Acta Metall Sin  2018, Vol. 54 Issue (5): 701-716    DOI: 10.11900/0412.1961.2018.00112
 Special Issue for the Solidification of Metallic Materials Current Issue | Archive | Adv Search |
Unified Analysis of Non-Equilibrium Solidification and Solid-State Phase Transformations
Feng LIU(), Xu ZHANG, Yubing ZHANG
State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China
Abstract

Considering both phase transition and material hot-working or material design, unified analysis of non-equilibrium solidification and solid-state phase transformations has profound significance of science and great prospect of engineering application. Here, non-equilibrium solidification and solid state transformation behavior, correlated with peritectic reaction, massive transformation, metastable-stable transformation, precipitation, recrystallization and grain growth, for single phase solid solution alloy, eutectic alloy, peritectic alloy, multi-component super alloy and aluminum alloy, have been systematically reviewed. Regarding further the influence of non-equilibrium solidification on subsequent solid-state transformations, the new transformation mechanism induced by non-equilibrium solidification and the integrated microstructure regulation, the physical correlation between non-equilibrium solidification and subsequent solid-state transformations were discussed, and eventually, the microstructure control under the joint action of non-equilibrium solidification and solid phase transformations was realized. This review is expected to provide theoretical support for quantitative characterization of non-equilibrium solidification effect and microstructure prediction under the joint action of non-equilibrium solidification and solid-state transformations.

 ZTFLH: TG113.12
Fund: Supported by National Key Research and Development Program of China (Nos.2017YFB0305100 and 2017YFB0703001), National Natural Science Foundation of China (Nos.51431008 and 51790481), Fundamental Research Funds for the Central Universities (No.3102017jc01002) and Research Fund of the State Key Laboratory of Solidification Processing of Northwestern Polytechnical University (No.117-TZ-2015)
 Fig.1  Typically measured recalescence curves and as-solidified microstructures, correspond to ΔT<ΔT *(a, b) and ΔT >ΔT *(c, d), respectively (ΔT is the undercooling, and recalescence behavior and as-solidified microstructure characteristic are quite different with ΔT *≈130 K as a critical point)[17](a, c) measured recalescence profiles, where T1δ, Tp and Tsδ are liquidus temperature of the δ phase, equilibrium peritectic reaction plateau temperature and solidus temperature of δ phase, respectively, τPR is peritectoid incubation time(b) typical microstructure with ΔT<ΔT * shows peritectic solidification characteristics: the primary δ dendrites (dark) are enveloped by the peritectic γ phase (white)(d) typical microstructure with ΔT>ΔT * etched with 3% (mass fraction) Nital's reagent to reveal the grain boundaries and the morphologies of second-phase particles (Inserts are the TEM bright field images of the room temperature microstructure, the left is the morphology of the matrix and the right is the morphology of the second-phase particles) Fig.2  TTT curves of δ /γ solid-state transformation of Fe-4.33%Ni alloy ($T?$is the cooling rate of the system)[12] Fig.3  Scanning electron photographs of the Ni3Si precipitates in as-solidified Ni-Si hypoeutectic alloy melt subjected to undercoolings of ΔT≈105 K (a, b) and ΔT≈220 K (c, d) after ageing at temperature T=973 K for 4 h (a, c) and 8 h (b, d)[23] Fig.4  A schematic diagram illustrating the solubility of Si atom in α-Ni solid solution in as-solidified Ni-Si hypoeutectic alloy. The experimental date is from EDS result and the non-equilibrium dendrite growth calculation is from Wang and Liu's model[24] (a), evolution of the growth rate with the ageing time, t, in the isothermal precipitation at T=973 K of as-solidified Ni-Si hypoeutectic