3.1.2. Surface roughness
The average surface roughness (Ra) of untreated Ti–15Mo alloy and those subjected to thermal oxidation at different temperatures, for various periods of time, is shown in Fig. 5 It is evident that irrespective of the treatment temperature and time, thermal oxidation caused an increase in the Ra of the Ti–15Mo alloy when compared with its untreated counterpart. The evolution of the microstructure of the oxide layer as a function of temperature and time is considered responsible for the observed increase in Ra.Other researchers have also attributed the increase in Ra of Ti alloys to the change in morphological features of the oxide layer following thermal oxidation at 400–1000◦C [33–36]. The differential rate of oxidation of individual grains, leading to the development of a stratified structure of the growing oxide layer, is also considered as a possible reason for the increase in surface roughness after thermal oxidation [28–31]. The increase in the Ra with an increase in temperature from 650 to 800◦C, suggests the existence of a statistically significant difference in roughness among these groups (p < 0.05; n = 3). Nevertheless, no statistically significant difference in roughness with an increase in treatment time could be observed among the samples treated at 650◦C. The higher Ra of the Ti–15Mo alloy treated at 800◦C for 8 h is due to the formation of the oxide layer with bigger oxide grains. The large scatter in the Ra values (higher standard deviation) could be due to the inhomogeneities in the oxide layer formed under such conditions. The increase in size and discontinuity of the oxide grains could have also contributed for the scattering in the Ra.
3.1.2 พื้นผิวที่ขรุขระThe average surface roughness (Ra) of untreated Ti–15Mo alloy and those subjected to thermal oxidation at different temperatures, for various periods of time, is shown in Fig. 5 It is evident that irrespective of the treatment temperature and time, thermal oxidation caused an increase in the Ra of the Ti–15Mo alloy when compared with its untreated counterpart. The evolution of the microstructure of the oxide layer as a function of temperature and time is considered responsible for the observed increase in Ra.Other researchers have also attributed the increase in Ra of Ti alloys to the change in morphological features of the oxide layer following thermal oxidation at 400–1000◦C [33–36]. The differential rate of oxidation of individual grains, leading to the development of a stratified structure of the growing oxide layer, is also considered as a possible reason for the increase in surface roughness after thermal oxidation [28–31]. The increase in the Ra with an increase in temperature from 650 to 800◦C, suggests the existence of a statistically significant difference in roughness among these groups (p < 0.05; n = 3). Nevertheless, no statistically significant difference in roughness with an increase in treatment time could be observed among the samples treated at 650◦C. The higher Ra of the Ti–15Mo alloy treated at 800◦C for 8 h is due to the formation of the oxide layer with bigger oxide grains. The large scatter in the Ra values (higher standard deviation) could be due to the inhomogeneities in the oxide layer formed under such conditions. The increase in size and discontinuity of the oxide grains could have also contributed for the scattering in the Ra.
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