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

ABSTRACTThe thick titanium nitrides coating was fabricated on LZ91 alloy by surface mechanical nano-alloying (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, Ti2N, TiN0.3, TiN0.61and Ti4N2.33phases and the surface layer of nitrided Ti-Al coated sample is composed of Ti2N, TiN0.9, TiN0.3, Ti4N2.33, AlN, Ti3Al2N2and AlTi2N 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.