Alloy Melt Research Articles

Role of Ca additive on the effect of phase composition and microstructure of BaZrO3 refractory and its interaction with titanium alloys

AbstractIn this study, the effect of different Ca additives (Ca(OH)2, CaO, and nano‐CaCO3) on the composition and microstructure of the fused BaZrO3 crucible were investigated, as well as their interaction with Ti2Ni alloy during vacuum induction melting. Results showed that the crucibles had the same phase compositions when the doping amounts of Ca additives were the same. Three kinds of Ca additives provided three different grain sizes of CaO precursors to participate in the solid solution reaction. When the doping amount of the Ca additive was 5.3 wt.%, the ZrO2 phase in the fused BaZrO3 was disappeared, and the CaZrO3 phase was founded. The composition of the crucibles doped with 7.7 wt.% Ca additives only consisted of Ba1‐xCaxZrO3 and CaZrO3 phase. The relative densities and erosion resistance of the crucibles were improved effectively with the increase of Ca additive content. Moreover, the crucible doped with 7.7 wt.% nano‐CaCO3 additive exhibited the highest density and the thinnest erosion layer. The Ba1‐xCaxZrO3 and CaZrO3 phases were dissolved by the alloy melt, according to the interaction analysis. In addition, the crucible doped with nano‐CaCO3 additive had a higher content of refractory element concentration in the alloy melts in comparision with the other two kinds of crucibles due to their higher number of pores.

Optical, electrical, and EPR studies of polycrystalline Al:Cr:ZnSe gain elements

Transition metal-doped II-VI (TM:II-VI) chalcogenides are well-known laser materials for optically pumped middle-infrared lasers. Cr:ZnSe is a key representative of this class of transition metal doped II-VI gain media and is arguably considered the material of choice for optically pumped middle-infrared lasers. In addition to effective mid-IR lasing under optical excitation, these crystals, being wide-band semiconductors, hold the potential for direct electrical excitation. One way to form n-type conductivity in ZnSe crystals is by annealing them in a melt of Zn-Al alloy. However, this annealing of Cr:ZnSe crystals results in their purification and transfer of chromium to the melt of Zn-Al alloy. In this article, we report on optimizing the doping technique for providing n-type conductivity in Al:Cr:ZnSe crystals while preserving the chromium concentration. Al:Cr:ZnSe samples with resistivities ranging from 10.8 to 992 Ω-cm were fabricated. While the 2 + valence state of Cr is typically dominant in Cr:ZnSe, both Cr2+ and Cr+ were detected in Al:Cr:ZnSe samples. The maximum level of Cr+ concentration was measured to be 4 × 1018 cm-3.

On the capability of grain refinement during selective laser melting of AlSi10Mg alloy

This work focuses on the origin and capability of grain refinement in the microstructure of selective laser-melted AlSi10Mg alloy. The grains in printed microstructure have been oriented in a random manner and there is no sign of preferred micro-texture. In the molten pool, columnar grains have been formed aligned with the building direction, and stretched toward the center of the molten pool. The fraction of refined equiaxed grains by the size of fewer than 10 μm is considerable (∼40%) which have been formed (i) during solidification owing to high solidification rate to thermal gradient ratio, or due to (ii) the occurrence of dynamic recrystallization during the manufacturing process after completion of the solidification. These refined equiaxed grains have been differentiated through plotting Grain Orientation Spread maps. The numerous thermal cycles experienced by each layer cause considerable tensile or compressive micro-plastic strains and give rise to dynamic recrystallization. The presence of incomplete grains can be clearly traced which are ready to be evolved into the recrystallized grains. This, besides the extensive substructure development and sub-grain formation, are main proof for governing of continuous mechanisms of recrystallization mechanisms. Finally, selective laser melting has been approached as a thermomechanical processing route, and the calculated micro-plastic strain has been compared with a critical strain of dynamic recrystallization obtained from the hot compression testing method.

