극저온 밀링과 탄화환원법을 이용한 나노 크기의 (Ti,W)(CN)-Ni 분말의 합성

권한중,강영재,정진관,강신후 한국분말야금학회 2004 한국분말야금학회 학술대회논문집 Vol.2004 No.1

텅스텐산암모늄 단계 생략 초경합금 슬러지 재활용 공정에 의해 제조된 텅스텐의 소결 및 경도 특성

권한중,신정민 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.1

In this paper, we suggest a novel recycling process for hard metal sludge that does not use ammonium paratungstate. Ammonia, which in the conventional recycling process is essential for removing sodium and crystallized tungstate, was not used in the novel process. Instead of ammonia, acid was used to remove the sodium and crystallized tungstate resulting in the formation of tungstic acid (H2WO4). Tungsten powders were successfully synthesized by hydrogen reduction of the tungstic acid through H2O decomposition, WO3 to WO2 reduction, and tungsten metal formation. The tungsten powders prepared from tungstic acid were spherical in shape and had a higher sintering density than the facet-shaped tungsten powders prepared from tungsten oxide. The spherical shape of the tungsten powders enhanced their sinterability and resulted in an increase in the size of grains. This is a result of the high diffusion rate of the atoms along the particle surfaces. Despite having a higher density, the hardness of the sintered tungsten was lower than that of tungsten from tungsten oxide. High energy milling effectively reduced grain size and improved hardness. The hardness of the tungsten prepared from milled tungstic acid was enhanced to a value (max. 471 HV) higher than the best previously reported value (389 HV). In sum, tungsten can be hardened, thereby improving its sinterability and reducing grain size, with tungstic acid prepared using the proposed recycling process.

고용 강화 금속 바인더(Co1-xWx) 적용을 통한 초경합금의 기계적 특성 향상

권한중 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.1

The metallic binder in WC-Co hard metals was effectively strengthened using the solid solution phases of Co and W. These metallic phases of Co and W (Co1-xWx, x<1), which consist of two kinds of structures (FCC and HCP), were successfully formed by hydrogen reduction of milled oxides mixtures (Co3O4 and WO3) at over 1000 oC. When hard metals are fabricated by pressureless sintering of mixed WC and Co1-xWx, the hard metals containing the WC2 and M6C phases (Co2W4C and Co4W2C) have brittleness, which degrades their mechanical properties, like hard metals fabricated from mixtures of WC, Co, and W. By rapidly sintering the WC-Co1-xWx hard metals for 5 min the W2C and M6C phases were eliminated, and a two-phase (WC and the metallic phase of Co and W) region was successfully obtained. The mechanical properties of the WC-Co1-xWx hard metals showed higher values for both hardness (max. 18.8 GPa) and fracture toughness (8.5 MPa·m1/2) than conventional WC-Co hard metal (HV: 15.9 GPa, KIC: 6.9 MPa·m1/2). The enhancement in toughness was attributed to the solid solution strengthening of the metallic binder and the elimination of the WC2 and M6C phases. The suppression of grain growth due to the short duration of sintering also played a positive role in improving the hardness of the WC-Co1-xWx hard metals. The phase-controlled solid solution metallic binder could be the key material to enhance the hardness and toughness of hard metals.

Phase Stability Diagrams of Ti–M–O–C (M = Zr, Hf, Nb, and Ta) Systems at 1800 K

권한중,Ahram Moon,Jiwoong Kim 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.2

Phase stability diagrams of Ti–M–O–C (M = Zr, Hf, Nb, and Ta) systems at 1800 K were constructed as a function of thecarbon activity, oxygen partial pressure, and solution formation characteristics, in order to determine the optimum conditionsfor the formation of (Ti0.75M0.25)C via carbothermal reduction of oxide mixtures. The tendency to form (Ti0.75M0.25)Cwas predicted on the basis of the standard Gibbs free energies of formation (ΔG◦f) of (Ti0.75M0.25)C solid-solution carbides,calculated by first-principles simulations. It was concluded that at 1800 K, the (Ti0.75Nb0.25)C and (Ti0.75Ta0.25)C phases aremore stable than the TiC–NbC and TiC–TaC mixtures, whereas the (Ti0.75Zr0.25)C and (Ti0.75Hf0.25)C phases are less stablethan the corresponding TiC–ZrC and TiC–HfC mixtures. The phase stability diagrams of the Ti–M–O–C systems were thendrawn using the calculated ΔG◦f values and used to predict the tendencies to form solid-solution phases. The validity of thetheoretical predictions was then verified using experimental results.

