The understanding of the tribological system and wear of ferrous-based materials is of high importance for diamond-impregnated tools application. In real performances, in fact, the wear of the matrix has a fundamental role in determining cutting or coring speed and insert lifetime. During material removal in reinforced concrete, the matrix materials are subjected to a complex 3-body abrasive system, constituted by abrasive concrete slurry and by the interaction concrete-matrix and rebars-matrix. The former leads to a pure abrasive wear mechanism, while the second can cause an adhesive wear mechanism due to the high chemical affinity between the two materials. To differentiate and study the two mechanisms, in the present work modified ASTM B611-13 is used with two different counter-bodies: SiC wheel and steel wheel. Wear mechanisms are analyzed and a correlation from a mechanical/microstructure perspective was sought. In particular, the role of matrix additives in the wearing system is investigated. Free graphite and sulfide formation turned out to be good matrix additives candidates to act as solid lubricants. The results show that specific additives can decrease the coefficient of friction and then protect from aggressive adhesive wear, and demonstrate how the study of microstructure/mechanical properties alone is not sufficient to fully characterize the wear system during real applications.
La comprensione del sistema tribologico e dell’usura di materiali metallici è di grande importanza per l’applicazione di diamond tools. Nelle reali applicazioni, infatti, l’usura della matrice ha un ruolo fondamentale nel determinare la velocità di taglio e la durata di vita dello strumento. Durante l’asportazione di materiale nel calcestruzzo armato, i materiali della matrice sono sottoposti a un complesso sistema abrasivo a tre corpi, costituito dal liquame abrasivo del calcestruzzo e dall’interazione calcestruzzo-matrice e armatura-matrice. Il primo porta a un meccanismo di usura puramente abrasivo, mentre il secondo può causare un meccanismo di usura adesiva a causa dell’elevata affinità chimica tra i due materiali. Per differenziare e studiare i due meccanismi, nel presente lavoro è stata utilizzata il test ASTM B611-13 modificata con due diversi controcorpi: ruota in SiC e ruota in acciaio. I meccanismi di usura sono stati analizzati e si è cercata una correlazione dal punto di vista meccanico/microstrutturale. In particolare, è stato analizzato il ruolo degli additivi della matrice nel sistema di usura. Grafite non dissolta nella matrice ferritica e la formazione di solfuri si sono rivelati un buoni candidati come additivi della matrice ad agire come lubrificanti solidi. I risultati dimostrano che l’additivo specifico può diminuire il coefficiente di attrito e quindi proteggere dall’usura adesiva, e dimostrano come lo studio delle proprietà microstrutturali/meccaniche da solo non sia sufficiente a caratterizzare completamente il sistema di usura durante le applicazioni reali.
Effect of additives on wear properties of sintered Fe-based materials
Sala, Nathan Sibeso
2022/2023
Abstract
The understanding of the tribological system and wear of ferrous-based materials is of high importance for diamond-impregnated tools application. In real performances, in fact, the wear of the matrix has a fundamental role in determining cutting or coring speed and insert lifetime. During material removal in reinforced concrete, the matrix materials are subjected to a complex 3-body abrasive system, constituted by abrasive concrete slurry and by the interaction concrete-matrix and rebars-matrix. The former leads to a pure abrasive wear mechanism, while the second can cause an adhesive wear mechanism due to the high chemical affinity between the two materials. To differentiate and study the two mechanisms, in the present work modified ASTM B611-13 is used with two different counter-bodies: SiC wheel and steel wheel. Wear mechanisms are analyzed and a correlation from a mechanical/microstructure perspective was sought. In particular, the role of matrix additives in the wearing system is investigated. Free graphite and sulfide formation turned out to be good matrix additives candidates to act as solid lubricants. The results show that specific additives can decrease the coefficient of friction and then protect from aggressive adhesive wear, and demonstrate how the study of microstructure/mechanical properties alone is not sufficient to fully characterize the wear system during real applications.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/211243