Effect of Ultrasonic Nanocrytalline Surface Modification on Hardness and Microstructural Evolution of Cu-Sn Alloy

Abstract

In this study, a Cu-Sn sintered bronze, used largely for con-rod bushing and automotive transmission, was treated by ultrasonic nanocrystalline surface modification (UNSM). Then, Vickers hardness and microstructural evolution of the treated region were investigated by using scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The hardness of the treated surface doubled, which is attributed to the developed of nanoscale grains, deformation twins, and high density of dislocations induced by the UNSM. Microstructural modification beneath the UNSM treated surface was typically characterized with increase of the depth: (i) nanoscale grains (top surface), (ii) intersection of deformation twins (~30 μm), (iii) high density nanoscale twin/matrix lamellae (~50 μm), (iv) interception of micro band and deformation twins (~100 μm), (v) dislocation arrays (~200 μm), (vi) low density dislocations (~300 μm) and (vii) pre-existing coarse grains and annealing twins in unaffected region (400 μm ~deeper).

A comprehensive review of nanostructured materials by ultrasonic nanocrystal surface modification technique

“…Also, it can be seen that the NG size increased with increasing the depth at the top surface. Li et al have pointed out the possibility of refining grain size of Cu‐Sn alloy by UNSM technique obtained using a cross‐sectional TEM images [9]. They have found that at a depth of about 300 µm from the surface, mechanical twins with dislocations are formed as shown in Fig.…”