Fluidity Of Melt Research Articles

Molecular dynamics research on the effect of selective laser melting parameters on porosity and properties of parts

Selective laser melting (SLM) is considered as a new production technology which has the potential to produce amorphous alloy parts. However, pores are often observed in parts prepared by SLM, which seriously affect the properties and life of the parts. In this work, an atomic model for SLM forming of Cu50Zr50 amorphous alloy is established. The effects of laser power and scanning speed on the porosity and mechanical properties of parts fabricate by SLM are researched using molecular dynamics methods. The results indicate that increasing laser power or reducing laser scanning speed could enhance the laser energy input of the molten pool and increase the molten pool temperature, which could improve the fluidity of the metal melt and prolong the existence time of the molten pool. The molten metal could fully fill the gaps between powders, which reduces the porosity and is beneficial to obtain dense parts. The tensile strength of samples formed by SLM is positively correlated with their porosity. Stress concentration occurs in the system with through holes and internal pores. Defects expand and interconnect rapidly under stress concentration, which leads to a decrease in strength and plasticity. The porosity could be reduced by adjusting the process parameters, thus improving the mechanical properties of the parts. This study provides a theoretical reference for a deeper understanding of the formation mechanism of SLM pores and the development of advanced alloys with high density.

Effect of oxygen contents on the fluidity of a newly developed metastable β titanium alloy

Fluidity of Ti-4Mo-3V-4Cr-0.5Fe-3.5Al-xO alloy with different contents of oxygen addition has been studied. The fluidity of alloy displays obviously improvement with the enhancement of oxygen contents up to 0.6 wt%.The influence of oxygen on the microstructure and thermophysical parameters is analyzed and discussed. With increase of the oxygen content, the changes of superheat, solidification interval width, viscosity, and density exhibit negative effects on the fluidity of alloy melt. However, the refined grains, enhanced crystallization latent heat, and declined thermal conductivity play positive effects on the evolution of fluidity for alloy melt. And positive effects dominate the evolution of fluidity. Therefore, the addition of oxygen can improve the fluidity of Ti-4Mo-3V-4Cr-0.5Fe-3.5Al.

Effect of ore types on high temperature sintering characteristics of iron ore fines and concentrate

Sinter quality (strength and reducibility) plays an important role in reducing the GHG emissions from the blast furnace ironmaking process and is significantly influenced by the reactions occurring in the sintering bed. Formation and fluidity of the initial sinter melt from adhering fines and its interactions with coarse nucleus particles are the key sintering reactions. Hence understanding of these high temperature characteristics of iron ore is urgently needed in order to produce strong and reducible sinter and optimise resource utilisation. In the present study, laboratory scale sintering tests were carried out to examine the effect of adhering fines and nucleus particles from various ores on the characteristics of initial sinter melt formation, fluidity, as well as penetration and assimilation. The formation ability and fluidity of the initial melts from various adhering fines were quite different, and various iron ore fines required distinct CaO contents to form the melt and spread out. The ore type of adhering fines and substrates affected the penetration and assimilation ability of the initial melt, but a good formation ability and fluidity of initial melt was the basis of good penetration and assimilation ability. Based on the micro and macro sinter structure, the high temperature characteristics were further related to the sinter quality and sintering performance. This information is expected to provide excellent tools in formulating and optimising future low cost and low emission sinter blends.

Effect of catalyst composition on growth and crack defects of large diamond single crystal under high temperature and pressure

