1. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden

2. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Liquid Metal Embrittlement Dominique Gorse (presented by Vassilis Pontikis) CEA-IRAMIS / CNRS, Laboratoire des Solides Irradiés 91191 Gif-sur-Yvette, FRANCE

3. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Outline Environment & Mechanical behavior What is LME ? Surfaces, Liquids & Wetting Experimental facts Empirical criteria Modeling Conclusive remarks

4. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Surfaces and mechanical behavior Surfaces control the nucleation of cracks and dislocations and the annihilation of dislocations as well. However, bulk phenomena are predominent in plasticity. “If dislocations are nucleated principally at the surface, we may expect that irradiation with alpha particles, which penetrate only a short distance, will affect the mechanical properties. The evidence is contradictory” F. R. N. Nabbarro in “Theory of Crystal Dislocations ”, Clarendon, 1967 P. 281

5. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Joffe effect, irradiated KCl, Rebinder et al., 1944 air 60 s H 2 O, dried, air H2OH2O

6. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Steel 316L + Hg, Medina-Almazan et al. (2005)

7. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden good wetting  <90° bad wetting  >90°  LV  SV  SL  L V S  GB  /2  SL  GB  S1L  S2L  S1P +  S2P =  GB 2  SP cos  /2 =  GB (SV, LV, SL) mechanical equilibrium chemical equilibrium  SV -  SL =  LV cos  (Young) Grain boundaries

8. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Liquid Metal Embrittlement: what is it ? Ensemble of phenomena, including wetting, whereby materials suffer a marked decrease in their ability to deform (loss of ductility) or in their ability to absorb energy during fracture (loss of toughness), with little change in other mechanical properties.

9. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Cd: ductile in inert environment is brittle in presence of Ga at room T. Zn: brittle at ≈150 °C in presence of Hg or Ga (Rozhanski et al.,1957, Goryunov et al. 1978). Al: can be cleaved in presence of Bi (Lynch, 1985). LME: Single crystals or polycrystals ? Al-T4/2024 Hardrath & McEvily (1961) The liquid metal may invade grain & interphase boundaries

10. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Macroscopic features - I Ratio of fracture stresses of 4145 steel with & without Pb(0.3%)

11. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Macroscopic features - II Room T 400 < T < 620 °F Steel 4145 Mostovoy & Breyer, (1968)

12. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden LME & Chemistry The effect of impurities Westwood et al., (1971) Polycrystalline Al

13. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden LME Delayed failure 2024-T4 Al alloy + Hg amalgam Rostoker et al. (1960) Static fatigue

14. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden LME and Grain Boundaries: Al/Ga Ludwig et al. (2006)

15. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden LME and Grain Boundaries

16. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden LME: consensus about facts Instantaneous failure under applied or residual stresses Delayed failure at a static stress level below the tensile strength Microstructure is important BUT LM’s embrittle amorphous alloys too ! Ashok et al. (1981) Plasticity is often present Stress independent (?) grain boundary penetration High temperature “corrosion”

17. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden From consensus: prerequisites & empirical criteria of occurrence However factors determining which liquid metal will embrittle which solid metal still remain unclear ! Presence of an external stress A pre-existing crack or plasticity (at least limited) & presence of obstacles to dislocation motion e.g. grain boundaries, twins, precipitates Adsorption of the active species at the obstacles and at the tip(s) of propagating crack(s) Limited mutual solubility of the liquid and the solid Little or no tendency of stable high T m compounds

18. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Is modeling understanding ? An heuristic approach (sometimes a random walk) Experiments Analytic theoryNumerical approaches LME ?

19. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Modeling LME & Crack propagation: Elasticity Adsorption of the liquid at the crack tip decreases  s and thus  c

20. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden LME & Crack propagation:....adding plasticity Griffith’s model is elastic (Orowan, Stoloff & Johnson, …) But… However… Small changes in   s large influence on  eff

21. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden “Thermodynamic” model: Successes & limitations Cu/Pb-melt Eborall et al. (1956) Al bicrystals/HgGa solution Kargoll et al. (1977) Al 6061/inclusions Bi, Cd, Pb Roth et al. (1980, 1982) No mechanisms No microscopic description of the SL interface No kinetics No understanding of plasticity at the crack tip BUT …

22. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden LME & Cracks & D uctile B rittle T ransition T emp System  s (J/m 2 ) Al1.0 Al-Pb0.344 Al-Cd0.298 Al-Bi0.288 Old & Trevena (1979)

23. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Limitations of this approach Lack of surface energy data (ab-initio ?) Physical parameters influencing LME do not appear in the model (e.g. microstructure) No insight into the mechanisms (atomistic scale) Consensus: reduction in  s is necessary but not sufficient

24. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden  plane Slip plane Slip plane   - Bond breaking - Crack length 2a Stress at the tip -  x 0 AIRC: the atoms of the liquid (black) reduce/increase the bond strength AIRC A dsorption I nduced R eduction in C ohesion

25. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Hardening is absent Enhanced plasticity at the crack tip and HT LME are not explained Transport mechanisms are not considered No realistic prediction of the crack velocity AIRC: present situation AIRC is widely accepted Consistent with several experimental findings (Zn-Hg, Zn- Ga, hydrogen, …) Explains impurity action BUT...

26. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden AIRC variants & improvements Wetting effects ? Rabkin et al, (19..)

27. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Modeling: Crystal-Liquid interface Geysermans et al. (2005)

28. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Conclusive remarks LME can affect several structural materials and be a major cause of damage Understanding of LME is still limited No general agreement exists about mechanisms There is lack of atomic scale description No predictions can be made i.e. which liquid metal embrittles which solid metal Research on LME could result in decisive advances in the physics & chemistry of interfaces

29. MATGEN-IV.2 February 2 - 7, 2009, Kiruna, Sweden Origins of Illustrations 1.http://www.tech.plym.ac.uk/sme/Interactive_Resources/tutorials/Failur eAnalysis/Fractography/Fractography_Resource4.htm