Andrea Morri

Replacement of Nitrided 33CrMoV Steel with ESR Hot Work Tool Steels for Motorsport Applications: Microstructural and Fatigue Characterization

AbstractIn this work tensile strength, fatigue resistance and fracture toughness of two electroslag remelted (ESR) tool steels and of 33CrMoV12 ESR steel (both in quenched and tempered condition, as well as nitrided condition) were evaluated. The role of hardness, residual stresses and inclusion sizes on the fatigue behavior was investigated. Tool steels have a tensile strength between about 1900 and 2300 MPa, fracture toughness between 35 and 33 MPa√m, while fatigue strength ranges between 725 and 992 MPa. The tensile strength and fracture toughness of the 33CrMoV12 ESR are, respectively, 1365 MPa and about 150 MPa√m. Nitriding induces a significant increase in fatigue strength from 560 to 980 MPa. These results highlight that appropriate ESR tool steels could replace nitrided steels.

Cast Al-Based Nanocomposites Reinforced with Thermal Plasma-Synthesized Ceramic Nanoparticles

The present study aims at producing Al-based nanocomposites reinforced with low fractions of ceramic nanoreinforcement produced by thermal plasma, evaluating the strengthening effects induced by their addition to the widely used A356 (Al-Si-Mg) cast aluminum alloy. Nanoparticles were produced using a lab-scale RF inductively coupled thermal plasma system designed by simulation as to optimize the plasma operating conditions and reactor geometry. During the casting route, ultrasonic treatment of the melt was performed to better disperse the reinforcing particles into the matrix. Ceramic spherodized microparticles were also synthesized and micro-reinforced Al-matrix composites were produced with the same route for comparison. Microstructural characterization of the cast samples was carried out by optical and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) analysis. BET analysis was also used for powder characterization. Hardness tests were performed to assess the enhancement in mechanical properties obtained by addition of nanoparticles with respect to both the microparticle reinforced and unreinforced Al-Si-Mg matrix.