Perpustakaan Digital ITB

Effect of temperature and Micro Spark Coating (MSC) on fatigue behavior of nickel-based superalloy Inconel718 was studied. Fatigue test at room temperature (RT) and 480C were conducted under stress ratio, R = 0.1 and 10 Hz frequency. At 480C, MSC was attached in the one side of specimen. The specimen used was Centre Crack Tension (CCT) specimen with 14 diameter of bar shape, 2x14 mm2 cross section of plate area in the middle part, which 1 mm machined notch length was employed. The different of fatigue fracture mechanism between RT and 480C was investigated using fractography analysis. Measurement of Young's Modulus by using vibration reed method was also carried out to support better understanding in fracture mechanism behavior. In the near-threshold regime, crystallographic and transgranular fracture mode was observed. Very fine fatigue striation present in the lower Paris regime. Then, fracture mechanism changed to a plasticity-controlled crack-tip blunting mechanism by formation of coarse striation, which happened in upper Paris regime. At high K regime, ductile-dimple with combination of coarse striation was observed as fracture mechanism mode. The result showed that FCP at 480C is almost comparable with FCP at RT. The difference of mechanical properties which is not so significant between elevated temperature and RT might be related with that phenomenon. FCP rate of coated specimen is a little higher than uncoated specimen. Threshold value at 480C is higher than that at RT. It indicates that resistance to encounter crack growth barrier was become higher at 480C and material become stronger at elevated temperature. However, threshold value of coated specimen is lower than uncoated specimen at 480C. The crack seems grew slower near the coating layer because of the appearance of shrinked tunneling effect in the interface area of coated specimen. Then, the significant step was observed in the near interface area. It seems that specimen was pulled out with force on this area, which might be because of the effect of coating. The detail effect of coating has not been clarified in this study. However, of particular important was that no disadvantage or reduction of fatigue strength caused by MSC found in this study, while most of coating usually reduces the fatigue resistance.