Chang-Young Son

Pohang University of Science and Technology, Andong, North Gyeongsang, South Korea

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Publications (16)19 Total impact

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    ABSTRACT: Zr-based amorphous alloy matrix composites reinforced with tungsten continuous fibers or porous foams were fabricated without pores or defects by liquid pressing process, and their microstructures and compressive properties were investigated. About 65–70vol.% of tungsten reinforcements were homogeneously distributed inside the amorphous matrix. The compressive test results indicated that the tungsten-reinforced composites showed considerable plastic strain as the compressive load was sustained by fibers or foams. Particularly in the tungsten porous foam-reinforced composite, the compressive stress continued to increase according to the work hardening after the yielding, thereby leading to the maximum strength of 2764MPa and the plastic strain of 39.4%. This dramatic increase in strength and ductility was attributed to the simultaneous and homogeneous deformation at tungsten foams and amorphous matrix since tungsten foams did not show anisotropy and tungsten/matrix interfaces were excellent.
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing - MATER SCI ENG A-STRUCT MATER. 01/2010; 527(16):4028-4034.
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    ABSTRACT: Zr-based amorphous matrix composites reinforced with metallic continuous fibers were fabricated by liquid pressing process, and their fracture property improvement was explained by directly observing microfracture processes. About 60vol.% of metallic fibers were homogeneously distributed inside the amorphous matrix. Apparent fracture toughness of the tungsten-fiber-reinforced composites was lower than that of monolithic amorphous alloy, while that of the tantalum-fiber-reinforced composite was higher. According to the microfracture observation, shear bands or cracks were initiated at the amorphous matrix, and the propagation of the initiated shear bands or cracks was effectively blocked by fibers, thereby resulting in stable crack growth which could be confirmed by the fracture resistance curve (R-curve) behavior. This increase in fracture resistance with increasing crack length improved fracture properties of the fiber-reinforced composites, and could be explained by the formation of multiple shear bands or multiple cracks at the amorphous matrix, blocking of crack or shear band propagation, and multiple necking at metallic fibers.
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing - MATER SCI ENG A-STRUCT MATER. 01/2010; 527(4):941-946.
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    ABSTRACT: In the present study, a Zr-based amorphous alloy matrix composite reinforced with tungsten porous foam (internal porosity; 30 vol.%) was fabricated without pores or defects by liquid pressing process. The compressive test results indicated that the composite was not fractured at one time after reaching the maximum compressive strength, but showed considerable plastic strain as the compressive load was sustained by the foam. The strength (2764 MPa) and ductility (39.4%) were greatly improved by homogeneously dispersing the stress applied to the matrix because the tungsten foam and matrix were simultaneously deformed without showing anisotropic deformation due to excellently bonded tungsten/matrix interfaces.
    Intermetallics 01/2010; 18(10):1880-1883. · 1.86 Impact Factor
  • Korean Journal of Metals and Materials. 01/2010; 48(2):109-115.
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    ABSTRACT: Alumina matrix composites reinforced with carbon nanotubes (CNTs) fabricated by CNT purification, mixing, compaction, and sintering processes, and the effects of the CNT addition on wear resistance were investigated in relation to the relative density, hardness, and fracture toughness. Wear resistance and fracture toughness were measured by the dry sliding wear test method and the indentation fracture test method, respectively. Zero to ~3volpct of CNTs were homogeneously distributed in the composites, although some pores existed. The wear resistance and fracture toughness increased with an increasing CNT fraction, but the composite specimen containing 3.0volpct of CNTs hardly showed an increase over the specimen containing 2.25volpct of CNTs. Observations of worn surfaces revealed that the wear mechanism involved both the abrasive and delamination wear modes in the specimens containing 0 to ~0.75volpct of CNTs, whereas the surface was worn largely in an abrasive wear mode in the specimens containing 1.5 to ~3.0volpct of CNTs. This was because CNTs helped to change the delamination wear mode to the abrasive wear mode by preventing crack initiation and propagation at alumina grains. The fracture toughness increase provided beneficial effects in the resistance to crack initiation and propagation, the reduction in delamination wear on the worn surface, and the consequent improvement in wear resistance. Because the effect of the porosity increase due to the CNT addition unfavorably affected the improvement of wear resistance and fracture toughness in the specimen containing 3.0volpct of CNTs, the appropriate level of CNT fraction was 1.5 to ~2.25volpct.
