Titanium nitrate coated high speed steel cutting tool inserts

• Main Author: Whittle, Neville C.
• Published: Loughborough University 1987
• Subjects: 671.5
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559206

A detailed study has been made of commercially produced, powder metallurgy, BT42 grade high speed steel (H.S.S.) indexable cutting tool inserts coated with a thin layer of titanium nitride (TiN) by chemical vapour deposition (C.V.D.). The characteristics of the coating before and after the obligatory substrate heat treatment were first ascertained using various techniques including X-ray diffraction, Auger electron spectroscopy, fractography, scanning and transmission electron microscopy, microhardness testing, profilometry, optical microscopy and scratch-adhesion testing. It was found that the characteristics of the TiN coating were not significantly affected by the substrate heat treatment and that they were comparable to those presented in the literature for similar C.V.D. coatings on cemented carbide inserts. The cutting properties of the fully characterised TiN coated H.S.S. inserts were then compared to those of uncoated inserts in a series of turning tests on 817M40 workpiece material, carried out under conditions of built-up edge (b.u.e.) formation at cutting speeds in the -1 range 30-60 m min. Comparison of the inserts with regard to tool life, tool wear, tool forces, apparent coefficient of friction, b.u.e. formation and workpiece surface finish, revealed that the TiN coated inserts had significantly improved cutting properties relative to the uncoated inserts. Additional tests showed that increasing coating thickness led to further improvements in cutting performance. The role of the TiN coating was studied from metallographic sections through worn inserts, and the reasons for its significant effect on the cutting properties of tbe H.S.S. inserts are discussed. Similar inserts coated with TiN by physical vapour deposition (P.V.D.) were also characterised and their cutting performance determined. The results obtained are compared to those for the C.V.D. TiN coated inserts. Differences in the cutting performance are related to the different characteristics of the two coatings arising from the processes used for their deposition.