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This work probes the effect of ultrasonic melt treatment (UST) on primary intermetallic particles and α-Al using pure Al and Al–Zr alloys (Al–0.3Zr–0.1Ti, Al–0.5Zr, Al–0.5Zr–0.5Mg–0.9Si) solidified at various cooling rates of 0.2–70 K s−1. The application of UST is shown to decrease the size and increase the number density and volume fraction of D0 23 -structured primary Al 3 Zr and Al 3 (Zr,Ti) particles with a high nucleation potency for α-Al formation. High-resolution transmission electron microscopy analysis reveals that the cavitation-induced wetting and dispersion of γ-Al 2 O 3 inoculant particles contribute to the refinement of primary intermetallic particles. The grain size of Al–Zr alloys increases with increasing cooling rate because of the concomitantly reduced formation of primary intermetallic inoculant particles. The UST-induced refinement of primary Al 3 Zr particles and the increased number density lead to grain refinement in Ti-free Al–Zr alloys. For the Ti-containing Al–Zr alloy, UST-induced grain refinement is achieved only at a very low cooling rate of 0.2 K s−1, possibly because of the side effects of UST on the growth-restricting influence of Ti. The fast cooling–induced solidification enables significant age-hardening by L1 2 -Al 3 Zr nanoprecipitation (~5 nm) and is not affected by UST. Thus, this study shows that UST can be used to reduce the degree of grain coarsening of age-hardenable Al–Zr alloys at high cooling rates. Image, graphical abstract [ABSTRACT FROM AUTHOR]

A mechanism describing the synergistic effect of ultrasonic melt treatment (UST) and subsequent fast cooling on the refinement of primary Si particles in a hypereutectic Al−Si alloy was investigated by examining inoculant particles via high-resolution transmission electron microscopy, serial sectioning, and melt filtration. The application of UST activated non-wetting MgAl 2 O 4 particles with diameters of ∼0.5 μm to nucleate the primary Si phase. The cavitation-enhanced wetting of MgAl 2 O 4 particles caused the formation of the AlP phase at the MgAl 2 O 4 interface, further improving the nucleation potential. The cavitation-enhanced wetting and dispersion of inclusions (such as MgAl 2 O 4 ) also resulted in the refinement and de-agglomeration of AlP particles. The UST-induced changes to the inoculant particles ultimately increased their number density, and the observed effects became more pronounced after increasing the degree of undercooling up to 20 K, leading to enhanced refinement of primary Si particles at higher cooling rates (up to 10 2 K s −1 ). [ABSTRACT FROM AUTHOR]

High speed steel (HSS) is widely used in the production of high-speed cutting tools and roll etc. Fe-Nb-Zr-N-B amorphous nanocrystalline powder inoculants are designed and prepared by melt and ball-milling. The carbides in inoculants are easy to act as the nucleus of heterogeneous nucleation during the solidification of the HSS melt, which can refine the grain size of as-cast HSS significantly. At the same time, it can further improve the morphology and distribution of carbides in the HSS matrix. The phase composition of rapid solidified Fe-Nb-Zr-N-B inoculants is analyzed using XRD and TEM. With the addition of Fe-Nb-Zr-N-B inoculant, the grain size of as-cast HSS refined evidently, the Net thickness and dendritic spacing decrease obviously, simultaneously, the distribution of the carbides in HSS matrix is more homogeneous. That results lead to a significant improvement of the microstructure and mechanical properties of the HSS. The grain size of HSS in quench state decreases obviously after inoculation treatment with Fe-Nb-Zr-N-B. Meanwhile, the hardness and red hardness as well as the abrasion performance are improved obviously. [ABSTRACT FROM AUTHOR]

