Evaluation of TiB2 coatings in sliding contact against aluminium

A major problem in machining aluminium alloys is abrasive wear of the cutting tool due to the presence of oxides and other hard particles in the metal. The strong tendency of aluminium to adhere to the tool and form built-up edges is another problem, which affects the finish of the cut surface. Bulk titanium diboride TiB2 is hard, and known to have a high chemical resistance when exposed to aluminium. These characteristics make this material an interesting candidate to be applied as a coating on tools aimed at machining aluminium alloys. Polycrystalline diamond (PCD) tools are often used today in operations involving both shaping (removal of large volumes) and surface finishing. However, they tend to produce too rough surfaces. In this paper, the possibility of magnetron sputtered TiB2 coatings reducing the ability of aluminium to be transferred to the tool surface has been experimentally evaluated by sliding against an aluminium alloy (AA7075). It was found that TiB2 coatings with relatively low residual compressive residual stress (−0.5 GPa) performed better than a reference TiN coating and uncoated cemented carbide as to the tendency of aluminium pick up. In addition, this TiB2 coating was more resistant to detachment and chemical wear as compared to highly stressed TiB2 (−6.1 GPa).