Conventional Powder Metallurgy Route Research Articles

Grain structure tailoring strategy for heterogeneous lamella SiCp/2024Al composites with exceptional strength-ductility synergy

In this work, a novel grain structure tailoring strategy using one-stepped planetary ball milling, different from conventional powder metallurgy routes that pre-prepared components with different microstructures and then mixed them up, was implemented to fabricate micro- and nano-sized SiC particles (m- & n-SiCp)/2024Al composites with heterogeneous lamella structure. The controllable transformation from homogeneous to heterogeneous grain structures is achieved via nonuniformly distributed n-SiCps induced local grain refinement. Heterogeneous lamella composites exhibit a superior modulus-strength-ductility synergy of 95.3 GPa in Young's modulus, 750.7 MPa in tensile strength and 4.9 % in uniform elongation, particularly with no less than 145 % and 175 % improvements in ductility and toughness, compared with homogeneous composites. Compressive stress relaxation experiments were conducted to reveal the structural dependence of plastic deformation behaviors. Sustainedly rising hetero-deformation induced (HDI) stress produced by extra geometrically necessary dislocation (GND) accumulation at heterogeneous soft/hard domain interfaces and sequential activation of multiple dislocation mediated mechanisms based on load transfer in heterogeneous lamella composites contribute to the enhanced strain hardening capacity, which offers intrinsic toughening. Also, extrinsic toughening originates from enhanced microcrack multiplication and crack-tip blunting.

Production and Characterization of Aluminum Reinforced with SiC Nanoparticles

Aluminum matrix nanocomposites have been the subject of much attention due to their extraordinary mechanical properties and thermal stability. This research focuses on producing and characterizing an aluminum matrix reinforced with silicon carbide (SiC) nanometric particles. The conventional powder metallurgy route was used to produce the nanocomposites, and the dispersion and mixing process was carried out by ultrasonication. The conditions of the dispersion and the volume fraction of the SiC were evaluated in the production of the nanocomposites. Microstructural characterization was carried out using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). Mechanical characterization was carried out using hardness and tensile tests. The dispersion agent was investigated, and isopropanol leads to better dispersion with fewer agglomerates. Increasing the volume fraction of the reinforcement improves the hardness of the nanocomposites. However, greater agglomeration of the reinforcement is observed for larger volume fractions. The greatest increase in hardness (77% increase compared to the hardness of the Al matrix) is obtained with 1.0 vol. % of SiC, corresponding to the sample with the best dispersion. The mechanical characterization through tensile tests attests to the effect of the reinforcement on the Al matrix. The main strengthening mechanisms identified were the load transfer, the texture hardening, Orowan strengthening, and the increase in the density of dislocations in the nanocomposites.

In Vitro and In Vivo Bone Regeneration Assessment of Titanium-Doped Waste Eggshell-Derived Hydroxyapatite in the Animal Model.

In this work, a titanium-doped hydroxyapatite (HAp) scaffold was produced from two different sources (natural eggshell and laboratory-grade reagents) to compare the efficacy of natural and synthetic resources of HAp materials on new bone regeneration. This comparative study also reports the effect of Ti doping on the physical, mechanical, and in vitro as well as in vivo biological properties of the HAp scaffold. Pellets were prepared in the conventional powder metallurgy route, compacted, and sintered at 900 °C, showing sufficient porosity for bony ingrowth. The physical-mechanical characterizations were performed by density, porosity evaluation, XRD, FTIR, SEM analysis, and hardness measurement. In vitro interactions were evaluated by bactericidal assay, hemolysis, MTT assay, and interaction with simulated body fluid. All categories of pellets showed absolute nonhemolytic and nontoxic character. Furthermore, significant apatite formation was observed on the Ti-doped HAp samples in the simulated body fluid immersion study. The developed porous pellets were implanted to assess the bone defect healing in the femoral condyle of healthy rabbits. A 2 month study after implantation showed no marked inflammatory reaction for any samples. Radiological analysis, histological analysis, SEM analysis, and oxytetracycline labeling studies depicted better invasion of mature osseous tissue in the pores of doped eggshell-derived HAp scaffolds as compared to the undoped HAp, and laboratory-made samples. Quantification using oxytetracycline labeling depicted 59.31 ± 1.89% new bone formation for Ti-doped eggshell HAp as compared to Ti-doped pure HAp (54.41 ± 1.93) and other undoped samples. Histological studies showed the presence of abundant osteoblastic and osteoclastic cells in Ti-doped eggshell HAp in contrast to other samples. Radiological and SEM data also showed similar results. The results indicated that Ti-doped biosourced HAp samples have good biocompatibility, new bone-forming ability, and could be used as a bone grafting material in orthopedic surgery.

