Structure of martensite formed in Cu-Al-Fe single crystals duringin situ HVEM pseudoelastic tensile experiment

Abstract

Single crystals of the CuAlFe alloy, containing 14.5 wt% Al and 2.2 wt% Fe were subjected toin situ tensile experiment using straining attachment in a 1 MV electron microscope. Loadelongation curves were obtained for three foil plane/tensile direction orientations: (001) [0 1 0], (0 0 1) [1 1 0] and (1 1 0) [¯1 1 2]. Each crystal was subjected to two cycles of pseudoelastic deformation up to maximum 2% strain, showing almost complete shape recovery. Structure observations and electron diffraction pattern indicated that during deformation of samples of (0 0 1) [1 1 0] and (1 1 0) [1 1 2] orientations, formation of ′γ ₁ martensite was observed and only at later stages narrow needles ofβ ₁ nucleate in front of ′γ₁. During pseudoelastic deformation in the (0 0 1) [1 0 0] direction, martensite forms as a mixture of narrow plates possessing either 2H or 18R structures. The following crystallographic relationship between the parent phase and both types of martensite was observed: [1 00]β ₁∥ [101]′γ ₁ and (0 0 1)β ₁ ∥ (0 1 0)′γ₁;(0 0 1)β ₁ ∥ (0 1 0)β ₁ and [1 1 0]β ₁ ∥ [0 0 1]β ₁. From the character of sidebands reflections presence of 〈1 0 1〉 〈1 0¯1〉 static displacement waves was inferred.