The Effects of Laser and Mechanical Forming on the Hardness and Microstructural Layout of Commercially Pure Grade 2 Titanium Alloy Plates

Abstract

This paper illustrates the effects of the laser and mechanical forming on the hardness and microstructural distribution in commercially pure grade 2 Titanium alloy plates. The two processes were used to bend commercially pure grade 2 Titanium alloy plates to a similar radius also investigate if the laser forming process could replace the mechanical forming process in the future. The results from both processes are discussed in relation to the mechanical properties of the material. Observations from hardness testing indicate that the laser forming process results in increased hardness in all the samples evaluated, and on the other hand, the mechanical forming process did not influence hardness on the samples evaluated. There was no change in microstructure as a result of the mechanical forming process while the laser forming process had a major influence on the overall microstructure in samples evaluated. The size of the grains became larger with increases in thermal gradient and heat flux, causing changes to the overall mechanical properties of the material. The thermal heat generated has a profound influence on the grain structure and the hardness of Titanium. It is evident that the higher the thermal energy the higher is the hardness, but this only applies up to a power of 2.5kW. Afterwards, there is a reduction in hardness and an increase in grain size. The cooling rate of the plates has been proved to play a significant role in the resulting microstructure of Titanium alloys. The scanning speed plays a role in maintaining the surface temperatures of laser formed Titanium plates resulting in changes to both hardness and the microstructure. An increase in heat results in grain growth affecting the hardness of Titanium.

Microstructure and Mechanical Properties of Laser and Mechanically Formed Commercially Pure Grade 2 Titanium Plates

“…Grain size depends largely on temperature attained during the laser forming process, and grain growth proceeds more quickly as temperature increases. All the figures shown clearly reveal the influence of temperature on the microstructure, and the portion affected by laser energy has grains which are much bigger than those not affected by heat [10]. This is the reason why there is variation in the microstructures.…”

“…Mechanical forming produces no heat, and therefore the similarities in microstructure are to be expected. There were no major changes to the microstructure as a result of this process when compared to the as received material [10]. The microstructure of a mechanically formed plate is shown in Figure 5.…”

“…Figure 6 shows the fine structure of titanium from the plates irradiated at a power of 1500 W using line energies of 35 and 47 kJ/m, respectively. There is a variation in the depth of the heat-affected zone (HAZ) for both line energies [10]. The unaffected material in both cases has equiaxed α-grains similar to those in the parent material.…”

“…The resulting microstructure from a line energy of 35 kJ/m points to a higher scanning velocity. The thermal energy from the laser managed to effect changes to a quarter of the plate's thickness [10]. The cycle took around 18 minutes to irradiate all the 10 plates in each batch at this power and line energy setting.…”

“…In multiple scan scenarios, each scan effects change on the microstructure. Differences in microstructure are brought about by the laser intensity power of 2.5 kW which makes a significant change in the microstructural layout [10]. Figure 8 also shows the microstructure of a sample irradiated at 3kW, and with this plate an increase in power results in gradual change to the microstructure of titanium.…”