• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.422-423
• /
• 2006

Ultrasonic-milling of metal oxide nanopowders for the preparation of tungsten heavy alloys was investigated. Milling time was selected as a process variable. XRD results of metal oxide nanopowders ultrasonic-milled for 50 and 100h showed that mean crystallite size reduced with increasing milling time and there was no evidence of contamination or change of composition by impurities. It was found that nanocomposite powders reduced at $800^{\circ}C$ in $H_2$ atmosphere had a composition of 93.1W-4.9Ni-2.0Fe by EDX analysis. Hardness of sintered samples of 50 and 100h was 390 and 463 Hv, respectively, which corresponds to the hardness of commercial products.

• Transactions of Materials Processing
• /
• v.8 no.3
• /
• pp.283-283
• /
• 1999

In the present study, the effect of microporosity on the tensile properties of as-cast AZ91D magnesium alloy was investigated through experimental observation and numerical prediction. The test specimens were fabricated by die-casting and gravity-casting. For gravity-casting, the inoculation and use of various metallic moulds were applied to obtain a wide range of microporosity. The deficiency of the interdendritic feeding of the liquid phase acted as d dominant mechanism on the formation of the micropores in the Mg-Al-alloys, rather than the evolution of hydrogen gas. Although tensile strength and elongation has a nonlinear and very intensive dependence upon microporosity, the yield strength appeared to have a linear relationship with microporosity. However, it was possible to quantitatively estimate the linear contribution of microporosity on the individual tensile property far a range of microporosity, which was below about B %. The numerical prediction suggests that the effect of microporosity on fractured strength and elongation decreased as the strain hardening exponent increased. Furthermore. the shape and distribution of micropores may play a more dominant role than local plastic deformation on the tensile behavior of AZ9lD alloy.

• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.16-16
• /
• 2009

Alloy 82/182로 용접된 원자력 발전소 주기기의 이종 금속 용접부는 장기간 운전 후 응력부식균열(SCC : Stress Corrosion Cracking)에 의한 결함이 나타나게 된다. 2000년대 이후로 원자력 주기기 Alloy 82/182 용접부에서 PWSCC(Primary Water Stress Corrosion Cracking)에 의한 Degradation이 급격히 증가하는 추세를 보이고 있으며, 국내에서도 이와 관련하여 원자력 발전소의 안전성에 대한 Issue 및 대비책에 대한 관심이 고조되고 있다. 이러한 Alloy 600 용접부에 대한 결함을 예방하기 위한 대표적인 기술로써 수명연장 오버레이 기술이 있다. 원자력 주기기 노즐부는 저탄소강으로 제작되어 있으며, 저탄소강에는 제작 시 용접후열처리가 적용된다. 후열처리를 하는 주된 이유는 Tempering을 통해 열영향부의 인성 및 연성의 회복과 강도를 감소시켜 모재와 동등 또는 이 이상의 물성을 갖도록 하는 데 그 목적이 있다. 그러나 수명연장 오버레이의 경우 현장 작업 시에 후열처리가 어렵기 때문에, 이를 대체하기 위한 기술로 템퍼비드 용접을 적용할 경우 후열처리를 면제해 주고 있다. 본 연구에서는 수명연장 오버레이 기술 개발의 일환으로써 저 탄소강에 대한 템퍼비드 용접 기술을 확립하였다. 실험에 사용된 모재는 원자력 주기기의 노즐에 사용되는 SA508 Gr.3 Cl.1을 사용하였으며, 용가재는 Alloy 52 및 52M을 사용하였다. 최적 조건 도출을 위해서 실험 매트릭스를 이용하여 기본 실험을 수행하였으며, 실험에는 자동 GTAW 용접을 적용하였다. 기본 실험을 통해 얻은 최적 조건을 사용하여 PQ 시험을 수행하여 WPS를 확보하였다. 분석은 용접 후 조직 및 경도 시험, 물리시험(인장시험, 굽힘시험 및 충격시험)을 수행하였다.

