• Tribology and Lubricants
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• v.36 no.4
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• pp.199-206
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• 2020

CoCr-based alloys have been developed as wear-resistant materials owing to their excellent mechanical properties and strong wear resistance. The purpose of this study is to experimentally assess the frictional and wear characteristics of CoCr-based alloys slid against two different counter materials subjected to various normal forces to determine the expansion applicability of CoCr-based alloys. CoCrMo and CoCr alloys were selected as the target materials and NiCr and NiCrB alloys as counter materials. Experimental tests were performed using a pin-on-reciprocating plate tribo-tester under dry lubrication. Before performing the tests, the surface of the specimens was observed through confocal microscopy and the hardness was measured using a micro-Vickers hardness tester. The wear volume of the plate was calculated at the end of the tests using confocal microscope data, and the wear rate was quantitatively obtained based on Archard's wear law. From the results, the wear rates of the CoCrMo specimens that slid against NiCr and NiCrB are 7.69 × 10^-6 ㎣/Nm and 5.26 × 10^-6 ㎣/Nm, respectively. The wear rates of the CoCr specimens that slid against NiCr and NiCrB were higher than those of the CoCrMo specimens by factors of approximately 4 and 8, respectively. The CoCrMo specimens further exhibited lower friction characteristics than the CoCr specimens. The findings of this study will be useful for expanded applications of CoCr-based alloys as wear-resistant materials for various mechanical parts.

• Journal of Powder Materials
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• v.27 no.3
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• pp.210-218
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• 2020

A T-800 (Co-Mo-Cr) coating material is fabricated using Co-Mo-Cr powder feedstock and laser cladding. The microstructure and melted Al erosion properties of the laser-cladded T-800 coating material are investigated. The Al erosion properties of the HVOF-sprayed MoB-CoCr and bulk T-800 material are also examined and compared with the laser-cladded T-800 coating material. Co and lave phases (Co₂MoCr and Co₃Mo₂Si) are detected in both the laser-cladded T-800 coating and the bulk T-800 materials. However, the sizes of the lave phases are measured as 7.9 ㎛ and 60.6 ㎛ for the laser-cladded and bulk T-800 materials, respectively. After the Al erosion tests, the erosion layer thicknesses of the three materials are measured as 91.50 ㎛ (HVOF MoB-CoCr coating), 204.83 ㎛ (laser cladded T-800), and 226.33 ㎛ (bulk T-800). In the HVOF MoB-CoCr coating material, coarse cracks and delamination of the coating layer are observed. On the other hand, no cracks or local delamination of the coating layer are detected in the laser T-800 material even after the Al erosion test. Based on the above results, the authors discuss the appropriate material and process that could replace conventional bulk T-800 materials used as molten Al pots.

• Journal of the Korean Magnetics Society
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• v.1 no.2
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• pp.37-41
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• 1991

Amorphous $Fe_{68.5}Co_5M_3Cu_1Si_{13.5}B_9(M=Nb, Mo, Mn, Cr)$ alloys were prepared by using rapidly quenching techinque and were annealed above their crystallization temperatures. Coercive force, initial permeability and AC power loss of the annealed $Fe_{68.5}Co_5M_3Cu_1Si_{13.5}B_9(M=Nb, Mo, Mn, Cr)$ alloys have been studied systematically. Nanocrystallines are formed in the annealed alloys which include Mo and Nb. Remarkably improved soft magnetic properties are obtained in the alloys whose average grain size is around 10 nm. However, soft magnetic properties of the alloys are degraded when grain size is less than IOnm or larger than 15nm. It is considered that the degradation of soft magnetic properties in the alloys whose average grain size is less than 10 nm is due to the Fe-rich amorphous phase retained at grain boundary during the initial crystallization process.

• Bulletin of the Korean Chemical Society
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• v.14 no.2
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• pp.266-271
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• 1993

The reaction of $(CO_5$)M=C(OMe)Tol (M=Cr, Mo, W and $Tol=p-C_6H_4Me)$ and $BBr_3$ followed by treatment with tetramethylethylenediamine (TMEDA) yields a mixture of two diastereomers, trans, $cis-Br(CO)_2(tmeda)M{\equiv}$CTol [M=Cr(1a), Mo(2a), W(3a)] and cis, $trans-Br(CO)_2(tmeda)M{\equiv}$CTol [M=Cr(1b), Mo(2b), W(3b)], respectively. These compounds have been isolated as crystalline solids and characterized by spectroscopic (infrared, mass, $^1H$ and $^{13}C-NMR)$ data. The trans, cis-Br(CO)2(tmeda)Cr${\equiv}$CTol (1a), has been examine via a single crystal X-ray diffraction study : $BrCrO_2N_2C_{16}H_{23}$, Mr=407.27, triclinic, $P{\bar{1}},\;a=12.792(2),\;b=13.400(5),\;c= 11.645(4)\;{\AA},\;{\alpha}=101.26(2)^{\circ},\;{\beta}=103.04(2)^{\circ},\;{\gamma}=91.88(2)^{\circ},\;{\nu}=1907(1){\AA}^3,\;Z=2,\;{\rho}(calcd)=1.418\;gcm^{-3},\;{\lambda}(MoK{\alpha})=0.71069\;{\AA},\;{\mu}=26.25 cm^{-1},\;F(000)=831.97,\;T=295K,\;R=0.0977$ for 1332 significant reflections $[F_0>5{\sigma}(F_0)]$. There are two essentially equivalent molecules in the crystallographic asymmetric unit. Each molecule is octahedral with the bromide ligand trans to the alkylidyne carbon, the two cis-carbonyl ligands, and the bidentate TMEDA ligand.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.4
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• pp.196-205
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• 2012

