Abstract：Ti-47.5Al-2.5V-1.0Cr titanium alloy has some advantages such as good high temperature ductility and strength, so it could be potentially applied to produce high-temperature components, for example, cast turbine, swirler and vane. Before the quantitative analysis of alloy or parts interior by laser-induced breakdown spectroscopy (LIBS), the samples and certified reference materials of titanium alloy should be pretreated to remove surface oxidation layer, cast reaction layer and contaminants. The titanium alloy belonged to fragile material at room temperature, so it should be prepared by grinding and polishing, but not cutting. However, the sample surface may be polluted due to the heating and stiction in grinding and polishing preparation, which would influence the LIBS analysis of components in titanium alloy. The effect of several pretreatment methods (grinding by milling machine, grinding by metallurgical milling machine, manual grinding, manual polishing and glow argon ion bombardment) on removal of surface oxidation layer and contaminants of titanium alloy reference material with different structures were evaluated by LIBS. LIBS analysis results indicated that the pollution in sample preparation process was mainly from the cement for abrasive paper production. The sample preparation was affected by linear velocity of grinding, particle size of grinding material and direction of polishing. Moreover, the removal efficiency of contaminants was also influenced by sample structure. The carbon pollution layer on titanium alloy sample surface which was ground with high speed by silicon carbide abrasive paper milling machine was deep with depth up to 15 μm, which was higher than that of the sample which was ground by water cooling metallurgical milling machine with intermediate speed. It indicated that the high temperature could accelerate the diffusion of carbon in titanium alloy. During grinding at medium and low speed, the absorption of carbon and calcium pollutants on sample surface increased with the increase of mark number of abrasive paper. In medium speed grinding process, the diffusion depth of elements such as calcium and aluminum with good affinity to α phase in titanium alloy with α structure was higher than that of titanium alloy with α+β and α2+γ respectively. The pollution depth of calcium was up to 10 μm. However, the diffusion of carbon on the surface of titanium alloy with different structures showed no significant difference. During manual grinding at low speed, the pollution layer of carbon and calcium on titanium alloy surface was shallow with depth of 1-3 μm, which was consistent with the grinding crack depth. The polishing effect of bidirectional or along the grinding texture was better than that when the grinding direction was vertical to the texture. The depth of residue pollutants was not higher than 1 μm, which was close to that of glow argon ion bombardment method.Consequently, the easily pollution problem of titanium alloy sample was solved, and the calibration curves of carbon in LIBS analysis were improved.Simultaneously, the determination precision was enhanced. The analytical results of Ti-47.5Al-2.5V-1.0Cr titanium alloy were in good agreement with those obtained by other methods.
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