Thermodynamic, Tribological and Chemical Interdiffusion Study of Ultra-Hard Ceramic AlMgB14 in the Machining of Aerospace Alloys

Abstract

There has been a growing concern about the reactivity at the tool/work-piece interface during machining, leading to lower tool life. The problem is more severe especially in the case of aerospace alloys such as Ti-6Al-4V and stainless steels. Recently, a new ultra hard ceramic material, AlMgB14, was reported with properties that show considerable promise as a cutting tool material for machining titanium alloys [1]. This paper investigates the chemical wear behavior of AlMgB14, in the machining of aerospace alloys. The mechanical properties of AlMgB14 are compared with leading cutting tool materials (WC-Co, Al2O3SiCw-TiC and Al2O3-TiC), which are used extensively in machining titanium and ferrous alloys. Materials characterization of candidate tool materials shows that AlMgB14 exhibits superior hardness, fracture toughness and abrasive wear resistance as compared to the other cutting tool materials. We also report on a study of chemical reactivity of tool materials (AlMgB14 and WC-6%Co) in machining various alloys such as Ti-6Al-4V and Fe-18Ni-8Cr. The chemical reactivity was investigated using diffusion tests conducted in vacuum at 1000°C for 120 hrs. Transverse sections of couples were characterized using electron probe micro analysis (EPMA), to determine the extent of diffusion zones. The results show that AlMgB14 shows considerably less reactivity with titanium alloys when compared with cemented carbide cutting tools. It was also observed that the boride reacts significantly with the iron based Fe-18Ni-8Cr alloy. The paper also reports on the evaluation of the free energy of formation of AlMgB14 using the thermochemical software program FactSage™.