Investigation on compaction pressure and sintering temperature suitable for Nimonic 90 superalloy

Fabrication of high strength, high temperature and corrosion resistant materials provide much assistance in aerospace, automotive, chemical and oil industries, as they have to withstand severe operating conditions. Traditionally, superalloys are widely used under these conditions that are prepared by casting method. Nowadays, powder metallurgy technique is gaining importance for preparing superalloys because of its capability of making homogeneous microstructure with near-net-shape. In this significant context, the processing of Nimonic 90 superalloy sample using conventional powder metallurgy route is discussed. Desired amount of metallic powders by weight percent are blended, uni-axially pressed and sintered in tubular vacuum furnace at different sintering temperatures. The influence of compaction pressure and sintering temperature on density, hardness, surface roughness and electrical resistivity is determined. Surface porosity and the effect of sintering temperature on the microstructural features are analyzed noticeably. It is found that the compaction pressure of 700 MPa and the sintering temperature of 1365℃ are the most desirable process parameters, essentially required for synthesizing the Nimonic 90 superalloy. Sample prepared under these conditions has achieved the desired density and hardness, as that of the standard Nimonic 90 alloy. Thus, the study paves the way for future researchers to appropriately identify the conditions suitable for preparing the superalloys as per the application needed.

Microstructural Characterization of Al/CNTs Nanocomposites after Cold Rolling.

The deformation behaviour of aluminium reinforced by carbon nanotubes (Al/CNTs) nanocomposites during cold rolling was investigated in this work. Deformation processes after production by conventional powder metallurgy routes may be an efficient approach to improve the microstructure and mechanical properties by decreasing the porosity. Metal matrix nanocomposites have enormous potential to produce advanced components, mainly in the mobility industry, with powder metallurgy being one of the most reported production processes. For this reason, it is increasingly important to study the deformation behaviour of nanocomposites. In this context, nanocomposites were produced via powder metallurgy. Advanced characterization techniques carried out the microstructural characterization of the as-received powders and produced nanocomposites. The microstructural characterization of the as-received powders and produced nanocomposites was carried out through optical microscopy (OM), and scanning and transmission electron microscopy (SEM and TEM), complemented by electron backscattered diffraction (EBSD). The powder metallurgy route followed by cold rolling is reliable for Al/CNTs nanocomposites. The microstructural characterization shows that the nanocomposites exhibit a different crystallographic orientation than the Al matrix. CNTs in the matrix influence grain rotation during sintering and deformation. Mechanical characterization revealed that during deformation, there is an initial decrease in the hardness and tensile strength for the Al/CNTs and Al matrix. The initial decrease was attributed to the Bauschinger effect being more significant for the nanocomposites. The difference in the mechanical properties of the nanocomposites and Al matrix was attributed to distinct texture evolution during cold rolling.

Development of WC-NiCrMo hardmetals

The demand for improved components with a wide range of properties is a reality in today's hardmetal market. Furthermore, supply shortages of raw materials such as W and especially Co resulted in rapid price fluctuations. Combined with stricter environmental legislation and health protection, these facts prompt the demand for alternative or modified binders. Therefore, in this work, WC-NiCrMo composites were developed as a potential alternative to conventional WC-Co hardmetals. To evaluate this new hardmetal composite, prototypes of submicrometric WC with approximately 15 vol% of NiCrMo binder were produced by conventional powder metallurgy route. Thermodynamic assessment, wettability testing and constant heating rate dilatometry were performed to design an adequate sintering route. A detailed characterization of the mechanical properties (Young's modulus, Vickers hardness and fracture toughness), together with corrosion resistance assessment (OCP, polarization curves, EIS) and abrasive wear (ball-cratering) resistance evaluation were undertaken. Good wettability of molten NiCrMo binder on WC surface was observed, and highly dense compacts could be successfully attained by gas pressure sintering. The new WC-NiCrMo composite has lower hardness but higher corrosion resistance and better wear resistance than the conventional WC-Co hardmetals.