Effect of mixing temperature on microstructure of an Al-Si alloy prepared by controlled diffusion solidification

The effects of mixing temperature, i.e., the temperatures of two precursor melts (pure Al and Al-12Si), on the temperature and solute fields of resultant mixture, the nucleation and growth, and the size and morphology of primary grains during controlled diffusion solidification (CDS) of Al-8Si alloy were investigated by using simulation and calculation. The results indicate that a lower mixing temperature is helpful for achieving more supercooled microscale Al-rich pockets in the mixture, and increasing the width and supercooling degree of supercooling zone in the Al-rich pockets, and thus, the nucleation rate. The nuclei grow up in nondendritic mode, resulting in spheroidal, at least, nondendritic grains. In a successful CDS, the superheat degrees of the two precursor melts should be limited within several degrees, and it is not necessary to extra stipulate the superheat degree of target alloy melt (Al-8Si) when the requirement about Gibbs energies of the three melts is matched. Subsequent observation on casting microstructures shows that the employed simulation and calculation processes are reasonable and the achieved results are reliable.

Additive manufacturing of titanium alloys with enhanced strength and uniform ductility via multi-element alloying

The application of commercially pure titanium (CP–Ti) has long been limited by its insufficient strength and plastic instability. However, strength enhancement typically comes at the expense of ductility since the two important mechanical properties are often mutually exclusive. In the present work, multi-element Fe–Cr–Ni–Mo in the form of 316L steel was added into CP-Ti by additive manufacturing (AM), so as to realize the simultaneous enhancement of strength and uniform ductility. The localized homogenization of CP-Ti and 316L alloy melts during laser melting deposition produced the microstructure comprised of basket-weave ɑ laths, discontinuous ɑGB, and retained β phases, which endowed Ti-1.35Fe-0.36Cr-0.24Ni-0.05Mo alloy with related higher ultimate tensile strength (635 MPa) and larger uniform ductility (12%). This approach could provide guidance for designing high-performance metal materials starting with elements powder through additive manufacturing.

INFLUENCE OF STRONTIUM ADDITION ON OXIDATION KINETICS OF INDUSTRIAL CAST ALUMINUM ALLOYS AL2, AL4 AND AL9

When melting cast aluminum alloys, their waste is observed, or more precisely, oxidation by the gas phase of the furnace. To select the optimal regime for melting alloys, it is necessary to know the physicochemical laws of this process, which are little studied. To study the kinetics of oxidation of metal melts, the method of continuous sample weighing is used, which is usually used in the study of high-temperature corrosion of solid metals. The mechanism of interaction of liquid metals with oxygen is similar in nature to high-temperature gas corrosion of solid metals. In both cases, adsorption of gas molecules on the metal surface, nucleation, and then growth of an oxide film take place. The kinetics of oxidation of strontium-modified AL2, AL4, and AL9 melts with atmospheric oxygen was studied by thermogravimetry. It is shown that the addition of strontium up to 0.1 wt % increases the oxidizability of melts. An increase in temperature promotes an increase in the rate of oxidation of these melts. The process of oxidation of the investigated melts obeys the parabolic law. The true rate of oxidation is on the order of 10–4 kg/m2 · s. The apparent activation energy of oxidation, depending on the amount of modifiers in the alloys, is: for AL2 alloy – 56.52–43.75, for AL4 alloy 59.74–37.09, for AL9 alloy 61.40–39.90 kJ/mol. The mechanism of influence of strontium on the kinetics of oxidation of melts AL-2, AL4 and AL9 has been established. Aluminum oxide Al2O3 plays a dominant role in the formation of a protective oxide film.

Potential assessment in laser powder bed fusion of bionic porous Ti scaffolds concerning compressive behavior, porosity, and surface roughness

