Influence of Tin Coating on Wear of High Speed Steel Tools as Studied by New Laboratory Wear Test

Abstract

A new laboratory wear test for simulating cutting tool wear is proposed in which the contact conditions in machining are reproduced by letting a tool material pin slide continuously against a fresh countermaterial surface. Wear tests with high speed steel (HSS) pins in the uncoated and TiN coated conditions have been performed. A wear mechanism analysis demonstrates that the simulated tool wear test is able to reproduce closely the major wear mechanisms operating when machining with HSS tools. The advantage of laboratory testing over machining is that the continuous tool wear processes can be studied without the overlapping effects from edge deterioration by plastic deformation and chipping. The new test setup has been used to study the effects of TiN coating on the wear processes on HSS cutting tools. The TiN coating was found to enhance tool wear resistance greatly when sliding against plain carbon steel or quenched and tempered steel. This is due to the superior resistance to both abrasive and adhesive wear of TiN compared to HSS and the fact that TiN promotes the formation of protective glassy layers on the pin surface. Eventually, cracks develop on the TiN surface due to thermal softening of the underlying HSS and segments of the coating are plucked from the surface. Glassy layer formation was not observed when sliding against austenitic stainless steel, and the TiN coating was removed rapidly by interfacial spalling.