Abstract
The mechanism of the heterogeneous nucleation of NbC on TiC precipitates was investigated systematically in this paper. The interfacial properties of NbC (100)/TiC (100), NbC (110)/TiC (110), and NbC (111)/TiC (111) interfaces were studied by first-principles calculations. The results showed that the NbC (111)/TiC (111) interface with the Nb–C bond is the most stable one, and the stability of interfaces with the C–Ti, Nb–Ti, and C–C bonds decreases in turn. The interface of the Nb/C-terminated and Third Layer (TL) stacking sequence (NCTL) has the largest adhesion work (10.15 J/m2) and the smallest equilibrium interface spacing (1.290 Å). In the range of low niobium (Nb) chemical potential and high carbon (C) chemical potential, the nucleation of NbC on TiC precipitates takes precedence over the epitaxy growth in the coherent relationship of [ 1 1 ¯ 0 ] ( 111 ) NbC / / [ 1 1 ¯ 0 ] ( 111 ) TiC , while the nucleation of NbC on TiC precipitates is prior to the epitaxy growth in the coherent relationship of [ 001 ] ( 100 ) NbC / / [ 001 ] ( 100 ) TiC in the range of high niobium (Nb) chemical potential and low carbon (C) chemical potential. Besides, the characteristics of heterogeneous nucleation precipitates in Nb–Ti microalloyed steels were analyzed by transmission electron microscopy (TEM). The orientation relationship between the (Ti, Nb) C and (Nb, Ti) C precipitates follows [ 1 1 ¯ 0 ] ( 111 ) ( Nb , TiC ) / / [ 1 1 ¯ 0 ] ( 111 ) ( Ti , Nb ) C , which is consistent with the calculated result.
Highlights
IntroductionPrecipitation strengthening, microstructural control, and grain refinement are usually used to obtain high-strength low-alloy steels (HSLASs) with excellent strength and toughness [1,2]
Precipitation strengthening, microstructural control, and grain refinement are usually used to obtain high-strength low-alloy steels (HSLASs) with excellent strength and toughness [1,2].Microalloying elements in steel can form carbides, nitrides, and carbonitrides with interstitial atoms C and N
Before investigating the properties of the NbC/TiC interface, it is necessary to determine the appropriate atomic layers of NbC and TiC slab models, which can guarantee that the atoms in the depth of the surface exhibit bulk atomic characteristics
Summary
Precipitation strengthening, microstructural control, and grain refinement are usually used to obtain high-strength low-alloy steels (HSLASs) with excellent strength and toughness [1,2]. Microalloying elements (such as Ti and Nb) in steel can form carbides, nitrides, and carbonitrides with interstitial atoms C and N. The second-phase particles precipitated from austenite are beneficial to grain refinement, while the particles precipitated from ferrite can improve dispersion strengthening [3,4]. Adding Ti to Nb-microalloyed steel can obviously improve the toughness of the welding heat-affected zone. The reason is that Ti-rich carbonitrides formed at high temperatures can inhibit the growth of austenite grains, and the Nb (C, N) formed at low temperatures will suppress the recovery recrystallization process, which is beneficial to refine the austenite and ferrite. The fine precipitates can achieve a certain degree of dispersion strengthening [5]
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