The Surface Nanocrystallization and Hardening (SNH) Process for Improved Fatigue Resistance

1. The Surface Nanocrystallization and Hardening (SNH) Process for Improved Fatigue Resistance Leon L. Shaw(University of Connecticut) & Peter K. Liaw (University of Tennessee), DMR-MET-0207729 A surface nanocrystallization and hardening (SNH) process has been developed to impart metallic engineering components with a nanocrystalline (nc) surface and coarse-grained interior. A schematic of SNH is shown on right. SNH is different from shot peening (SP) in terms of the kinetic energy of impacting balls, the deformation depth, and the formation of a nc layer at the surface of the component. High speed balls Ar, N2, or other atmosphere Component to be processed Finite element modeling (the table on right) shows that SNH generates a thicker plastic deformation layer and higher plastic strain than SP, which leads to the formation of a thicker nc surface layer in the SNH process.

2. The Surface Nanocrystallization and Hardening (SNH) Process for Improved Fatigue Resistance 100nm 200nm Leon L. Shaw(University of Connecticut) & Peter K. Liaw (University of Tennessee), DMR-MET-0207729 Surface nanocrystallization in the Ni-C2000 alloy proceeds with twin-twin intersections dividing the original coarse grains into submicron- and nano-sized regions (Fig. A), followed by interactions between twin boundaries and trapped dislocations (Fig. B), and finally the formation of diffuse, non-equilibrium, high-angle grain boundaries (Fig. C) also due to the twin-dislocation interactions. A B C 20 mm from the impacted surface At the impacted surface 100 mm from the impacted surface

3. The Surface Nanocrystallization and Hardening (SNH) Process for Improved Fatigue Resistance Leon L. Shaw(University of Connecticut) & Peter K. Liaw (University of Tennessee), DMR-MET-0207729 This NSF-sponsored program offers excellent opportunities for undergraduate students to participate in research and for the PIs and graduate students to promote science and engineering. Juan Villegas (center), a graduate student in this project (UConn), is doing materials demos in CPTV Science Expo. Misael Manjarres, an engineering freshman (UConn), is using a 3-D non-contact optical profilometer to measure the surface roughness of a SNH-processed sample. The PI Shaw was the faculty advisor to the UConn Student Chapter with five (5) national awards including the 2004 Materials Outreach Awards shown on right. Zachary Stone, a senior student (UConn), worked on this project, and is a co-author of the paper on “surface roughness evolution of SNH-processed Al alloys” published at Acta Materialia.