Jeffrey L. Evans

Influence of Grain Boundary Character and Annealing Time on Segregation in Commercially Pure Nickel

Commercially pure nickel (Ni) was thermomechanically processed to promote an increase in Σ3 special grain boundaries. Engineering the character and chemistry of Σ3 grain boundaries in polycrystalline materials can help in improving physical, chemical, and mechanical properties leading to improved performance. Type-specific grain boundaries (special and random) were characterized using electron backscatter diffraction and the segregation behavior of elements such as Si, Al, C, O, P, Cr, Mg, Mn, B, and Fe, at the atomic level, was studied as a function of grain boundary character using atom probe tomography. These results showed that the random grain boundaries were enriched with impurities to include metal oxides, while Σ3 special grain boundaries showed little to no impurities at the grain boundaries. In addition, the influence of annealing time on the concentration of segregants on random grain boundaries was analyzed and showed clear evidence of increased concentration of segregants as annealing time was increased.

Creep-Fatigue-Environment Crack Tip Kinetics of Ni-Base Superalloys

Several time-dependent damage mechanisms can operate during creep-fatigue loading. In the crack tip region, creep deformation, stress relaxation, oxygen diffusion along grain boundaries, and grain boundary oxidation are all occurring during the hold period of a creep-fatigue cycle. These conditions can lead to grain boundary embrittlement; however, it depends on the rates of the different processes. A comparison of the kinetics can determine which mechanisms are operational and which mechanism is the rate limiting step in the time-dependent damage process during creep-fatigue crack growth. This paper presents results for intergranular embrittlement occurring within a 10 s hold period and compares the kinetics of the processes.

Undergraduate Student Experiences with Composite Materials

Composite materials are being used in a variety of important strategic lightweight applications, especially in aerospace structural designs. Undergraduate students need greater exposure to this critical area of engineering materials selection and design than most curricula currently provide. Mechanical and aerospace engineering undergraduate students at the University of Alabama in Huntsville (UAH) have had a number of opportunities to learn hands-on skills in designing with composites and fabricating a number of structural components. They have had these opportunities in undergraduate student competitions and associations such as the NASA Great Moon Buggy Race, the Formula SAE team, and the UAH Charger Rocket Works Club. Additionally, real industrial applications of composites are learned through co-operative employment experiences. This paper describes some of the experiences that UAH undergraduate students have encountered.