A Focus on Dynamic Modulus: Effects of External and Internal Morphological Features

The present work examines the effects of external and internal morphological features on the dynamic elastic modulus and its measure. It consists of two parts. The first part considers the effect of geometrical features of probes and shows the key role of roughness as source of a systematic error leading to the underestimation of the Young’s modulus. The second one is focused on the effect of porosity. Several models which consider the porosity as an ideal regular microstructure and the relative equations describing the Young’s modulus vs. porosity have been reviewed and critically discussed. The values of the relative modulus Er predicted by different models are similar for materials with low porosity (p < 0.2) and isolated pores whereas they strongly diverge if p > 0.2 and interconnected pores are present. Moreover, such models fail to describe the elastic behavior of materials correctly also with low porosity (p ≈ 0.1) such as sintered steels in the case of pores with a preferred orientation and an irregular shape.

Wear Behavior of Fe-Cr-C Sintered Steels

The paper is focused on the elaboration of some sintered steels with Cr concentration between (1-2 %) wt., carbon as graphite with a concentration of 0,4% wt. and Fe for the balance. The samples were die pressed at 600 MPa and sintered at 1150 °C in argon atmosphere. The samples were studied from the point of view of wear behavior against three types of counter balls, alumina (Al2O3), steel (100Cr6) and stainless steel 440C. The results shows that the lowest value for the friction coefficient was attained for the steel with 1,5% Cr. Also, microhardness tests were performed and reveal that the highest value was equal to 229 HV05.