Evaluation of Shot Peened Aluminum by Doppler Broadening of Positron Annihilation Radiation Technique

Author:  K. Ono, Y. Koiso, K. Oguri, Y. Watanabe, K. Hattori
Source:  Conf Proc 2014: ICSP-12 Goslar, Germany (pgs.288-292)
Doc ID:  2014091
Year of Publication:  2014
Abstract:  
Shot peening has been applied to fatigue improvement of aircraft parts. Recently, fine particle shot peening (FPSP) technology has been developing to obtain superior fatigue property compared with conventional shot peening (CSP). Process of shot peening is controlled by intensity measurement using almen strip. X-ray diffraction (XRD) residual stress measurement, including its depth profile by chemical etching, is supplementary applied for more detailed understanding of the shot peened material. The Doppler broadening of positron annihilation radiation (DBAR) technique is a powerful tool to analyze disordered metal crystals, including vacancy, interstitial and dislocation, while it has been already applied to the investigation of polymer materials. Aluminum specimens were prepared and treated by FPSP and CSP with various conditions, i.e. media material, size and intensity. Evaluation of the aluminum specimens has been made with residual stress measurement by XRD and S-parameter by DBAR. The DBAR measurement system consists of a γ-ray Ge detector and a multi-channel analyzer. A sealed positron source of ²²Na was placed on the shot peened specimens, and the energy spread of annihilation γ-ray photo peak (S-parameter) was measured to evaluate the density of lattice defects introduced through the shot peening process. Surface compressive residual stress by XRD method properly represents the surface sensitive property of FPSP. While DBAR results suggest that S-parameter corresponds to integrated value of compressive residual stress of both FPSP and CSP.