National Kangshan Agricultural Industrial Senior High School

Kaohsiung, Taiwan

National Kangshan Agricultural Industrial Senior High School

Kaohsiung, Taiwan
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Huang K.-T.,National Kangshan Agricultural Industrial Senior High School | Chang S.-H.,National Taipei University of Technology | Hsieh P.-C.,National Taipei University of Technology
Journal of Alloys and Compounds | Year: 2017

Different amounts of niobium carbide (NbC) powder (5, 10 and 15 wt%) are mixed and added to 440C stainless steel powder. The composite powders are sintered at 1260, 1270, 1280 and 1290 °C for 1 h, respectively. The experimental results show that the optimal sintering temperature for the 440C-NbC composites is 1270 °C. Meanwhile, the 440C specimens with 5% NbC addition possess the optimal transverse rupture strength (TRS) value of 1985.2 MPa, as well as the highest polarization resistance of 1.01 × 102 Ω cm2. While the 440C specimens contain or with 15 wt% NbC show the highest hardness value of HRA 80.9 after sintering at 1280 °C. Furthermore, the microstructural evaluation reveals that the rod-shaped M7C3 carbides located on the grain boundaries are gradually reduced after NbC particles are added, and the spherical-shaped M7C3 carbides are precipitated and dispersed in the matrix. After heat treatment, the primary M7C3 carbides are converted to M23C6 carbides, which results in a secondary hardening. The results clearly show that heat treatment effectively improves the particle size of the carbides and strengthens the matrix of the 440C-NbC composites. © 2017 Elsevier B.V.


Chang S.-H.,National Taipei University of Technology | Li C.-L.,National Taipei University of Technology | Huang K.-T.,National Kangshan Agricultural Industrial Senior High School
Materials Transactions | Year: 2017

The aim of this work is to find the optimal sintering parameters of Cr-31.2 mass% Ti alloys and simultaneously investigate the effects of the TiCr2 Laves phases. In this study, Cr-31.2 mass% Ti alloys are fabricated by vacuum hot-press sintering. Different compositions of submicron titanium (760 nm) powders are added to micron chromium (4.66 μm) powders. The experiments utilize various hot-press sintering temperatures (1250, 1300, 1350 and 1400°C) with the pressure maintained at 20 MPa for 1 h, respectively. The experimental results show the optimal parameters of the hot-press sintered Cr-31.2 mass% Ti alloys to be 1400°C at 20 MPa for 1 h. The relative density reaches 99.96% and the hardness and TRS (transverse rupture strength) reach 81.93 HRA and 475.73 MPa, respectively. In addition, the increase in temperature of the hot-press sintering is effectively decreased the Cr3Ti3O and slightly enhanced TiCr2 phases, which will lead to the better mechanical properties. Significantly, the optimal hot-press sintered Cr-31.2 mass% Ti alloys possess a dense microstructure, excellent mechanical property and good electrical conductivity value (1.51 × 104 Scm-1). © 2017 The Japan Institute of Metals and Materials.


Huang K.T.,National Kangshan Agricultural Industrial Senior High School | Chang S.-H.,National Taipei University of Technology | Yeh P.-T.,National Taipei University of Technology
ISIJ International | Year: 2017

In this study, different amounts of TaC powders (10, 15 and 20 mass%) are mixed and added to Vanadis 4 tool steel powder. The composite powders are sintered at 1 250, 1 300 and 1 325°C for 1 h, respectively. After that, a series of heat treatments is performed to determine the optimal parameters of the Vanadis 4 composites. The experimental results show the optimal vacuum sintering temperature for the Vanadis 4 composites to be 1 300°C. The Vanadis 4 specimens with a 10% TaC added possess the highest transverse rupture strength (TRS) value of 1 974.2 MPa and a suitable hardness (82.6 HRA). When the optimally sintered specimens of the Vanadis 4 composites then undergo a heat treatment, the TRS shows a significant increase to 2 069.4 MPa, while the hardness declines slightly to 81.5 HRA. In addition, the microstructural evaluation reveals that the plate-shaped carbides (M7C3) located on the grain boundaries disappear after the TaC powders are added and that clustered TaC carbides appear in the grain boundaries instead. Meanwhile, with TaC as the nucleation sites of the VC carbides, the result is the generating of VC carbides in the grain boundaries. Moreover, the VC carbides decompose and re-precipitate the refined carbides (Fe3C), which are uniformly distributed within the grains. The results also show that heat treatment effectively improves the microstructure and strengthens the Vanadis 4 composites. © 2017 ISIJ.


