Structure and Functional Properties of Precipitation-Hardening Fe-Mn Alloys with Controlled Shape Memory Effect

The structure and physical-mechanical properties of new high-strength alloys of the Fe-20Mn-2Si-2V-0.2(1.0)C type, in which the shape memory effect (SME) can be controlled by carbide aging at different temperatures (with precipitation of VC particles of different fineness) and gamma-epsilon-gamma transformations, have been studied. Maximum strengthening (the yield stress  = 1600-1900 MPa) of the Fe-20Mn-2Si-0.4Ñ shape memory alloy (SMA) was achieved after aging and fractional rolling (30-90%) at 400-600C. Also, ultrathin nanostructured strips 1.5-3 mm wide were made by the melt spinning method. An insufficient amount of the epsilon-martensite (20-40%) is formed in the low-strength austenitic alloys like Fe-18Mn and Fe-20Mn-2Si-0.2(0.4)Ñ at small degrees of cold deformation (4-5%). Oppositely, small deformation of aged alloys like Fe-20Mn-2Si-0.4Ñ  with uniformly distributed VC nanocarbides leads to formation of 70-90% epsilon-phase. VC particles contribute to splitting of perfect dislocations to partial dislocations, leading to the formation of stacking faults and the epsilon-phase. Authors [1] found that b-Mn nanoparticles increased SME from 1.8 to 2.3%  in Fe-31Mn-6Si SMA. This increase can be explained (analogously to the effect of VC particles) by the formation of a large amount of the strain-induced e-martensite in the decomposed solid solution of the austenite.

This work was partially financed by RFBR (project No. 03-06-32715).

1.      Gavriljuk V.G., Bliznuk V.V., Shanina V.D., Kolesnik S.P.  MSE(A), 2005, v.406, 1, p.1-10.