Under the condition of 5.6 GPa and 1250–1450 ℃, the diamond single crystals are synthesized in a cubic anvil high-pressure and high-temperature apparatus. High-purity FeNiCo solvents or NiMnCo solvents are chosen as the catalysts. High-purity (99.99%) graphite powders selected as a carbon source. High-quality abrasive grade diamond single crystals with relatively developed (100) or (111) crystal planes are used as crystal seeds. The effects of catalyst composition on crack defects in diamond single crystals are studied carefully. Firstly, using FeNiCo and NiMnCo catalysts respectively, we carry out the diamond single crystal growth experiments. It is found that under the same crystal growth condition, the probability of crystal crack defects in diamond single crystals grown with FeNiCo catalyst is significantly higher than that of crystals grown with NiMnCo catalyst. We believe that this is related to the high viscosity, poor fluidity of FeNiCo catalyst melt, and the large specific surface area of the crystal during growth, which leads to its high requirements for the stability of growth conditions. Secondly, the relationship between the growth time and the limit weight gain speed of the diamond single crystal synthesized, respectively, by FeNiCo catalyst and NiMnCo catalyst are investigated. The results are shown below. 1) The limiting growth rate of diamond single crystal increases with the growth time going by. 2) In the same growth time, the limit growth rate of diamond crystal grown with NiMnCo catalyst is higher than that of diamond crystal grown with NiMnCo catalyst. Thirdly, by scanning electron microscopy (SEM), we calibrate the surface morphology of the synthesized diamond single crystal. The test results show that the diamond single crystal has a high surface flatness. Even for the crystals with crack defects in the interior, the surface flatness is still good. However, Fourier transform infrared (FTIR) measurements show that the nitrogen impurity content of diamond crystal grown by FeNiCo catalyst with crack defect is about 3.66×10<sup>–4</sup>. The content of nitrogen impurity in the crystal grown by NiMnCo catalyst without crack defect is about 4.88×10<sup>–4</sup>. The results show that there is no direct correlation between nitrogen impurity content and crack defects in diamond crystal.

Experimental Investigation and Numerical Simulation of the Fluidity of A356 Aluminum Alloy

The fluidity of A356 aluminum alloy was experimentally determined at the melt temperatures and vacuum degrees by a series of suction fluidity tests. In order to achieve different cooling rates during the test, quartz tubes, as well as stainless steel tubes, were employed as the fluidity channels. As the melt temperature increased from 650 to 730 °C, fluidity lengths either linearly increased from 26 to 36 cm or parabolically increased from 13 to 29 cm when quartz tubes or stainless steel tubes were employed, respectively. As the vacuum degree of the fluidity test increased from 0.005 to 0.03 MPa, fluidity increased from 25 to 43 cm in quartz tubes while the smaller increase in fluidity from 20 to 31 cm was observed in stainless steel tubes. Shorter fluidity lengths in stainless steel tubes than those in quartz tubes under the same fluidity measurement condition were due to faster solidification speed confirmed by microstructural analysis. In order to predict the fluidity of the A356 alloy obtained from the suction fluidity tests, a mathematical model was developed based on heat and mass transfer equations coupled with thermodynamic calculations by ChemApp software. The simulation results show good agreement with the fluidity length obtained in the present study. From a series of model calculations, the effects of casting parameters on the fluidity of the A356 melt were discussed.

Effect of Powder Mold Release Agent on Aluminum Alloy Melt Under Gravity Casting Conditions

To explore the influence of the release agent on the fluidity of the aluminum alloy melt, continuous experiments were carried out. First, through a flat mold filling experiment, the aluminum alloy melt and temperature change of the flat mold were obtained via measurements under the condition in which the mold was coated with a powder mold release agent. Stable and minimal, the excellent thermal insulation performance of heat transfer coefficient. Then, fluidity measurement experiments and computer simulation were conducted to verify the influence of the density change of the powder mold release agent on the fluidity of the aluminum alloy melt during the casting process. It was found that this relationship was affected by the temperature difference between the mold and aluminum alloy melt. The experimental results showed that changes in the powder mold release agent density changed the distribution density of its components through the thickness of the coating, thereby affecting the fluidity and thermal insulation function.

New β-type Ti-Zr-V-Nb alloys used for laser-based direct energy deposition: Design, microstructure, and properties

To develop new titanium alloys for laser-based direct energy deposition, Ti-Zr-V-Nb alloys were designed from a basic Ti60.94Zr39.06 congruent composition alloyed with constant V content and varying Nb contents. The microstructure and properties of the alloys, fabricated by laser-based direct energy deposition, were systematically studied. The results show that all as-deposited alloys consist of near-equiaxed β grains with multiple orientations. The difference is that the lattice parameter of the phase enlarges and its grain size reduces with increasing Nb content, which leads to a continuous increase in hardness, strength, wear and corrosion resistance. But the ductility shows a reverse variation due to the combination of enhanced solid solution strengthening and dislocation strengthening. Owing to the combined effect of fluidity and spreadability of melt, the surface roughness firstly decreases and then increases with the increase of Nb content. The optimized alloy with 3.91 at.% Nb exhibits a good match of mechanical, tribological, and chemical properties compared with Ti60.94Zr39.06 congruent alloy, being a promising candidate used for laser-based direct energy deposition.

