Tool Wear Mechanisms of Physical Vapor Deposition (PVD) TiAlN Coated Tools Under Vegetable Oil Based Lubrication

Abstract

Titanium alloys are mainly utilized in the aerospace, biomedical, power generation, automotive and marine sectors due to their high hot hardness, ability to operate at higher operating temperatures and resistance against corrosion. Alpha-beta titanium alloy (Ti6Al4V) is the most frequently used titanium alloy, mainly preferred for the applications such as blades, discs, jet engine airframes and biomedical implants. TiAlN coating is highly favored for the metal cutting applications due to its superior cutting performance. The high cutting performance of TiAlN coating is linked with the addition of aluminum to the traditional TiN coating. The addition of aluminum results in the formation of aluminum oxide on the cutting tool surface resulting in ability to sustain high cutting temperatures. In this study a series of machining experiments were conducted to evaluate the machinability of difficult-to-cut titanium alloy (Ti6Al4V) by using PVD-TiAlN coated carbide tools under vegetable oil assisted minimum quantity cooling lubrication (MQCL). The cutting insert consists of substrate based on tungsten carbide with 6% cobalt to maintain high hot hardness and fracture resistance. Thin PVD-TiAlN coating on the substrate provides excellent adhesion resistance to prolong the cutting edge sharpness and results in enhanced tool life. In this study the influences of vegetable oil flow rate was taken into consideration to evaluate machinability. The study incorporated two different oil flow rates of 60 and 80 ml/h using a specially designed tool holder with internal coolant delivery channels for MQCL arrangement. The MQCL based results were also compared with the dry cutting. Detailed study on micro-wear mechanisms at the cutting edge was conducted by utilizing scanning electron microscopy (SEM). The study revealed adhesion, micro-edge chipping, abrasion and attrition as major wear mechanisms when using PVD-TiAlN coated tools for machining Ti6Al4V.