Solidification experiments were carried out for Al-Bi alloys with the addition of TiC. It is demonstrated that the average size of the Bi-rich minority phase particles (MPPs) shows a tendency of keeping constant, increasing, decreasing and then keeping constant again with the increase of the additive amount of TiC. The MPPs can be refined effectively with the addition of an appropriate amount of TiC. A model was developed to describe the kinetic behavior of the TiC particles in the melt and the microstructure evolution during the liquid-liquid (L-L) phase transformation of the Al-Bi alloys with the addition of TiC. The numerical results show that TiC particles may dissolve and coarsen during the heating period, and precipitate out during the cooling period of the melt. There may be two kinds of TiC particles: the one remained during holding temperature and the one precipitated during a cooling of the melt. Both of them can work as the inoculants for the nucleation of the minority phase droplets. What determines the refining efficiency is the resultant number density of the TiC particles in the melt cooled to the binodal line temperature. This research demonstrates that inoculation is an effective method for controlling the L-L phase transformation. The addition of the efficient inoculant may promote the formation of a monotectic alloy with a well dispersed microstructure. [ABSTRACT FROM AUTHOR]

A Cu 6 Sn 5 layer is an integral part of many electronic interconnections. Here we show that, although primary Cu 6 Sn 5 is not a potent nucleant for Sn, the Cu 6 Sn 5 layer plays a key role in Sn nucleation and microstructure formation in solder joints. Combining thermal analysis, FIB-tomography and EBSD, we show that conical cavities are present between the scallops of the Cu 6 Sn 5 layer that act as geometric nucleation sites for Sn, that Sn grows from the Cu 6 Sn 5 layer, and that reproducible nucleation orientation relationships (ORs) exist between Cu 6 Sn 5 and Sn. With these ORs, a near-random distribution of Sn orientations is predicted from joint to joint even for Cu 6 Sn 5 layers with a strong [0001] fibre texture. It is shown that the nucleation undercooling is strongly affected by manipulation of the Cu 6 Sn 5 layer shape, and that it is possible to prevent nucleation on the Cu 6 Sn 5 layer by adding more potent nucleants. [ABSTRACT FROM AUTHOR]

Abstract: During Pb-free soldering, βSn often requires a high nucleation undercooling and there is an ongoing effort to develop nucleation catalysts. It is shown here that NiSn4, PdSn4 and PtSn4 are heterogeneous nucleants for βSn, reducing the nucleation undercooling to ∼4K when these intermetallics are present either in the bulk solder or as the interfacial layer. Nucleation catalysis occurs by βSn nucleating on the (008) facet of XSn4 crystals with an orientation relationship (OR) (100)Sn||(008)XSn4 and [001]Sn||[100]XSn4 where there is a planar lattice match of ∼5%. This OR is also the origin of well-aligned lamellar βSn–XSn4 eutectic morphologies, even though the eutectics contain less than 2vol.% of faceted NiSn4, PdSn4 or PtSn4. [Copyright &y& Elsevier]

Paper presents formation of nodular graphite on the basis of the law of thermodynamic equilibrium of the chemical elements from a metallic system formed from two thermodynamic phases liquid metallic matrix and the thermnodynamic phase created by the inoculating agent. The inoculating agent creates gaseous, liquid and solid thermodynamic phases. Annulment of carbon thermodynamic activity gradient guides to diffusion of the carbon particles (C4+) through the overheated liquid metallic matrix, to new-created thermodynamic phases by the inoculating agent. Thus, graphite nuclei are created round about new phases thanks to reaching of 1 value of the carbon thermodynamic activity. Graphite nuclei grow inside gaseous or liquid thermodynamic phases or round about solid thermodynamic phases. [ABSTRACT FROM AUTHOR]

Abstract: We propose Monte Carlo simulations of the NbC grain boundary (GB) precipitation kinetics in α-iron, based on an atomic description of the main mechanisms that control the kinetic pathway. The simulation involves realistic diffusion mechanisms, with a rapid diffusion of C atoms by interstitial jumps and a slower diffusion of Fe and Nb atoms by vacancy jumps; a simple model of the GB which reproduces the equilibrium segregation properties of Nb and C; and a point defect source which drives the vacancy concentration towards its equilibrium value. Depending on the precipitation conditions, Monte Carlo simulations predict different kinetic behaviours, including early segregation of C atoms at the grain boundaries, transient precipitation of metastable carbides, and homogeneous and heterogeneous NbC precipitation. [Copyright &y& Elsevier]