New ternary powder metallurgy Ti alloys via eutectoid and isomorphous beta stabilisers additions

A group of new ternary Ti alloys bearing eutectoid and isomorphous beta stabilising elements was created to be manufactured through the conventional powder metallurgy route. The effect of the simultaneous addition of the same amount of Mn and Nb on the manufacturability, properties, and hardening behaviour was investigated. The ternary alloys are composed of the α-Ti and β-Ti phases and have a lamellar microstructure resulting from the slow cooling upon sintering. However, the size of the equiaxed α grains and of the α + β lamellae is monotonically reduced, especially the interlamellar spacing, as the amount of alloying elements increases. Due to their physical properties, Mn enhances and Nb hinders densification during sintering resulting in a decreasing trend of the relative density with the alloying elements content. Consequently, the resistance to plastic deformation increases (UTS, 514–726 MPa), the ductility decreases (elongation, 13.2–2.6%), and the fracture mode changes from intergranular to transgranular. The new ternary alloys share the same hardening mechanism, but the amount of deformation after necking is, generally, higher for lower amounts of Mn and Nb.

Polymer‐derived β‐SiAlON:Eu2+ phosphors

AbstractA series of β‐SiAlON:Eu2+ phosphors were synthesized from single‐source precursors, perhydropolysilazane chemically modified with Al(OCH(CH3)2)3, AlCl3, and EuCl2. The single‐source precursors were converted to β‐SiAlON:Eu2+ phosphors by pyrolysis under flowing N2 or NH3 at 1000°C, followed by heat treatment at 1800°C under an N2 gas pressure at 980 kPa. By varying the molar ratio of the chemical modifiers, β‐SiAlON:Eu2+ with the compositions close to the theoretical ones expressed as Si6−zAlzOz−2yN8−z+2y:yEu2+ were synthesized, where the z values and Eu2+ contents were controlled in the ranges of .44–.78 and .35–1.48 mol%, respectively. The polymer‐derived β‐SiAlON:Eu2+ phosphors exhibited green emission under excitation at 460 nm attributed to the 4f7–4f6(7f3)5d1 transition of dopant Eu2+. High‐angle annular dark‐field‐scanning transmission microscopy analysis confirmed that the doped‐Eu2+ existed interstitially within the channels along the c axis of host β‐SiAlON. Compared with the conventional powder metallurgy route, the polymer‐derived ceramic route in this study offers some advantages in the grain growth of host β‐SiAlON and photoluminescence properties in terms of green emission intensity under excitation at 460 nm, and the highest intensity was achieved for the polymer‐derived β‐SiAlON:Eu2+ with z = .64 and .37 mol% Eu2+.

Low-Voltage Capacitor Electrical Discharge Consolidation of Iron Powder

Commercially pure iron powder has been processed by the capacitor electrical discharge consolidation technique. This consolidation technique applies an external pressure and, at the same time, heats a metallic powder mass by the Joule effect of a high-voltage and high-intensity electric current. In this work, a capacitor charged at low voltage has been used instead. The effect of the initial porosity of the Fe powder mass, i.e., of the precompaction pressure, and the number of discharges from the capacitor have been studied. The densification and remaining porosity, the sintering level, the Vickers microhardness, and the electrical resistivity of the sintered compacts have been studied. Compacts sintered by the conventional powder metallurgy route of cold pressing and furnace sintering were also prepared for comparison. Results show that a high initial porosity provides a high electrical resistance in the powder column, a necessary requisite for the Joule effect to increase densification with the number of discharges. Thus, the final porosity decreases to 0.22 after 50 discharges in the powder mass with an initial porosity of 0.30. With this initial porosity, the sintering process increases Vickers microhardness from 29 to 51 HV10 and decreases the electrical resistivity of the powder mass from 3.53 × 10−2 to 5.38 × 10−4 Ω·m. An initial porosity of 0.2 does not make the compacts densify, but a certain bond between particles is attained, increasing microhardness and decreasing electrical resistivity as the number of discharges increases. Lower initial porosities make the powder mass behave as an electrical conductor with no appreciable changes even after 50 electrical discharges.

