Powder Extrusion Research Articles

Significant Corrosion Resistance in an Ultrafine-Grained Al6063 Alloy with a Bimodal Grain-Size Distribution through a Self-Anodic Protection Mechanism

The bimodal microstructures of Al6063 consisting of 15, 30, and 45 vol. % coarse-grained (CG) bands within the ultrafine-grained (UFG) matrix were synthesized via blending of high-energy mechanically milled powders with unmilled powders followed by hot powder extrusion. The corrosion behavior of the bimodal specimens was assessed by means of polarization, steady-state cyclic polarization and impedance tests, whereas their microstructural features and corrosion products were examined using optical microscopy (OM), scanning transmission electron microscopy (STEM), field emission scanning electron microscopy (FE-SEM), electron backscattered diffraction (EBSD), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) techniques. The bimodal Al6063 containing 15 vol. % CG phase exhibits the highest corrosion resistance among the bimodal microstructures and even superior electrochemical behavior compared with the plain UFG and CG materials in the 3.5% NaCl solution. The enhanced corrosion resistance is attributed to the optimum cathode to anode surface area ratio that gives rise to the formation of an effective galvanic couple between CG areas and the UFG matrix. The operational galvanic coupling leads to the domination of a “self-anodic protection system” on bimodal microstructure and consequently forms a uniform thick protective passive layer over it. In contrast, the 45 vol. % CG bimodal specimen shows the least corrosion resistance due to the catastrophic galvanic corrosion in UFG regions. The observed results for UFG Al6063 suggest that metallurgical tailoring of the grain structure in terms of bimodal microstructures leads to simultaneous enhancement in the electrochemical behavior and mechanical properties of passivable alloys that are usually inversely correlated. The mechanism of self-anodic protection for passivable metals with bimodal microstructures is discussed here for the first time.

Highly stable microtubular cells for portable solid oxide fuel cell applications

In this work, extruded support tubes based on Nickel Oxide-YSZ (yttria stabilized-zirconia) were manufactured by Powder Extrusion Moulding (PEM). An YSZ layer is then deposited by dip coating as the electrolyte and subsequently, standard La0.8Sr0.2MnO3-δ (LSM)/YSZ composites were deposited by dip coating as oxygen electrodes. Microstructure of the anode support was optimized in order to achieve the maximum fuel utilization and as a consequence, a high performance of the cells. Experiments as a function of the fuel composition showed power densities above 500 mWcm−2 at 800°C at 0.7V, with high fuel utilization (∼75%). Long-term durability studies were also performed for a period above 1000hours. The experiment was conducted at 800°C using pure humidified hydrogen at a fixed voltage of 0.8V. It was observed that the current density of the cell is significantly evolving during the initial period of about 100hours, as a consequence of reconditioning of nickel particles at the anode support. Once the system is stabilized, no degradation was observed up to 1000hours under operating conditions, obtaining current densities in the range of 400 mAcm−2 at 0.8V and 800°C.

Effects of heat treatment on the microstructure and mechanical properties of in situ inhomogeneous TiBw/Ti6Al4V composite fabricated by pre–sintering and canned powder extrusion

Heat treatments with different parameters were performed on the as–extruded 4.5 vol% TiBw/Ti6Al4V composite rods with TiBw columnar reinforced structure fabricated by pre–sintering and canned powder extrusion to pursue further performance optimization for high temperature applications. Microstructure observations reflected that the fraction of martensite α′ phase, which was transformed from high–temperature β phase after water quenching, increased with the rising solution temperature and then stabilized above 1000 °C, resulting in a significant enhancement in hardness/strength of the composite; both the fraction and size of the dispersed (α + β) phases, which were decomposed from martensite α′ phase during aging, increased monotonously with the rising aging temperature, leading to an effective improvement of the toughness with sacrificing strength moderately. Under the treatment of water quenching at 1000 °C and aging at 600 °C for 6 h, a plus 11% increase in ultimate strength could be achieved in the heat–treated TiBw/Ti6Al4V than that in the as–extruded below 600 °C on the premise of good interface bonding between TiBw and Ti matrix, resulting in 1520 MPa at ambient temperature, 1173 MPa at 400 °C and 947 MPa at 500 °C. Optimizing matrix alloys/composition is suggested to retard interface debonding arising from the softening of Ti matrix for further strengthening above 600 °C.

