SUS304 stainless steel wire was micro spot melted by using YAG laser to investigate the applicabilty to the fabrication of biomedical devices. Effects of laser conditions such as laser power input or pulse duration were investigated on the microstructure and tensile strength of spot melted wires. Width of the melted metal decreased by laser irradiation with a shorter pulse duration and was about 0.3 mm for the 0.35 mm diameter wires. On the contrary, laser spot melting with a shorter pulse duration needed more precise control of laser conditions to achieve the sound melting free from burn out of the samples. Similarly, melting of thinner wire needed more precise control of laser conditions. Melted metal exhibited a rapidly quenched austenite cell microstructure with a cell size of less than about 5 µm. Tensile strength of the spot melted wires was 660 MPa, which was almost the same as that of annealed base materials. Besides, corrosion resistance in a quasi biological environment was hardly degraded by spot melting. Crosswise joints was also successfully prepared by laser spot welding of wires, suggesting the laser micro welding is applicable to the fabrication of biomedical devices.
In order to improve a wear resistance of aluminum alloy, we proposed a diode laser cladding of iron-based alloy on the surface of an aluminum alloy. In the first part of this research, an applicability of diode laser to laser cladding was evaluated. In this experiment, irradiation conditions were varied to investigate the effect of process parameters on the formation of clad layers. From this result, application of diode laser made it possible to obtain stable beads in low heat input compared with CO 2 laser, which has been conventionally used for laser cladding. Secondly, we investigated effects of the irradiation conditions on the dilution ratio and the microstructure of a Fe-Cr-C clad layer. It was confirmed that decrease in laser power and increase in traverse speed made the dilution ratio suppressed. According to the increase in aluminum content in the clad layer, the microstructure of the clad layer changed as (8-20%)! þ (10-30%)!Fe 3 Al(30%-). At the interface between the clad layer and the aluminum alloy substrate, the reaction layer consisting of Fe 2 Al 5 and FeAl 3 formed. The obtained complex frequently included cracks within the clad layer or in the reaction layer, each of which was caused by different factors. The cracks in the clad layer decreased with decreasing the hardness of the clad layer and formation of the ferrite in the austenite phase, which was achieved by controlling the dilution ratio and the carbon content of the cladding material. With respect to the interface cracks, it was found that the addition of copper for reduction of the thermal stress arising at the interface had a beneficial effect on suppressing the interface cracks. In the abrasion Fe-Cr-C and the Fe-Cr-Cu-C clad layers exhibited a higher wear resistance compared with the aluminum alloy.
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