Fatigue and Damping Behavior of PM Produced Aluminum Matrix Composites after Shot Peening

Author:  A. Kasakewitsch, C. Teichmann and W. Riehemann
Source:  Conf Proc 2014: ICSP-12 Goslar, Germany (pgs.130-135)
Doc ID:  2014063
Year of Publication:  2014
Abstract:  
Two Aluminum (Al) materials were produced by hot extrusion of different powder mixtures at 350°C. For the first material only gas atomized powder of micro-scale 99.98 Al was consolidated. The second powder was mixed by ball milling of the same Al powder with 0.35 vol.% nano-scale hexagonal Boron Nitride (BN) before hot extrusion. Ball milling and subsequent hot extrusion resulted in a Metal Matrix Composite (MMC) strengthened by fine and homogenously dispersed BN particles. Due to this dispersion hardening the tensile strength of the produced the MMC increased by 65% compared to the PM material without BN dispersions with negligible loss of high ductility (18% plastic strain). Both materials have a high potential of hardness and fatigue strength increase by cold working or shot peening because they were dynamically recrystallized after hot extrusion. Fatigue strength of the dispersion hardened material could be increased using shot peening by about 20%. The Damping is increased for low and decreased at high strain amplitudes by the dispersions. Damping increases immediately after shot peening and ages afterwards whereas both the damping increase and the ageing strength are independent of the presence of dispersions. These measurements can be explained by the interaction of dislocations with point defects like vacancies and solid solutes. They can also be used to investigate crack nucleation and growth and to predict impending failure.