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ADC12 다이캐스팅 합금의 미세조직 및 기계적 특성에 미치는개량 원소 첨가의 영향
강연지,윤상일,김동현,이기안 한국소성∙가공학회 2019 소성가공 : 한국소성가공학회지 Vol.28 No.1
In this study, various alloying elements (Cr, Sr, Ca, Cd) were added to improve the mechanical properties of ADC12 fabricated by a die casting process. The effect of alloying elements on the microstructure and mechanical properties were investigated. The phase analysis results of the modified ADC12 alloy with conventional ADC12 alloy, showed the similar characteristics of Al matrix, Si phase, CuAl2 phase and the Fe intermetallic phase. As a result of the microstructure observation, the secondary dendrite arm spacing (SDAS) was shown to have decreased after the addition of the alloying elements. The eutectic Si phase, which existed as flake form in the conventional ADC12 alloy, was modified finely as a fiber form in the modified ADC12 alloy. It was observed that the CuAl2 phase as the strengthening phase was relatively finely distributed in the modified ADC12 alloy. The Fe intermetallic appeared as a Chinese script shaped Al6 (Mn,Fe) which is detrimental to mechanical properties in conventional ADC12 alloy. On the other hand, in the modified ADC12 alloy, polyhedral α-Al15Si2 (Fe,Mn,Cr)3 was observed. The tensile properties were improved in the modified ADC12 alloy. The yield strength and tensile strength increased by 12.4% and 10.0%, respectively, in the modified ADC12 alloy, and the elongation was also seen to have been increased. As a result of the pin on disk wear test, the wear resistance properties were also improved by up to about 7% in the modified ADC12 alloy. It is noted that the wear deformation microstructures were also observed, and it was found that the fine eutectic Si and strengthening phases greatly improved abrasion resistance.
고속 화염 용사 공정으로 제조된 WC계 및 Cr<sub>3</sub>C<sub>2</sub>계 Cermet 코팅 소재의 미세조직 및 마모 특성
강연지,함기수,김형준,윤상훈,이기안,Kang, Yeon-Ji,Ham, Gi-Su,Kim, Hyung-Jun,Yoon, Sang-Hoon,Lee, Kee-Ahn 한국분말야금학회 2018 한국분말재료학회지 (KPMI) Vol.25 No.5
This study investigates the microstructure and wear properties of cermet (ceramic + metal) coating materials manufactured using high velocity oxygen fuel (HVOF) process. Three types of HVOF coating layers are formed by depositing WC-12Co, WC-20Cr-7Ni, and Cr3C2-20NiCr (wt.%) powders on S45C steel substrate. The porosities of the coating layers are $1{\pm}0.5%$ for all three specimens. Microstructural analysis confirms the formation of second carbide phases of $W_2C$, $Co_6W_6C$, and $Cr_7C_3$ owing to decarburizing of WC phases on WC-based coating layers. In the case of WC-12Co coating, which has a high ratio of $W_2C$ phase with high brittleness, the interface property between the carbide and the metal binder slightly decreases. In the $Cr_3C_2-20CrNi$ coating layer, decarburizing almost does not occur, but fine cavities exist between the splats. The wear loss occurs in the descending order of $Cr_3C_2-20NiCr$, WC-12Co, and WC-20Cr-7Ni, where WC-20Cr-7Ni achieves the highest wear resistance property. It can be inferred that the ratio of the carbide and the binding properties between carbide-binder and binder-binder in a cermet coating material manufactured with HVOF as the primary factors determine the wear properties of the cermet coating material.
강연지(Y. J. Kang),백민석(M. S. Baek),함기수(G. S. Ham),김종호(J. H. Kim),이시우(S. W. Lee),이기안(K. A. Lee) 한국소성가공학회 2016 한국소성가공학회 학술대회 논문집 Vol.2016 No.4
본 연구에서는 압출공정으로 제조된 Al-12%Si 합금의 T6 열처리에 따른 내마모 특성을 Scratch tester를 이용해 평가하였다. 그에 따라 모든 시험은 열처리 전 소재(F 합금)와 열처리 후 소재(T6 합금)에 대하여 동일 조건에서 각각 시행되었다. 상기 소재의 공정Si상의 크기는 F 합금에서 약 2.3㎛, T6 합금에서는 약 2.5㎛로 측정되었다. XRD를 이용한 상분석 결과, Al 기지에 Si상과 Al₂Cu, Al₃Ni, Mg₂Si의 미세상이 존재하며 열처리 전•후 합금 내 존재하는 상의 종류에는 변화가 없었다. 그러나 FESEM-EDS과 EPMA를 통한 미세조직 관찰결과 Al 기지내 존재하는 Al₂Cu상이 T6 열처리 후 크기와 분포가 더욱 고르고 미세해진 것을 관찰할 수 있었다. T6열처리 전후 기계적 특성을 비커스 경도시험과 스크래치 테스트의 결과로써 나타내었다. 비커스 경도는 열처리 전 F 합금에서 52HV, 열처리 후 T6 합금에서는 125HV로 향상되었다. 스크래치 테스트는 CLST(constant load scratch test)와 MPST(multipass scratch test) 조건에서 각각 시행되었으며, 각각의 조건에서 residual depth를 측정하여 열처리 전후의 마모특성을 평가하였다. Scratch tester로 얻은 scratch coefficient는 마모저항성을 나타내는데 순수한 마모저항성을 도시하기 위해 본 연구에서는 접촉면적 A로 나누어줌으로써 열처리 전 후 합금의 내마모 특성을 비교하였다. 추가적으로 FESEM를 사용하여 MPST 마모 시험과정에서 발생하는 미세조직 변형 매커니즘을 분석하였다.
AISI 1045 강의 인장 및 고주기 피로 특성에 미치는 Cr 도금층 두께의 영향
함기수,강연지,김형준,윤상훈,이기안 대한금속·재료학회 2019 대한금속·재료학회지 Vol.57 No.3
This study investigated and compared the tensile and high-cycle fatigue properties of AISI 1045 steel and Cr electroplated AISI 1045 steel. First, tensile and fatigue specimens were machined from AISI 1045 steel (substrate), and two kinds of Cr electroplating layers with different layer thickness were applied. The substrate, AISI 1045 steel consisted of an a-Fe matrix and pearlite, and the two Cr electroplating layers were measured to have thicknesses of 13.1 μm and 53.9 μm, respectively. The Cr layer did not show signs of peeling from the substrate, but initial micro cracks were present within the Cr electroplating layer. Tensile test results confirmed that the Cr electroplated specimens had similar yield strengths and tensile strengths to those of the substrate AISI 1045 steel, but elongation decreased significantly. High cycle fatigue results confirmed that the fatigue limit (~107 cycles to fatigue failure) of the substrate steel was 600 MPa, and the fatigue limit decreased significantly to 500 MPa (13.1 μm thickness) and 325 MPa (53.9 μm thickness) as the Cr electroplating layers were formed. This study also observed fracture surfaces of tensile and high cycle fatigue fractured specimens, and the deformation mechanisms of the Cr electroplated steel were suggested in connection with microstructures.