Abstract
M.Ing. (Mechanical Engineering)
This study focused on laser cladding of Ti6Al4V, used as both the substrate and the powder material. The goal was to determine the most effective parameters for laser cladding, when using this alloy. The criteria used were both efficiency (i.e. how quickly a certain amount of area / volume could be cladded) and quality. To determine the most efficient and the highest quality cladding, the following was done: firstly, the samples were prepared by cladding multiple tracks, using varying scanning speeds for each track. The scanning speed was varied from 3.5m/min to 0.5m/min in increments of 0.5m/min; while the laser power, powder flow rate and gas flow rate was kept constant. Thereafter, a geometrical analysis, porosity analysis, microscopic analysis in the form of optical microscopy and scanning electron microscopy, atomic force microscopic analysis, Vickers microhardness testing and corrosion testing were all performed.
One observation made from the optical and scanning electron microscopy was that the microstructure of the cladded area was consistent for sample scanning speeds ranging from 0.5m/min to 2.0m/min. This consistency also showed in the microhardness testing with the average hardness values for the scanning speeds ranging from 0.5m/min to 2.0m/min being almost equal at approximately 340HV.
Corrosion resistance testing confirmed that the corrosion resistance of the clad was related to the scanning speed at which the clad tack was produced. In general it was shown that the slower the scanning speed the better the corrosion resistance.
Further geometrical analysis of the micrographs obtained through optical microscopy revealed that sample five, with a scanning speed of 1.5m/min, yielded the best all-round clad, being the most efficient clad for the quality produced. The clads with higher scanning speeds, between 2.0m/min and 3.5m/min, could achieve area cladding rates greater than 50 000mm2/min; however the quality of the clad was not acceptable. The clads produced with slower scanning speeds (0.5 and 1.0m/min), did not produce a significant (or any) increase in the quality of the clad, when being compared with sample five.
Overall this work proved successful; and it also yielded a number of ways whereby the current understanding and capabilities when considering the Laser Cladding of Titanium Alloys can be further improved.