타이타늄 밀링/터닝 스크랩의 절삭공구 소재화

권한중,임재원,Kwon, Hanjung,Lim, Jae-Won 한국자원리싸이클링학회 2021 資源 리싸이클링 Vol.30 No.2

Scraps are a byproduct of the machining process used for transforming titanium ingots into useful mechanical parts. Scraps take two forms, namely, bulky scraps, which are produced by cutting, and chipped scraps, which are produced by milling. Bulky scraps are comparatively easier to recycle because of their small surface area and less oxygen content; as a result, they pose only a small risk of explosion. In contrast, chipped scraps pose a higher risk of explosion, because of which, their recycling is complicated, resulting in most such scraps being discarded. With the aim of avoiding this waste, we proposed a novel process for converting chipped scraps into stable carbide materials. Methods typically applied to reduce particle size and impair the formation of solid solution type phase in the carbide materials were used to improve the mechanical properties of carbides prepared from chipped scraps. Our novel recycling process reduced carbide production costs and improved carbide quality.

실리콘 기판 슬러지로부터 고순도 탄화규소 분말 합성

권한중,김민희,윤지환 한국자원리싸이클링학회 2022 資源 리싸이클링 Vol.31 No.6

This study presents the carburization process for recycling sludge, which was formed during silicon wafer machining. The sludge used in the carburization process is a mixture of silicon and silicon carbide (SiC) with iron as an impurity, which originates from the machine. Additionally, the sludge contains cutting oil, a fluid with high viscosity. Therefore, the sludge was dried before carburization to remove organic matter. The dried sludge was washed by acid cleaning to remove the iron impurity and subsequently carburized by heat treatment under vacuum to form the SiC powder. The ratio of silicon to SiC in the sludge was varied depending on the sources and thus carbon content was adjusted by the ratio. With increasing SiC content, the carbon content required for SiC formation increased. It was demonstrated that substoichiometric SiCx (x<1) was easily formed when the carbon content was insufficient. Therefore, excess carbon is required to obtain a pure SiC phase. Moreover, size reduction by high-energy milling had a beneficial effect on the suppression of SiCx, forming the pure SiC phase. 본 논문에서는 반도체용 실리콘 기판 가공 과정에서 발생한 슬러지 재활용을 위해 탄화 반응에 의한 탄화규소(SiC) 분말 합성 공정을적용한 결과를 제시하고자 한다. 입수한 슬러지는 실리콘 기판을 탄화규소 연마재를 사용하여 가공하는 과정에서 발생하므로 실리콘과탄화규소가 혼합된 형태였으며 가공 설비로부터 발생한 철 불순물이 포함되어 있었다. 슬러지는 절삭유가 포함되어 있어 점성이 있는 유체 형태였으며 대기 건조를 통해 분말 형태로 변화된 후 산 세정을 통한 철 성분 제거 및 탄화에 의한 탄화규소 분말 합성 과정을 거치게된다. 슬러지에 포함된 실리콘과 탄화규소의 비율에 따라 탄화 반응에 필요한 탄소량이 달랐으며 탄화규소의 함량이 커질수록 탄소 부족현상으로 인해 비화학량론적 탄화물(SiCx, x<1) 형성이 촉진되어 순수한 탄화규소 합성이 이루어지지 않는 것을 확인하였다. 이러한 비화학량론적 탄화물은 잉여 탄소 추가와 고에너지 밀링에 의한 탄화 반응성 증가를 통해 제거할 수 있었으며 결과적으로 산 세정과 밀링과정에 의해 슬러지로부터 순수한 탄화규소 분말 합성이 가능함을 확인할 수 있었다.

