Temporal-spatial resolved laser-induced breakdown spectroscopy of T91 steel of different aging grades

Abstract

As a representative heatproof martensitic steel, T91 steel is extensively used for building industrial pressure-bearing heat-exchange surface. The mechanical properties and metallographic structure of the steel components will gradually change in long-term operation (also known as material aging). It will seriously endanger the operation safety and reduce the lifespan of the equipment. In this study, in order to deeply understand the mechanism of steel degradation surface measurement by laser-induced breakdown spectroscopy (LIBS), the temporal-spatial evolutions of spectral line emissions of T91 steel specimens with different aging grades were observed by using grating spectrometer with intensified charge coupled device detector (ICCD). The time-resolved line intensity ratios of ionic to atomic and matrix element to alloying element of specimens with different aging grade were investigated. Besides, the time-resolved plasma temperatures of different specimens were studied. And the three-dimensional surface topographies of ablated craters of specimens with different aging grades were analyzed. The study results show that the line emissions are located at greater height above surface for the specimen with lower steel aging grade during the early stage of the plasma expansion (300–700 ns delay time). The integrated line intensities which are close to the specimen surface (at≈0–500 μm above specimen surface) increase with the increase of steel aging grade during 300–700 ns delay time. The line intensity ratios are correlated with the steel aging grade at specific height above specimen surface during 500–700 ns delay time, and these correlations are sensitive to the delay time and observation distance from specimen surface. In addition, it was found that the plasma temperatures of specimens with lower aging grades are higher during 300–700 ns delay time. And the depth and volume of ablated crater increase with the increase of the steel aging grade. The investigations create a better understanding of physical mechanism in LIBS steel degradation analysis, and provide a good reference for practical measurement.