Korznikov A.V. (*), Idrisova S.R. (*), Pakiela Z. (**), Kurzydlowski K.J. (**)
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(*) Institute for Metals Superplasticity Problems, Russian Academy of Sciences, Khalturina, 39, Ufa 450001, Russia.
(**) Departament of Material Science and Engineering, Warsaw University of Technology, Woloska 14102507, Warsaw, Poland.
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The structure and mechanical properties of the intermetallic compounds Ni3Al and Ni3Al+0.1wt.%B subjected to severe plastic deformation on a Bridgman anvil-type unit (P=8 GPa, n=5 rotation) and subsequent annealing were investigated.
It was shown that due the severe plastic deformation the entirely disordered structure with a grain size of 20 nm was formed in both materials. The microhardness of samples was 6200 MPa, bending strength was 2800 MPa (2538 MPa*) and a maximum bending was 0,4 mm ((1,4 mm*). The non-monotonic dependence of mechanical properties at 293K on temperature annealing was revealed:
In the temperature range 293-420 K the long-range ordering parameter S, grain size, internal stresses and microhardness do not change.
In the temperature interval 420-560 K a sharp growth in the long-range ordering parameter S to a value of 0,42 is observed. Towards the end of this stage the crystallite size increases slightly. An increase in temperature to 533 K leads to a sharp decrease in ductility to zero in Ni3Al (and to 0.15 mm in Ni3Al+B) and ultimate strength to 1350 MPa (1984 MPa*).
In the temperature range 620-1150 K the value S does not almost change and is equal to (0.6. The TEM investigations show that mean crystallite size grows to 10 (m (2 (m*). At T=1313 K the value S rises to S=0.77 (S=1*).The striking result of the present investigations is that with rising annealing temperature to 860 K an increase in ductility accompanied by an increase in ultimate strength and yield strength is observed. The material in an entirely disordered nanocrystalline state has the maximum strength and ductility in both compound.
Boron microalloying increases thermal stability of Ni3Al by 60 K.
The changes in mechanical properties were explain on the basis of structure and fracture surface relief investigations.
* - data for boron microalloyed compound.

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1. Influence of Structure on the Microhardness of Ni3Al