Competitive precipitation of amorphous and crystalline silicon nitride in ferrite: Interaction between structure, morphology, and stress relaxation

Unusual Iron Nitride Formation Upon Nitriding Fe-Si Alloy

“…Therefore, nitriding studies have been performed on relatively simple iron-based binary alloys, especially in recent years. On the one hand, most work has been done on the alloying element nitride precipitation in ferritic substrates (responsible for enhancing the fatigue resistance), Fe-Al, [8][9][10][11][12] Fe-Cr, [13,14] Fe-Si [15][16][17][18][19][20] and Fe-V, [21,22] and ternary alloys, such as Fe-Cr-C, [12,23] Fe-Cr-Al, [24] Fe-Cr-Ti [25] and Fe-Me-Si. [26] On the other hand, the effect of alloying elements on the formation of the surface iron nitride (c¢-Fe 4 N 1Àx and e-Fe 2 N 1Ày ) compound layer, usually indicated as the ''white layer'' (responsible for improved wear and corrosion resistances), has only recently been investigated.…”

“…[34,35] After the first demonstration that silicon nitride precipitates in ferrite in a highly unusual amorphous state, [36] only recently have the kinetics of this amorphous silicon nitride precipitation been investigated more extensively. [18][19][20]26] It was shown that the precipitation of amorphous silicon nitride in the ferrite matrix takes place only very slowly because of the large volume misfit, which has to be accommodated upon precipitating silicon nitride in the ferrite matrix. Thus, Si is effectively a weak nitride former, [26] although, from a chemical point of view, Si is a strong nitride-forming element.…”

Contribution of Local Analysis Techniques for the Characterization of Iron and Alloying Elements in Nitrides: Consequences on the Precipitation Process in Fe–Si and Fe–Cr Nitrided Alloys

“…Second, the strengthening from nitrogen both in solid solution and precipitated in nitrides leads to high mechanical properties [ 2 , 3 ]. Finally, the presence of nitride forming elements can induce a very fine and intense precipitation of nitrides in α-Fe having a density significantly lower than iron, decreasing the density of the final material through composite effect [ 4 ]. However, the low solubility of nitrogen in liquid iron (0.046 wt.% at 1600 °C) constitutes however the main barrier to the development of low-alloy nitrogen steel through regular steelmaking [ 5 ].…”

“…The nanometre size and high density of these particles significantly increase the hardness of the alloy, and the low density of silicon nitrides decreases the mass of a structure [ 6 , 8 ]. A transition to crystalline precipitation occurs when excess nitrogen is removed during annealing [ 4 , 9 ]. The origin of such behaviour is still controversial as evidenced by some recent lively discussions in [ 4 , 6 , 7 , 8 , 9 ].…”

Formation Mechanisms of Alloying Element Nitrides in Recrystallized and Deformed Ferritic Fe-Cr-Al Alloy

“…Fundamental research on nitride precipitation processes until now has been largely devoted to recrystallized, i.e., more or less deformation-less, specimens and has focused on binary Fe-Me 1 iron-based alloys: Fe-Cr, [12][13][14][15][16] Fe-Al, [10,17] Fe-V, [18,19] Fe-Ti, [20][21][22] and Fe-Si. [23][24][25] Only relatively few of such studies were devoted to recrystallized, ternary, iron-based Fe-Me 1 -Me 2 alloys, where two types of dissolved elements, Me 1 and Me 2 , compete with each other in reacting with nitrogen. [26][27][28][29][30][31][32][33][34][35][36][37] In a number of cases, the surprising development of metastable ternary mixed (Me 1 , Me 2 )N nitrides was observed: cubic NaCl-type Cr 1Àx Al x N, Cr 1Àx Ti x N, and Cr 1Àx Mo x N in Fe-Cr-Al, Fe-Cr-Ti, and Fe-Cr-Mo alloys, respectively.…”