The fabrication of cellular structures with biocompatible materials for implants has increased in recent years because of human aging and traffic road accidents. Laser powder bed fusion or Selective laser melting (SLM) can fabricate various load-bearing implants with mass customization in design and manufacturing. This work involves a manufacturability study in selective laser melting of biomedical Ti alloy implant plug for Osteoarthritis patients. The investigation involved the control variables like laser power (175,185,195) watt, scanning speed (1100,1250,1400) mm/s, and hatch spacing (0.065,0.0725,0.08) mm alongwith output responses such as Compressive yield strength, Elastic modulus, porosity, and surface roughness. The experiments were performed using Box Behnken design in Response surface modelling for collaborative optimization. The results were explicitly explained with an in-depth process physics supported with Characterization involving Scanning electron microscopy, Electro-dispersive spectroscopy, X-ray diffraction, micro-computed tomography, optical profilometry analyses, and process schematics. The optimal setting with laser power (195 W), scanning speed (1100 mm/s), and hatch spacing (0.068 mm) yielded high compressive yield strength (22.41 MPa), near trabecular bone Elastic modulus (0.891GPa), controlled porosity formation (29.32 %), and optimal surface roughness (3.647 μm). Topography resulted in a prominent lack of fusion pores because of low energy density levels, whereas the optimal settings produced around 15 % improvement from design of experiments data.

Effect of melt purification treatment on the solidified microstructure of hypereutectic Al-Si alloys

In this paper, hypereutectic Al-Si alloys were purified by a composite sodium salt, and the solidified microstructure of hypereutectic Al-Si alloys before and after melt purification was studied by OM, SEM/EDS, XRD, and TEM. The results showed that the Fe content decreased from 0.73 wt% to 0.23 wt% after purification with the Na salt. This also prevented an increase in heterogeneous nucleation. The Si content remained almost unchanged, which excluded the possibility of removing Si from the molten Na salt. According to DSC analysis, Na salt purification increased the undercooling degree of the melt, so that the hypereutectic Al-Si alloy melt was deeply undercooled to the pseudo eutectic region, and a nearly-perfect pseudo eutectic structure was obtained. Moreover, it was confirmed that NaAlSi changed the growth of eutectic Si, thereby changing its microstructure. At the same time, nanoscale spherical precipitates formed by trace Fe in the alloy could significantly promote the nucleation of eutectic Si.

The effect of cracks and alloy phase conditions on the hydrolysis characteristics of Al-10Bi alloy powder (composites)

The Al-water reaction has attracted many attentions as it's a convenient method for on-demand hydrogen generation. Although a variety of additives have been demonstrated to promote the activity of Al, the most likely mechanism is simply the inference made from surface conditions and reaction characteristics. In this study, the activation of two kinds of active Al-10Bi alloys powders was prepared by both melting alloy and mechanical alloy methods. The activity of the as obtained powders was analyzed through various methods including XRD, SEM. 3D characterization of active Al powders was conducted using synchrotron X-ray tomography to reveal the inner structure of ball milled active Al alloy powders. Results show that ball milling could effectively introduce a large number of cracks both on the surface and the inner of powders. The number of cracks increased further after adding salt during ball milling. The relation between the inner structure of the Al alloys and their hydrolysis reaction products was also discussed. The specific surface area, the number and distribution of cracks alloy phase are all important factors that influence the hydrolysis reaction of the active alloy powder.

Wetting and Brazing of Superhard Materials Based on Dense Boron Nitride Polymorphs with Braze Alloy Melts

Wetting and Brazing of Superhard Materials Based on Dense Boron Nitride Polymorphs with Braze Alloy Melts

Effect of stirring speed and temperature on the microstructure and mechanical properties of A356 alloy under vacuum

In this work, an effective method was proposed to purify aluminum alloy melt under stirring and vacuum. The formation mechanism of pore defects and their effects on the mechanical properties of A356 alloy were investigated. The results showed that compared with the untreated alloy, the mechanical properties of the purified A356 alloy were significantly improved. The purification parameters, including stirring speed and stirring temperature, had crucial effects on determining the size of dendrites and pores. The optimized stirring speed and stirring temperatures were 65 rpm and 730 °C, respectively. In this condition, grains with an average diameter of 279 μm and pores having an average diameter of 79.5 μm were obtained; the ultimate tensile strength, yield strength and elongation of the purified alloy reached 203.7 ± 4.3 MPa, 81.6 ± 3.3 MPa and 10.2 ± 0.5%, respectively. The variation in the microstructure and mechanical properties was associated with the bubble breakup mechanism, which accelerated the removal of bubbles in the melt during stirring in vacuum. Furthermore, the interaction between pore and solidified microstructure was also discussed.

