The scientists used a scanning electron microscope to obtain high-resolution images of around 10 nanometers to discover where the first cracks “nucleate” and where they extend.

Mechanical and on-site characterization tests performed in the scanning electron microscope have been used in ‘understanding the mechanisms of fracture,’ which, until this research, scientists have never been able to determine, according to one of the authors of the study, Elena Bernardo, from the UC3M Powder Technology Group.

Automobile steels

The materials that are the subject of the research are commercial sintered steels obtained through powder metallurgy or powder technology and are widely used in the automobile industry. In this study, published in the journal Powder Metallurgy, several steels currently on the market were evaluated. Specifically, an Fe-C steel, a steel pre-alloyed with molybdenum (Astaloy Mo grade, from Höganäs AB) and the well-known Distaloy AE (also from Höganäs), which is iron alloyed by diffusion with copper, nickel and molybdenum, were analyzed. 

The results have helped in understanding the connection between microstructure and properties, which in these materials entails a technological challenge, as not only the phases but also the residual porosity that composes their microstructure come into play. ‘The research has revealed, among other things, that the most angular and irregular pores are the first points of “nucleation,” that is, those that initiate the breaking,’ said José Manuel Torralba, full professor in the UC3M department of Materials Science and Engineering and Deputy Director of the IMDEA Materials Institute.

The methodology used is reportedly applicable to any type of alloy and can not only to test its behavior under pressure, but also its behavior at high temperatures.