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									                                                  SEMINAIRE

                                      Aaron KRAWITZ
                                              University of Missouri
                                             Columbia, Missouri, USA


             Neutron Diffraction Studies of Residual and Applied Stresses in

                                       Cemented Carbide Composites


                            Mercredi 9 juin 2004 à 14 h 30
                       Salle de Conférence (Bâtiment 563, salle 15)


Cemented carbide composites are used as cutting tool inserts for high-speed machining, and
exploration and mining of oil, gas and minerals. They are particulate composites, typically made
with tungsten carbide (WC) particles in a cobalt (Co) binder, although we have often used nickel
(Ni) binders for our neutron diffraction studies. In the first part of the talk, the nature of thermal
residual stresses in cemented carbides will be presented. This will include the magnitude of the
stresses in each phase, and some aspects of their point-to-point distribution in the microstructure.
In addition, the variation of the residual stresses with temperature and WC particle size is
discussed. This work was done on the General Purpose Powder Diffractometer at the Intense
Pulsed Neutron Source at Argonne National Lab and at the University of Missouri.

In the second part of the talk, results of recent in situ studies of cemented carbides under
compressive loads are presented, including evidence of the role of thermal residual stresses in the
unusually high toughness of these materials. The samples contained 5, 10 and 20 wt.% Ni, with 1
  m WC particles. Load response to –2000 MPa was evaluated in 250 MPa increments. Diffraction
strain measurements in both phases were made simultaneously in the axial and transverse
directions at each load level. The SMARTS instrument at the Los Alamos Neutron Science Center
was used. Residual stresses were measured in the samples prior to and after the loading
sequences using the MURSI stress instrument at the University of Missouri.




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