Evaluation of burnished subsurface mechanical behavior using nanoindentation

The performance and life of machined components in service are mainly effect by their surface integrity. Burnishing process is a kind of chipless processing which improve the surface integrity obviously. A subsurface "hardness film" is formed during the processing. Subsurface mechanical behavior is the main part of surface integrity. Since the very small scale of the subsurface in burnished surface nanoindentation is used to identify how the local changes of microstructure influence the hardness distributions of subsurface mechanical properties. This study focuses on the relationships between burnishing parameters (burnishing feed and burnishing depth) and nanohardness. A series of burnishing processing experiments and nanoindentation tests were conducted on the surface of the burnished samples. The microstructure and nanoindentation research results indicate that there is no visible phase transformed region in the subsurface of burnished specimens, the hardening film is larger than 4 micro meters, the nanohardness is about 2.2∼3.5Gpa which depends on the burnishing parameters and distribution and position of the second phase particles, while the nanohardness in turned material is about 1.8Gpa.