Conventional Powder Metallurgy Techniques Research Articles

Higher mechanical and thermal properties of Cu-rGO composites

Here, the author fabricated copper-reduced graphene oxide composites by using conventional powder metallurgy technique by varying the amount of reduced graphene oxide. SEM and Raman analysis were used to characterize micro-morphology and disorder in the bulk composites. Tensile, thermal and microhardness testing were conducted to observe the behaviour of Cu-rGO composites. Interesting results were obtained after testing; the materials ultimate tensile strength, ductility, thermal conductivity and hardness were increased significantly compared to pure Cu. An increase in 31% ultimate tensile strength, ~200% ductility, 9.5% thermal conductivity and 90% hardness were noticed by using a very small amount of rGO 0.5 wt%. Laser irradiation test was also proved the good heat dissipation properties of Cu-rGO composites by increasing the amount of rGO. This extraordinary simultaneous increase in mechanical and thermal properties is remarkable and gave us a new way for the fabrication of higher strength-ductility and strength-conductivity based composites.

Microstructure, mechanical and wear properties of aluminum borate whisker reinforced aluminum matrix composites

Abstract The microstructural features and the consequent mechanical properties were characterized in aluminium borate whisker (ABOw) (5, 10 and 15 wt.%) reinforced commercially-pure aluminium composites fabricated by conventional powder metallurgy technique. The aluminium powder and the whisker were effectively blended by a semi-powder metallurgy method. The blended powder mixtures were cold compacted and sintered at 600 °C. The sintered composites were characterized for microstructural features by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. Porosity in the composites with variation in ABOw contents was determined. The effect of variation in content of ABOw on mechanical properties, viz. hardness, bending strength and compressive strength of the composites was evaluated. The dry sliding wear behaviour was evaluated at varying sliding distance at constant loads. Maximum flexural strength of 172 MPa and compressive strength of 324 MPa with improved hardness around HV 40.2 are obtained in composite with 10 wt.% ABOw. Further increase in ABOw content deteriorates the properties. A substantial increase in wear resistance is also observed with 10 wt.% ABOw. The excellent combination of mechanical properties of Al−10wt.%ABOw composites is attributed to good interfacial bonds, less porosity and uniformity in the microstructure.

Core loss reduction for Fe-6.5wt%Si soft magnetic composites doped with Co element

Co element was doped in Fe-6.5Si alloy and the corresponding soft magnetic composites were fabricated successfully by conventional powder metallurgy techniques in this work. Saturation magnetization of Co-doped Fe-6.5Si powder increases compared to powders without Co and the coercivity increases because of grain refinement. Co addition is helpful to improve the electrical resistivity of Fe-6.5Si alloy. After doping Co, it shows a significant trend towards a decrease for core loss of Fe-6.5Si SMCs by reducing both eddy current loss and hysteresis loss. The effective permeability of Co-doped Fe-6.5Si SMCs decreases monotony with the Co content changing from 0 to 7.0 wt%. Fe-6.5Si-1.0Co SMCs shows best magnetic performances (100 mT/50 KHz) with core loss of 781.03 mW/cm3 and effective permeability of 103.36.

Process optimization and mechanical properties of oxide dispersion strengthened nickel-based superalloy by selective laser melting

Oxide dispersion strengthened nickel-based superalloy (ODSN) is widely used in structural materials such as aerospace and nuclear industry, but its uniform dispersion distribution of particles makes it only necessary to manufacture using conventional powder metallurgy technique. Selective laser melting (SLM) is first selected as a novel method for manufacturing ODSN. The influence of SLM process parameters (laser power, scanning speed, hatch spacing) on the microstructure and mechanical property in ODSN has been investigated, using Taguchi method (TM) and Response surface methodology (RSM). Orthogonal array and Box-Behnken design were utilized to design the experiments. Analysis of variance, signal-to-noise ratio, main influence diagrams, 3D response surface, and the corresponding contour plots were measured to evaluate the effects of factors on the tensile strength. By comparing the results of the experiment showed that optimum parametric combination from TM and RSM induced better tensile strength. The optimum process parameters were predicted, validated, and subsequently employed to build samples to assess mechanical properties during 25–1000 °C. The samples produced using SLM showed approximate tensile strength, compared to hot extruded ODSN of similar composition. Fracture morphology results good agreement with mechanical property at room and elevated temperature.

Effect of Mo addition mode on the microstructure and mechanical properties of TiC–high Mn steel cermets

In TiC- and Ti(C,N)-based cermets, the wettability of the ceramic phase with the metallic binder is commonly increased through supplementation with Mo in the form of pure Mo powder or Mo2C. Herein, TiC–high Mn steel cermets were fabricated by conventional powder metallurgy techniques using Fe–Mo pre-alloyed powders as binders to guarantee uniform Mo distribution, and the cermet preparation process was optimized and investigated in detail. The microstructures of the thus obtained cermets were observed by scanning electron microscopy and compared to those of a Mo-free cermet and a cermet prepared using pure Mo powder. The grain size of Fe–Mo powder cermets exceeded that of the Mo-free cermet but was much smaller and more homogeneous than that of the Mo powder cermet. For Fe–Mo powder cermets, angular and tetragonal TiC particles were observed at Mo contents of <1.2 wt%, while round shapes became dominant at higher Mo contents. The hardness of Fe–Mo powder cermets increased with increasing Mo content, as did transverse rupture strength, which was maximal (2264 MPa) at a Mo content of 2.4 wt%, while impact toughness was maximal (11.2 J/cm2) at a Mo content of 1.2 wt%. The above values exceeded those reported for similar conventional cermets, and the use of Fe–Mo pre-alloyed powder as a metallic binder was therefore concluded to be an attractive strategy of increasing the strength and toughness of TiC–high Mn steel cermets.

