Inoculant Particles Research Articles

Improving comprehensive properties of Cu−11.9Al−2.5Mn shape memory alloy by adding multi-layer graphene carried by Cu51Zr14 inoculant particles

Improving comprehensive properties of Cu−11.9Al−2.5Mn shape memory alloy by adding multi-layer graphene carried by Cu51Zr14 inoculant particles

Role of TiB2 inoculation particles during welding of a AlCoCrFeNi high entropy alloy

High entropy alloys (HEAs) are a novel class of materials that represent an evolution of common engineering alloys to a wider array of compositional and properties possibilities. As such, the exploration of methodologies to achieve improved microstructure and mechanical characteristics of these materials for potential applications in industry is a requirement that is experiencing extended research efforts. One example of a processing method able to expand the potential applications of these alloys is Gas Tungsten Arc Welding (GTAW), which allows to evaluate the metallurgical evolution and corresponding mechanical performance, associated to the impact of a localized heat input on the material. However, GTAW and related fusion-based welding processes are known to generate large grain sized-structures in the fusion zone, which often is detrimental to the joint performance. Thus, the integration of high temperature inoculant particles on the fusion zone during welding is a potential way to improve this region’s microstructure and, therefore, its mechanical performance. In this work, we discuss the effect that the addition of TiB2 micron-sized particles have on the microstructure of a GTAW AlCoCrFeNi-based HEA. For this, the microstructure of the welds was evaluated by means of optical and electron microscopy, synchrotron X-ray diffraction and CalPhaD-based simulations. Mechanical testing was performed using microhardness mapping and tensile testing coupled with digital image correlation. The results evidenced that successful inoculation with TiB2 proved capable of altering the microstructure of the fusion zone (FZ), refining it. Nevertheless, preferential deformation in the relatively softer heat affected zone during tensile testing resulted on premature failure of the inoculated joints, due to the concomitant higher hardness of the FZ.

Investigating the influence of thermal behavior on microstructure during solidification in laser powder bed fusion of AlSi10Mg alloys: A phase-field analysis

The utilization of the laser powder bed fusion (L-PBF) method in additive manufacturing experiments has revealed the intriguing potential to induce morphological evolutions within the solidification microstructure by manipulating the thermal conditions. Transitions of this nature can have a substantial impact on the ultimate texture and material properties of the product. This study utilizes numerical investigations to examine the microstructure evolution of the AlSi10Mg alloy, which is fabricated using the L-PBF process, under different thermal conditions. In order to investigate the changes in the microstructure, we employ a parameter phase-field (PF) model. This model effectively replicates the natural development of nuclei from inoculant particles and accurately simulates the transitions in the morphology. The PF model’s validity is determined through the numerical investigation of morphological transitions during directional solidification of the AlSi10Mg alloy. The model’s predictions are then compared to the analytical Hunt model. The formation of a columnar microstructure with a significantly reduced secondary dendrite arm spacing is observed when the ratio of the temperature gradient (G) to the solidification rate (R) is increased.

Modelling microstructure formation in TiAl by isomorphic inoculation

Ti-Al alloys have replaced Ni-based superalloys in the last stages of some aircraft engines to improve fuel efficiency. In order to improve their properties, grain refinement has been investigated via isomorphic inoculation with Ti-Al-Nb particles. This inoculation method is orders of magnitude more efficient on a particle-by-particle basis than traditional inoculation, rather than multiple inoculant particles added to form a solidified bulk phase grain, in isomorphic inoculation each particle added results in the formation of multiple grains. As the particles are indistinguishable from the matrix after solidification, a model was used to elucidate this mechanism. Two phenomena were considered to calculate the number of particles acting during solidification: particle breakup along grain boundaries and complete particle dissolution. The grain size of the particles was calculated with an empirical model from initial TKD analysis of the particles and high temperature molten salt heat treatments. Particle dissolution was estimated via mass transport of the slowest diffusing Nb species. This showed the population of isomorphic inoculant particles which can act during solidification is near a 1:1 ratio with the number of grains formed, confirming the mechanism of grain refinement by direct epitaxial growth from the particles.

Melt pool geometry dependent microstructural evolution induced by inoculants in IN718 processed by selective laser melting

This preliminary study aims to clarify how Co, TaCr2 and TiB2 grain refinement inducing inoculants influence the melt pool physics and resulting grain structure in superalloy IN718 processed by laser powder bed fusion (L-PBF). It was demonstrated that the presence of solid inoculant particles could affect the melt pool convection leading to a noticeable reduction in the melt pool width and penetration depth as well as the balling phenomenon. Interestingly, it was found that the penetration depth of the melt pool in samples containing TiB2 appeared to be unchanged due to the presence of nano-particles. Characterization of the resulting grain structures of the various samples revealed that the difference in melt pool geometries contributed to a predominant columnar-grained structure with< 101 > texture in samples containing Co or TaCr2 inoculants while an equiaxed-grained structure with< 001 > texture in samples containing TiB2 inoculants. The effectiveness of inoculants was found to be closely related to their impact on the melt pool physics, in addition to the degree of lattice disregistry with the IN718 matrix.

