Structure changes in steels and hard metal induced by nanosecond and femtosecond laser processing

摘要

Investigations on the occurrence of structure and hardness changes (for two sorts of steel and for a hard metal substrate) in the immediate vicinity of laser induced craters are presented in this work. Experiments with femtosecond pulses were performed in air with a Ti:sapphire laser (800 nm, 100 fs) at mean fluences of 2, 5 and 10 J/cm~2. Series of microcraters were induced with 100 to 5'000 laser pulses per hole. Experiments with similar fluences, but 10 to 40 pulses per hole, were performed on the same materials using a Nd:YAG delivering 100 ns pulses. After laser irradiation, cuts were made through the processed samples and the changes occurred in the crystalline structure of the target materials were evidence by metallographical analysis of the resulting cross-sections. Hardness measurements were performed in points situated in the immediate vicinity of the laser induced pores. Affected zones in the material surrounding laser induced pores were always found in the ns- regime, however with different properties for various laser parameters. In the fs-regime, zones of modified materials were also found and in such zones a significant hardness increasing was evidenced; the limit of the low fluences regime, where no structure changes occured, was found to be slightly above 2 J/cm~2.