# Thermal Behavior of Single-Crystal Diamonds Catalyzed by Titanium Alloy at Elevated Temperature
## 3 Results and Discussion of Thermal Analysis Experiments  
### Diffusion of Carbon Atoms from Diamond into Titanium Alloy  
Under high temperature, the carbon atoms in Ti alloy-cutting with the diamond tool easily diffuse into the titanium alloy workpiece on the tool/work contact interface in diamond-cutting of titanium alloys. Not only because there is a large difference in carbon concentration between titanium alloys and diamond crystals, but also because the atomic radius of the carbon atom is smaller than that of the titanium atom. This results in the diffusion wear of the diamond tool in cutting process.  
In this work, the tool wear caused by the diffusion of carbon atoms from the diamond tool into the workpiece material during the titanium alloy cutting with diamond tool was studied. Scanning electron microscopy (SEM) and X-ray energy spectrum analyzer (EDS) were used to examine the energy spectrum of Ti-6 Al-4V samples before and after the thermal analysis experiment. The micromorphology of Ti-6 Al-4V samples in the contact zone with the diamond was also inspected after thermal analysis experiment.  
Figure 2 shows the EDS diagram of the titanium alloy sample before and after the thermal analysis experiment in argon. It can be seen from Figure 2 that the carbon content on the surface of the titanium alloy sample significantly increased from 3.01% (before the experiment) to 23.31% (after the thermal analysis experiment), indicating that the diffusion reaction occurred at the contact interface between the diamond and titanium alloy flakes in the process of heating. It could be inferred that in the cutting process of titanium alloy by diamond tool, the carbon atoms in the diamond tool could diffuse into the titanium alloy material as long as the cutting temperature is high enough, which causes the diffusion wear of the diamond tool.  
Figure 3 shows the microscopic morphology and EDS analysis data of the corrosion surface of titanium alloy sample in argon. It can be seen from Figure 3 that the carbon content of the white particles was as high as 28.2%, and it is inferred that the oxidation reaction between the carbon atom and titanium atom occurs, therefore, the surface of the titanium alloy flakes contained TiC after the reaction.  
Figure 4 shows the EDS diagram of the titanium alloy sheet in the thermal analysis experiment in the air. It can be obtained from Figure 4 that the original carbon content of the titanium alloy sample before the test was 3.01%, and it increased to 4.52% on the corrosion surface after the experiment. This indicated that a slight diffusion activity of carbon atoms from the diamond crystal into the titanium alloy sample occurs during the heating process. Due to the presence of oxygen in the air, both the carbon atoms in the diamond and titanium atoms in the titanium alloy sample reacted with oxygen, which in turn, caused a certain influence on the diffusion reaction. In the air, the increase in the carbon content of the titanium alloy sample on the corrosion surface in the thermal analysis experiment was not large.  
Figure 5 shows the microstructure and EDS analysis results of the corrosion surface of titanium alloy flakes in the air. It can be seen from Figure 5 that the white particles had an oxygen content of 28.2% and a carbon content of 5%, while the white particles in Figure 3 had an oxygen content of only 1.68%, from which it was inferred that the surface between titanium alloy flake and diamond occurred a serious oxidation reaction.  
Figure 4: EDS of the titanium alloy sample surfaces before and after heated in air. (**a**) Before experiment; (**b**) after experiment.  
Figure 3: Micromorphology and EDS analysis of surface of titanium alloy after heated in argon. (**a**) Micromorphology; (**b**) EDS analysis.  
Figure 2: EDS analytical results of the titanium alloy sample surfaces before and after heated in argon. (**a**) Before experiment; (**b**) after experiment.