激光淬火及熔覆层性能与物相变化的拉曼光谱研究

Study on the Properties and Phase Transition in Laser Quenching and Cladding Layers by Raman Spectroscopy

利用拉曼光谱研究了45#钢激光淬火层的抗氧化性能和碳在淬火层内的状态,同时研究了镍基合金激光熔覆层内碳的结构形态转变和抗氧化性能。研究结果表明,45#钢中的碳主要表现为纳米非晶石墨和类金刚石结构,激光淬火可以明显提高45#钢表面的抗氧化性能并使碳颗粒细化。随着测试激光功率的增大,激光淬火层表面和次表面的拉曼光谱保持不变,而激光淬火层内部和基体的拉曼光谱发生非常明显的变化,出现了很强的-αFe2O3的拉曼信号。这表明45#钢激光淬火层的表面具有非常优异的高温抗氧化性能。发现在激光熔覆Ni02合金层与基体的接合部非晶碳可以转化为金刚石结构。熔池底部高的温度梯度和快速凝固过程中在界面处产生巨大的瞬间压力,可能是在该区域内非晶碳直接转化为金刚石的主要原因。

Anti-oxidation properties, carbon structures and related phase transition in laser quenched layer of 45^# steel and in laser clad-NiO2 alloy layers are studied by Raman spectroscopy. It is shown that laser quenching elevates the anti-oxidation capacity greatly for the surface of 45^# steel and refines the particle sizes of carbon, which appears mainly as amorphous graphite in 45^# steel. With increasing excitation laser power, the Raman spectra of the surface and sub-surface layer remain unchanged, whereas those of the uniformly phase transition layer and the substrate changes enormously. Intense Raman signals of α-Fe2 O appear for the latter. These indicate that the laser quenched surface layer has unique high-temperature anti-oxidation capacity, which is much superior to that of the laserquenched inner layer as well as the original material. It is found that a phase transition from amorphous carbon to diamond occurs around the interface between the substrate and laser cladding layer of NiO2 alloy. This is explained by the high-temperature gradient at the bottom of the melt pool and the transient pressure produced during cooling process at the interface between the clad layer and the substrate.