Search

Direct laser melting (DLM) technology can be applied to restore damaged steel dies. To understand the effects of DLM process parameters such as the laser power and scan rate, a series of experiments was conducted to determine the optimal operating parameters. To investigate the laser melting characteristics, the depth/height ratio, depth/width ratio and micro-hardness as a function of the laser energy density were analyzed. Fe-Cr and Fe-Ni layers were deposited on a steel die with 11.38 J/mm2 of energy input. The wear-resistance and the friction coefficient of the deposited layer were investigated by a pin-on-disk test. The penetration depth decreased as the scan rate increased as a consequence of the shorter interaction time. The depth/height ratio of the deposited layer decreased with an increase in the scan rate. The depth/width ratio increased as laser power increased and the scan rate decreased. The deposition shape of the Fe-Ni powder was relatively shallow and wide compared with that of the Fe-Cr powder. The scan rate had a substantial effect upon the deposition height, with the Fe-Cr powder melting more than the Fe-Ni powder. The micro-hardness of the layer melted from the powders is higher than that of the substrate, and the hardness of the laser-surface-melted layer without any metal powder is higher compared to that of the metal-powder-melted layer. The direct laser melting process with Fe-Ni powder represents a superior method when restoring a steel die when the bead shape and hardness of the restored surface are important outcome considerations.

In marine engines, the wear between the piston-ring face and the cylinder liner is an extremely unpredictable and hard-to-reproduce phenomenon that significantly decreases engine performance. This study investigates the characteristics of wear arising between both hard and soft piston-ring coatings and the running surface of the cylinder liner. A detailed tribological analysis using a Pin-on-Disk (POD) testing machine compares the wear rate and the friction coefficient between piston-ring coatings and the cylinder liner for various test parameters, such as test temperature, roughness of the liner, and lubrication. The experimental results show that the wear rate and the friction coefficient of soft coatings were higher than those of hard coatings. The wear rate and the friction coefficient were also found to be influenced by test temperature, due to the lubrication effect of the wear-protective oxidized layers that developed at elevated temperatures. The surface roughness of the cylinder liner on the wear rate strongly influenced the soft coating but was much less apparent for the hard coating. The morphological features of the scuffed cylinder liner revealed that a harder piston-ring coating enhances scuffing of the cylinder liner.