Medium-Frequency Electrical Resistance Sintering of Soft Magnetic Powder Metallurgy Iron Parts

The fabrication of soft magnetic Fe parts by the medium-frequency electrical resistance sintering (MF-ERS) technique is studied in this paper. This consolidation technique involves the simultaneous application to metallic powders of pressure and heat, the latter coming from the Joule effect of a low-voltage and high-intensity electric current. Commercially pure iron powder was used in the consolidation experiences. The porosity distribution, microhardness, electrical resistivity and hysteresis curves of the final compacts were determined and analysed. The results obtained were compared both with those of compacts consolidated by the conventional powder metallurgy (PM) route of cold pressing and vacuum furnace sintering, and with fully dense compacts obtained by double cycle of cold pressing and furnace sintering in hydrogen atmosphere.

TriBeam tomography and microstructure evolution in additively manufactured Alnico magnets

The Alnico 8 alloy has been printed using the selective laser melting additive manufacturing approach, resulting in material with magnetic properties in the as-printed state comparable to properties produced by conventional casting or powder metallurgy routes. Microstructural characterization in 3D, via electron backscattered diffraction (EBSD) in a TriBeam microscope, simultaneously reveals a fine-scale grain structure, grain orientations and sub-grain misorientation gradients as a function of proximity to spherical pores that form during the print process. The nanostructure of the 3D printed part has the same highly coherent spinodal α1//α2 structure observed in conventionally fabricated Alnico 8, which gives rise to a coercivity (Hc) of 51.2 kA m-1. Further investigation of the phase constituents by TEM analysis provides an understanding of the microstructure evolution during the additive manufacturing process. Modified processing pathways for improved microstructure and properties are discussed.

Ti(C,N)-Fe15Ni10Cr cermets as alternative hard materials: Influence of the processing route and composition on their microstructure and properties

Processing route is a determining factor that affects the properties of hard materials. Although processing routes are well defined for WC-Co hardmetals, a complete study is needed to understand the factors influencing the properties when alternative compositions are developed. In this investigation, Ti(C,N)-Fe15Ni10Cr cermets were produced following conventional powder metallurgy routes. Two types of milling – attritor and planetary, using different vessel/ball materials – and of sintering regimes – sinter-HIP and high-vacuum – were used to process the specimens and compare their final properties. Carbon content was also included in the study as experimental variable. Density, porosity, microstructure, mechanical and magnetic properties, and corrosion behaviour of the resulting cermets were determined by using a wide range of characterization techniques. Optimization of their production led to materials with a competitive hardness-toughness combination, comparable to those exhibited by plain WC-Co grades. Evaluation of corrosion confirmed the improved resistance when Cr is included as alloying element and also compared to cobalt, as well as the superior corrosion response of Ti(C,N) with respect to WC.

Nickel Porous Compacts Obtained by Medium-Frequency Electrical Resistance Sintering.

A commercially pure (c.p.) nickel powder was consolidated by Medium-Frequency Electrical Resistance Sintering (MF-ERS). In this consolidation technique, a pressure and the heat released by a high-intensity and low-voltage electrical current are concurrently applied to a metal powder mass. A nickel powder with a high tap porosity (86%) and a low applied pressure (only 100 MPa) is chosen in order to be able to obtain compacts with different levels of porosity, to facilitate the study of the porosity influence on the compact properties. The influence of current intensity and heating time on the global porosity values, the porosity and microhardness distribution, and the electrical conductivity of the sintered compacts is studied. The properties of the compacts consolidated by MF-ERS are compared with the results obtained by the conventional powder metallurgy route, consisting of cold pressing and furnace sintering. A universal equation to describe the porosity influence on all the analyzed properties of powder aggregates and sintered compacts is proposed and validated.

