| Summary: | 碩士 === 逢甲大學 === 材料科學所 === 94 === The major failure in chain pins of a typical transmission component, is attributed to the wear during service. Traditional chromizing process has been widely applied to enhance surface wear resistance of chain pins, however, it would cause some problems, such as energy consumption, long treatment time, hazardous by-products and relatively low realibility. PVD has been broadly applied in mechanical industries. An attempt in this study is to survey the microstructure and mechanical properties of the chain pin with chromium nitride on it deposited by PVD Arc ion plating. The chromium nitride deposited chain pins were assembled and dynamically tested to reveal the possibility as an alternative process to chromizing.
Many successful applications have been considered the protective coating of chromium nitride, especially in die surface protection due to thermal stability, corrosion and wear resistance of chromium nitride film. Literatures show that the coated films consist of mainly Cr、Cr2N and CrN, that strongly depends on the nitrogen partial pressure during the deposition process. Maximum hardness value of the deposited film appears when CrN and Cr2N coexist. The nitrogen partial pressure were therefore controlled to obtain the optimized film in terms of maximum hardness value. Scanning electron microscope and X-ray diffractometer were used to observe micro-morphology and crystal structure, respectively. Dynamic test of the chain assembled with chromized pin and AIP-coated pin were carried out to reveal their wear resistance. The results show that both chromium nitride coated pin and chromized pin presented the same wear resistance under sand-free dry environment. Once the substrate was annealing soften during the depositing process because of the elevated substrate temperature, the chromium nitride coated pin greatly decrease wear resistance. To solve this problem, a post heat treatment were carried out after coating process. By increasing film thickness up to 15 um, wear resistance can be significantly increased due to the increased load-carry-capacity of the film and the decreased shear stress, that is caused by friction force. The later distributed along the substrate-coating interface determines film delamination or not. The increased film thickness brings a negative side effect of abrading serverely the counterface – the inner wall of the chain plate. By reducing the surface roughness from 1.19 to 0.45 um of the coated pins by using stearic acid polishing, significant wear loss can be obtained.
This study has shown that the wear resistance of the chromium nitride coated chain pin is comparable to chromized chain pin and is promising to be the alternative clean and energy saving process.
|
|---|
