THE EFFECT OF DENSITY ON FRETTING WEAR OF SINTERED IRON

Fretting wear of sintered irons of three different relative densities, 0.8, 0.85 and 0.9, was investigated. Wear was generated in air without any lubrication between specimens of the same density with nominal contact area 100 mm2 under normal load 1000 N and sliding speed 0.01 m s-1. Three different sliding amplitudes, 0.05 mm, 0.2 mm and 0.5 mm were used and the total sliding distance was 100 m. Density had little effect on the wear of sintered iron at a low sliding amplitude of 0.05 mm, wear was slight and characterised by the formation of a little amount of brown alpha-Fe2O3 on the surfaces. The effect of density on wear increased with increasing sliding amplitude and it was found that the closure of the interconnected pores had a critical effect on wear mechanism by eliminating the open pores on the surfaces. The weight loss and volume loss of the 0.9 iron at 0.5 mm was more than seven times and three times higher respectively than those of the two lower density irons, while the 0.8 and 0.85 irons behaved similarly at all the three sliding amplitudes. The wear mechanism of 0.8 and 0.85 irons at over 0.2 mm is abrasive wear and both the on-surface and the loose debris are brown alpha-Fe2O3 with the average particle size 50 nm. The wear mechanism of 0.9 iron at over 0.2 mm is either oxidative wear if oxide was formed before debris was generated, or spalling or fatigue induced delamination if metallic debris was generated first and then oxidised. The on-surface wear debris is black Fe3O4 with the average particle size 500 nm, and the loose wear debris is black alpha-Fe2O3 with the same particle size as that of the brown alpha-Fe2O3. Fe3O4 could be more harmful than Fe2O3 in wear when it exists in the form of particles because of its higher strength and larger particle size.