Grain Refiner Settling and Its Effect on the Melt Quality of Aluminum Casting Alloys.

Grain refiner particles, which are intended to induce the formation of fine equiaxed grain structure during the solidification of aluminum alloys, are prone to settling during the holding of the liquid metal, which phenomenon can affect not only the grain size but the spatial distribution of the double oxide films in the melt. In this study, the settling of Al3Ti inoculant particles, as well as its effects on melt quality and grain refinement, were studied. During the experiments, the Ti-concentration of a liquid Al-Si-Mg-Cu alloy was increased to 0.3 wt.% by the addition of Al-10%Ti master alloy at different melt temperatures. Particle settling and grain size evolution were studied by quantitative metallography, while the interactions of grain refiners and bifilms were investigated by scanning electron microscopy (SEM). The evolution of melt quality was assessed by the computed tomographic (CT) analysis of reduced pressure test (RPT) samples. It was found that effective grain refinement was only realized when the introduced blocky Al3Ti particles were dissolved and re-precipitated in the form of (Al,Si)3Ti at a lower temperature. Without dissolving at higher holding temperatures, Al3Ti particle settling has taken place within 10 min. The settling of (Al,Si)3Ti particles improved melt quality by the aided sedimentation of bifilms in the melt.

Effect of FeTi-FeB inoculation on the shape of carbide reinforcements in hypoeutectic high chromium white cast iron

Abstract FeTi-FeB was added to molten high chromium white cast iron in amounts of 0.5–2.5 wt% at 50 °C above the melting temperature. The samples were produced in four groups. The first group samples were investigated as cast, the second group homogenized at 1000 °C for 1 h, and the other two groups were also homogenized at 1000 °C but for 3 and 6 h, respectively. To study the effect of FeB and FeTi on the microstructure, the samples were characterized by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and hardness tests. Wear tests were performed using a pin-on disc. A homogeneously dispersed carbide microstructure was produced by the homogenization heat treatment method. The addition of FeTi-FeB inoculants to high Cr white cast iron played an important role in the distribution of hard carbides. The chemical rate and the carbide volume varied on account of the added hard inoculant particles. TiB2, Cr3C2, M7C3, M23C6, and γ-FeCr phases formed on the surfaces. The hardness and wear resistance were improved considerably due to FeTi-B inoculation.

Effect of Inclusion and Filtration on Grain Refinement Efficiency of Aluminum Alloy

It is well known that the filtration efficiency of ceramic foam filters (CFF) on aluminum melt can be significantly reduced by the addition of grain refiner particles under a high inclusion load. Also, it is usually considered that the filtration process has little impact on grain refinement efficiency. In this work, the influence of inclusions and filtration on the grain refinement effect of AA 6060 alloy has been studied. This was done through TP-1 type solidification experiments where the aluminum melt prior to and after the filter during a pilot-scale filtration test was investigated. In the experiments, 80 PPi CFFs were used to filtrate aluminum melt with an ultra-high inclusion load and two addition levels of Al–3Ti–1B master alloys. It is found that both inclusions and filtration significantly reduce the grain refinement efficiency of the grain refiner master alloys. A detailed characterization of the used filters shows that the reduction of grain refinement efficiency is due to the strong adherence of TiB2 particles to the oxide films, which are blocked by the CFF during filtration. A grain size prediction model based on deterministic nucleation mechanisms and dendritic growth kinetics has been applied to calculate the solidification grain size and estimate the loss of effective grain refiner particles during filtration. It is shown that due to the strong adherence between TiB2 particles and oxide films in the melt, the high addition level of aluminum chips also has an influence on reducing the grain refinement efficiency of aluminum melt without filtration. The results of this study extended our understanding of the behavior and performance of inoculant particles in CFF and their interactions with the inclusions.

Effect of Ultrasonic Melt Treatment on Solidification Microstructure of Al–5Ti–1B Alloy Containing Numerous Inoculant Particles

Effect of Ultrasonic Melt Treatment on Solidification Microstructure of Al–5Ti–1B Alloy Containing Numerous Inoculant Particles

Insight to agglomeration and chemical reactions of CoAl2O4 inoculants in IN718 processed by selective laser melting

