Laser surface modification treatment of aluminum bronze with B ₄ C

One technique to improve tribological properties of aluminum bronze surfaces is to introduce laser controlled melting at the surface in the presence of a composition-modifying film. In this work, a 40 μm thick organic film, containing B ₄ C particles, was formed at the workpiece surface prior to laser treatment. The organic coating provides enhanced absorption of the incident laser radiation and distributes the B ₄ C particles uniformly across the surface. Morphological and microstructural changes in the laser treated layer were examined using scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. The microhardness of the laser treated layer was measured and the residual stress formed at the treated surface was evaluated by X-ray diffraction using the sin ² ψ technique. It was found that the laser treated surface produced is relatively free from defects and asperities with a microhardness that is notably higher than that of the as-received bronze substrate. This hardening effect can be attributed to the development of a dense layer consisting of fine grains, partially dissolved B ₄ C particles, and formation of Cu ₃ N compounds. The residual compressive stress obtained from X-ray diffraction peak evaluation is of the order of -400 MPa.