By: Che Zhi-gang
The technique of laser shock process (LSP) is an advanced surface treatment, which import high pressure shock wave induced by laser beam into target materials to improve their performance. The fatigue life of the materials is prolonged by times through changing the stress distribution. The hardness and strength are increased remarkably and corrosion resistance is improved after LSP. Compared with other treatment techniques, LSP have many advantages, such as high pressure, high energy, high strain rate, noncontact, no heat-affected zone, better controllability and roughness and remarkable processing effect.
The high energy pulse laser (reaching 50 J) suitable for LSP was developed by BAMTRI. The great achievements have made for the LSP on complicated structures, such as titanium aeroengine blades and holes. The quality monitoring system online was developed basing the natural frequency measurement of LSP blades (illustrated in Fig.1), which realized quality test performance analysis and detecting online of shock effect. BAMTRI has realized the LSP with square spot through optical lens firstly in China. The square spot has the advantages of uniform energy distribution, smooth surface of shocked zone avoiding the stress cavity in shocked center and the smaller overlapping rate. And BAMTRI has the ability to treat irregular surface (crankshaft or circular surface) using several different shapes spot shown in Fig.2.
Recently, the shock pressure model was improved basing on the Fabbro et al’s work in 1990. The technology of coating wave layer was imported in LSP to decrease reflection effect. The nanocrystallation of titanium alloy surface through LSP was realized firstly, which improved greatly the performance of titanium alloy.