The investigation aims to clarify the influence of scan parameters on the morphology and phase constitution of CoAl2O4 inoculants in Inconel 718 (IN718) superalloy processed by selective laser melting (SLM). Gas atomized IN718 powder feedstock was uniformly blended with 0.2 wt% of CoAl2O4 flakes and processed with a range of laser scan parameters to understand the effect of the inoculant additions on microstructure. Similar to the reactions observed in investment cast Ni-superalloys, the CoAl2O4 particles were found to chemically react with elemental Al, Cr, and Ti present in the melt pool of IN718 and become reduced into Al2O3, Cr2O3, and TiO2 oxides after the SLM process. Analyses of single melt pool beads revealed the existence of Co-rich metallic particles distributed along the surface of the oxides. However, since SLM processing involves remelting of the previously deposited layers to minimize the occurrence of porosity, this results in the dissolution of the Co-rich metallic particles that form when the CoAl2O4 particles are reduced in the melt pool. As such, the ability of the metallic Co particles to contribute to grain refinement becomes limited during SLM processing. Furthermore, the inoculant particles were found to agglomerate along the scan direction. The underlying mechanisms can be attributed to the Marangoni convection following the moving center of laser beam. It was found that decreasing energy density and increasing scan speed can effectively reduce the size and number density of the agglomerated oxide particles. Faster laser scan velocities lead to reduced convective flow within the melt pool and reduce the tendency for agglomeration. However, the reduced magnitude of energy input limited the time over which the CoAl2O4 particles could react with the melt pool. This led to the formation of lack of fusion defects and incomplete chemical reaction between CoAl2O4 and IN718 after the SLM process. The effectiveness of CoAl2O4 inoculant particles on grain refinement in as-built SLM IN718 microstructures is strongly dependent on the melt pool physics and laser scan conditions.

Characterizing the microstructural effect of build direction during solidification of laser-powder bed fusion of Al-Si alloys in the dilute limit: A phase-field study

Additive manufacturing experiments using the laser powder bed fusion (LPBF) method reveal that changing the build direction can stimulate morphological transitions in the solidification microstructure. As a result, the final texture and material properties can be altered. In this work, we conduct numerical investigations to explore the effect of building direction on the microstructure evolution of dilute Al-Si alloy produced by the LPBF process. A finite element thermal model is developed to incorporate the effect of build direction on the thermal characteristics of the melt pool for a vertically and horizontally printed Al-Si powder layer. We then utilize a multi-order parameter phase-field model to probe the microstructure evolution of LPBF Al-Si alloy in the dilute limit under the aforementioned thermal conditions for horizontal and vertical printing strategies. The phase-field model described here can self-consistently emulate spontaneous formation of nuclei from inoculant particles and simulate morphological transitions. The accuracy of the phase-field model is validated through the numerical examination of morphological transitions under directional solidification conditions of a dilute Al-Si alloy and compared to the predictions of the analytical CET theory of Hunt [1]. The phase-field simulations and subsequent grain analysis of the microstructure under transient thermal conditions reveal that the nucleation rate and hence equiaxed to columnar microstructure ratio is notably higher in the horizontally built samples. These results are in consistence with experimental observations.

Effect of Agglomeration on Nucleation Potency of Inoculant Particles in the Al-Nb-B Master Alloy: Modeling and Experiments

Effect of Agglomeration on Nucleation Potency of Inoculant Particles in the Al-Nb-B Master Alloy: Modeling and Experiments

Experimental assessment of the gray cast iron production by inoculant injection

An initial assessment of the gray cast irons production by injecting an inoculant with a conveying gas into a molten iron bath was evaluated at a laboratory scale. A numerical simulation was carried out to determine the hydrodynamic behavior between the inoculant particles injected into the molten iron. It was determined that an optimal interaction between the particles with the molten iron occurred at a lance depth of 7 cm and for the particle sizes fine (211 to 297 ?m) and medium (421 to 590 ?m), and the residence time was of 0.38 and 0.4 s, respectively. The melting time was calculated at 0.0008 and 0.003 s for the particle sizes fine and medium, respectively. After the injection, the FeSi of the inoculant melted quickly, releasing the elements of the inoculant which interacted with the molten iron and formed oxides and sulfides creating nucleating sites during solidification. The injection technique allowed obtaining a type-A graphite distribution for the fine and medium particle sizes. The number of eutectic cells increased when the inoculant particle size decreased despite of the low graphitisers elements and manganese contents used in the gray cast iron manufacturing.

Mechanism of ultrasound-induced microstructure modification in Al–Zr alloys

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 D023-structured primary Al3Zr and Al3(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-Al2O3 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 Al3Zr 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 L12-Al3Zr 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.