Реологические свойства металлонаполненных систем на основе полиэтилена низкой плотности и алюминия

The paper considers the fundamental principles of the study of the rheological features of the melt flow of the initial low-density polyethylene and its filled compositions with aluminum powder, depending on the filler concentration, temperature and shear rate. To improve the compatibility of metal-polymer systems, a compatibilizer was used, which is a graft copolymer of low density polyethylene with 5 – 7 wt. % maleic anhydride content. First, the values of the melt flow rate of low density polyethylene were determined depending on the concentration of aluminum powder. The filler concentration was varied in the range 0.5 – 30 wt. %. It is shown that with the loading of 0.5 wt. % aluminum powder, the maximum fluidity of the composites melt is achieved. The flow curves, the dependence of the effective viscosity on the shear rate of the initial low-density polyethylene and composites with 0.5 wt. % and 5.0 wt. % content of aluminum powder were determined. The theoretical substantiation of the regularities of changes in rheological properties is given. The regularity of the change in the effective viscosity of the melt on temperature in Arrhenius coordinates has been established. On the basis of the curves obtained, the values of the activation energy of the viscous flow are determined. It was found that with the loading of the filler, an increase in the activation energy of the viscous flow is observed. A temperature-invariant characteristic of the viscosity properties of composites has been constructed, which makes it possible to predict the change in the value of this indicator at high shear rates, close to their processing by extrusion and injection molding. The developed materials have passed industrial testing at the METAK LLC enterprise in Azerbaijan.

Effect of cooling rate on fluidity and glass-forming ability of Zr-based amorphous alloys using different molds

Herein, the effect of cooling rate on fluidity and glass-forming ability (GFA) of the Zr41.2Ti13.8Cu12.5Ni10Be22.5 amorphous alloy is systematically studied by using a self-designed fluidity testing system and gravity casting. The molds are made of refractory steel, purity graphite and copper with spiral cavities. Moreover, the fluidity model of amorphous alloy is established and flow length is calculated based on the heat balance theory. Furthermore, the fluidity of amorphous alloy melt is quantitatively and qualitatively analyzed by comparing the calculated and experimentally measured flow lengths. The results reveal that the cooling capacity of mold mainly influences the flow length of amorphous alloy melt. Moreover, the discrepancy between experimentally measured and theoretically calculated flow lengths can be ascribed to the difference between actual and theoretical thermophysical parameters. X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM) reveal the traces of crystalline phase in samples prepared using steel and graphite molds, however, the crystalline phase is not observed in the case of copper mold. The results demonstrate that the mold material renders a certain influence on GFA of Zr41.2Ti13.8Cu12.5Ni10Be22.5 amorphous alloy.

Sintering Characteristics of Iron Ore Blends Containing High Proportions of Goethitic Ores

Two ore blends containing substantial channel iron deposit (CID) and Marra Mamba (MM) ores were assessed. The blends granulated well with addition of hydrated lime, which was found to improve the morphology and strength, and consequently the bed permeability of the resultant green granules. Compared with Blend 2 (a simulated industry blend), Blend 1, containing more MM and less CID ores was slightly less permeable but required similar moisture to achieve its optimum permeability. Both blends showed similar sintering characteristics as evidenced by sintering productivity and sinter quality, suggesting that Blend 1 was comparable to Blend 2. This was further supported by observations of sinter macro- and microstructure. Addition of hydrated lime improves the bed permeability and the formation and fluidity of sinter melt, consequently leading to improved sinter yield and strength along with sintering productivity. To achieve sinter return balance, the sinter return ratio had to decrease as the coke addition increased.

Non-isothermal Crystallization, Melting Behavior, Thermal Decomposition, Fluidity and Mechanical Properties of Melt Processed Poly(L-lactic acid) Nucleated by N,N'-Adipic Bis(piperonylic acid) Dihydrazide