The purpose of this study is to enhance the hardenability and the mechanical properties by the addition of alloying elements such as Ni, Cr, Mo and B for the development of Cr-Mo plastic mold steel with uniform hardness and microstructure. The ingots were prepared by vacuum induction melting and forged to ${\Phi}35mm$ round bar. Forged bars were quenched and tempered at $200{\sim}600^{\circ}C$ for 1.5 hour. Jominy test, boron distribution observation, microstructual observation, tensile test and charpy impact test were conducted. It was confirmed that the hardenablity of these steels was improved by increasing of alloying elements and further promoted by the addition of boron. The critical rate of cooling required to obtain the bainitic structure for 0.27C-1.23Cr-0.28Mo-B steel was $0.5^{\circ}C/sec$. Hardness and strength of Cr-Mo steels decreased with increasing tempering temperature, but elongation and reduction of area increased with increasing tempering temperature. However, impact energy tempered at $400^{\circ}C$ showed the lowest value in the range $200{\sim}600^{\circ}C$ due to the temper embrittlement.

• Journal of the Korean Applied Science and Technology
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• v.30 no.4
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• pp.649-655
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• 2013

Methanol was directly produced by the partial oxidation of methane with perovskite and mixed oxide catalysts. Perovskite ($ABO_3$) catalysts were prepared by the malic acid method with changing A and B site components. Three-component mixed oxide catalysts that have Mo and Bi as a main component were prepared by the co-precipitation method. Among the perovskite catalysts, $SrCrO_3$ showed the highest methanol selectivity of 11% at $400^{\circ}C$. For the three-component mixed oxide catalysts, there were no remarkable changes in methane conversion. Among the mixed oxide catalysts, Mo-Bi-Cr mixed oxide catalyst showed the highest methanol selectivity of 15.3% at $400^{\circ}C$. The catalytic activity and methanol selectivity of the three-component mixed oxide catalysts were directly proportional to the surface area of the catalysts.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.111-112
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• 2006

Injection molding of corrosive super engineering plastics and engineering plastics with various fillers is conducted under severe conditions and causes corrosion and wear problems. We have developed $Mo_2NiB_2$ boride base cermets, which have excellent corrosion-and wear-resistances, and tried to apply them into plastic molding machine parts. In this paper, the effects of V substitution for Cr on the mechanical properties, corrosion resistance and microstructure of Ni-5.0B-51.0Mo-(17.5-X)Cr-XV (mass%) model cermets were investigated. Both transverse rupture strength (TRS) and hardness increased monotonically with increasing V content and reached 2.94GPa and $87.2R_A$ at 10.0%V, respectively. The improvements of TRS and hardness were attributed to microstructural refinement.

• Bulletin of the Korean Chemical Society
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• v.15 no.5
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• pp.379-386
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• 1994

Reactions of 1',2-bis(diphenylphosphino)-l-(N,N-dimethylaminomethyl)ferrocene (FcNPP) with $M(CO)_6$ (M=Cr, Mo, W) in the presence of TMNO (Trimethylamine oxide) in a stoichiometric ratio of 1 : 1.5 : 3.5 produced a series of Gp 6 metal carbonyl derivatives with a variety of coordination modes: M(CO)$_4({\eta}^2$-FcNPP-P,P) (M=Cr, Mo, W), $M(CO)_5({\eta}^1-FcNPP-P) (M=Mo, W)\;,\; M_2(CO)_9({\eta}^1\;,\;{\eta}^2-FcNPP-P,P,N) (M=Cr, Mo)\;,\;M_2(CO)_{10}({\eta}^1\;,\;{\eta}^1-FcNPP-P,P) (M=Cr, Mo, W)\;, and\;W(CO)_4({\eta}^2-FcNPP(O)-P,N)$. All these complexes were characterized by microanalytical and spectroscopic techniques. In one case, the structure of W(CO)$_4({\eta}^2$-FcNPP(O)-P,N) was determined by X-ray crystallography. Crystals are monocinic, space group P$2_{1/C}$, with a=10.147(2), b=19.902(3), c=19.821(4) ${\AA},\;{\beta}=96.88(2)^{\circ},\;V=3974(l){\AA}^3$, Z=4, and $D_{calc}=1.64 g cm^{-3}$. The geometry around the central tungsten metal is a distorted octahedron, with the nitrogen and phosphorus atoms being cis to each other. Some of these complexes exhibited catalytic activities in the allylic oxidation and epoxidation of cholesterly acetate. Other oxidation products were also formed with the different chemical yields and product distribution depending upon the ligand and the central metal.