Chang S.-H.,National Taipei University of Technology | Yeh P.-T.,National Taipei University of Technology | Huang K.-T.,National Kangshan Agricultural Industrial Senior High School
Vacuum | Year: 2017

In this study, different ratios (1, 3 and 5 mass%) of niobium carbide (NbC) powders were added to Vanadis 4 alloy steel powders. The composite powders utilized vacuum sintering at 1250, 1275 and 1300 °C for 1 h, respectively. The experimental results show that good mechanical properties were obtained by the addition of 5 mass% NbC sintered at 1275 °C for 1 h. Meanwhile, the apparent porosity was decreased to 0.13%, and the transverse rupture strength (TRS) and hardness reached 1822.6 MPa and 81.9 HRA, respectively. When optimally sintered Vanadis 4 composites then underwent a heat treatment, the TRS showed a significant increase to 2093.3 MPa, but the hardness declined slightly to 81.5 HRA. Notably, the heat treatment improved the distribution and size of the VC carbides, which effectively enhanced the strength. The decrease in hardness could be ascribed to the release of internal stress after the tempering process. Consequently, the heat treatment process is effective in improving the microstructure and strengthens the sintered Vanadis 4 composites. © 2017 Elsevier Ltd


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.


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.


Chang S.-H.,National Taipei University of Technology | Lee C.I.,National Taipei University of Technology | Huang K.-T.,National Kangshan Agricultural Industrial Senior High School
ISIJ International | Year: 2014

In this study, diamond-like carbon (DLC) films were prepared by DC-pulsed plasma CVD after the oxynitride treatment of AISI H13 tool steel. In order to investigate the tribological properties of DLC films, a Raman spectroscopy analysis, wear test, adhesion and roughness tests were performed. The main parameters of the DC-pulsed plasma CVD process includes various pretreatment times of argon plasma (15, 30, 45 and 60 min). Experimental results showed that an oxynitride layer and the DLC films could be completely obtained after DLC/oxynitriding duplex treatment. The duplex coating layers had optimal adhesion (critical load reached to 10.65 N) and wear properties after DC-pulsed plasma was CVD treated via a low pulse voltage (-1.5 kV), pretreatment times of the argon plasma were 15 min and the substrate temperature was kept at 40°C. Meanwhile, the optimal DLC/oxynitriding duplex treated specimens possessed the lowest wear volume (2.25 × 10-3 mm3) and a lower friction coefficient (0.06). © 2014 ISIJ.


Huang K.-T.,National Kangshan Agricultural Industrial Senior High School | Chang S.-H.,National Taipei University of Technology | Wu M.-W.,National Taipei University of Technology | Wang C.-K.,National Taipei University of Technology
ISIJ International | Year: 2016

This study utilized two different sizes of 440C pre-alloy powders for vacuum sintering under different sintering temperatures (1 523, 1 533, 1 543 and 1 553 K) to explore the microstructure and mechanical properties of 440C stainless steel. The experimental results indicated that the sintered specimens of the refined alloy powders had good hardness and transverse rupture strength (TRS), due to the smaller grain size of the sintered body and the uniform distribution of the carbides. In addition, two types of carbide precipitates appeared in the microstructure. Fine carbides (M23C6) within the grains and rod-shaped types of carbide (M7C3) on the grain boundaries were observed after sintering at 1 543 K for 1 h. The research also showed that a suitable amount of carbides is helpful in improving the TRS. However, the fine carbides (M23C6) within the grains almost disappeared and the rod-shaped types of carbide (M7C3) on the grain boundaries coarsen after sintering at higher temperatures (1 553 K), and so detrimental to the TRS. © 2016 ISIJ.


Chang S.-H.,National Taipei University of Technology | Tang T.-C.,National Taipei University of Technology | Huang K.-T.,National Kangshan Agricultural Industrial Senior High School | Liu C.-M.,Lunghwa University of Science and Technology
Surface and Coatings Technology | Year: 2015

In this study, diamond-like carbon (DLC) films are coated onto oxynitriding-treated ASP23 high-speed steel by DC-pulsed PECVD. The main research parameters of the DC-pulsed PECVD process are the various duty cycles (5%, 10%, 15% and 20%) used to examine the coating characteristics. In order to investigate the DLC film properties, a Raman spectroscopy analysis, wear test, adhesion, and hardness tests are performed. The experimental results show that the duplex coating layers have optimal properties when DLC films are treated with a low-pulse voltage (-1.5kV), a coating time of 90min and duty cycles maintained at 10%. As a result, the DLC/oxynitriding duplex-treated specimens with the highest surface hardness (Hv0.01 1931) and the lowest wear volume loss (3×10-3mm3) can be acquired. In addition, compared with non-treated (polarization resistance Rp=5×103Ωcm2) and oxynitriding-treated (Rp=8×103Ωcm2) specimens, the optimal DLC/oxynitriding duplex-treated ASP23 high-speed steel possesses the lowest corrosion current (Icorr=8×10-6Acm-2) and highest polarization resistance (Rp=1×104Ωcm2) in 3.5wt.% NaCl solutions. This result confirms that the DLC/oxynitriding duplex treatment enhances optimal wear and corrosion resistance. © 2014 Elsevier B.V.


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.

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