• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.6
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• pp.313-318
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• 2017

The microstructure of a cobalt-base superalloy (ECY768) obtained by an investment casting process was studied. This work focuses on the resulting microstructures arising from different melt and mold temperatures in normal industrial environmental conditions. The characterization of the samples was carried out using optical microscopy, field emission scanning electron microscopy and energy-dispersive spectroscopy. In this study, the as-cast microstructure is an ${\alpha}-Co$ (face-centered cubic) dendritic matrix with the presence of a secondary phase, such as $M_{23}C_6-type$ carbides precipitated at grain boundaries. These precipitates are the main strengthening mechanism in this type of alloy. Other minority phases, such as the MC-type phase, was also detected and their presence could be linked to the manufacturing process and environment.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.144-144
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• 2003

니켈계 내열합금의 성형은 수백 $^{\circ}C$에 이르는 고온에서 이루어지기 때문에 열간성형 과정에서 소재 내부의 미세조직 변화에 대한 이해는 부품의 특성 제어 측면에서 매우 중요하다. 특히 열간 동적 재결정에 의해 발생되는 결정립 구조의 변화를 적절히 조절함으로써 부품의 특성을 극대화 할 수 있다. 본 연구에서는 Ni-Fe계 초내열합금에 대한 고온 압축실험과 압축시편에 대한 EBSD 분석을 통해 열간 변형 과정에서 발생하는 소재 내부의 동적인 결정립 구조의 변화를 정량적으로 분석하고자 하였다. 고온 압축시험은 101$0^{\circ}C$, 1066$^{\circ}C$의 온도 조건과 0.5s-1, 0.005s-1의 변형율 속도 조건에서 최대 진변형율 0.7까지 수행하였으며 진변형율에 따른 결정립 조직 변화를 관찰하기 위해 진변형 율에도 변화를 주어 실험을 수행하였다. 이들 고온 압축시편은 응력방향에 평행한 면에 대한 미세조직 관찰을 통해 재결정립 크기, 분율 및 결정립계의 특성 변화에 대한 정량적 연구를 수행하였다.

• Journal of the Korean institute of surface engineering
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• v.31 no.6
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• pp.334-344
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• 1998

Yew coating pmccss t.o form a surface layer ol CrN phasc on mild steel (A81 1020!, AlSI Hi3, 1Cr-0.5Mo steel (ASTM A213 and Nickrl-base superalloy (Inconel 718) was developed. Surlaces of various alloys t,n.ateii by chromizing for the formation ol Cr diffusion layer was subsequently trcaled by plasma nitriding in order t.o form the hard CrS coating layer on the surfaces. This duplex plasma surface tri-atments of chromizing and plasma nitriding have induced a lormation of a duplex-lrcated surfacr hyer of approximat~ls 70-80 $\mu\textrm{m}$thickncss with a iargcly improved microiiardnrss up to approxiniateW 1500Hv(50gf). The main cause for the lage improvment in the surface hardncss is altribilted to [.he fact that CrN and $Fe_xN$ phases are created successfully by ccliromizins and plasma nilriding treatment. High tenipera1,urc wear resislance of the duplex-treated mild steel and HI3 steels at $600^{\circ}C$ was examined. Comparing the duplex-treated specimens with the specimens treated only by chromizing, the rcsults shovmi that, thc wear volume of the duplex-treated mild skcl and 1113 stcel aSt.er a wear test, at $600^{\circ}C$ were reduced hy a Iactor of 8 and 3, respectively. Characteristics of the CrS phase by duplrx treatment were compared with $CrN_x$,/TEX> film by ion plating and the wear behaviors of CrN film lormed by two different nroccsses arc nea.riy identical.