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18th Plansee Seminar - 2013
Paul H. Mayrhofer (P.H. Mayrhofer)
Talk
"Impact of Al on Structure and Mechanical Properties of NbN and TaN"
Zehua Z.1, Rachbauer R.1, Holec D.1, Mayrhofer P.2
1Montanuniversitt Leoben, Austria
2Vienna University of Technology, Austria
Transition metal nitrides (TMN) are widely used as wear-resistant hard coatings for e.g., machining, casting or hot-forming applications. However, TMNs rapidly oxidise and often form porous oxides allowing for rapid scale growth. Therefore, ternary TM(1-x)AlxN coatings are the focus of many research activities as Al-incorporation promotes the formation of dense oxides. But the superior thermal and mechanical properties of TM(1-x)AlxNs are mainly obtained for face-centred-cubic (fcc) structures, requiring the need for detailed information on phase stability ranges. Especially NbNy and TaNy coatings are highly complex due to the variety of crystallographic phases present. Stoichiometric NbN as well as TaN can crystallize in either hexagonal or cubic structure. Through the incorporation of Al, soon the fcc structure is stabilised for x=0.1?0.44 (Nb(1-x)AlxN) and 0.1?0.36 (Ta(1-x)AlxN). Highest hardnesses are obtained for Nb0.56Al0.44N with ~32 GPa and Ta0.64Al0.36N with ~34 GPa. Single phase hexagonal Nb(1-x)AlxN and Ta(1-x)Alx coatings are accessible for Al contents above x=0.61 and 0.65, exhibiting hardnesses of ~23 GPa, respectively. The results obtained are in excellent agreement to computational predictions.
 


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