Abstract: We propose Monte Carlo simulations of the precipitation kinetics of NbC on dislocations in α-iron based on an atomistic description of the main mechanisms controlling the kinetic pathway. The algorithm takes into account realistic diffusion properties, with a rapid diffusion of C atoms by interstitial jumps and a slower diffusion of Fe and Nb atoms by vacancy jumps. A simple model of dislocation includes interactions with solute atoms, through local segregation energy and long range elastic fields. The relative importance of local segregation energies and long range elastic stresses on the precipitation characteristics, such as early segregation of carbon atoms on dislocations, transient precipitation of metastable carbides, and homogeneous and heterogeneous NbC precipitation, is discussed. [Copyright &y& Elsevier]

Abstract: A considerable amount of B2 phase with a cellular morphology is retained in a 4Zr–4Nb-containing TiAl-based alloy. Heterogeneous precipitation of ordered ω from B2 is found to occur readily after HIPping: B2→ω with the B82-structure in cell regions and B2→ω with the D88-structure in cell-wall regions. Congregated D88-ω domains and particles form as a network surrounding the well-developed B82-ω cells. The heterogeneous formation of different ω variants is caused by a heterogeneous distribution of Zr+Nb elements across B2, which plays an important role in stabilizing vacancies and promotes the formation of D88-ω. Fine D88-ω particles are also observed to precipitate from the B82-ω cell matrix after ageing at 700°C for 1000h, showing a transformation path of β→B2→B82-ω→D88-ω for the aged cells. The heterogeneous formation of a D88-ω network and B82-ω cells is found to be detrimental to ductility and fatigue strength. A very brittle fine-grained TiAl alloy is produced as a result. [Copyright &y& Elsevier]

The precipitation of α2 phase based on Ti3Al from Ti–14Al–2Zr–3Sn–3Mo–0.5Si titanium alloy homogenized at different temperatures in the (α+β) two-phase field has been characterized. Minimal lattice mismatch between the α and α2 phase leads to a massive ordering transformation upon cooling and results in morphologies distinct from the ellipsoidal shape of the α2 particles. Enrichment of Al in front of growing β grains due to the Gibbs–Thomson effect, together with preferential diffusion of Al along 1 1 2¯ 0 produces a layer of acicular α2 particles apparently perpendicular to the α/β phase boundaries. Removal of the capillarity-induced composition inhomogeneity by subsequent aging at 750 °C results in disappearance of the acicular shape of the α2 particles. [Copyright &y& Elsevier]

Laser powder bed fusion (L-PBF) additive manufacturing was utilized to fabricate high-strength copper (Cu) alloys through inoculation of pure Cu powder with cobalt (Co) submicron particles. It was found that when the addition level of Co is lower than its maximum solid solubility in Cu (4.75 wt.%), the microstructure of Cu-Co alloys is characterized by coarse columnar grains. Further addition of Co over 4.75 wt.% led to a heterogeneous grain structure, with large equiaxed grains or columnar grains near the centers of melt pools whereas ultrafine equiaxed grains sitting on the melt pool boundaries. Microstructure characterization showed that the in-situ formed dual phase nanoparticles with Co shell and cobalt oxide (CoO) core acted as heterogeneous nucleation sites of Cu, which allowed ultrafine, equiaxed grains to form. The heterogeneously structured as-built Cu-Co alloy achieved a tensile strength of 381.4 ± 2.9 MPa and an elongation of 31.6 ± 1.3%. Co nanoprecipitation driven by post L-PBF heat treatment further increased the tensile strength of the Cu-Co alloy up to 491.1 ± 12.6 MPa without notably sacrificing the ductility. The combination of high strength and high ductility distinguishes Cu-Co alloys from most conventionally and additively manufactured Cu alloys. This study shows a strategy to produce Cu alloys with high performance through remarkable grain refinement by heterogeneous nucleation. [Display omitted] [ABSTRACT FROM AUTHOR]