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SUMMARY:Nanocrystalline alloys: Impervious to Fatigue Failure?
DTSTART:20140917T110000
DTEND:20140917T120000
DTSTAMP:20260504T103401Z
UID:7026cbe9db1136d4cb72db05b10e78c26e9f99db35380fb2937f1393
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr. Brad Boyce\, Sandia National Laboratories in Albuquerque\,
  New Mexico\, USA\nBio : Dr. Boyce is a Distinguished Member of the Techni
 cal Staff at Sandia National Laboratories in Albuquerque\, New Mexico\, US
 A.  Dr. Boyce received the B.S. degree from Michigan Technological Univer
 sity in 1996 in Metallurgical Engineering and the M.S. and Ph.D. degrees i
 n 1998 and 2001 from the University of California at Berkeley in Materials
  Science and Engineering.  Dr. Boyce joined the technical staff at Sandia
  in 2001 where his research interests lie in micromechanisms of deformatio
 n and failure.  He was promoted to Principal Staff in 2005\, and received
  the special appointment of Distinguished Staff in 2014.  He has over 70 
 peer reviewed archival publications (H-index=23) in areas such as microsys
 tems reliability\, nanoindentation\, fracture in structural alloys\, weld 
 metallurgy\, ocular tissue viscoelasticity\, and fatigue mechanisms.  Dr.
  Boyce has served as a Key Reader for Metallurgical and Materials Transact
 ions\, and has served as a guest editor for Thin Solid Films\, Experimenta
 l Mechanics\, International Journal of Fatigue\, and International Journal
  of Fracture as well as several MRS proceedings books.  He has organized 
 10 technical symposia at international conferences and has chaired the Rio
  Grande Symposium on Advanced Materials.  Dr. Boyce is a past recipient o
 f the Hertz Foundation fellowship\, TMS Young Leader award\, and ASM’s M
 arcus A. Grossman Young Author award.  Dr. Boyce leads several large-team
  research programs at Sandia\, totaling over $4M in annual funding.\nAbstr
 act : Fatigue failure is the process by which materials break during repet
 itive loading.  These failures cost the US economy several billion dollar
 s each year.  In metals and alloys\, fatigue cracks nucleate by an atomic
 -scale process called ‘persistent slip’.  Transmission electron micro
 scopy studies of conventional coarse grained metals show persistent slip b
 ands as dislocation ladder structures with dimensions of several 100’s o
 f nanometers to micrometers.  However\, in nanocrystalline alloys the gra
 in size itself is less than 100 nanometers\, thereby suppressing the forma
 tion of a persistent slip structure.  We have examined this phenomenon in
  three nanocrystalline nickel based alloys and compared behavior to their 
 annealed coarse grained counterparts.  In all three nanocrystalline nicke
 l alloys\, failure is preceded by fatigue-driven grain growth.  Only when
  the grains are grown mechanically to several 100’s of nanometers\, does
  crack nucleation occur.   These nanocrystalline alloys demonstrate subs
 tantial enhancement in fatigue resistance compared to conventional structu
 ral metals\, even when scaled by the Hall-Petch strength enhancement.
LOCATION:ME B3 31 http://plan.epfl.ch/?room=MEB331
STATUS:CONFIRMED
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