Huayun Du

Structural characteristics of nanocrystalline copper after carbon ion implantation.

A gradient structure was produced in a pure copper plate by means of surface mechanical attrition treatment (SMAT). The microstructure of the surface layer was reduced to nanoscale and the grain size increased gradually along the depth of the treated sample. In situ transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) observation was performed on the nanocrystalline copper after implantation of carbon. Carbon atoms first precipitated along the edges of the copper substrate or at the surface, then formed amorphous carbon layers. Subsequently, onion-like fullerenes were formed under electron-beam irradiation. The effects of ion implantation, electron beam irradiation, nanostructure of the substrate and interaction of C and Cu atoms on the formation of the onion-like fullerenes are discussed.

EFFECT OF VELOCITY OF BALLS ON THE STRAIN AND STRESS OF LOW CARBON STEEL SURFACE LAYER DURING SMAT

By means of finite element method, the effect of velocity of balls on the strain and stress of low carbon steel surface layer during the course of surface mechanical attrition treatment (SMAT) are investigated. The effect of different impact velocity on strain rate and grain refinement mechanism is also analyzed. Calculation results confirm that there exists severe plastic deformation in the surface layer: strain, strain rate and stress gradually decrease along the depth of the treated sample during SMAT, which is in agreement with the microstructures observed in corresponding locations. Strain and strain rate play an important role in the grain refinement process and the resultant grain sizes upon plastic deformation.

Hydroxyapatite (HA) Modified Nanocoating Enhancement on AZ31 Mg Alloy by Combined Surface Mechanical Attrition Treatment and Electrochemical Deposition Approach

Hydroxyapatite (HA) nanocoating was electrodeposited on the surface mechanical attrition treated (SMATed) AZ31 magnesium alloy. Phases, morphologies and the adhesion of coating were characterized by X-ray diffraction, scanning electron microscopy (SEM) and 3D optical profiler. The corrosion resistance of the HA coating was tested by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that the HA coating on SMATed sample had a better crystallization than that on original one. The thickness of HA coating increased from 25 to 40 μm. The bonding strength between HA coating and SMATed substrate was higher than that between the coating and untreated counterpart. Potentiodynamic polarization and EIS demonstrated that the corrosion current density of HA coating on SMATed substrate decreased by 30.84% than that on original. The corrosion potential shifted 80.3 mV to the positive direction. The corrosion resistance of coatings on SMATed sample was significantly enhanced. The immersion experiments showed that the HA coatings on SMATed sample exhibited a better biological activity.

Evolution of intergranular corrosion resistance for HR3C heat-resistant austenitic stainless steel at elevated temperature

ABSTRACT An attempt has been made to investigate the evolution of intergranular corrosion (IGC) resistance of HR3C heat-resistant austenitic stainless steel. The double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests were conducted to evaluate the IGC resistance of HR3C steel. The results show that the side peaks can be observed in active–passive region of DL-EPR curves due to inhomogeneous distribution of the chromium dissolved in matrix. The variation of the degree of sensitisation (DOS) during sensitising at 800°C can be divided into three regions (sensitisation dominant region, desensitisation dominant region and equilibrium region). When HR3C steel is sensitised at 800°C for over 24 h, the equilibrium state in DOS can be reached. Simultaneously, the IGC morphologies after DL-EPR tests can correlate well with the DOS. On the basis of the equilibrium state in DOS, proper heat treatments and corrosion protection measures can be taken to avoid IGC of HR3C steel.