엔진오일 환경에서의 ZrCuSiN 나노복합체의 저마찰 및 내마모 특성에 관한 연구

Abstract

본 연구에서는 자동차 엔진이 작동할 때 엔진오일 환경에서 ZrCuSiN 나노복합체의 마찰과 마모에 대한 저항을 연구하였다. 자동차 연비 개선을 위해 엔진 개발 기술이 변화함에 따라 연비에 영향을 주는 마찰과 마모의 개선에 대한 연구도 진행되었다. 자동차 부품의 코팅으로는 DLC(diamond-like carbon)를 이용하였지만 고온·고압의 환경에서는 내구성이 저하되는 단점이 있다. 자동차 업계에서는 코팅 물질의 두께를 10 ㎛ 이상 요구하지만 현재 DLC로는 8 ㎛밖에 제조하지 못하는 한계가 있다. 또한 엔진오일 첨가제인 MoDTC (Molybdenum DialkyldiThioCarbamate)와의 호환성 문제로 인해 마모가 심한 단점이 있다. 이를 개선하기 위해 ZrCuSiN 나노복합체를 고안하였다. 본 연구를 위해 piston ring, SKD 11종 시편에 reactive hybrid sputtering으로 ZrCuSiN 박막을 침착시켰다. Sputtering 공정을 실시할 때 솔레노이드 전원의 작동 유무와 N2 gas의 유량의 증가를 조건으로 삼았다. 솔레노이드 전원이 작동하고 N2 gas의 유량이 증가할수록 경도는 평균적으로 8.56 GPa 증가하였고 마찰계수가 감소하였다. ZrCuSiN 박막의 저마찰과 내마모 특성이 우수한 정도를 알기 위해 SRV 시험을 실시해 기존에 자동차 엔진 부품에 적용되었던 CrN 박막과 비교했다. SRV 시험 결과 CrN과 ZrCuSiN 박막의 마찰계수는 큰 차이가 없지만 마모에 대한 저항은 ZrCuSiN 박막이 더 우수하다. SRV 시험을 실시하는 동안 CrN과 ZrCuSiN 박막의 마모 영역에 엔진오일 성분을 지닌 tribofilm이 생성되었다. CrN 박막의 마모 영역에는 엔진오일의 성분인 S, P, 그리고 Ca과의 반응을 통해 비정질층인 150 nm의 tribofilm이 생성되었다. 반면에, ZrCuSiN 박막의 경우 마모 영역의 미세 구조를 관찰한 결과 세 종류의 layer가 형성되었다. 세 개의 layer가 마찰·마모 시험을 하는 동안 형성되는 것으로 보아 ZrCuSiN 박막의 특이한 점으로 보인다. ZrCuSiN 박막이 침착한 piston ring을 자동차 엔진에 장착한 후 점도 0W20의 엔진오일 분위기에서 상온과 100℃에서 마찰·마모 시험을 한 결과, 상온에서는 CrN 대비 ZrCuSiN의 마모율이 60%, 100℃에서는 75% 정도 개선되었다. 본 연구를 통해 ZrCuSiN 나노복합체가 다른 종류의 박막보다 저마찰 및 내마모 성질이 향상된 것을 확인하였다. |In this study, the friction and wear properties of ZrCuSiN nancocomposites in engine oil environment was investigated in the condition of an inter combustion engine working. The enhancement of friction and wear properties has been considered as a critical issue for improving the fuel efficiency of automobile engines. DLC (diamond-like carbon) has been widely used as a coating material for reducing the friction of automobile components. However, the durability of DLC coating layers is known to be deteriorated under high temperature and high pressure working conditions. The thickness of DLC coating layers is required to be more than 10 ㎛, but it is currently difficult to deposit more than 8 ㎛. In addition, the DLC layers showed poor abrasion behavior due to bad compatibility with one of the engine oil additives, i.e., MoDTC (Molybdenum DialkyldiThioCarbamate). Thus ZrCuSiN nanocomposite was devised to overcome the above problems. ZrCuSiN nanocomposites were deposited on piston rings and SKD 11 alloy sheets by reactive hybrid sputtering. The operating solenoid power and the nitrogen gas flow rate were varied to optimize the process. Compared with CrN coating, it was found that the abrasion resistance of ZrCuSiN thin film was superior through the SRV test. However, there was no noticeable difference of the friction coefficients between CrN and ZrCuSiN thin film layers. The tribofilms containing the engine oil components were produced on the abrasive areas of both CrN and ZrCuSiN layers while performing the SRV test. It was observed that a 150 nm thick amorphous tribofilm was formed through the reaction with the engine oil components (sulfur, phosphorous, and calcium) on the wear area of the CrN films. In contrast, three types of layers were found in the ZrCuSiN thin films. In order to investigate the wear properties, piston rings coated with ZrCuSiN thin films were examined at room temperature and 100℃ in the 0W20 engine oil atmosphere. After the test, it was found that the wear rate was reduced by 60% at room temperature and 75% at 100℃ compared with the CrN film. This indicates that ZrCuSiN nanocomposite should be much better than other types of thin films in regard to the low friction and antiwear.; In this study, the friction and wear properties of ZrCuSiN nancocomposites in engine oil environment was investigated in the condition of an inter combustion engine working. The enhancement of friction and wear properties has been considered as a critical issue for improving the fuel efficiency of automobile engines. DLC (diamond-like carbon) has been widely used as a coating material for reducing the friction of automobile components. However, the durability of DLC coating layers is known to be deteriorated under high temperature and high pressure working conditions. The thickness of DLC coating layers is required to be more than 10 ㎛, but it is currently difficult to deposit more than 8 ㎛. In addition, the DLC layers showed poor abrasion behavior due to bad compatibility with one of the engine oil additives, i.e., MoDTC (Molybdenum DialkyldiThioCarbamate). Thus ZrCuSiN nanocomposite was devised to overcome the above problems. ZrCuSiN nanocomposites were deposited on piston rings and SKD 11 alloy sheets by reactive hybrid sputtering. The operating solenoid power and the nitrogen gas flow rate were varied to optimize the process. Compared with CrN coating, it was found that the abrasion resistance of ZrCuSiN thin film was superior through the SRV test. However, there was no noticeable difference of the friction coefficients between CrN and ZrCuSiN thin film layers. The tribofilms containing the engine oil components were produced on the abrasive areas of both CrN and ZrCuSiN layers while performing the SRV test. It was observed that a 150 nm thick amorphous tribofilm was formed through the reaction with the engine oil components (sulfur, phosphorous, and calcium) on the wear area of the CrN films. In contrast, three types of layers were found in the ZrCuSiN thin films. In order to investigate the wear properties, piston rings coated with ZrCuSiN thin films were examined at room temperature and 100℃ in the 0W20 engine oil atmosphere. After the test, it was found that the wear rate was reduced by 60% at room temperature and 75% at 100℃ compared with the CrN film. This indicates that ZrCuSiN nanocomposite should be much better than other types of thin films in regard to the low friction and antiwear.