melt extruded Al-Cu alloy bar were improved after the T6 treatment.

Various TiO2/SiO2 composite nanoparticles were prepared by vapor phase hydrolysis of Titanium Tetraisopropoxide (TTIP) and Tetraethylorthosilicate (TEOS) in a tubular reactor heated by electrical furnace by changing the methods of reactant mixing, the molar ratio of the precursors and the set temperature of the furnace. These variables affected the average size and the bulk composition of the particles as well as their morphological and crystalline structures. The morphological structures of the particles were reconfirmed as T-S, S-T and T/S as in the previous study. Various correlations were obtained between the molar ratio of the precursors, and the size, the composition and the TiO2 main peak intensity of the particles as a parameter of the mode of reactant mixing. In general, it was found that high content of silicon constituent showed translucent envelopes surrounding primary particles, which increased the dispersion diameter of the particles, reduced the thermal stability, retarded the anatase-to-rutile transformation and the initial photocatalytic degradation of phenol in an aqueous solution.