CARL J. BOEHLERT DEPARTMENT OF CHEMICAL ENGINEERING AND MATERIALS SCIENCE, MICHIGAN STATE UNIVERSITY, USA

Lunes 11 de Abril de 2011

In-situ scanning electron microscopy (SEM) is now being routinely performed around the world to characterize the surface deformation behavior of a wide variety of materials. The types of loading conditions include simple tension, compression, bending, and creep as well as dynamic conditions including cyclic fatigue with dwell times. These experiments can be performed at ambient and elevated temperatures and in different environments and pressures. Most modern SEMs allow for the adaptation of heating and mechanical testing assemblies to the SEM stage, which allows for tilting and rotation to optimal imaging conditions as well as energy dispersive spectroscopy X-ray capture. Perhaps some of the most useful techniques involve acquisition of electron backscatter diffraction (EBSD) Kikuchi patterns for the identification of crystallographic orientations. Such information allows for the identification of phase transformations and plastic deformation as they relate to the local and global textures and other microstructural features. Understanding the microscale deformation mechanisms is useful for modeling and simulations used to link the microscale to the mesoscale behavior. In turn, simulations require verification through in-situ microscale observations. Together simulations and in-situ experimental verification studies are setting the stage for the future of material science, which undoubtedly involves accurate prediction of local and global mechanical properties and deformation behavior given only the processed microstructural condition.

Recently our group has developed an in-situ tensile-creep testing methodology to investigate the effect of the grain boundary character distribution on the grain boundary cracking behavior. This methodology involved using an Ernest Fullam, Inc. tensile stage to maintain a sample at a constant load while heating it with a resistive heater at temperatures up to 760ºC. Deformation in the form of grain boundaries cracking was observed. EBSD patterns were acquired before, during, and after the deformation without stopping or pausing the experiment. Such experiments have revealed the susceptibility of general high-angle grain boundaries (HAB) to creep cracking and the resistance of special boundaries to cracking. Together these results provide firm evidence that the LAB and CSLB in this alloy are more resilient to cracking during creep. Using a similar testing methodology, in-situ tensile and tensile-fatigue experiments have been performed on a variety of alloys and the results will be summarized in the presentation.

Seminarios Internacionales de Fronteras de la Ciencia de Materiales Aula de Seminarios Departamento de Ciencia de Materiales E. T. S. de Ingenieros de Caminos, UPM C/ Profesor Aranguren s.n. 28040 Madrid

Para más información contactar con: Dr. José Ygnacio Pastor (+34) 913 366 684. [email protected].

Vídeo Realizado por el Gabinete de Tele-Educación de la Universidad Politécnica de Madrid, grabado por el departamento ciencia de los materiales.