Study of Laser Surface Transformation Hardening on Cast Iron and the Characteristics of Hardened Layers
| Autor: | Chen, Jau-Ren, 陳昭仁 |
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| Rok vydání: | 1997 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 85 In this work, the relationship between laser processing parameters including laser power, scanning speed and laser beam diameter (defocus), and the characteristics of hardened layer of FCMP 60 cast iron including hardness distribution of the hardened layer, geometrical features (the width and depth of hardened layer) and surface roughness after laser treatment was investigated. There was a general tendency that the hardened depth increased as the laser power increased. The hardened depth also increased withdecreasing scanning speed and laser beam diameter. The microstructure of hardened layer mainly consisted of plate martensite if no surface melting occurred. With surface melting, the surface region consisted of eutectic ledeburite (white iron) and the molten region was very shallow comparing to the whole hardened layer. In multi-track hardening, there was tempering effect occurred in the overlapped region between the previous track and the next track. This led to hardness reduction as a result of formation of tempered martensite. In addition, the influence of graphite flakes in laser transformation hardening on cast iron was also discussed in this work.Sliding wear test was carried out on both base metal and hardened layer under different wear loads. The wear resistance of hardened layer was significantly improved after laser treatment in comparison with base metal, especially under extreme wear load. The wear mechanism varied with the wear load both on base metal and hardened layer. Under higher wear rate of base metal, the cutting and ploughing wear were the dominant the wear mechanism. The higher hardness and microstructure of hardened layer provided an effective wear resistance against severe abrasive wear. Lower wear rate after sliding wear test was expected accordingly. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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