The Role of Grain Refiner in the Nucleation of AlFeSi Intermetallic Phases During Solidification of a 6xxx Aluminum Alloy

Primary grain refinement using inoculant additions and intermetallic compound (IMC) phase selection are critical aspects in the solidification of commercial aluminum alloys, controlling the final mechanical properties in service. Although there have been studies which suggest there are explicit interactions between the two phenomena, they have yet to be fully elucidated. Here, through study of intermetallic phase particles extracted from an inoculated casting, key features relating to the nucleation of different intermetallic phases via eutectic reactions are recognized and explained. In particular, rake-like IMCs are identified as initiation points for the deleterious beta -AlFeSi IMC phase in a model 6xxx series Al alloy. A mechanism is proposed for how {text{TiB}}_{2} inoculant particles, which are commonly used for primary phase refinement, play a role in enhancing the nucleation of intermetallic phases during eutectic reactions at the liquid/alpha -Al interface in the final stages of solidification. The implication of this mechanism is that, after the event of primary grain refinement, any unused {text{TiB}}_{2} inoculant particles could be contributing to IMC formation thereby affecting the overall type, size, and distribution of intermetallic phases in the solidified alloy.

Special corrosion behavior of an inoculant refined Cu-Al-Mn shape memory alloy during electropolishing process

The Cu-11.9Al-2.5Mn (wt%) shape memory alloy (SMA) refined by the Cu51Zr14 inoculant exhibits special corrosion behavior in electropolishing process, which makes the surface of the alloy look like a beautiful ink-washing painting. Transmission electron microscope (TEM) observation reveals that this can be ascribed to the stress layers existing near the Cu51Zr14/Cu-Al-Mn interfaces. Fortunately, these stress layers do not disturb the perfect lattice matching relationship between the Cu51Zr14 particle and the Cu-Al-Mn SMA. This study provides a simple and efficient method to pursue the distribution of inoculant particles in the refined alloys and to help us to reveal the refining mechanism.

Predicting primary dendrite arm spacing in Al–Si–Mg alloys: effect of Mg alloying

Directional solidification experiments were performed on Al–Si–Mg alloys to examine the effect of compositional variation on dendritic growth and to develop a novel growth model for the prediction of primary dendrite arm spacing in solidification microstructures. Instead of relying on the growth restriction factor or inoculant particle efficacy, this model examines solute effects to describe the final primary dendritic arm spacing. Increased Mg concentration was shown to decrease the dendritic growth velocity by decreasing constitutional undercooling. Solute enrichment at the solid/liquid interface was shown to limit lateral coarsening of primary dendrite arms and create a region of local solute depletion. This phenomenon allowed increased nucleation due to an increase in the resulting local liquidus temperature, and ultimately produced a refined primary dendrite arm spacing. Primary and secondary dendrites were measured and quantitatively analyzed in validation of the model. The model, which shows increased accuracy compared to existing models, was developed with aid of the three-dimensional cellular automaton method and experimentally verified.

In situ Investigation of the Heterogeneous Nucleation Sequence in Al-15 Weight Percent Cu Alloy Inoculated by Al-Ti-B

The sequence of heterogeneous nucleation events is investigated in situ via synchrotron-based X-ray radiography on Al-15 wt pct Cu alloy. In addition to the normal wave-like nucleation, which is predominant ahead of the solidification front when the temperature gradient moves across the field of view, two other types of nucleation are observed: nucleation among the growing grains and nucleation at one site. The nucleation among the growing grains occurs on the less potent TiB2 particles and accounts for ~ 20 pct regardless of the cooling rates. The third type is the nucleation at one site at cooling rates below 8 K/min and gradually weakens with the increasing cooling rate, which is probably due to the agglomeration of inoculant particles. The latter two types of nucleation are believed to be important for increasing the efficiency of nucleant particles.

Heterogeneous nucleation in crystallization: Impact of impurities and local melt inhomogeneity

Literature data on inoculation of metallic melts are analyzed. Ability of solid particles to facilitate heterogeneous nucleation is explained by impurity adsorption, stabilizing flat facets on inoculant particles. A new concept of initiating heterogeneous nucleation, premised on chemical inhomogeneity of melt in the vicinity of solid particles, is proposed. It is supposed that ordering in liquid phase structure in the vicinity of solid-liquid interface favors formation of crystallization nuclei.

The Challenges Associated with the Formation of Equiaxed Grains during Additive Manufacturing of Titanium Alloys

It is well established that columnar grain structures usually form when metal alloys are used to additively manufacture components. A challenging goal is to produce an equiaxed grain structure throughout the component to remove anisotropy and refine the grain size in order to improve its mechanical performance. The high cooling rates and associated high temperature gradients are the main reasons for the formation of columnar grains via epitaxial growth of each added layer of material. There appear to be limited strategies for promoting equiaxed nucleation of grains. In addition to cooling rate and temperature gradient, we explore other variables such as the potency of natural or added inoculant particles and the composition of the alloy, and their possible impact on the nucleation of equiaxed grains. Although changing the composition can help, finding a suitably potent nucleant particle is a major challenge. Operating parameters can also influence the microstructure and optimization to produce equiaxed grains may be possible. The limitations of these strategies and possible ways to overcome them are evaluated.