Influence of Processing Parameters on the Conduct of Electrical Resistance Sintering of Iron Powders

The influence of the applied pressure and electrical parameters on the macrostructure of specimens consolidated by the medium-frequency electrical resistance sintering technique (MF-ERS) is analysed in this work. This technique is based on the application of pressure to a mass of conductive powder that, simultaneously, is being crossed by a high intensity and low voltage electric current. The simultaneous action of the pressure and the heat released by the Joule effect causes the densification and consolidation of the powder mass in a very short time. The effect of the current intensity and heating time on the global porosity, the porosity distribution, and the microhardness of sintered compacts is studied for two applied pressures (100 and 150 MPa). For the different experiments of electrical consolidation, a commercially available pure iron powder was chosen. For comparison purposes, the properties of the compacts consolidated by MF-ERS are compared with the results obtained by the conventional powder metallurgy route (cold pressing and furnace sintering). Results show that, as expected, higher current intensities and dwelling times, as well as higher pressures and the consolidation of compacts with lower aspects ratios, produce denser materials.

Synthesis, structure, and mechanical response of Cr0.26Fe0.24Al0.5 and Cr0.15Fe0.14Al0.30Cu0.13Si0.28 nanocrystallite entropy alloys

The present research work has concentrated to synthesize nanocrystalline (NC) Cr0.26Fe0.24Al0.5 (medium entropy alloy, 3E-MEA) and Cr0.15Fe0.14Al0.30Cu0.13Si0.28 (high-entropy alloy, 5E-HEA) non-equiatomic (equal weight fraction) alloys through mechanical alloying (MA); which studied the influence of entropy effect on structural properties, microstructural characterization, and mechanical behaviour. Further, the same non-equiatomic ratio of two coarse grain alloys (CGAs) was manufactured by conventional powder metallurgy (PM) route (blending method, 3E-CGA, 5E-CGA) for comparison. All synthesized powders were hot-pressed (HPed) at 723 k for 30 min subsequently mechanical properties in terms of compressive stress-strain and hardness were examined. The samples of as-milled powders, HPed, and fractured were investigated using X-ray diffraction (XRD) and advanced electron microscopes. The HPed sample of 3E-MEA of Cr0.26Fe0.24Al0.5 produced 94% BCC and 6% FCC crystal structures due to more dissolution of Al atoms in the stronger bonding atoms of Cr-Fe lattice. Whereas 5E-HEA of Cr0.15Fe0.14Al0.30Cu0.13Si0.28 sample has exhibited 72.1% FCC phase and 27.9% BCC phase due to balance between the dissolution of FCC elements (Al, Cu, Si) and BCC elements (Cr, Fe). Further, 3E-MEA and 5E-HEA have exhibited the ultimate compressive strength (UCS) of 1278 ± 6.75 MPa and 2060 ± 2.8 MPa respectively whereas the corresponding conventionally blended alloys produced 268 ± 5 MPa and 615 ± 3 MPa for 3E-CGA and 6E-CGA respectively. Vicker’s hardness strength (VHS) of 5E-HEA of Cr0.15Fe0.14Al0.30Cu0.13Si0.28 has exhibited 68% more when compared to 3E-MEA of Cr0.26Fe0.24Al0.5, 3.26 times higher compared to blended alloys. Further, several strengthening mechanisms on the mechanical behaviour of MEA and HEA were investigated in which dislocation strengthening mechanisms followed by solid solution strengthening mechanisms have influenced more as compared to grain boundary strengthening mechanisms.

Co-existence of Ferroelectric and Ferromagnetic Properties of Bi+3 Substituted M-type Barium Hexaferrites

Co-existence of ferroelectric and ferromagnetic nature in bismuth substituted M-type barium hexaferrites has been investigated in this current project. A series of samples with formula BaBixFe(12-x) (where x varies from 0.2 to 1.2 with step size of 0.2) have been prepared by conventional powder metallurgy route. The structural, functional group analysis, surface morphology, optical, dielectric, ferroelectric, and ferromagnetic properties of samples are characterized using X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), UV-visible spectroscopy (UV-Vis), LCR meter, ZT-IA, and vibrating sample magnetometer (VSM) respectively. XRD and FTIR confirm the single phase of hexagonal structure of bismuth doped M-type barium hexaferrite. The platelet like structures is observed on the surface of the samples. The optical band gap energy decreases due to the formation of intermediate states between the valence and conduction bands as the concentration of Bi ions increases. The variation in dielectric constant and ac conductivity depends upon the frequency of the applied field as well as the composition of the samples. P-E loop shows clear ferroelectric behavior. The maximum saturation polarization of 5.42 μC/cm2 is observed. The presence of FeO6 octahedron at three (12 k, 2a, and 4f2) crystallographic sites in the hexagonal unit cell is the origin of induced polarization. Magnetic properties reveal the strong ferromagnetism of bismuth doped M-type barium hexaferrite at room temperature.

