| CAO Li-qin,SUN Li-na,XUAN Fu-zhen,WANG Zheng-dong.Experimental Study on the Cracking Behavior in Laser-assisted Nitriding Process[J],42(6):1-5,36 |
| Experimental Study on the Cracking Behavior in Laser-assisted Nitriding Process |
| Received:July 10, 2013 Revised:August 16, 2013 |
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| DOI： |
| KeyWord:laser nitriding microstructure cracking stress |
| Author | Institution |
| CAO Li-qin |
Yanshan University, Qinhuangdao , China;East China University of Science and Technology, Shanghai , China |
| SUN Li-na |
Yanshan University, Qinhuangdao , China |
| XUAN Fu-zhen |
East China University of Science and Technology, Shanghai , China |
| WANG Zheng-dong |
East China University of Science and Technology, Shanghai , China |
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| Abstract: |
| Objective To study the cracking behavior of the nitride layer during the laser-assisted nitriding process. Methods CO2 laser was used to prepare titanium nitride coating on titanium alloy surface. The investigation was focused on the effects of sample thickness and process parameters on the surface topography and the cracking behavior . The macroscopic and microscopic morphology of the nitride layer was observed. A detailed analysis of crystalline structure and measurement of residual stress were performed. Results Inhomogeneous nitride layers with dendritic crystal along the main axis were successfully prepared by single or multiple laser scanning. Meanwhile, there were unequal size and number of cracks in the nitride layers. For the residual stress on the nitride surface exerted by single track of laser nitriding, thinner sample showed lower compressive stress state, and tensile stress took precedence in the thicker specimen conversely. However, the nitride surfaces by multiple laser nitriding showed residual compressive stress state. Conclusion The dendritic nitride layer was tightly bound to the matrix and did not easily fall apart .However, the formation of micro cracks in the cooling process was due to the internal heat stress, under the influence of the substrate constraints. Meanwhile, there was a progressive increase of crack density and dimension along with the increase of sample thickness and the area of nitride. It seriously affected the quality of the titanium nitride layer. The residual stress was the sum of the thermal stress and the phase transformation stress. When laser tracks were overlapped to produce a large area of nitride surface, there might be enough phase transformation to produce higher compressive stresses. In addition, the thermal stress level was reduced due to the effects of post-heat by successive overlapping tracks. Thus, the nitride surfaces by multiple laser nitriding showed residual compressive stress state. |
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