**4. Conclusions**

*Titanium Alloys - Novel Aspects of Their Manufacturing and Processing*

**Maximum composition of elements wt%** C 10.5 N 11.8 O 4.6 Al 23.6 Ti 41.1 V 0.5 Cr 0.4 Ba 13.7 W 1.9

subjected to thermal and mechanical loads and could not be able to resist the wear during the interrupted cutting in the end milling process. The chip shape, segmented or continuous, decides the cutting temperature formation inciting to thermoplastic shear localization at the contact length, resulting in the diffusion process. The chip constituents and the rate of diffusion are controlled by cutting temperature. In the machining of titanium alloys, the machining parameters, particularly, cutting speed, influence the cutting temperature origination at the tool edge for initiating the diffusion process. The earlier researchers verified that cutting speeds generate high cutting temperature, a short contact length, a low shear angle and a high cutting pressure. Chip segmentation and tribological parameters—the physical medium—may be causing the coating delamination for both the coated tools while machining the titanium alloy. Since the thermal conductivities of the coating constituents are different, the heat flux q flows through the coating layer and penetrates the tool substrate. The reason behind the diffusion process at the tool substrate surface might be due to chemically instable Co binder elements. Adhesive surface between the coating layer and tool substrate surface was completely eliminated gradually by diffusion process as depicted in **Figures 7–12** and

Adhesive, diffusion, abrasive and oxidation wear were the major means on the flank face. The elements observed on the cutting tool edge and workpiece indicate the diffusion process has taken place. From the EDS and SEM analyses, the existence of workpiece material constituents V, Al and Ti on the rake face wear land with built-up layer of cutting edge indicates diffusion might take place. Increasing cutting speed leads to the decrease in presence of V and Al at the tool cutting tool tip and it might be imaginable that Ti only sticks to the cutting tool edge. It has therefore been considered reasonable to suggest that the built-up layer was started through the sticking of Ti by different bonding actions, that is, directly proportional with temperature. Under very high speed cutting conditions, tool life depends directly on the formation of crater wear. Thin titanium oxide layer formation was observed on cutting edge of both the tools. In high-speed cutting conditions, cratering becomes so severe that the tool edge is weakened and eventually fracture which has been observed for the AlTiN and TiAlN tools at 110,000 rpm spindle speed, 0.1 mm depth of cut and 8 μm/tooth feed rate. At higher and lower

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confirmed through EDS analysis.

*EDS analysis results for coated AlTiN tools.*

*3.2.2 EDS analysis*

**Table 6.**

Tool wear analysis of PVD-coated TiAlN and AlTiN and uncoated tungsten carbide tools in high-speed micro-end milling of alpha + beta Ti-6Al-4V ELI titanium alloy (Grade 23) was investigated by tool wear mechanisms formation using SEM and EDS analysis and cutting force analysis. If the spindle speed is maintained at constant rpm while increasing feed rate and depth of cut, then tool wear increases dramatically. By increasing spindle speed from 30,000 to 70,000 rpm while varying feed rate and depth of cut, then (i) tool wear remains constant for uncoated tools, (ii) tool wear increases for AlTiN-coated tools and (iii) tool wear remains constant for TiAlN-coated tools. By increasing spindle speed from 70,000 to 110,000 rpm while varying feed rate and depth of cut, then tool wear increases for all the tools. If coated TiAlN and coated AlTiN tools are compared, then TiAlN tools performed better for machining this alloy. Based on the investigations, it can be suggested that PVD-coated TiAlN tungsten carbide tools give better performance than PVDcoated AlTiN and uncoated tungsten carbide tools in HSMEM at 110,000 rpm when machining alpha + beta Ti-6Al-4V ELI titanium alloy (Grade 23). SEM and EDS analyses for the considered machining operating parameters indicate the built-up edge, built-up layer and craters appearing at rake face and flank face of the cutting edge representing the adhesive, diffusion, oxidation and abrasive wear phenomenon on the tool surfaces when machined on both titanium alloys. Based on the investigations, the tool and work material properties, feed rate, depth of cut and cutting speed influence the tool wear.

## **Acknowledgements**

The authors gratefully acknowledge the support offered by Professor Dr. Ramesh Kumar Singh, Machine Tools Lab, Mechanical Engineering Department, IIT Mumbai, Maharashtra, India, in providing all the facilities for conducting the research work. This research program is financially supported under Approval Note No.368. MED/Institute Annual Grant provided by the Mechanical Engineering Department, SVNIT, Surat, Gujarat, India. The authors thank Technician Mr. Sagar Jagtap at Sophisticated Instrumentation Centre at SVNIT, Surat.
