Comparison of Surface Characteristics and Thermal Residual Stress Relaxation of Laser Peened and Shto Peened AISI 4140

Author:  Menig, Schulze and Vohringer
Source:  Conf Proc: ICSP-8 Sept. 16-20, 2002 Garmisch-Partenkirchen, Germany
Doc ID:  2002065
Year of Publication:  2002
Authors Rainer Menig, Volker Schulze and Otmar Vohringer Institut fur Werkstoffkunde I, Universitat Karlsruhe (TH), Karlsruhe, Germany Abstract Laser peening is a relatively new mechanical surface treatment which causes deep zones bearing compressive residual stresses. This is accomplished by applying shock waves to the material surface using short laser pulses. Quenched and tempered steel AISI 4140 was laser peened using a Nd:glass slab laser with a pulse energy of 25 Joule and a wavelength of 1053 nm. Afterwards the mechanically affected zones were analyzed according to their topography, residual stress state and work hardening state and compared to shot peened samples. It is well known that the effect of mechanical surface treatments strongly depend on the stability of the induced residual stress state. Therefore, annealing treatments at different temperatures and times were performed to analyze the thermal residual stress relaxation behavior. Using an iterative mathematical procedure based on a least squares algorithm the activation enthalphy for thermal residual stress relaxation was determined and the responsible mechanisms were identified. The results were evaluated according to the amount of cold work caused by the different surface treatments.

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