Enhancing on the crystallization ability of poly(L-lactic acid) (PLLA) during practical processing is one of the most effective way to overcome the poor heat resistance. In this work, N,N '-adipic bis(piperonylic acid)dihydrazide (PAAH) was synthesized to be firstly used as a heterogeneous nucleating agent to evaluate its influence on the performances, including the crystallization, melting behavior, thermal stability, fluidity and mechanical property, of PLLA. The nucleation effect of PAAH was determined via the melt-crystallization of PLLA with various PAAH concentrations from 0.5 to 3 wt % at different cooling rates, as well as the different final melting temperature Tf . The results revealed that the PAAH could significantly accelerate the crystallization of PLLA in cooling, and the melt-crystallization peak shifted toward the higher temperature with increasing of PAAH concentration, resulting from an increase of nucleation density in PLLA matrix. Additionally, both the cooling rate and Tf were two critical factors to crystallization, a higher cooling rate could weaken the crystallization ability of PLLA/PAAH, and the 200°C was the optimum melting process temperature. For cold-crystallization, PAAH had an inhibition for the cold-crystallization of PLLA, but the cold-crystallization peak moved toward the higher temperature with increasing of heating rate because of thermal inertia. There existed only a single melting peak after melt-crystallization at cooling of 1°C, which further confirmed the advanced nucleation effect of PAAH, but the double-melting peaks appeared after isothermal crystallization at 110°C, which was attributed to the melt-recrystallization. The other measurements showed that, compared to the neat PLLA, the addition of PAAH decreased the thermal stability and tensile modulus of PLLA, but PLLA/PAAH samples had the better fluidity, the higher tensile strength and the longer elongation at break.

Effect of surface texture and ultrasonic on tensile property of 316L/PET dissimilar joints

316 L stainless steel (316 L) was successfully joined to PET as a result of laser lap welding from metal side. An excellent joint with a large interfacial bonding was achieved by optimizing laser power and pulse width. Effects of surface texture and ultrasonic on 316 L/PET joint strength were clarified. The results showed that mechanical and chemical bonding were the main connection methods of 316 L/PET joint. Mechanical anchoring effect was the key factor of surface texture to improve the joint strength. There were two positive effects for ultrasonic on 316 L/PET joint strength. On the one hand, the acoustic streaming effect improved the fluidity of PET melt and made it easier to fill the texture. On the other hand, ultrasonic cavitation reduced the bubble rate in the weld and generated high pressure. For received samples, the maximum tensile strength reached 45 MPa, which was close to 86.5 % of the strength of PET matrix.

Influence of reinforcing particle distribution on the casting characteristics of Al-SiCp composites

Abstract SiC particulate reinforced A356 alloy metal matrix composites (MMCs) are synthesized using intensive melt shearing. The effect of reinforcing particle distribution on the fluidity of cast A356/10 vol.% SiCp composites is studied. Spiral length representing the fluidity of the composite melt was measured and liquid flow and solidification behaviour were analysed. Improvement in the fluidity of composites is attributed to the uniform distribution of reinforcing particles by intensive melt shearing treatment. From the casting performance point of view, uniform dispersion of reinforcing particles achieved with the aid of intensive shearing improves the mechanical properties of A356/10 vol.% SiCp cast composites. Improved strength, rigidity and wear resistance of composites is attributed to the bulk homogeneity, significantly reducing casting defects.

MICROSTRUCTURE PERFORMANCE OF La2O3-MODIFIED TUNGSTEN INERT GAS CLAD COMPOSITE COATING

A hard coating free of obvious defects is produced on a Ti–6Al–4V (TC4) alloy substrate by means of tungsten inert gas clad (TIGC) of the Deloro22–WC–La2O3 mixed powders, which greatly increased the surface performance of the substrate. Test results indicated that large quantities of needle-shape precipitates were formed in the Deloro22–WC TIGC coating, increasing the microhardness significantly, and also lots of pores are produced in this coating, weakening the wear resistance. It was noted that a fine/compact microstructure is obtained in the Deloro22–WC–La2O3 TIGC coating, also the defects cannot be observed obviously. La2O3 addition can effectively improve the fluidity of melt and hinder the growth of grains in TIGC pool, favoring a fine/compact microstructure to be produced, and also improving the wear property of the TIGC coating.

The Effect of Zirconium on the Formation Processes of Layered Composition Materials of Titanium–Aluminum and Durability of Aluminum Clutch with Titanium

The processes of wetting and spreading of zirconium-doped aluminum over titanium were studied under the conditions of the formation of layered aluminum-titanium composite materials with the activation of the surface of titanium with flux based on K2TiF6 salt. It is established that zirconium, owing to an increase in viscosity and a decrease in the fluidity of the melt, reduces the area of ​​spreading of aluminum over titanium. Doping the intermetallic layer between aluminum and titanium with zirconium leads to an increase in the adhesion strength of the composite layers. The maximum values ​​of adhesion strength are observed at a process temperature of 950°C and a zirconium concentration of 0.25%.

