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

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, Al₂O₃SiC_w-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™.