Nitriding behaviour of Mg-Li alloy with surface mechanical nano-alloying pretreatment

Abstract

The thick titanium nitrides coating was fabricated on LZ91 alloy by surface mechanical nanoalloying (SMNAT) combined with gas nitriding. Experimental results showed that a nanostructured titanium coating with thickness of 50-80 μm was formed on surface of LZ91 alloy by SMNAT with pure titanium powders for 30 min. By adding of the aluminium powders into titanium powders during the SMNAT, a thicker Ti-Al composite coating with improved continuity and uniformity was obtained. After nitriding at 450°C, the whole Ti and Ti-Al coating were successfully nitrided. The surface layer of nitrided Ti coated sample is mainly composed of TiN, Ti 2 N, TiN 0.3 , TiN 0.61 and Ti 4 N 2.33 phases and the surface layer of nitrided Ti-Al coated sample is composed of Ti 2 N, TiN 0.9 , TiN 0.3 , Ti 4 N 2.33 , AlN, Ti 3 Al 2 N 2 and AlTi 2 N phases. The hardness measurements demonstrated that the surface hardness of nitrided Ti coated and nitrided Ti-Al coated samples reached to 634 and 734 HV, respectively.