Positive temperature dependence of strength observed in ordered cu3pt single crystals

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Abstract
The composition and temperature dependences of strength of ordered and disordered single crystalline Cu3Pt alloys involving ternary additions are investigated. The relation between deformation behaviour and relative phase stability of L12 ordered phase with respect to L12 −s long period ordered phase is discussed in relation to the antiphase domain (APD) morphology observed in each alloy. Direct observation of APDs by transmission electron microscopy shows that maze-like APDs are formed during ordering in Cu-23at.%Pt alloy, while in (Cu-23at.%Pt)-1 at.%In and Cu-19at.%Pt alloys swirl-like APDs are formed. This implies that the relative phase stability of L12 phase with respect to L12 −S phase in Cu-23 at.%Pt alloy is lower than that in (Cu-23at.Pt)-l at.%In and Cu-19at.%Pt alloys. Compression tests of an ordered single crystal of each alloy at various temperatures reveal a positive temperature dependence of critical resolved shear stress (CRSS) in Cu-23 at. %Pt alloy, but not in (Cu-23 at.%Pt)-1 at.%In and Cu-19at.%Pt alloys. Also, it is shown that disordered Cu-23 at.%Pt alloy dose not exhibit the positive temperature dependence of the CRSS. On the basis of these facts, it is demonstrated that the Kear-Wilsdorf mechanism involving thermally activated cross slip from the (111) primary glide plane to (010) non-glide plane is responsible for the positive temperature dependence of strength in ordered Cu-23 at.%Pt alloy.

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