# Influence of Cutting Parameters and MQL on Surface Finish and Work Hardening of Inconel 617
## 4 Results and Discussion  
### Study A: Tool Coatings  
The uncoated K313 tungsten carbide tool lasted a total distance of 5460 m cutting length before reaching the tool failure criterion of 300 \(\upmu\)m flank wear as per ISO 3685 Section 8.2.2b. Rapid failure began to occur at 4850 m after a short period of steady-state tool wear. No initial break in region was identified for the uncoated tool. The final cutting lengths for the tested coatings and uncoated tool is summarized in Table 6. It can be observed that the majority of the tool coatings increased the life of the tool, while the Balzers Balinit(r)r Aldura and Ionbond coatings had significantly shorter lifespans than the uncoated tool. A possible explanation for this phenomenon is that these two coatings are multi-layered, which increases the susceptibility to delamination between coating layers and cracking that promotes the rapid fracture of these tools [43,44]. This delamination and failure of multilayered coatings was also seen in the machining of Inconel 718, suggesting a commonality between the sister alloys and machining with multilayered coatings [27,45].  
\begin{table}
\begin{tabular}{c c} \hline
**Tool** & **Final Cutting Length (m)** \\ \hline Balzers Balinit® Aldura & 946.87 \\ Balzers Balí® Altinos & **10,923.00** \\ Balzers Balinit® B & 6159.72 \\ CemeCon Hyperlox Plus & 7304.27 \\ Ionbond & 158.34 \\ Uncoated & 5260.83 \\ \hline \end{tabular}
\end{table}
Table 6: Tool lives of the tested tool coatings and the uncoated tool.  
The tool coating that provided the longest tool life is the AITiN coating provided by Balzers, also known as the Balzers Baliq(r) Altinos coating. This tool coating increased the tool life to a cutting distance of 10,923.00 m, as shown in Figure 2. The rapid failure of this coated tool occurred at 10,350 m of cutting. The steady-state region of tool wear began for the majority of the coatings around the 2000 m cutting distance, after the initial break in region, if they did not exhibit rapid tool failure.  
The tool lives for the uncoated tool and the tested tool coatings are depicted in Figure 2, which shows the flank wear measured for the duration of its entire tool life until it reaches 300 \(\upmu\)m. From the experiment, the AITiN PVD-coated tool can be seen to nearly double the lifespan of the cutting tool, as well as generating a very gradual increase in tool wear in the steady-state region of the tool. The rate of flank wear in this steady-state region was measured to be 6.72 \(\upmu\)m/km of cutting. This is a 75.89% improvement from the uncoated tool's rate of flank wear of 27.87 \(\upmu\)m/km of cutting. The observed improvement in tool life using a monolayer coating is much greater than those presented in similar machining studies performed on Inconel 718, where the tool life was only increased by 40% at high speeds [46] or at similar speeds, which tended to reduce the tool's life [27]. This suggests that monolayer coatings are most effective in machining Inconel 617. The results indicate that the presence of a hard protective coating is effective in reducing the abrasion caused by the hard workpiece due to the slow progression of flank wear. Of the tested coatings, the AITiN coating by Balzers provided the longest tool life. It was from this test that the PVD AITiN coating was chosen to conduct further experiments.  
Figure 2: Tool life tests for turning of Inconel 617 with uncoated tool and all tested tool coatings. Ionbond coating is not shown due to rapid failure of coating.