NUCLEAÇÃO DE TRINCAS EM MOLDES DE INJEÇÃO DE ALUMÍNIO COM TRATAMENTO DE SUPERFÍCIES DUPLEX.

The premature nucleation of cracks in an aluminum injection die with duplex surface treatment (plasma nitriding and physical vapor deposition coating, PVD) is studied. The manufacturing and operating conditions were documented and the study included the following analytical techniques: hardness profile, X-ray diffraction for phase identification, microscopic observations by optical microscopy, scanning electron microscopy The latter with energy dispersive X-ray has the capability for chemical analysis. Preliminary observations reveal a microstructure consisting of coarse tempered martensite and a considerable surface roughness. A detailed analysis of crack initiation sites shows the presence of sulfur inclusions between the substrate material and the coating. The presence of sulfur is attributed to the use of sulfur impregnated grinding stones in the final polishing of the die. Consequently, the failure mechanism is presented in view of this evidence. [ABSTRACT FROM AUTHOR]