Laboratory characterisation of the wear behaviour of PVD-coated tool steels and correlation with cutting tool performance

Four different characterisation tests have been used to study the wear behaviour of a series of thin (1-4 mu m) PVD coatings of TiN, TiCN, TiAlN and CrN on identical M2 tool steel substrates. These include two novel tests involving micro-abrasion and erosion durability. The abrasion method provides values for the intrinsic wear behaviour of both the coating and the substrate from a single test. The erosion test establishes the critical mass of erodent particles required to impact unit area of the coating to cause removal. Standard scratch tests were also performed, and coating failure characterised by both acoustic emission signals and post-test optical examination of the scratches. The performances of the coatings in these tests were compared with those of coated end mills in accelerated cutting tests. The micro-abrasion and scratch tests both showed good correlation with the results of the milling tests; although the erosion test generally discriminated between the coatings, correlation with the other test results was poor.