CP Ti Fabricated by Low Temperature Extrusion of HDH Powder: Application in Dentistry

Powder metallurgy (PM) commercial purity titanium (CP Ti) was fabricated and studied, with an aim of utilization for dental application. PM CP Ti was manufactured using a cost effective approach, where affordable hydrogenation–dehydrogenation (HDH) process Ti 99.4 wt.% powder was consolidated via the following sequence of PM techniques: cold isostatic pressing, warm vacuum pressing at 420 °C and warm direct extrusion at 500 °C. The paper presents the first studies on processing, microstructure, testing of mechanical properties, fatigue performance and bonding strength with different veneer coatings. By employed consolidation process sound material with low porosity (1.5%) and sustained oxygen content (0.21 wt.%) was attained. The tensile properties obtained for PM CP Ti (UTS = 701 MPa, YS0.2 = 512 MPa, ε = 13 %) were improved over to those for cast / milled CP Ti Grade 4 reference, the material commonly used in dentistry. Tested using the ISO 14801 standard for dental implants, the samples machined from PM CP Ti showed fatigue performance similar to CP Ti Grade 4. PM CP Ti used as a metal base material in restoration metal – ceramic systems showed very good bond strength with three commercially available veneering ceramics and complied with the ISO 9693 standard. Within the limitations of this paper, the preliminary results demonstrated that performance of economic PM CP Ti is equal or superior to CP Ti Grade 4 reference material and it can be used in prosthodontics.

Porous Ni-YSZ planar anodes by powder extrusion moulding employing PMMA as pore former

Porous Ni-YSZ planar supports to be used as anodes in solid oxide fuel cells were obtained by powder extrusion moulding. The addition of poly-methyl methacrylate beads as pore-former provided an improved gas flow through the anode. Feedstocks were prepared employing a multicomponent binder based on polypropylene, paraffin wax and stearic acid in a volume ratio 42/42/16. The effect of particle size was also studied using two kinds of NiO. Poly-methyl methacrylate substituted the powder loading in a 5 vol.-% to increase the porosity. The thickness of green anodes was close to 1 mm, and subsequently removal of the binder was performed by a combined cycle: solvent and thermal debinding. After sintering and reduction stages, nickel presence was confirmed by X-ray diffraction. The porosity reached employing fine NiO was similar than employing coarse one (16%), however the mechanical strength of this anode was higher (∼140 MPa) and more suitable for the application.

Effect of silicon carbide nanoparticles on hot deformation of ultrafine-grained aluminium nanocomposites prepared by hot powder extrusion process

The flow behaviour of Al–SiC nanocomposites prepared by mechanical milling and hot powder extrusion methods was studied at different temperatures (350–500°C) and strain rates (0.005–0.5 s−1). The flow of the Powder metallurgy nanocomposites exhibited a peak stress followed by a dynamic flow softening behaviour. It was shown that mechanical milling increased high-temperature strain rate sensitivity of ultrafine-grained (UFG) aluminium while decreasing its flow dependence to temperature. Constitutive analysis of the hot deformation process by Zener–Hollomon parameter (Z) also indicated a remarkable increase in the deformation activation energy (about 40%). Likewise, SiC nanoparticles (up to 2vol.-%) were shown to contribute in the high-temperature strengthening of UFG aluminium with a significant effect on its thermal stability. The findings were explained based on the pinning effect of hard nanoparticles on grain boundaries and mobile dislocations as well as microstructure stabilisation at elevated temperatures.

Microstructure and mechanical properties of equimolar FeCoCrNi high entropy alloy prepared via powder extrusion

An equiatomic FeCoCrNi high alloy (HEA) with both high tensile strength and ductility was produced by a powder metallurgy (P/M) method. The P/M process includes a gas atomization and a hot extrusion of pre-alloyed HEA powder. Microstructures and mechanical properties were characterized using optical microscopy (OP), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and tensile tests. The results show that the P/M FeCoCrNi HEA has a single face centered cubic (fcc) structure and an equiaxed microstructure. No obvious porosity and brittle intermetallic phase was found. The as-extruded alloy exhibits a very high tensile strength of 712.5 MPa, and still maintains an elongation as high as 56%. The improvement of the tensile properties is caused by the solid solution strengthening, grain boundary strengthening and homogenous microstructure. Therefore, the powder hot extrusion can be considered as a promising way for preparing large-sized HEAs with high mechanical properties.

