Effects of Undersized Inclusions on Ductile Fracture Behavior of FeNi42 Alloy in Sheet Tension

In-situ tension tests with special designed SEM had been conducted to trace the process of microvoids nucleation, growth and coalescence at the nonmetallic inclusions in FeNi42 alloy. The fracture surfaces were examined by scanning electron microscopy. The main results are as follows. The fracture of the tensile specimen of FeNi42 alloy is along the plane of maximum shear stress (45deg to the tensile axis), and there are a lot of dimples in the fracture surface. So this is a typical ductile fracture. At earlier stages of deformation, microvoids nucleated at bigger inclusions, and grew up independently. When the microvoids grew up to critical size, they began to coalesce. Coalescence of microviods occurs only in localized necked regions. When the space of adjacent microviods is smaller, they coalesced directly. Oppositely, when the space is bigger, they are usually linked by several smaller voids nucleated presumably by fine carbides or very small inclusions as result of the high local strains required to separate the intervening matrix.