Mechanism of primary Si and Fe-segregation for a hypereutectic 90 wt.% Si–Ti alloy melt in directional solidification via electromagnetism

Mechanism of primary Si and Fe-segregation for a hypereutectic 90 wt.% Si–Ti alloy melt in directional solidification via electromagnetism

Phase-Field Study of the History-Effect of Remelted Microstructures on Nucleation During Additive Manufacturing of Ni-Based Superalloys

In the current work we employ multi-phase-field simulations to understand the effect of remelting on microstructure evolution, especially on nucleation of new grains during selective electron beam melting (SEBM) of Ni-based super alloy. The phase-field model is coupled to both mass and heat transport phenomena including release of latent heat of solidification. We run remelting simulations in both as cast and homogenized conditions. Experimental observations show that remelting triggers the nucleation of new grains at the melt pool border. The simulation results shed more light on the local conditions at the melt pool border thereby enhancing our understanding of the mechanisms responsible for the nucleation. The simulation results are validated with experimental results obtained for the Ni–20.5 mol pct Al model binary alloy.

Facile Synthesis of Al-20Si@Al2O3 Nanosheets Composite Powders and Its Refinement Performance on Primary Silicon in Al-20Si Alloy

In this work, Al(OH)3 nanosheets are synthesized in situ on the surface of an Al-20Si alloy via the water bath method, and Al–20Si@Al2O3 composites are then obtained after calcination. The growth mechanism of the Al(OH)3 nanosheets is revealed, and a pathway is demonstrated to obtain Al–20Si@Al2O3 nanosheets with the desired structure and thickness. Furthermore, the influence of different Al–20Si@Al2O3 contents on the primary silicon phase in the Al–20Si alloy is investigated, and the mechanism of such an influence is theoretically analyzed. The mechanical properties of the modified Al–20Si alloy are tested, and the effects of the morphology and particle size of the silicon phase on the alloy properties are studied. The results show that Al–20Si@Al2O3 synthesized in situ by water bath has good dispersion in the melt. There is a lot of γ-Al2O3 dispersed in the matrix of the alloy, and the primary silicon of the Al-20Si alloy is obviously refined. By increasing the content of the modifier, the average size of primary silicon decreases first and then increases. When 15 wt% of the modifier is added, the refinement effect of primary silicon reaches its peak, and the size of primary silicon is reduced from unmodified 86.4 μm to 28.5 μm. The hardness and tensile strength of 75.2 HB and 120.3 MPa are increased to 107.2 HB and 185.9 Mpa by 42% and 55%, respectively. Compared with adding γ-Al2O3 directly, this experiment provides a simple method to synthesize the modifier, and γ-Al2O3 can be dispersed evenly in the aluminium-silicon alloy melt more easily by in-situ generation, without ultrasonic treatment or other ways. During mass production, the cost can be better controlled and good results can be achieved at the same time.

Nozzle clogging in vacuum induction melting gas atomisation: influence of gas pressure and melt orifice diameter coupling

ABSTRACT The clogging problem of close-coupled nozzles in the vacuum induction melting gas atomisation (VIGA) process is studied by numerical simulation and industrial experiments. To understand the factors affecting lick back on the nozzle, volume of fluid (VOF) multiphase flow model simulation was adopted to visualise the motion of alloy melt around the outer wall of the delivery tube in the primary atomisation process. When the melt orifice diameter is 4 mm and the atomisation pressure is close to 3.5 MPa, the atomisation process is continuous, the powder particle size is fine, and the atomiser can be reused. When the orifice diameter is 5 mm, and the atomisation pressure is greater than 2.5 MPa, the risk of nozzle clogging is avoided, the powder size is relatively coarse. In the case of using the same atomiser structure, this study explains the mechanism of lick-back and the resulting nozzle damage in VIGA units.

