Failure and fracture analysis of a high-alloy Ni-Al bronze chain connector of a tube drawing machine, Engineering Failure Analysis 2020, 110, 104432
Abstract
The investigation of a fractured Ni-Al bronze alloy connector, from a chain assembly,
was performed in order to determine the potential cause of the observed failure. It is
shown that the fracture occurred by fatigue due to the combined result of poor
machining quality and the brittle nature of the as-cast component. This synergistic
effect facilitated intergranular crack propagation through the “microstructurally
sensitized” interdendritic regions. Various irregular and coarse-shaped intermetallic
phases, corresponding to κ-type phases, were detected and their detrimental role on
crack propagation was evaluated. Thermodynamic and kinetic simulation of
solidification and phase transformation was elaborated in order to verify qualitatively
and quantitatively the presence of the microscopically detected phases.
Thermodynamic results were in agreement with metallographic observations. Kinetic
results showed that increased cooling rate affects solidification particularly at high
content of substitutional elements, such as Fe, Ni and Mn, since their diffusion is
restricted and the completion of solidification is decelerated. Moreover, the high
content of these elements favors the appearance of κΙ precipitates. The formation of
shaped κΙ-phase cannot be eliminated, however its fraction and size can be suppressed
by increasing cooling rate. The alteration of chemical composition of cast component
could provide promising results as it shows a reducing tendency of κI-phase
intermetallics’ formation and a higher homogeneity, even at moderate cooling rates.