John W. Bean, Manufacturing Engineering and Engineering Technology
This report will summarize the efforts and results of the research conducted by John Bean on the role of grain boundary misorientations in intergranular cracking of copper-based metals. This research was conducted during the period of Sept. 1993 toApril1994. I was not able to prove all that I had originally proposed to do because of certain difficulties I will explain below. My research was ended when the equipment I was using was moved at the end of the 1994 winter semester. This report will briefly describe the purpose of my research and the difficulties that I encountered.
It was my original hypothesis that the intergranular corrosion of copper could be improved increasing the population of certain low-energy grain boundaries. The population of these grain boundaries was increased through deformation and annealing in a vacuum furnace. (Dr. Tom Mason proved this could be done in his dissertation conducted through Yale University.) Intergranular corrosion was induced through exposure to a 30% ammonium hydroxide solution while the specimens were under compressive and tensile stress. This stress was maintained by bending the specimens in a C-formation with a bolt through the ends. The corroded specimens were examined with the Orientation Imaging Microscopy techniques used on a scanning electron microscope. In theory, by examining the grain boundaries surrounding a crack, it can be shown that cracks progress along higher energy boundaries as opposed to the low-energy boundaries mentioned above. This final portion of my research provided difficulties that I was not able to overcome in my semesters at BYU.
The major area of difficulty was in obtaining intergranular cracks that could be mapped for grain boundary misorientations. I first attempted this research with pure copper. No cracks developed in the month that it sat in solution. It was determined that copper alone was not as susceptible to cracking as a copper alloy. The second attempt was conducted with yellow brass. To work well, the cracks must be intergranular in nature and still create the poor image quality necessary for the computer to identify them as cracks and not just grain boundaries. Due to the small grain size of the brass, the cracks that formed were not intergranular because they were more than one grain boundary wide. This prevented the examination of these cracks with ordinary boundary mapping methods. It was my intent to perform a manual scan of the grain map to determine the grain boundary misorientation between grains on opposite sides of the cracks. This was not possible to complete because of the transfer of the microscope to its new room.
I was able to gain a better understanding of the importance of proper grain boundary misorientation in metals and the techniques used to map grain boundaries. While I was not able to complete my research, I was able to provide the groundwork for further study in this areas by other students under Dr. Adams or myself.