초경합금 슬러지 재활용 공정 산물을 활용한 텅스텐 탄화물 제조 및 특성 평가

권한중,신정민 한국자원리싸이클링학회 2022 資源 리싸이클링 Vol.31 No.4

In this study, tungsten carbide (WC) powder was prepared using a novel recycling process for hard metal sludge that does not use ammonium paratungstate. Instead of ammonia, acid was used to remove the sodium and crystallized tungstate, resulting in the formation of tungstic acid (H2WO4). The WC powder was successfully synthesized by the carbothermal reduction of tungstic acid through H2O decomposition, reduction of WO3 to W, and formation of WC. The carbon content and holding time at the carbothermal reduction temperature were optimized to remove free carbon from the WC powder. As a result, most of the free carbon in the WC powder prepared from sludge was removed, and the content of free carbon in the synthesized WC powder was lower than that in commercial WC powder. Moreover, the crystallite size of WC prepared from H2WO4 was much smaller than that of commercial micron-sized WC powder produced from APT. The small crystallite size of WC induces grain growth during the sintering of the WC-Co composite; thus, a WC-Co composite with large WC grains was fabricated using the WC powder prepared from H2WO4. The large WC grains affected the mechanical properties of the WC-Co composite. Further, due to the large grain size, the WC-Co composite fabricated from H2WO4 exhibited a higher toughness than that of the WC-Co composite prepared from commercial WC powder. 본 연구에서는 텅스텐산암모늄(APT, Ammonium Paratungstate, (NH4)10[W12O46H10])이 사용되지 않는 친환경 초경합금 슬러지 재활용 공정을 통해 초경합금 주원료인 텅스텐 탄화물 분말을 합성하고자 하였다. 초경합금 슬러지에 대한 산 처리를 통해 텅스텐산(H2WO4) 추출 및 결정화를 수행하고 결정화된 텅스텐산을 텅스텐 탄화물의 원료로 사용하였다. H2WO4에 대한 탄화환원을 통해 텅스텐탄화물 (WC) 분말이 합성되었고 합성된 WC 분말은 200~700nm 수준의 결정립으로 구성되어 있음이 확인되었다. 이는 현재 절삭공구로가장 널리 사용되는 1~3μm 입도의 상용 WC 분말에 비해 미세한 것으로 텅스텐 금속 분말에 대한 고온(1,700℃ 이상) 고상 탄화법을 통해 제조되는 상용 WC 분말과 달리 H2WO4 나노 결정립에 대한 탄화환원을 통해 WC 분말이 합성되었기 때문으로 사료된다. H2WO4로부터 합성된 WC 분말의 경우 탄화환원에 의해 탄소의 제거가 수월하여 상용 WC 분말에 비해 잔류 탄소가 적은 것으로 확인되었으며 작은 결정립 크기로 인해 초경합금 원료로 사용되었을 때 WC-Co 복합체 내 WC 입자의 성장이 활발하게 일어나 H2WO4로부터 합성된WC 분말이 적용된 WC-Co 복합체의 경우 WC 입자가 조대하고 파괴인성이 우수한 것으로 확인되었다.

계면 개선을 통한 타이타늄 탄/질화물 금속 복합재료의 기계적 물성 향상

권한중 한국세라믹학회 2020 세라미스트 Vol.23 No.1

Fracture in the titanium carbonitride-metal composites occurs by crack propagation through the carbonitride grains or in the interfaces. Thus, intrinsic properties of the carbonitride need to be enhanced and the interfaces should be also modified to coherent structure to strengthen the composites. Especially, interfacial structure can be the main factor to determine the mechanical properties of titanium carbonitridemetal composites because the interfaces between carbonitride grains and metallic phase are weak parts due to heterogeneous nature of carbonitride and metallic phase. In this paper, methodologies for improving the interfacial structure of titanium carbonitride-metal composites are suggested. Total area of the interfaces can be reduced using solid solution type carbonitrides as raw materials instead of a mixture of various carbonitrides in the composites. Also, synthesis of titanium carbonitride-metal composite powders and the low-temperature sintering of the composite powders for short time can be the way for formation of coherent interfaces. The sintering of the composite powders for short time at low temperature can reduce the potential of formation of interfaces by dissolution and precipitation of carbonitride in the liquid metal. As a result of formation of coherent boundaries due to low-temperature and short-time sintering, interfaces between titanium carbonitride grains and metallic phase have the favorable structure for the enhanced fracture toughness. It is believed that the low-temperature sintering of solid solution type composite powders for short time can be the way to improve the low toughness of the titanium carbonitride-metal composites.

MXene 합성용 탄화물 원료 제조 기술

권한중(Hanjung Kwon),구종민,오정민 한국고분자학회 2023 한국고분자학회 학술대회 연구논문 초록집 Vol.48 No.2

절삭공구용 초경합금 기계적 물성 개선

권한중(Hanjung Kwon) 한국세라믹학회 2023 세라미스트 Vol.26 No.3

The cutting tools used to machine metallic ingots are produced using hard metals with excellent wear resistance. These hard metals consist of hard phases (transitional metal carbides) and tough phases (metallic phases), though microstructural variables such as grain size, mean free path, and coherency in interfaces between the phases will also affect the properties of the hard metals. Accordingly, the mechanical properties of hard metals can be improved by strengthening both phases, or by adjusting various other factors that affect the microstructure and mechanical properties of the hard metals. In this paper we review the factors that have been identified as controlling the microstructure and associated properties, as well as the diverse research concerning the improvement of hard metals. We ultimately conclude that fine grains of solid-solution strengthened carbides with hard metallic phases are necessary for producing hard metals with superior mechanical properties, as is the formation of a coherent interfacial structure, as the interfacial area is relatively weaker than the grain inside.