• 대한공업교육학회지
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• v.31 no.1
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• pp.200-210
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• 2006

This C-ring test, normally employed for evaluating susceptibility to stress-corrosion cracking, was determined to be a suitable small scale test to evaluate PWHT(Post-Weld Heat Treatment) cracking susceptibility. This test is possible to incorporate an actual weld, to introduce a notch into the coarse grained HAZ(Heat Affected Zone), to load the coarse grained HAZ any level of stress ad, most importantly, since the C-ring is an approximately constant strain type test, the stress decreases with time at temperature in a manner similar to that of an actual steel weldment. The procedure employed in making the C-ring was presented in the experimental procedure section, however, several points deserve further discussion. The walls of the weld groove are made along radial lines form the center of th var in order to obtain an HAZ which is oriented perpendicular to the walls of the machined C-ring. Therefore, the plane of maximum stress will be aligned through the HAZ and, therefore, crack propagation will not be forced to deviate form the plane of maximum stress in order to remain in the coarse grained HAZ as is the case with the Y groove test.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.62-62
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• 2009

석탄화력발전소의 CO2배출량 감소와 고효율, 대용량화로 인해 초초임계압(USC:Ultra Super Critical) 화력발전소의 건설이 증가하고 있다. USC 발전소는 효율향상을 위한 증기온도와 압력의 상승 때문에 보일러 고온고압부에 기존의 소재에 비해 고온강도와 내산화성의 재료물성이 향상된 신소재 적용이 불가피하다. 특히 사용된 신소재 중에서 보일러 본체를 구성하는 수냉벽관(Water wall), 과열기와, 재열기용 튜브 및 후육부인 헤더와 배관재로 기존의 2.25Cr-1Mo강을 개량한 2.25Cr-1.6W계 내열강이 적용되고 있다. 2.25Cr-1.6W강은 SMI와 MHI가 공동개발한 소재로 1995년 튜브제품이, 1999년에 단조, 파이프재, 플레이트제품이 ASME code case로 등재되었고, 2009년 ASME code case 2199-4로 개정되어 사용 중이다. 이 소재는 2.25Cr-1Mo강에 고온강도 개선을 위해 석출강화효과가 있는 V과 Nb을 첨가하였고, 탄화물의 열적안정성과 고용강화효과 증대를 위해 W을 첨가하였다. 그리고 제작성과 용접성 및 재료의 인성 향상을 위해 B첨가와 C함량을 낮추었다. 합금성분의 첨가와 조정에 의해 고온강도는 개선되었지만, 보일러 설치 및 보수를 위한 용접과정에서 용접금속과 CGHAZ(Coarse Grain HAZ)에서 용접균열이 발생하였다. 대부분의 용접균열은 용접결함이나 고온 혹은 저온균열이 아닌 2.25Cr-1.6W계강의 강도 개선을 위해 첨가한 V과 Nb이 용접후열처리 도중 입내에 MX형태의 미세석출로 입내를 강화시킴으로서 발생한 재열균열 민감성 증대에 기인된 것으로 판단된다. 이에 본 연구에서 용접 및 후열처리 과정에서 용접금속과 HAZ에서 발생하는 용접금속의 응력분포를 전산해석을 통해 확인하고 실제 후육파이프 용접부에서 잔류응력을 측정해 비교하였다. 용접부 응력분포는 SYSWELD 프로그램을 사용해 해석을 수행하였고, 발전소 실배관재의 용접부 응력측정은 수평부 측정이 용이하도록 지그를 부착한 Potable 잔류응력측정기를 사용해 Hole Drilling Method(HDM)를 적용하여 잔류응력을 측정하였다. 해석 결과 CGHAZ부위의 잔류응력이 용접금속과 기타 부위에 비해 높은 응력분포를 나타냈으며, 이는 CGHAZ와 용접용융선 부근에서 균열이 발생하는 실제값과 일치하는 결과를 보였다. 실제 배관재 용접부에서 측정한 잔류응력값은 항복응력의 약 50% 이하 응력값을 나타냈다. 배관 구조에 기인한 시스템응력의 영향을 제거하기 위해 배관재 용접부를 중심으로 양끝단을 절단 후 용접부에서 측정한 응력은 항복응력 대비 25%수준의 낮은값을 보였다. 그러나 배관재가 장기간 고온환경에 노출되었고 용접금속 내부의 균열이 발생한 상태에서 측정하였기 때문에 용접잔류응력은 상당부분 해소되어 상대적으로 낮은 응력값이 얻어진 것으로 판단된다.