Microstructure-property relations in as-atomized and as-extruded Sn-Cu (-Ag) solder alloys

Rapidly solidified Sn-based solder alloys can provide metallurgical features such as low segregation and fine intermetallic compounds (IMCs). These features can be obtained in a controlled way by Impulse Atomization that provides powders of various sizes corresponding to a variety of cooling rates and undercoolings to which diverse microstructures are associated. In the present investigation, rapid solidification of Sn-0.7 wt%Cu and Sn-0.7 wt%Cu-3.0 wt%Ag alloys have been examined through the production of a wide size range of impulse atomized powders. The microstructures and hardness resulting from the generated powders have been compared with those of directionally solidified (DS) specimens. Regular cells > dendrites and reverse dendrites > cells transitions were identified, and high-speed eutectic cells were found to prevail for the examined Sn-0.7 wt%Cu powders of size smaller than 300 μm. It is shown that the Vickers microhardness of the ternary Sn-3.0 wt%Ag-0.7 wt%Cu alloy is directly influenced by both the presence of tertiary dendrite arms (λ3) and the cooling rate/powder size dependent eutectic fraction. Also, compaction and extrusion of the atomized powders were carried out in order to consolidate the samples so that tensile tests could be carried out. Tensile strength and ductility of samples corresponding to different powder sizes and compositions were thus measured and the results are found to be consistent with their microstructures.

Obtenção de amidos termoplásticos para a extrusão de pós cerâmicos

Resumo Polímeros termoplásticos podem ser utilizados como veículo orgânico (VO) em processos de conformação de peças cerâmicas por extrusão. Neste contexto, termoplásticos à base de amido surgem como uma alternativa sustentável ao emprego das poliolefinas convencionalmente utilizadas na formulação de pastas cerâmicas. O passo inicial para o desenvolvimento de um feedstock (carga extrudável) é a seleção adequada do sistema polimérico ligante, o qual é responsável por conferir propriedades reológicas adequadas durante o processamento. O presente trabalho se propôs a caracterizar termoplásticos a base de amido obtidos na presença de ácido cítrico e avaliar o potencial de utilização destes materiais na extrusão de pós cerâmicos. A processabilidade das pré-misturas de amido foi avaliada em extrusora dupla-rosca e em reômetro de torque. A variação dos teores de água e glicerol na composição das pré-misturas de amido influenciou significativamente as interações entre as cadeias poliméricas, promovendo alterações nos valores de densidade e de viscosidade para a maior parte das amostras analisadas. O amido foi parcialmente esterificado como efeito da ação do ácido cítrico no sistema. Dentre as formulações investigadas, a amostra hidratada e processada com 34% p/p de glicerol (H-34) foi a que apresentou as melhores propriedades de pasta, podendo ser futuramente empregada em processos de conformação de pós cerâmicos.

Highly CO2 sensitive extruded fluorescent plastic indicator film based on HPTS.

Highly-sensitive optical fluorescent extruded plastic films are reported for the detection of gaseous and dissolved CO2. The pH-sensitive fluorescent dye used is 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS, PTS(-)) coated on the surface of hydrophilic fumed silica and the base is tetrabutylammonium hydroxide (TBAH). The above components are used to create an HPTS pigment (i.e. HPTS/SiO2/TBAH) with a high CO2 sensitivity (%CO2 (S = 1/2) = 0.16%) and fast 50% response (t50↓) = 2 s and recovery (t50↑) = 5 s times. Highly CO2-sensitive plastic films are then fabricated, via the extrusion of the HPTS pigment powder in low-density polyethylene (LDPE). As with the HPTS-pigment, the luminescence intensity (at 515 nm) and absorbance (at 475 nm) of the HPTS plastic film decreases as the %CO2 in the ambient gas phase increases. The HPTS plastic film exhibits a high CO2 sensitivity, %CO2 (S = 1/2), of 0.29%, but a response time <2 min and recovery time <40 min, which is slower than that of the HPTS pigment. The HPTS plastic film is very stable under ambient conditions, (with a shelf life >six month when stored in the dark but under otherwise ambient conditions). Moreover, the HPTS-LDPE film is stable in water, salt solution and even in acid (pH = 2), and in each of these media it can be used to detect dissolved CO2.

High-performance Ni–YSZ thin-walled microtubes for anode-supported solid oxide fuel cells obtained by powder extrusion moulding

A fast near-net-shape and cost-effective manufacturing method (PEM) were applied to produce Ni–YSZ thin-walled microtubes for anode-supported SOFCs applications. The effects of NiO particle size on rheology and final microstructure are addressed.

