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Description
Laser shock peening (LSP) is an effective method for enhancing the fatigue durability and corrosion resistance of components in mechanical and aero-engine engineering. This technique induces minimal heating, with the formation of a residual compressive stress field resulting from a shock wave generated by high-energy, short-pulse laser impact. A weak plastic deformation and microstructural transformation occur within a surface layer approximately 1 mm deep, while the bulk material retains its initial state, and its mechanical properties remain unchanged (the stress-strain diagrams for the base and treated specimens are identical). However, the dynamics of heat transfer in LSP-treated specimens during their deformation remains a relevant question.
This study presents the characteristic deformation curves of base and LSP-treated specimens made of Ti-6Al-4V titanium alloy, along with the evolution of the average temperature in the gauge section as a function of strain, recorded using infrared thermography. It is shown that although the deformation diagram does not change, the temperature of the LSP-treated specimens increases compared to the base ones.
The aim of this work was to identify the causes of the abnormal temperature rise in LSP-treated specimens based on experimental data and numerical modeling of heat release during elastoplastic deformation under quasi-static tension.
The investigation consisted of two stages. The first stage aimed to determine the effective thermophysical constants of the material after LSP. This involved studying the dynamics of heat propagation after local point heating, both experimentally (using infrared thermography) and numerically. It was established that LSP led to an increase in specific heat capacity from 526 to 546 J/(kg•K) and a decrease in thermal conductivity from 7.5 to 6 W/(m•K).
The second stage was aimed at verifying the reliability of the thermophysical constant changes identified in the first stage and determining the fraction of dissipated energy during the deformation of base and LSP-treated specimens. Mechanical tests involving quasi-static tension of flat specimens were conducted with simultaneous recording of the temperature field in the gauge section using an infrared camera. Numerical modeling of the thermoelastoplastic effect demonstrated that the obtained changes in thermophysical properties lead to an increase in the effective value of the Taylor-Quinney coefficient from 0.39 for the base specimen to 0.45 for the LSP-treated specimen.
Thus, it has been established that LSP alters the effective thermophysical properties of the material without affecting its mechanical characteristics. After treatment, the specific heat capacity increases, and thermal conductivity decreases. These changes modify the overall heat release process, which is reflected in the increase of the dissipated energy fraction (the Taylor-Quinney coefficient) in the treated specimens.
Microstructural studies revealed a reduction in the volume fraction of grains with low crystallographic misorientation. Instead, substructures with high local misorientation and a developed network of low-angle boundaries are formed in the surface layer. These changes may serve as the primary reason for the formation of a residual compressive stress field and the modification of the material's thermal response after LSP.