    Metallurgical and Materials Transactions A 01/2010; 41(2):380-388. · 1.73 Impact Factor
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    ABSTRACT: This study aims at investigating fracture mechanisms occurring in Cu-based amorphous alloy matrix composites containing ductile Cu or brass particles. Amorphous alloy powders were mixed with 20–40vol.% of Cu or brass powders, and were consolidated at 460°C for 1/2min under 700MPa by spark plasma sintering (SPS) equipment. The consolidated composites contained Cu or brass particles homogeneously distributed in the amorphous matrix, and showed a considerable plastic strain under a compressive loading condition, whereas their strength was lower than that of the monolithic amorphous alloy. Microfracture mechanisms were investigated by directly observing microfracture processes using an in situ loading stage. Cu or brass particles present in the composites acted as blocking sites of the propagation of cracks initiated at the amorphous matrix, and provided the stable crack growth. In front of some Cu or brass particles, the crack blunting, deflecting, and bridging were also observed, and the final crack propagation path showed frequent stops of cracks. These findings suggested that the composites consolidated by the SPS presented new possibilities of application to structural materials or parts satisfying excellent mechanical properties and large size requirements.
    Materials Science and Engineering A 05/2009; 508(1):15-22. · 2.41 Impact Factor
  • Chang-Young Son, Tae Shik Yoon, Sunghak Lee
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    ABSTRACT: In this study, the powder injection molding (PIM) process was applied to Fe-alloy powders. Microstructure, hardness, wear resistance, and corrosion resistance of the PIM specimens were analyzed and compared with those of a conventional stainless steel, SS316L. When Fe-alloy powders were injection molded and then sintered at 1200°C or 1250°C, completely densified specimens with almost no pores were obtained. They contained 63 to 80volpct of hard (Cr,Fe)2B dispersed in the austenite or martensite matrix. Since these (Cr,Fe)2B borides were very hard, thermally stable, and corrosion resistant, hardness, high-temperature hardness, wear resistance, and corrosion resistance of the PIM specimens of Fe-alloy powders were 2 to 5times as high as those of the stainless steel. Such property improvement suggested new applicability of the PIM products of Fe-alloy powders to structures and parts requiring excellent mechanical properties.
    Metallurgical and Materials Transactions A 01/2009; 40(5):1110-1117. · 1.73 Impact Factor
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    ABSTRACT: In this study, alumina matrix composites reinforced with carbon nanotubes (CNTs) were fabricated by CNT purification, mixing, compaction, and sintering processes, and their relative density, electrical resistance, hardness, flexure strength, and fracture toughness were evaluated. 0–3 vol.% of CNTs was relatively homogeneously distributed in the composites, although some pores existed. The three-point bending test results indicated that the flexure strength increased with increasing volume fraction of CNTs, and reached the maximum when the CNT fraction was 1.5 vol.%. The fracture toughness increased as the CNT fraction increased, and the fracture toughness of the composite containing 3 vol.% of CNTs was higher by 40% than that of the monolithic alumina. According to the observation of the crack propagation path after the indentation fracture test, a new toughening mechanism of grain interface bridging-induced CNT bridging was suggested to explain the improvement of fracture toughness.
    Materials Science and Engineering: A. 01/2009; 517:293-299.
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    ABSTRACT: In the present study, a powder-injection molding (PIM) process was applied to Cu-based amorphous alloy powders and Fe-based metamorphic alloy powders, and microstructure, hardness, and wear resistance of the PIM products were analyzed and compared with those of conventional PIM stainless steel products. Injection-molded Cu-based amorphous powders were hardly sintered even at temperatures just below the melting temperature as most of amorphous phases were replaced by crystalline phases. When Fe-based metamorphic powders were injection-molded and then sintered at 1200°C, completely densified products with almost no pores were obtained. They contained 34vol.% of (Cr,Fe)2B borides dispersed in the austenitic matrix without amorphous phases. Since these (Cr,Fe)2B borides were very hard and thermally stable, hardness, high-temperature hardness, and wear resistance of the PIM products of Fe-based metamorphic powders were twice as high as those of conventional PIM stainless steel products. Such property improvement suggested new applicability of the PIM products of Fe-based metamorphic powders to structures and parts requiring excellent mechanical properties.
