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Huang K.-T.,National Kangshan Agricultural Industrial Senior High School | Chang S.-H.,National Taipei University of Technology | Lui T.-S.,National Cheng Kung University
Materials Transactions | Year: 2015

This study prepared a 5052H112 alloy under different cold-rolled reductions to explore its microstructure and mechanical properties. The experimental results indicated that the cold-rolled specimens had good tensile properties and better vibration fracture resistance, due to the high densities of dislocation and small aspect ratio of crystal grain. The stress-elongation curves of all specimens showed the serrated yielding. The high densities of dislocation and small aspect ratio of crystal grain introduced by cold-rolling could hold the mobile dislocations long enough to let Mg atoms form atmospheres around them. In addition, the crack propagation behavior of all specimens showed that slip bands can be observed in the vicinity of the main crack and be suppressed by increasing the cold-rolled reduction. Crack propagation showed that rolled specimens exhibit decreasing crack propagation rates with increased matrix strengthening (cold-rolling). Therefore, it can be concluded that a large number of dislocation tangles introduced by cold-rolling are effective in improving mechanical properties. © 2015 The Japan Institute of Metals and Materials. Source


Chang S.-H.,National Taipei University of Technology | Chen S.-H.,National Taipei University of Technology | Huang K.-T.,National Kangshan Agricultural Industrial Senior High School
Materials Transactions | Year: 2013

The aim of this paper is to study and produce Cr70Cu30 alloys via vacuum sintering, hot isostatic pressing (HIP) and hot pressing (HP) of powder metallurgy technology. The experimental results show that a lower density of Cr70Cu30 alloys is produced after vacuum sintering, owing to the many pores existing in the sintered Cr70Cu30 alloys, which are not completely removed by HIP treatment. Conversely, the HP treatment of Cr70Cu30 alloys at 1000°C 60MPa for 1 h achieves the optimal density (97.82%), lower apparent porosity (0.65%) and higher international annealed copper standard (IACS) value (22.78%). Moreover, it also obtains the highest hardness (HRB 68.7) and transverse rupture strength (TRS) value (843 MPa). The results indicate that the closed pores can be effectively eliminated and that the mechanical properties of Cr70Cu30 alloys are obviously improved by HP treatment. Meanwhile, the Cr70Cu30 alloys also have an improved microstructure and electrical conductivity. © 2013 The Japan Institute of Light Metals. Source


Chang S.-H.,National Taipei University of Technology | Liang C.,National Taipei University of Technology | Huang J.-R.,National Taipei University of Technology | Huang K.-T.,National Kangshan Agricultural Industrial Senior High School
Powder Metallurgy | Year: 2016

In this study, two different compositions of submicrometre copper and chromium powders were mixed and the Cr50Cu50 alloys were fabricated via the powder metallurgy technique. The research imposed various hot pressing pressures, while the temperature was maintained at 1050°C for 1 h, respectively. The experimental results showed that the Saint Venant's effect obviously appeared in 1050°C, 48 MPa, 1 h hot pressing Cr50Cu50 alloys, which led to differences in the surface and internal hardness of the specimens. As a result, the optimal parameters of hot pressing of Cr50Cu50 alloys were 1050°C, 36 MPa for 1 h possessing the highest transverse rupture strength value (921.69 MPa). Moreover, the surface hardness increased to HV0.2 221.78 (HRB 95.4), the relative density reached 97.15% and apparent porosity decreased to 0.10%, respectively. Furthermore, the resistivity decreased to 5.28 × 10−6 Ω cm, and ICAS was enhanced to 32.65% after the optimal procedure. © 2016 Institute of Materials, Minerals and Mining. Source


Chang S.-H.,National Taipei University | Chang M.-H.,National Taipei University | Huang K.-T.,National Kangshan Agricultural Industrial Senior High School
Journal of Alloys and Compounds | Year: 2015

Abstract In this work, four different vacuum sintering temperatures (1250 C, 1300 C, 1350 C and 1400 C) were studied to determine the optimal process parameters of nano WC-15 wt% (Fe-Ni-Co) and WC-15 wt% Co sintered hard metal alloys. Experimental results showed that the optimal sintering temperatures for nano WC-(Fe-Ni-Co) and WC-Co alloys were 1300 C and 1350 C for 1 h, respectively. The sintered nano WC-(Fe-Ni-Co) and WC-Co hard metal alloys showed a good contiguity of 0.44 and 0.42; hardness was enhanced to HRA 90.83 and 90.92; the transverse rupture strength (TRS) increased to 2567.97 and 2860.08 MPa; and KIC was 16.23 and 12.33 MPa√m, respectively. Although the nano WC-(Fe-Ni-Co) alloys possessed a slightly lower TRS value, they exhibited superior fracture toughness (KIC) and hardness similar to that of the nano WC-Co material. Significantly, nano WC-(Fe-Ni-Co) alloys could be sintered at a lower temperature and still retained their excellent mechanical properties. © 2015 Elsevier B.V. Source


Chang S.-H.,National Taipei University of Technology | Chen J.-C.,National Taipei University of Technology | Huang K.-T.,National Kangshan Agricultural Industrial Senior High School | Chen J.-K.,National Taipei University of Technology
Materials Transactions | Year: 2013

This study investigated Ni-50 mass% Cr alloys produced by the vacuum sintering and hot isostatic pressing (HIP) of powder metallurgy technology. The experimental results showed that the relative density of Ni-50 mass% Cr alloys reached 98.67%, the apparent porosity decreased to 1.33%, transverse rupture strength (TRS) increased to 454.29MPa and electrical resistivity decreased to 4.284 × 10-4ω ·cm after 1345°C sintering for 1 h. Meanwhile, laminar eutectic precipitations appeared in the sintered Ni-50 mass% Cr alloys. In addition, the relative density increased to 99.73%, the apparent porosity decreases to 0.27% and TRS was obviously enhanced to 1181.4MPa after 1260°C 175 MPa 4 h HIP treatment. Moreover, the electrical resistivity decreased to 3.346 × 10-4ω ·cm after the optimal HIP treatment. This study showed that the HIP process is effective in eliminating internal pores and improving the mechanical and electrical properties of the sintered Ni-50 mass% Cr alloys, thus obtaining the high density and optimum properties of the sintered materials. © 2013 The Japan Institute of Metals and Materials. Source

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