Fabrication and characterization of Al2O3 nanoparticle reinforced aluminium matrix composite via powder metallurgy

In this study, aluminium-aluminium oxide (Al-Al2O3) metal matrix nanocomposites (MMNCs) with the different volume content of Al2O3 reinforcement were prepared. Three different types Al- Al2O3 nanocomposite specimens comprise of 10%, 15% and 20% volume fractions of Al2O3 were fabricated using conventional powder metallurgy (PM) route and their microstructure and mechanical properties were determined. The samples were prepared under 200 kN compaction load and 630 °C sintering temperature. The correlation between microstructure and mechanical properties due to the inclusion of Al2O3 nanoparticles were investigated. The optical micrographs revealed that the Al2O3 nanoparticles are almost uniformly distributed in the Al matrix with good bonding between matrix and reinforcement. Moreover, the mechanical properties including hardness, tensile strength and compressive strength of the nanocomposite increase with increasing volume fraction of the reinforcement. However, the impact strength decreases once the Al2O3 nanoparticles increase in the composite.

Strengthening mechanisms of Ti via Al addition

Pure Ti is characterised by an interesting combination of performance from an engineering point of view. The addition of Al to Ti can be used to reduce the intrinsic cost of the material, decrease the density of the alloy, and increase the mechanical performance. This study is focused on evaluating the physical properties, microstructural evolution and mechanical behaviour of Ti-xAl alloys (where x = 1–6 wt%) in order to scientifically understand the strengthening mechanisms of the addition of Al to pure Ti manufactured via the conventional powder metallurgy route of cold uniaxial pressing plus solid state sintering. The addition of Al to Ti does not affect the compressibility of the alloy but changes the consolidation and densification of the alloy. The incremental addition of Al results in the progressive strengthening of Ti via the simultaneous contribution from substitutional solid solution and grain refinement strengthening which outdo the negative effect of the residual porosity.

Effect of particle size distribution on green properties and sintering of Ti-6Al-4V

In this study, the conventional powder metallurgy route of pressing and sintering was employed to study the effects of the particle size of blended elemental Ti-6Al-4V powders on the properties of powder mixtures, green and sintered densities. The -45 μm and -150 μm 60Al-40V master alloy powder were blended with the titanium powder to produce the -45 μm and -150 μm Ti-6Al-4V blend. Powders were pressed at 580 to 870 MPa and sintered in a tube furnace. Taguchi method was used to optimise the sintering parameters, temperature and time, and ANOVA was employed to determine the significant parameters and their contribution to the sintered density. The optimum parameters maximising the density were found to be sintering temperature of 1300 °C and sintering time of 180 mins, for both particle sizes. The green density was higher for the coarser powder and the sintered density was higher for the finer powder.

Influence of the processing route on the properties of Ti(C,N)-Fe15Ni cermets

This study aims to understand the influence of powder preparation and processing steps on the microstructure and properties of Ti(C,N)-Fe15Ni cermets with 70 and 80 vol% of ceramic phase. Two routes were used for powder preparation: (i) a colloidal approach, consisting of the preparation of stable aqueous suspensions of the powder particles and spray-drying to obtain easy-to-press granules, and (ii) conventional powder metallurgy route, consisting on wet ball milling of powders, with subsequent drying in rotary evaporator. The resultant powder mixtures were uniaxially pressed and sintered in high-vacuum at 1450 °C for 2 h. Sintered samples were characterized in terms of their density, porosity, microstructure (FESEM, image analysis), composition (EDX and XRD), small-scale hardness and sliding contact response by means of massive nanoindentation and nanoscratch testing. C content of the mixture powders was lower for conventional route, lost during milling. After sintering, all the materials, despite the processing route and composition, show C reduction, although that outflow is higher for the conventional powder metallurgy route, and more evident for the composition with higher binder content. As a result, COL samples exhibit a more homogeneous microstructural assemblage, higher small-scale hardness and mechanical integrity under sliding contact conditions. Compositions of materials must then be adjusted to adequate initial C addition with respect to the employed processing route, to account for the effects of the mixtures preparation stage.