Abstract
M.Ing. (Mechanical Engineering)
Laser metal deposition (LMD) presents a competitive and attractive single stage process for producing complex shapes in typically difficult to machined materials like titanium alloys compared to the traditional machining process. It specifically provides incentives for the production of components with improved surface properties for enhanced lifetime performance in aerospace, defense, marine and power applications. But, a major complexity in the process is the lack of complete understanding of the influence of some laser processing parameters on the production of defect-free metal deposits on substrate metallic workpiece. Therefore, in this research, an attempt was made to explore LMD for the deposition of Ti + TiB2 powders on aerospace grade titanium alloy for improved wear and corrosion resistance properties using different powder compositions of Ti + TiB2 at a constant laser power, scanning speed and beam spot size. Microstructural analysis of the deposited composite samples indicated that LMD at a high powder composition of Ti in the range of 50 % to 90% of Ti powder produced a larger heat affected zone, high dilution ratio, and lower porosity because of the greater interaction between the laser beam and the workpiece; whereas higher powder composition of TiB2 powder in the range of 70 % to 100 % and low laser power generated a smaller heat affected zone. There was an incomplete melting of the deposited composites; which have resulted in poor physical, mechanical, metallurgical and corrosion properties due to the high percentage of TiB2. widmanstätten structures were equally apparent in these conditions due to the high cooling rate associated with the laser melting. Microhardness of the laser deposited composite produced at a powder composition of 50 % Ti + 50% TiB2 was increased by 219 % whilst the wear rate was improved by 682 % compared to the Ti6Al4V alloy substrate and the other laser deposited samples. The corrosion resistance under this condition was equally improved by 89 % in seawater corrosive medium. The results further showed that as the proportion TiB2 powder increases, the volume of deposit was decreased due to the small particle size of the TiB2 powder. However, this has led to the reduction in physical, mechanical and metallurgical properties. On the contrary, at a low composition of TiB2 powder, a high-quality deposit is produced. Therefore, the powder composition at 50 % Ti + 50 % TiB2 was established as the optimum composition for the deposition of defect-free Ti + TiB2 composite on aerospace grade titanium alloy for improved surface properties. Thus, a new composite material with enhanced physical, mechanical and metallurgical properties was successfully deposited on titanium alloy...