    Materials Science and Engineering A 03/2008; 476(1):69-77. · 2.41 Impact Factor
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    ABSTRACT: Powder injection molding (PIM) process was applied to Cu-based amorphous alloy powders and Fe-based metamorphic alloy powders, and microstructure, hardness, and wear resistance of the PIM products were analyzed. When Cu-based amorphous powders were injection-molded and sintered at 470 °C, sintering was not made since most of amorphous phases were replaced by crystalline phases. When sintered at higher temperatures, volume fraction of pores inside the sintered specimens decreased, but sintering was not properly conducted. When Fe-based metamorphic powders were injection-molded and then sintered at 1200 °C, completely densified products with almost no pores were obtained. They contained 34 vol.% of (Cr, Fe)2 B borides dispersed in the austenitic matrix without amorphous phases. Since these (Cr, Fe)2 B borides were hard and thermally stable, hardness, high-temperature hardness, and wear resistance of the PIM products of Fe-based metamorphic powders were twice as high as those of conventional PIM stainless steel products. These findings suggested new applicability of the PIM products of Fe-based metamorphic powders to structures and parts requiring excellent mechanical properties.
    ASME 2008 2nd Multifunctional Nanocomposites and Nanomaterials International Conference; 01/2008
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    ABSTRACT: Effects of high-temperature hardness and oxidation on sticking phenomena occurring during hot rolling of two STS 430J1L ferritic stainless steels were investigated in this study. Hot-rolling simulation test was conducted using a high-temperature wear tester. The sticking started from the initial nucleation stage in which the rolled materials were stuck onto the roll specimen surface, proceeded to the growth stage in which stuck fragments grew further, and reached the saturation stage. The modified 430J1L steel had a smaller number of sticking nucleation sites and slower growth rate than the conventional 430J1L steel because of higher high-temperature hardness, thereby leading to less serious sticking. When the simulation test was conducted at 1070 °C, Cr oxides were formed on the surface of the rolled materials, and thus the sticking was drastically reduced because of the increased surface hardness of the rolled materials. In order to prevent or minimize the sticking, thus, it was suggested to improve high-temperature properties of stainless steels in the case of hot rolling at 900–1000 °C, and to promote the formation of oxides in the case of hot rolling at temperatures higher than 1000 °C.
    Materials Science and Engineering: A. 01/2008; 492:49-59.
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    ABSTRACT: Mechanisms of sticking phenomenon occurring during hot rolling of two ferritic stainless steels, STS 430J1L and STS 436L, were investigated in the present study. A hot-rolling simulation test was carried out using a high-temperature wear tester capable of controlling rolling speed, load, and temperature. The test results at 900 °C and 1000 °C revealed that the sticking process proceeded with three stages, i.e., nucleation, growth, and saturation, for the both stainless steels, and that STS 430J1L had a smaller number of sticking nucleation sites and slower growth rate than the STS 436L because of higher high-temperature hardness, thereby leading to less serious sticking. When the test was conducted at 1070 °C, the sticking hardly occurred in both stainless steels as Fe-Cr oxide layers were formed on the surface of the rolled materials. Thus, in order to prevent or minimize the sticking, it was suggested to improve high-temperature properties of stainless steels in the case of hot rolling at 900 °C to 1000 °C, and to establish appropriate rolling conditions and alloy compositions for ready formation of oxide layers in the case of hot rolling at higher temperatures than 1000 °C.
    Metallurgical and Materials Transactions A 01/2007; 38(11):2776-2787. · 1.73 Impact Factor
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    ABSTRACT: Hardness and corrosion resistance of steel-based surface composites fabricated with Fe-based metamorphic powders by high-energy electron-beam irradiation were investigated in this study. Metamorphic powders were deposited on a plain carbon steel substrate, and then electron beam was irradiated on these powders without flux to fabricate a one-layered surface composite. A two-layered surface composite was also fabricated by irradiating electron beam again onto the powders deposited on the one-layered surface composite. The two-layered composite contained 48 vol.% of hard Cr2B crystalline phases in the Cr0.19Fe0.7Ni0.11 matrix, and thus its hardness was 2.5 times greater than that of the steel substrate. The corrosion resistance of the two-layered composite was better than that of an STS304 stainless steel or a coating fabricated by high-velocity oxygen fuel spraying of Fe-based metamorphic powders. This is because the Cr0.19Fe0.7Ni0.11 matrix of the surface composites and coating was selectively corroded, while Cr2B borides were retained inside pits. In the coating, the localized corrosion additionally occurred along splat boundaries, and thus the corrosion resistance of the coating was worse than that of the two-layered surface composite. These findings suggested that various applications of the fabricated surface composites to materials requiring high resistance to wear and corrosion were expected.