Preparation and Hydration Mechanisms of Low Carbon Ferrochrome Slag-Granulated Blast Furnace Slag Composite Cementitious Materials

Low carbon ferrochrome slag (LCFS) is the metallurgical waste slag from the carbon ferrochrome alloy smelting process. Compared with high carbon ferrochrome slag, LCFS has great potential as cementitious material; the chemical compositions of the two types of slag are quite different. In this research, composite cementitious materials are prepared which use low carbon ferrochrome slag and granulated blast furnace slag (GBFS) as the main raw material. Steel slag mud (SSM) and flue gas desulfurization gypsum (FGDG) are used as the activator. In order to find the variety rule of compressive strength on the composite cementitious materials, a three-factor three-level Box-Behnken design is used to discuss the following independent variables: LCFS content, GBFS content, and water-binder ratio. Moreover, the hydration characteristics of the LCFS-GBFS composite cementitious materials is studied in this paper in terms of hydration product, micromorphology, and hydration degree, based on multi-technical microstructural characterizations. The results show that the compressive strength of the LCFS-GBFS composite cementitious materials is significantly affected by single factors and the interaction of two factors. The mechanical property of the mortar samples at 3, 7, and 28 days are 26.6, 35.3, and 42.7 MPa, respectively, when the LCFS-GBFS-SSM-FGDG ratio is 3:5:1:1 and the water-binder ratio is 0.3. The hydration products of LCFS-GBFS composite cementitious materials are mainly amorphous gels (C-S-H gel), ettringite, and Ca(OH)2. With the increase of LCFS content, more hydration products are generated, and the microstructure of the cementitious system becomes more compact, which contributes to the compressive strength. The results of this research can provide a preliminary theoretical foundation for the development of LCFS-GBFS composite cementitious materials and promote the feasibility of its application in the construction industry. Deep hydration mechanism analysis and engineering applications should be studied in the future.

Wettability and Interfacial Heat Transfer During Solidification of Al–Si Alloy (A413) Melt Droplets on Metallic Substrates

Wettability and Interfacial Heat Transfer During Solidification of Al–Si Alloy (A413) Melt Droplets on Metallic Substrates

Investigation of Induction Heating Process for Selective Melting of Aluminum Alloy for the Repair of Exit Hole Defect in Friction Stir Welding Process

Investigation of Induction Heating Process for Selective Melting of Aluminum Alloy for the Repair of Exit Hole Defect in Friction Stir Welding Process

A New Strategy on Designing Fluxes for Aluminum Alloy Melt Refinement.

With the aim of obtaining a refining flux that is stable and provides effective refining of aluminum melt, a new strategy of designing the flux composition has been proposed. Ten fluxes were designed, by selecting ten molten salt compounds according to their thermophysical parameters, physical properties, and thermodynamic analysis. The melting points of the ten fluxes, and the phases transformation of the fluxes after melting, were studied by DSC and XRD, respectively. The contact angles between four groups of fluxes and alumina at refinement temperatures were studied, and the effect of refinement was characterized by a metallographic microscope. The process of the fluxes removing inclusions and degassing was analyzed thermodynamically. The research findings indicate that flux #10 (11.0 wt.%NaF, 29.5 wt.%NaCl, 46.5 wt.%Na2CO3, 3.0 wt.%CaF2, 10.0 wt.%Na3AlF6) has a melting point (562.2 °C) below the refining temperature. At the refining temperature (760 °C), flux #10 has the lowest contact angle, of 12.78°. In addition, compared to that of flux STJ-A3, currently used in practice, flux #10 has a better refining effectiveness, with the pores and inclusions content of the sample being reduced to 1.11% from 2.96%.

Activity of strontium in liquid Sr-modified Al-7Si alloy

ABSTRACT In the present study, the Henrian activity coefficient of strontium , dissolved in liquid Al-7Si alloy at 725–730°C has been determined to be in the order of 10−2, using the numerical thermodynamic analyses. By knowing the , formation of the compounds, Sr(OH)2 and SrH2 through the reaction of dissolved elements in Al-7Si alloy melt has been analysed. The results indicated that the free energy of the formation reaction of Sr(OH)2 and SrH2 in the alloy melt are positive at different temperatures, showing that these compounds may not be formed in the liquid aluminium alloys.