An atomic-scale investigation on the initial precipitation behavior of nitrides in TiAl alloys

Abstract

In the present work, the initial precipitation behavior of nitrides in TiAl alloys was investigated by monitoring the morphology, distribution, crystallographic orientation relationship and interface atomic structure of the nitride precipitates using TEM and HRTEM. It is found that there are two kinds of nitride precipitates (Ti2AlN and Ti3AlN) forming in the initial precipitation stage of Ti-49Al-1N alloys. The rod-like Ti2AlN precipitates tend to distribute at γ(TiAl)/α2(Ti3Al) interface with the crystallographic orientation relationship of [112‾0]Ti3Al//[112‾0]Ti2AlN//[1‾01]TiAl, (0001)Ti3Al//(0001)Ti2AlN//(111)TiAl. Both the Ti3Al(0001)/Ti2AlN(0001) interface and Ti2AlN(0001)/TiAl(111) interface display a plane-to-plane matching with coherent atomic correspondence. The plate-like Ti3AlN precipitates tend to distribute in the γ(TiAl) matrix with the crystallographic orientation relationship of [1‾10]Ti3AlN//[1‾10]TiAl, (111)Ti3AlN//(111)TiAl. The Ti3AlN(111)/TiAl(111) interface displays an edge-to-edge matching with coherent atomic correspondence. The morphology, distribution, crystallographic orientation relationship and interface atomic structure of nitride precipitates are determined by the crystal structure and lattice misfit of nitride precipitates and matrix. The understanding here will be useful in guiding morphology design and dispersion controlling of the nitride precipitates in TiAl alloys, and will further be benefit for improving the mechanical properties of TiAl alloys.