    Surface and Coatings Technology 12/2006; 201:835-841. · 1.94 Impact Factor
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    ABSTRACT: In this study, amorphous matrix composites, whose matrix was a Zr-based amorphous alloy and reinforcements were tungsten continuous fibers or porous foams, were fabricated by the liquid pressing process, and their dynamic compressive properties were investigated. Approximately 65 to 69 vol pct of tungsten fibers or foams were distributed homogeneously in the amorphous matrix, whereas defects such as misinfiltration or pores were eliminated. According to the dynamic compressive test results of the tungsten-fiber-reinforced composite, tungsten fibers worked to withstand a considerable amount of applied loads, whereas the amorphous matrix sustains bent or bucked fibers, thereby leading to the maximum strength of 3328 MPa and the plastic strain of 2.6 pct. In the tungsten-foam-reinforced composite, the compressive stress continued to increase according to the work hardening after the yielding, thereby leading to the maximum strength of 3458 MPa and the plastic strain of 20.6 pct. This dramatic increase in maximum strength and plastic strain was attributed to the simultaneous and homogeneous deformation at tungsten foams and amorphous matrix because tungsten foams did not show anisotropy and tungsten/matrix interfaces were excellent. These findings suggested that tungsten-foam-reinforced composite could be applied to penetrators, in which the self-sharpening should be well promoted while keeping high specific gravity, sufficient strength, and plastic strain because cracks were formed at some heavily deformed tungsten foams by the shear fracture.
    Metallurgical and Materials Transactions A 43(6). · 1.73 Impact Factor
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    ABSTRACT: This study aims at investigating ballistic impact properties of Zr-based amorphous alloy (LM1 alloy) matrix composites reinforced with woven stainless steel or glass continuous fibers. The fiber-reinforced composites with excellent fiber/matrix interfaces were fabricated without pores and misinfiltration by liquid pressing process, and contained 35 to 41 vol pct of woven continuous fibers homogeneously distributed in the amorphous matrix. The woven-STS-continuous-fiber-reinforced composite consisted of the LM1 alloy layer of 1.0 mm in thickness in the upper region and the fiber-reinforced composite layer in the lower region. The hard LM1 alloy layer absorbed the ballistic impact energy by forming many cracks, and the fiber-reinforced composite layer interrupted the crack propagation and blocked the impact and traveling of the projectile, thereby resulting in the improvement of ballistic performance by about 20 pct over the LM1 alloy. According to the ballistic impact test data of the woven-glass-continuous-fiber-reinforced composite, glass fibers were preferentially fragmented to form a number of cracks, and the amorphous matrix accelerated the fragmentation of glass fibers and the initiation of cracks. Because of the absorption process of ballistic impact energy by forming very large amounts of cracks, fragments, and debris, the glass-fiber-reinforced composite showed better ballistic performance than the LM1 alloy.
    Metallurgical and Materials Transactions A 43(3). · 1.73 Impact Factor
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    ABSTRACT: A Zr-based amorphous matrix composite reinforced with tungsten continuous fibers in an amorphous LM2 alloy matrix containing ductile β dendrites was fabricated without pores or defects by the liquid pressing process, and its tensile and compressive properties were examined in relation with microstructures and deformation mechanisms. Overall, 68 vol pct of tungsten fibers were distributed in the matrix, in which 35 vol pct of β dendrites were present. The LM2 composite had the greatly improved tensile strength and elastic modulus over the LM2 alloy, and it showed a stable crack propagation behavior as cracks stopped propagating at the longitudinal cracks of tungsten fibers or ductile β dendrites. According to the compressive test results, fracture did not take place at one time after the yield point, but it proceeded as the applied loads were sustained by fibers, thereby leading to the maximum strength of 2432 MPa and plastic strain of 16.4 pct. The LM2 composite had the higher strength, elastic modulus, and ductility under both tensile and compressive loading conditions than the tungsten-fiber-reinforced composite whose matrix did not contain β dendrites. These distinctively excellent properties indicated a synergy effect arising from the mixing of amorphous matrix and tungsten fibers, as well as from the excellent bonding of interfaces between them.
    Metallurgical and Materials Transactions A 43(11). · 1.73 Impact Factor