Conventional and high-resolution electron microscopies were used to investigate the microstructure and precipitation mechanism of four kinds of γ′–Fe4N nitrides, formed at the surface during nitriding of polycrystalline pure iron sheet. γ′ nitrides in the top columnar compound layer were thin plates (3–12 nm), which precipitated from ε–Fe2−3N grains with orientation relationship of (111)γ′//(0001)ε and [011]γ′//[1210]ε. Those in the transition compound layer remained as equiaxed grains (1–1.5 μm), which grew from the α–Fe substrate during nitriding. In the diffusion layer, striated γ′ nitrides nucleated from α″–Fe16N2 nitrides with orientation relationship of (100)γ′// (110)α″ and [011]γ′//[111]α″ while unstriated γ′ nitrides precipitated from the α–Fe substrate with the orientation relationship of (100)γ′//(110)α and [011]γ′//[111]α.
采用传统电子显微镜和高分辨率电子显微镜研究了多晶纯铁板氮化过程中表面形成的四种γ′-Fe4N氮化物的显微结构和析出机理。顶部柱状化合物层中的γ′氮化物为薄板(3-12 nm),由取向关系为(111)γ′//(0001)ε和[011]γ′//[1210]ε的ε-Fe2-3N晶粒析出。过渡化合物层中的晶粒仍为等轴晶粒(1-1.5 μm),它们是在氮化过程中从α-Fe基底上长出来的。在扩散层中条纹状γ′氮化物由α″-Fe16N2 氮化物成核,取向关系为(100)γ′//(110)α″和[011]γ′//[111]α″。而从α-Fe基底析出的非条状γ′氮化物的取向关系为(100)γ′//(110)α和[011]γ′//[111]α。