Investigation of microscopic residual stress and its effects on stress corrosion behavior of NiAl bronze alloy using in situ neutron diffraction/EBSD/tensile corrosion experiment

Abstract For complex multiphase NiAl bronze (NAB) alloys, microscopic residual stress is one of the main reasons for its stress corrosion cracking. Understanding of the microscopic residual stress (including the magnitude and distribution) and its effects on the stress corrosion behavior of NAB alloy is of great significance to improve the stress corrosion resistance of the alloy. In this work, microscopic residual stress was introduced via tensile deformation (including elastic and plastic deformation). In situ neutron diffraction and EBSD techniques were used to study the magnitude and distribution of microscopic residual stress, then in situ stress corrosion experiment was carried out to investigate their effects on stress corrosion behavior of NAB alloy. The results show that after stretched at tensile stress of above 300 MPa, compressive and tensile residual stresses were formed on the α-Cu matrix and (Fe, Ni) Al second phases in NAB alloy. These residual stresses gradually increase with increasing tensile stress, and the maximum values are 135 MPa and 560 MPa respectively. The distribution of the microscopic residual stress in the alloy is not uniform, and mainly distributes around the α-Cu/(Fe, Ni) Al phase interfaces. In the initial stage of corrosion, increasing the tensile stress can reduce the corrosion potential of the NAB alloy, but the stress can also lead to the formation of more martensite twins, which can improve the electrochemical corrosion properties of the alloy because of the rapid growth of protective film. After long time immersion, the stress corrosion cracking tendency of the NAB alloy significantly increases with increasing tensile stress. Stress corrosion cracks mainly locate in the area where the microscopic residual stress is concentrated, i.e. around the α-Cu/(Fe, Ni)Al phase interfaces.