Laser surface treatment of AISI 304 steel with the presence of B₄C particles at the surface

AISI 304 steel surface is pre-prepared to form a thin carbon film containing 5% B₄C particles prior to the laser-treatment process. The carbon film improved the absorption of the incident beam and accommodated B₄C particles uniformly at the workpiece surface. The morphological and the metallurgical changes are examined in the treated layer by using optical and electron microscopes, energy dispersive spectroscopy, and X-ray diffraction. The microhardness and the residual stress formed at the treated surfaces are measured. It is found that the laser-treated surface is free from asperities and defect sites. The microhardness of the laser-treated surface increases significantly, which is attributed to the presence of B₄C particles at the treated surface. In addition, the residual stress increases with the addition of B₄C particles at the surface. The nitride phases are formed at the treated surface, which also contribute to the microhardness increase at the surface.