Cyclic plasticity behavior and deformation mechanism of 1Cr18Ni10Ti pressure pipe subjected to in-service loadings

Abstract

Fatigue performance and durability application have always been the key issues impeding the understanding of aero-engine pressure pipe due to its non-standardized shape, making tests more challenging. This paper constructs an optimized testing system to elucidate the plastic shakedown and ratcheting behavior of 1Cr18Ni10Ti pressure pipe subjected to in-service loadings. Moreover, microstructural evolution's role in regulating the cyclic plasticity behavior is qualitatively established. Experimental results indicate that the pipe deformation exhibits compressive ratcheting behavior in plastic shakedown state, and the initial cyclic hardening followed by cyclic saturation occurs during the whole cyclic response. This corresponds to a decreasing ratcheting displacement rate followed by a steady state appears. Except for the first two similar deformation stages mentioned above, the abrupt cyclic softening and the resultant increasing ratcheting displacement rate are obtained at the final fracture stage of the pipe deformation in ratcheting state. A series of detailed microstructural characterizations, including optical microscopy (OM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and acoustic emission (AE) are combined to reveal the underlying microstructural mechanisms during cyclic deformation. The volume fraction of austenite and ferrite and the average grain size change during different stages of plastic shakedown and ratcheting deformation. The synergistic effects of dislocation structure multiplication, destruction, and dissolution at different stages of plastic shakedown and ratcheting deformation dominate the cyclic plasticity behavior.