• Journal of the Korean Applied Science and Technology
• /
• v.33 no.3
• /
• pp.441-448
• /
• 2016

Heavy metal removal study is conducted from synthetic waste water by reduction and oxidation(redox) reaction of Cu-Zn metal alloy and adsorption reaction of aluminium silicate. Heavy metal whose ionization tendency is smaller than zinc are reducted in an aqueous solution, and the concentration of ionized zinc is reduced by adsorption reaction. The average diameter of metal alloy micro fiber is about $200{\mu}m$, and the surface area is wide enough to get equilibrium in a single cycle treatment. A single cycle treatment of redox reaction of Cu-Zn metal alloy, could remove 100.0 % of Cr(III), 98.0 % of Hg, 92.0 % of Sn and 91.4 % of Cu respectively. An ionization tendency of chromium is very close to zinc, but removal efficiency of chromium by redox reaction is significant. This result shows that trivalent chromium ion is expected to generate hydroxide precipitation with $OH^-$ ion generated by redox reaction. Zinc ion generated by redox reaction is readily removed by adsorption reaction of aluminium silicate in a single cycle treatment. Other heavy metal components which are not perfectly removed by redox reaction also showed very high removal efficiency of 98.0 % or more by adsorption reaction. Aluminium ion is not increased by adsorption reaction of aluminium silicate. That means heavy metal ion removal mechanism by adsorption reaction is turned out to be not an ion exchange reaction, but an adsorption reaction.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.3
• /
• pp.497-504
• /
• 2002

The purpose of this study is to analyze thermal cycles and to investigate microstructures of heat affected zones for a low alloy carbon steel pipe under a multipass weld. The commercial finite element code SYSWELD is used to compute thermal cycles during multipass weld. The numerical results such as thermal cycles and size of heat affected zone are compared with those of the experiment and the two results show a good agreement. In addition, the microstructure and hardness are investigated from the weldment in detail. The weakest location is founded at intercritical region near the base metal.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2000.10a
• /
• pp.55-61
• /
• 2000

Tungsten heavy metal is characterized bi a high density and novel combination of strength and ductility. Among them, 90W-7Ni-3Fe is used for applications, where the high specific weight of the material plays an important role. They are used as counterweights, rotating inertia members, as well as for defense purposes(kinetic energy penetrators, etc.). Because of these applications, it is essential to detemine the dynamic characteristics of tungsten alloy. In this paper, Explicit FEM(finite element method) is employed to investigate the dynamic characteristics of tungsten heavy metal under base of stress wave propagation theory for SHPB, and the model of specimen is divided into two parts to understand the phenomenon that stress wave penetrates through each tungsten base and matrix. This simulation results were compared to experimental one and through this program the dynamic stress-strain curve of tungsten heavy metal can be obtained using quasi static stress-strain curve of pure tungsten and matrix.

• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.8 s.173
• /
• pp.92-99
• /
• 2005

Tungsten heavy metal is characterized by a high density and novel combination of strength and ductility. Among them, 90W-7Ni-3Fe is used for applications, where the high specific weight of the material plays an important role. They are used as counterweights, rotating inertia members, as well as fur defense purposes(kinetic energy Penetrators, etc.). Because of these applications, it is essential to detemine the dynamic characteristics of tungsten alloy. In this paper, Explicit FEM(finite element method) is employed to investigate the dynamic characteristics of tungsten heavy metal under base of stress wave propagation theory for SHPB, and the model of specimen is divided into two parts to understand the phenomenon that stress wave penetrates through each tungsten base and matrix. This simulation results were compared to experimental one and through this program, the dynamic stress-strain curve of tungsten heavy metal can be obtained using quasi static stress-strain curve of pure tungsten and matrix.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 1998.10b
• /
• pp.28-28
• /
• 1998

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 1999.04a
• /
• pp.39-39
• /
• 1999

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 1996.11a
• /
• pp.8-8
• /
• 1996