Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Optimization of sintered high speed steel type composite materials

Microstructural and mechanical properties of the sintered M3/2 composites were studied including the transverse rupture strength (TRS), fracture stress and Young's Modulus. Studies were made of microstructure, microcomposition, roughness, mechanical properties and microcracking. For each material, the different stresses involved in the cracking process were determined by surface replica microscopy and linked to the defects associated to a crack. In fretting, it was concluded that cracking is a fatigue phenomenon and nucleates on porosities for a maximal contact stress greater than 1.2 GPa. This value corresponds to the crack nucleation stress in the matrix. Case studies were carried out on worn components. Fretting and pin-on-disc tests reproduced well the observed damage. In general, the increase of the applied load resulted in the increase of wear, depending on wear mechanisms. The analysis of wear mechanisms showed that titanium carbide is a good additive regarding wear resistance. Analysis of the material parameters showed that for wear resistance, the better behaviour is given by the M3/2 + 5% titanium carbide composite regarding fretting, pin-on-disc and abrasion tests. Concerning cracking, the better behaviour is given by the M3/2 + 5% titanium carbide + 5% manganese sulphide composite. Crack nucleation occurs more frequently in this composite than in M3/2 or M3/2 + 5% manganese sulphide, but cracks do not propagate in this composite, because the carbide complexes stop or slow the cracks.