Cyclic deformation and strain burst behavior of Cu–7at.%Al and Cu–16at.%Al single crystals with different orientations

Abstract

[ 1 ̄ 12] Cu–7at.%Al single crystals as well as [ 1 ̄ 23], [ 1 ̄ 17] and [023] Cu–16at.%Al single crystals were cyclically deformed under constant plastic strain control at room temperature. The cyclic hardening curve of [ 1 ̄ 12] Cu–7at.%Al single crystal can be divided into three stages, namely initial non-hardening stage, rapid hardening stage and saturation stage. The cyclic stress–strain (CSS) curve exhibited a plateau region in the range of γ pl, from 1.1×10 −3 to 4.5×10 −3. The saturation stress of the plateau is about 27 MPa. The occurrence of strain burst depends on the applied plastic strain amplitude γ pl. No strain burst was detected when γ pl, was below 4.4×10 −4 or above 1.1×10 −3. The cyclic deformation and strain burst behavior of [ 1 ̄ 23], [ 1 ̄ 17] and [023] Cu–16at.%Al single crystals are different from that of [ 1 ̄ 12] Cu–7at.%Al single crystal. The cyclic deformation of all three differently oriented Cu–16%Al single crystals is unstable with the frequent occurrence of irregular strain bursts. The specimens cyclically hardened at a very low rate and saturation was not attained at high strain amplitudes. The experimental results indicate that the crystallographic orientation has almost no effect on the cyclic deformation and strain burst behavior of Cu–16at.%Al single crystals. The evolution of slip bands during cyclic deformation in both Cu–7at.%Al and Cu–16at.%Al single crystals is similar to the development of Lüders band. The percolation of slip bands along the gauge length is generally accompanied by strain bursts. The above experimental results were explained in terms of the variation of slip mode with Al content in the alloys and the corresponding strain localization during cycling.