Microstructure,mechanical,and corrosion properties of surface of CuNi alloy produced by punching and annealing treatment

The influence of annealing on the formation of nanocrystalline of CuNi alloy surface was investigated by evaluating the microstructure, mechanical properties, and corrosion behavior of asprocessed condition （using severe plastic deformation by punching process） and its annealed condition. It was observed that the microstructure changed after annealing of punched sample using an atomic force microscope. Mechanical resistance and corrosion resis tance were also characterized using nanoindentation test, electrochemical test, electron work function, and micro tribometer test. It was found that the punched and sub sequent annealed samples have increasing hardness, elastic behavior 07）, and corrosion resistance. Therefore, anneal ing can lead to the final formation of nanocrystalline and corresponding stability of grain boundary, which are responsible for the increasing mechanical properties and corrosion resistance.

Nanoindentation behavior and creep-induced cracking of long-term crept austenitic steel at 650℃

The grain boundary(GB)damage of long-term crept HR3C(25Cr–20Ni–Nb–N)austenitic steel with solid solution state was investigated by nanoindentation test accompanied with in-situ electron back-scattered diffraction.The corresponding microstructure was characterized by scanning electron microscopy and transmission electron microscopy.Results show that the increase in nanoindentation hardness at the GBs and triple grain junctions may be related to the dislocation accumulation and carbide growth during the creep.Coarsened M23C6 and dislocations piling-up at the GB accelerate the nucleation and coalescence of creep cavity along the GB.The nanoindentation hardness in grains varies with orientation of the stress axis.The orientation difference of neighbor grains may induce local high geometrically necessary dislocation densities and strain gradients near the GB,consequently causing stress concentration and subsequent crack growth at specific GBs.

Corrosion resistance behavior of gradient microstructure induced by punching deformation and recovery treatment on cupronickel alloy surface

In this study, the gradient grain induced by punching deformation and recovery treatment on a cupronickel alloy surface sample were investigated, and their effects on corrosion resistance were measured by atom force microscopy(AFM), X-ray diffraction(XRD),electrochemical measurement, electron work function(EWF), and contact electrical resistance(CER). The cupronickel alloy surface experienced punching deformation for 60 min and recovery at 300 ℃ for 1 h to produce gradient surface. The grain size measured by XRD is bigger than that measured by AFM, due to X-ray intensity of95 % produced at the depth of 12-20 μm for the crystal planes of(111),(200), and(220). The gradient grain surface, compared to the original surface, shows a 13.7-fold decrease in passivation current density(i), and corrosion potential(Ec) increases by approximately 9.8 %. These results are attributable to the increase in EWF and formation of passivation film with better adhesion and compactness after treatment.