A Processing Map for Hot Deformation of an Ultrafine-Grained Aluminum-Magnesium-Silicon Alloy Prepared by Mechanical Milling and Hot Extrusion

Uniaxial compression test at different temperatures [573 K to 723 K (300 °C to 450 °C)] and strain rates (0.01 to 1 s−1) was employed to study the hot deformation behavior of an ultrafine-grained (UFG) Al6063 alloy prepared by the powder metallurgy route. The UFG alloy with an average grain size of ~0.3 µm was prepared by mechanical milling of a gas-atomized aluminum alloy powder for 20 hours followed by hot powder extrusion at 723 K (450 °C). To elaborate the effect of grain size, the aluminum alloy powder was extruded without mechanical milling to attain a coarse-grained (CG) structure with an average grain size of about 2.2 µm. By employing the dynamic materials model, processing maps for the hot deformation of the UFG and CG Al alloy were constructed. For investigation of microstructural evolutions and deformation instability occurring upon hot working, optical microscopy, scanning electron microscopy coupled with electron backscattered diffraction and transmission electron microscopy were utilized. It is shown that the grain refinement increases the deformation flow stress while reducing the strain hardening and power dissipation efficiency during the deformation process at the elevated temperatures. Restoration mechanisms, including dynamic recovery and recrystallization are demonstrated to control microstructural evolutions and thus the deformation behavior. Coarsening of the grain structure in the UFG alloy is illustrated, particularly when the deformation is performed at high temperatures and low strain rates. The manifestations of instability are observed in the form of cracking and void formation.

Fabrication of miniature hollow helical gear by powder extrusion of gas-atomized Zn-22wt%Al powder

A powder extrusion pr°Cess based on the superplastic behavior of Zn-22wt%Al eutectoid alloy is proposed as a means to achieve fine microstructures in the manufacture of miniature hollow helical gears by reducing the forming load. In this paper, the Zn-22wt%Al powder compromising fine spherical particles is first produced by gas atomization, compacted, and then consolidated by solution heat treatment. This is found to produce billets with a very fine-grained microstructure, which were subsequently utilized in extruding helical gears at a temperature of 250°C and a strain rate of 2.36×10−3s−1. The specifications of these helical gears are: module, 0.2; number of teeth, 12; helix angle, 20°; pitch diameter, 2.55 mm; and internal diameter, 1.5 mm. An investigation of the mechanical properties of the extruded gears through Vickers hardness test and extrusion load measurement, and SEM observation, confirms the effectiveness of superplastic Zn-22wt%Al eutectoid alloy powders for the production of miniature hollow helical gears.

Mixing quality of powder-liquid mixtures studied by near infrared spectroscopy and colorimetry

In many industries, mixing powder with a low amount of liquid is a frequently used process step, e.g. in order to generate agglomerate/granule product structures or for sintering and extrusion of wet powders or pastes. There are still great difficulties in achieving a homogeneous mixture due to local agglomeration and lump formation. A new mixing methodology has therefore been developed, in which the liquid is transformed into a solid powder by spray chilling, generating so-called powder-liquids. These powder-liquids are then mixed with other dry powders.An even liquid distribution, as well as the related even distribution of functional components in the final product is of high relevance. We thus aimed to evaluate the mixing quality of such powder/powder-liquid mixtures studied by near infrared (NIR) spectroscopy and colorimetry. For this purpose we quantified the homogeneity of fat based powder-liquids mixed with flour. NIRS is a well-recognized quantification method that successfully has been used to analyze powder mixtures before, while colorimetry is a method less used for such an application. The results demonstrated that both methods are applicable for quantifying the mixing behavior of such powder mixtures. We showed that cheap, easy and fast colorimetry is as reliable as NIRS measurements and hence can be a first choice validation method in industry. Comparing the powder-liquid mixing with spraying the liquid directly into the powders, the powder-liquids mixed faster and resulted in better homogeneity. Our results support the use of powder-liquids to process new highly homogeneous products required in functional foods or pharmaceutical products.

Cyclic CO2 capture characteristics of a pellet derived from sol-gel CaO powder with Ca12Al14O33 support

A novel calcium-based pellet was prepared by extrusion of sol-gel CaO powder and cement with high aluminum-based content. Limestone was used for comparison. The cyclic CO2 capture performance and carbonation kinetics of the sorbents were investigated in a thermogravimetric analyzer (TGA). The changes in phase and microstructure were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer Emmet Teller (BET) surface area, respectively. The results indicate that the pellet consisted of CaO and Ca12Al14O33 after initial calcination. Limestone reactivity decreased dramatically with the increase in the cycle number, whereas the pellet showed a relatively stable cyclic CO2 capture performance with high reactivity. The CO2 capture capacity of the pellet achieved 0.43 g CO2/g sorbent after 50 cycles at 650 °C and 850 °C for carbonation and calcination, respectively. Moreover, the pellet obtained fast carbonation rates with slight decay after multiple cycles. The porous microstructure of the pellet contributed to the high reactivity of the sorbent during high temperature reactions, and the support material of Ca12Al14O33, enhanced the cyclic durability of the calcium-based sorbents.

