• Journal of the Korean institute of surface engineering
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• v.33 no.2
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• pp.115-125
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• 2000

TiN films were deposited onto Stellite 6B alloy (Co base) by the reactive magnetron sputter ion plating. As the bias increases, TiN film changes from columnar structure to dense structure with great hardness and smooth surface due to densification and resputtering by ion bombardment. The content of oxygen and carbon impurities in the TiN film decreases greatly when the substrate bias is applied. The preferred orientation of the TiN films changes from (200) to (111) with decreasing $N_2$/Ar ratio, and from (200) to (111) and then (220) with increasing the substrate bias. The change of the preferred orientation is discussed in terms of surface energy and strain energy which are related to the impurity contents and the ion bombardment damage. The hardness of the TiN film increases with increasing compressive stress generated in the film by virtue of ion bombardment. It becomes as high as up to 3500kgf/mm$^2$ when an appropriate substrate bias is applied.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.52-58
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• 1996

본 연구에서는 반응성 마그네트론 스퍼터 이온플래이팅법에 의해 Co계 합금인 stellite 6B 기판 위에 증착된 TiN 박막의 증착특성을 조사하였다. 증착된 박막의 증착속도는 기판에 인가된 bias 가 증가함에 따라 박막의 치밀화와 resputtering으로 인해 감소하였으며 박막의 형상은 bias가 인가되지 않은 상태에서의 open columnar 구조에서 bias가 인가된 경우 columnar 구조가 사라진 매끈하고 치밀한 구조로 변화하였다. 기판 bias가 인가된 경우 N/Ti 조성비는 거의 stoichiometry를 만족하였으며 증착된 박막의 우선성장 방위는 $N_2$의 양이 감소할 수록 (200)에서 (111)로, bias 증가에 따라서는 (200)에서 (111)을 거쳐 (220)으로 변화하였다. 박막의 경도는 박막이 압축응력을 나타낼수록 증가하였으며, bias가 인가된 경우 약 2000~3300kgf/$\textrm{mm}^2$의 높은 경도를 나타내었다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2001.11a
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• pp.63-63
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• 2001

As a new approach to substitute for a hard alloy of stellite 6B containing Co which is radioactive in nuclear system, a hard-phase coating of CrN will be applicable to protect 12Cr steel from erosion at leading edge on steam turbine blade. The CrN coating was prepared by arc ion plating on 12 Cr steel and was undertaken in liquid impact test at the velocity of 35Om/sec, which simulate the environment in the last stage of blade. The erosion resistance of coating was evaluated by optical observation on damaged surface. The threshold number of impact was closely related with surface hardness. And thus, it was confirmed that surface hardening improves the life time of steam turbine blade.

• Journal of Welding and Joining
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• v.32 no.6
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• pp.41-46
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• 2014

In this study, cracking susceptibility of laser cladding was investigated according to the processing parameters such as laser power, scan speed and feeding rate with blended powders of stellite#6 and technolase40s (WC+NiCr). The solidification microstructure of clad was composed of Co-based dendrite structures with ${\gamma}+Cr7C3$ eutectic phases at the dendritic boundaries. The crack propagation showed transgranular fracture along dendritic boundaries due to brittle chrome carbide at the eutectic phases. From results of fractography experiments, the fracture surface was typical cleavage brittle fracture in the clad and substrate. The number of clad cracks, caused by a tensile stress after the solidification, increased with increase of laser power, scan speed and feeding rate. Increase of the laser power caused large pores by facilitating WC decarburizing reaction. And the pores affected increase of crack susceptibility. High scan speed caused increment of clad cracks due to thermal stress and WC particle fractures. Also, increase of the feeding rate accompanied an amount of WC particles causing crack initiation and decarburizing reaction.

• Journal of Powder Materials
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• v.4 no.2
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• pp.113-121
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• 1997

The densification of the compacts of Co+32%Cr+20%W+l.5%C, Co+32%Cr+20%W+3.0%C and Co+32%Cr+20%W+4.5%C sintered under $H_2$ gas or vacuum was investigated. The effect of V and B addition on the densification was also investigated. The densification of these compacts were always incomplete regardless of sintering atmosphere, temperature and time. The amounts of oxygen and carbon in compacts sintered in $H_2$ for 3.6ks at 1523K were 0.105~0.160 mass% and 0.33~0.89 mass%, respectively. And those in vacuum were 0.028~0.032% and 0.957~4.08%, respectively. Relative density(Ds) of Co+29%Cr+17%W+3.0%C compact containing 6%V and Co+32%Cr+20%W+2.97%C compact containing 0.03%B were 99 and 100%, respectively, indicating complete densification by solid phase sintering. Victors hardness of sintered compacts containing 6%V or 0.03%B were 632 and 568, showing 50~60% increase in comparison to those without V or B. These results can be explained in terms of oxidation/reduction of oxides and equilibrium pressure of CO in isolated pore, instead of presence of liquid formation and grain boundary separation from pores due to large grain growth.

• Corrosion Science and Technology
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• v.9 no.6
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• pp.310-316
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• 2010

Recently a fuel oil of the diesel engine of the marine ship is being changed with heavy oil of low quality as the oil price is higher more and more. Therefore the wear and corrosion in all parts of the engine such as cylinder liner, piston crown, spindle and seat ring of exhaust valves are predominantly increased. In particular the degree of wear and corrosion of piston crown is more seriously compared to the other parts of the engine due to operating in severe environment such as the high temperature of exhaust gas and repeating impact. Thus the repair weldment of the piston crown is a unique method to prolong the its life in a economical point of view. In this case, filler metals having a high corrosion and wear resistance such as stellite 6, Inconel 625 and Inconel 718 are mainly being used for repair welding. However it has been often happened that piston crown on the ship,s job site is being actually inevitably welded with mild filler metals. Therefore in this study, filler metals such as E4301, E4313 and E4316 were welded at SS401 steel as the base metal, and corrosion property of their weld metals in the case of post weld heat treatment or not was investigated with some electrochemical methods such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram and polarization resistance etc. in 0.1% $H_2SO_4$ solution. Corrosion resistance of the weld metal of E4301 was better than the other weld metals in the case of no heat treatment, however, its resistance was considerably decreased with post weld heat treatment(annealing:$625^{\circ}C$, 2 hr) compared to other weld metals. The weld metals of E4313 and E4316 showed a relatively good corrosion resistance by post weld heat treatment.