Activating Precursors for Brazing Processes that Deposit Two Layers through Melting

We present the manufacturing process, by melting in a controlled environment, of specific alloys that have a benefic effect on the diffusion phenomena’s in the base material of the addition coated rods for brazing. The friable precursors obtained by melting are grinded with the purpose of integrating them in the coat of the rods, namely the addition material. The metallurgic activation activity of the precursors is enhanced by using them as nano-powders in the coat of the rods.Of major importance for deep joint capillary brazing are the fluidity and superficial tension of the melt - addition material, or, in case of non-ferrous alloys, the degree of de-oxidation of base materials. In order to improve the above mentioned characteristics, we made precursors type: 5o% Cu-45% Sn-5% P (CIF); 92% Cu-2% Si 6% P- (RAV). The batch design was done by two distinct melting processes, in high frequency currents (CIF) and electric arc (RAV) in a controlled environment. The melts were cast in graphite forms as loose briquettes. The briquettes thus obtained were analyzed structurally and sclerometrically, and after testing, they were grinded in planetary mills until we obtained nano-powders. The resulting powders will be used, as required, to prepare brazing sheaths.

Characterization of the Fluidity of the Ultrasonic Plasticized Polymer Melt by Spiral Flow Testing under Micro-Scale.

The fluidity of a molten polymer plasticized by ultrasonic vibration was characterized by spiral flow testing based on an Archimedes spiral mold with microchannels. Mold inserts with various channel depths from 250 to 750 µm were designed and fabricated to represent the size effect under micro-scale. The effect of ultrasonic plasticizing parameters and the mold temperature on the flow length was studied to determine the rheological nature of polymers and control parameters. The results showed that the flow length decreased with reduced channel depth due to the size effect. By increasing ultrasonic amplitude, ultrasonic action time, plasticizing pressure, and mold temperature, the flow length could be significantly increased for both the amorphous polymer polymethyl methacrylate (PMMA) and the semi-crystalline polymers polypropylene (PP) and polyamide 66 (PA66). The enhanced fluidity of the ultrasonic plasticized polymer melt could be attributed to the significantly reduced shear viscosity.

Micro-injection molding using a polymer coated mold

We applied an insulating polymer layer to the surface of mold cavity to injection-mold large plastic parts with a microsized thickness. Polyimide (PI) was coated on the mold wall using spray coating method. A thin light guide plate (LGP) was designed and fabricated via micro-injection molding. The polymeric coating layer could enhance the fluidity of polymer melt in the cavity during filling stage by minimizing the formation of the skin layer during injection molding. The surface roughness and pattern transfer rate of the LGPs were analyzed experimentally. In addition, numerical simulation was carried out to understand the insulation effect of the layer in the injection molding.

Application of SHS process for fabrication of copper-titanium silicon carbide composite (Cu-Ti3SiC2)

The results of the study of possibility of using a simple, energy-saving powder technology, based on the process of self-propagating high-temperature synthesis (SHS) or combustion synthesis, for the single-stage preparation of Cu-Ti3SiC2 composite from relatively inexpensive powders of its constituent elements are presented. Placing the Cu powder briquette between two adjacent charge briquettes 3Ti + 1,25Si + 2C for the synthesis of MAX-phase of Ti3SiC2, it was possible to use a large heat effect of SHS for melting the Cu briquette and infiltration of Ti3SiC2 porous skeleton by Cu melt. For the successful realization of this process, it is necessary to ensure the required fluidity of Cu melt and wetting Ti3SiC2 through a high temperature of the melt and the alloying of the melt with silicon, as well as to ensure the delay in the transfer of the melt into pores of SHS product.

Effect of Melt Purification on Microstructure and Mechanical Properties of 3003 Aluminum Alloy

The 3003 aluminum alloy melt was treated with three types of melt purification, and the effect of melt purification on the microstructure and mechanical properties of the alloy was investigated. The results show that the impurity content of 3003 aluminum alloy with untreated (UT) reached 0.6801 %. After the process of conventional purification treatment (CPT) and efficient purification treatment (EPT), the impurity content of the alloy decreased significantly, and the fluidity of aluminum melt was improved. Finely dispersed inclusions particles can promote nucleation, refine the size of the cast crystal. Alloy strength and plasticity have increased using the process of CPT and EPT, in particular, EPT is the most obvious. It shows that the purity of aluminum melt plays a key role in the mechanical properties of the alloy.