J0330304 発砲アルミ押出し材の積層

To produce aluminum foams with complicated shape, an additive process of aluminum foam is proposed. Experiments of producing aluminum foam by extruding and foaming of precursor from heated die are conduced to deposit aluminum foam on a stage for the additive process. The precursor is made by hot powder extrusion of A6061 and TiH_2. The speed and the die temperature in the extruding and foaming of precursor are examined. The experimental results show the density distribution within the aluminum foam.

Structural and magnetic properties of backward extruded Nd–Fe–B ring magnets made by different punch chamfer radius

Radially oriented Nd–Fe–B ring magnets were prepared by backward extrusion of MQ-C powder. The punch chamfer radius has a great impact on the microstructure and magnetic properties of the ring magnet. With the chamfer radius changing from 2, 5 to 8 mm, the cracks in the inner wall decrease obviously while the crystallographic alignment drops. Furthermore, the mechanism of c-axis growth was suggested to be a combination of shear deformation in the corner and solution-precipitation under the stress parallel to radial direction. The alignment drops on the top of ring because the grains grow freely and some textured grains grow through nucleation and recrystallization. In the present work, the optimal punch chamfer radius is found to be 2 mm, and in this case, the remanence, coercivity, and maximum energy product of the ring magnet achieve 1.4 T, 670 kJ·m, and 342 kJ·m, respectively.

Annealing Effects in Mg-Y-Zn Alloys Prepared by Powder Metallurgy and by Squeeze Casting

Response to isochronal annealing up to 440°C was investigated in squeeze cast Mg2Y1Zn alloy and in the same alloy prepared by powder metallurgy and extrusion at 280°C (PM). Electrical resistivity measurements at 77 K and at room temperature after each annealing step and differential scanning calorimetry performed at various heating rates characterized phase changes proceeding during the heat treatments. Transmission and scanning electron microscopy and optical microscopy revealed ribbons of a long-period ordered structure and a relatively high density of stacking faults in grain interiors of the cast alloy having the grain size of ~50 μm. Well pronounced subgrains were observed in the PM prepared alloy. Secondary phase particles decorate grain boundaries in this alloy. Electrical resistivity response of the cast alloy to isochronal annealing up to 440°C shows three precipitation processes, whereas one significant process was revealed in the PM alloy. Activation energies of precipitation processes were determined. Microhardness exhibits good thermal stability in the whole temperature range in the cast alloy and up to 360°C in the PM alloy.

Design of industrially scalable microtubular solid oxide fuel cells based on an extruded support

The current work describes the adaptation of an existing lab-scale cell production method for an anode supported microtubular solid oxide fuel cell to an industrially ready and easily scalable method using extruded supports. For this purpose, Ni–YSZ (yttria stabilized zirconia) anode is firstly manufactured by Powder Extrusion Moulding (PEM). Feedstock composition, extruding parameters and binder removal procedure are adapted to obtain the tubular supports. The final conditions for this process were: feedstock solid load of 65 vol%; a combination of solvent debinding in heptane and thermal debinding at 600 °C. Subsequently, the YSZ electrolyte layer is deposited by dip coating and the sintering parameters are optimized to achieve a dense layer at 1500 °C during 2 h. For the cathode, an LSM (lanthanum strontium manganite)–YSZ layer with an active area of ∼1 cm2 is deposited by dip coating. Finally, the electrochemical performance of the cell is measured using pure humidified hydrogen as fuel. The measured power density of the cell at 0.5 V was 0.7 W cm−2 at 850 °C.

The Effect of Sc on the Microstructure and Mechanical Properties of Hypereutectic Al-Si Alloy Fabricated by a Gas Atomization Process

In this study, the effect of Sc addition on the microstructure and mechanical properties of Al-20Si alloys fabricated by extrusion of powders was investigated. The Al-Si-(Sc) powders produced by high pressure gas atomization were used in starting materials. The microstructure and structural characterization were performed by optical microscopy (OM), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDS). Mechanical properties of extruded bars were investigated by micro hardness test, tensile test and wear test. With increasing the Sc contents in Al-Si alloys, mechanical properties were significantly increased. These enhanced mechanical properties can be explained based on the refinement of primary Si due to the suppression of growth of primary Si by the well-surrounded and uniformly distributed Sc. Keywords: Al-Si Alloys powder technology, gas atomizer, hypereutectic, scandium, Si particle.