Alternative binder hardmetals for steel turning
Abstract: The goal of this work is to understand how the wear and deformation mechanisms of hardmetalinserts change when the cobalt binder phase is replaced with a dierent metal or analloy. The focus is on inserts for steel turning. The work presented in this licentiate thesisconsists of the rst steps.Cobalt is the most common binder phase in hardmetal tools based on tungsten carbide asthe hard phase. Metallic cobalt powder, present during the manufacturing, has been associatedwith lung diseases and an increased risk for lung cancer if inhaled. Therefore it is importantto investigate alternative binders as one possible solution.This work studies binder phase alloys from the iron-nickel-cobalt system. These alloyscan be either austenitic, martensitic or a mixture of the two phases. By changing the binderphase composition to change the crystal structure it is possible to tailor the macroscopic mechanicalproperties of the material. It is also possible to tailor the composition in such a waythat the binder is transformation toughening, forming martensite as a response to mechanicaldeformation.The majority of inserts for steel turning are coated, and it is important to investigate if thehardmetals with alternative binder can be coated and if the coating adhesion is sucient forsteel turning.Four dierent alternative binder alloys and one reference with cobalt binder coated bychemical vapour deposition were investigated by scratch testing to determine the adhesion.The scratch test adhesion was sucient on all samples, but signicant variations in coatingadhesion were found.One alternative binder with 86wt%Ni and 14wt%Fe and a reference with cobalt binder manufacturedto mimic state of the art turning inserts were tested in steel turning. The alternativebinder grades had a lower resistance to plastic deformation and this was attributed to earlyaking of the coating due to a lower coating adhesion. Focused ion beam and scanning electronmicroscopy were used to study the deformation of the hard metal in the used cuttinginserts.
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