alloy (b) and the effect of non-equilibrium solidification on evolution of Ni3Si particles at T=973 K (c)[23] Fig.5  Eutectic Si morphologies of A356 Al alloys subjected to T4 treatment and cooling rates of 2.6 K/s (a), 0.6 K/s (b), 0.22 K/s (c) and 0.12 K/s (d)[25] Fig.6  Evolution of yield strength of A356 alloy under different cooling rates subjected to solid solution treatment at 813 K (a) and artificial ageing at 453 K (b)[27] Fig.7  The as-annealed microstructures of granular grains solidified under ΔT=140 K at 0.5 h (a), 8 h (b), 24 h (c), and ΔT=250 K at 0.5 h (d), 16 h (e), 30 h (f)[28] Fig.8  Evolution of the average grain size with the annealing time for Ni-1.5%B alloy annealed at 1173 K[28] Fig.9  Calculated stress in dendrite network versus initial melt undercooling of DD3 superalloy[30] Fig.10  EBSD orientation mapping of the microstructures of the highly undercooled Ni-Cu alloy quenched after recalescence with undercooling ΔT=225 K (a), grain boundaries of Fig.10a (b); the pole figure of Fig.10a showing a nearly random texture (c) and misorientation distribution figure of the grain boundaries in Fig.10a (d)[31] Fig.11  TEM bright field images of substructures in the rapidly solidified Ni80Cu20 alloy quenched with ΔT=225 K[31](a~c) dense dislocation networks in deformed grains (d) SAED pattern of a high angle grain boundary in Fig.11c Fig.12  EBSD orientation mapping of the microstructures of the quenched Ni-Cu alloy with ΔT=225 K after annealing at 1273 K for about 30 min (a), grain boundaries of Fig.12a (b); the IPF of Fig.12a (c) and the misorientation distribution figure of the grain boundaries in Fig.12a (d)[31] Fig.13  XRD spectra of the as-solidified and annealed Fe83B17 alloy with hypercooling of 445 K (Three structures all include α-Fe and Fe3B. No trace of Fe2B is found)[34](a) as cast(b) annealed at 858 K for 3 h(c) annealed at 858 K for 16 h Fig.14  The change in free energy of an atom as it takes part in a transition. The "reaction coordinate" is any variable defining the progress along the reaction path[34] Fig.15  Microstructures of the RS+PHT (rapid solidification with post-solidification heat treatment) processed A356 alloys[27](a) typical morphology of the solidification microstructure of A356 alloys (cooling rate upon RS: 96 K/s)(b) highly dispersed nanoscale Si particles in matrix and a few Si particles are associated with rod-like β' phase(c) TEM bright field image of a nanoscale Si particle associated with a β' (Mg9Si5) phase; the upper and lower insets are the electron diffraction pattern taken from the selected area circled by the white dash line and the corresponding image at higher magnification(d) TEM bright field image of the eutectic Si decorated by the nanoscale Al particles; the inset is the high resolution TEM image of an Al particle decorated in Si matrix Fig.16  Measured engineering stress-strain curves of the A356 alloys processed by the RS+PHT and the subsequent T6 heat treatment[27] Fig.17  SEM micrograph of γ' precipitation in DD3 superalloy solidified at undercooling of 45 K (a), 125 K (b), 200 K (c), 250 K (d), respectively[30], and variation of γ' precipitate size as a function of the melt undercooling of DD3 superalloy (e)[38] Fig.18  The tensile strength (σb) and elongation (δ) of DD3 superalloy solidified at different undercoolings[38] Fig.19  The cross section microstructures for the sample with ΔT=280 K before (a) and after heat treatment at 1173 K for 60 h (b), the thicknesses of the recrystallized γ-(Fe, Ni) phase layer from experimental measurement and fitting (c)[42] Fig.20  The strain-stress curves for the samples with ΔT=70 K and ΔT=250 K before and after heat treatment at 1173 K for 60 h[42] Fig.21  The connection between driving force / energy barrier of phase transition and strength / ductility of material, and both of them are mutual exclusive, while big driving force and energy barrier in processing correspond to high strength and ductility in microstructure