Porous Titanium for Biomedical Applications: Evaluation of the Conventional Powder Metallurgy Frontier and Space-Holder Technique

Titanium and its alloys are reference materials in biomedical applications because of their desirable properties. However, one of the most important concerns in long-term prostheses is bone resorption as a result of the stress-shielding phenomena. Development of porous titanium for implants with a low Young’s modulus has accomplished increasing scientific and technological attention. The aim of this study is to evaluate the viability, industrial implementation and potential technology transfer of different powder-metallurgy techniques to obtain porous titanium with stiffness values similar to that exhibited by cortical bone. Porous samples of commercial pure titanium grade-4 were obtained by following both conventional powder metallurgy (PM) and space-holder technique. The conventional PM frontier (Loose-Sintering) was evaluated. Additionally, the technical feasibility of two different space holders (NH4HCO3 and NaCl) was investigated. The microstructural and mechanical properties were assessed. Furthermore, the mechanical properties of titanium porous structures with porosities of 40% were studied by Finite Element Method (FEM) and compared with the experimental results. Some important findings are: (i) the optimal parameters for processing routes used to obtain low Young’s modulus values, retaining suitable mechanical strength; (ii) better mechanical response was obtained by using NH4HCO3 as space holder; and (iii) Ti matrix hardening when the interconnected porosity was 36–45% of total porosity. Finally, the advantages and limitations of the PM techniques employed, towards an industrial implementation, were discussed.

Effect of reinforcement spatial distribution on mechanical properties of MgO/ZK60 nanocomposites by powder metallurgy

0.5 vol% MgO/ZK60 nanocomposites with two reinforcement arrays were successfully fabricated by a conventional powder metallurgy technique. Specifically, the combination of powder oxidization and extrusion consolidation was used to obtain a composite microstructure that was characterized by fiber-like MgO rich bands embedded in an ultrafine-grained Mg matrix. Meanwhile, a homogeneous microstructure containing MgO nanodispersoids throughout the matrix was also achieved by introducing an extra high-energy ball milling. Compared with the unreinforced matrix alloy, both nanocomposites exhibited improved strength and marginally reduced elongations. Furthermore, the homogeneous nanocomposite showed a higher strength than that of inhomogeneous counterpart. Quantitative analysis indicated that fiber-like MgO rich bands only acted as load-carrying units and nanodispersoids activated multiple strengthening mechanisms which involved grain refinement, Orowan and dislocation strengthening.

Microstructural comparison and mechanical properties of stainless steel 316L fabricated by selective laser melting and metal injection moulding processes

Selective laser melting (SLM) process is one of an additive manufacturing technology that has the capabilities of fabricating complex geometries with an excellent accuracy and resolution. Compared to conventional powder metallurgy techniques metal injection moulding (MIM), SLM has several advantages such as low production cost for small batch fabrication, high degrees of geometrical freedom and customisation, and short cycle time. The present work analyses and compares the tensile properties and metallography differences of the stainless steel 316L compacts fabricated by two powder-based manufacturing processes; SLM and MIM, respectively. The SLM compact was built at 0-degree building orientation by SLM 125 HL machine with default optimum processing parameters for stainless steel 316L powder. On the other hand, MIM process produced similar dimension of tensile-shaped compacts differently that by sintered at three different sintering conditions in highly pure argon flow atmosphere. The tensile testing revealed that SLM tensile compact was higher in tensile strength (29% more) and elongation (62% more) at fracture as compared to MIM compact. From microstructure observation, the MIM compact showed the presence of significant amount of porosity which led to moderate mechanical properties compared to SLM compact performances.

Microstructural comparison and mechanical properties of stainless steel 316L fabricated by selective laser melting and metal injection moulding processes

Selective laser melting (SLM) process is one of an additive manufacturing technology that has the capabilities of fabricating complex geometries with an excellent accuracy and resolution. Compared to conventional powder metallurgy techniques metal injection moulding (MIM), SLM has several advantages such as low production cost for small batch fabrication, high degrees of geometrical freedom and customisation, and short cycle time. The present work analyses and compares the tensile properties and metallography differences of the stainless steel 316L compacts fabricated by two powder-based manufacturing processes; SLM and MIM, respectively. The SLM compact was built at 0-degree building orientation by SLM 125 HL machine with default optimum processing parameters for stainless steel 316L powder. On the other hand, MIM process produced similar dimension of tensile-shaped compacts differently that by sintered at three different sintering conditions in highly pure argon flow atmosphere. The tensile testing revealed that SLM tensile compact was higher in tensile strength (29% more) and elongation (62% more) at fracture as compared to MIM compact. From microstructure observation, the MIM compact showed the presence of significant amount of porosity which led to moderate mechanical properties compared to SLM compact performances.

Study on Effect of EAFD Particulate Reinforcement in AA7075 Aluminum Matrix Composites

Eletric arc furnace dust is dangerous solid waste that is generated in steel manufacturing processes. The utilization of the dust from these industries avoids disposing it into industrial waste landfills and saves costs. In this study, an attempt has been made to fabricate aluminum matrix composites reinforced with EAFD particulate, throught the conventional powder metallurgy technique. Al-5%EAFD proposed was then compared to the AA7075 alloy, manufactured under the same conditions. According to the results obtained, the addition of EAFD into aluminum matrix resulted in increased microhardness values and had significant contributuion to improve Storage modulus compared with the base metal. The reinforcement particle was uniformly dispersed into the matrix and intermetallic phases were not observed in the content of waste blended into the composite.

Effect of WС Content on the Mechanical Properties and High Temperature Oxidation Behavior of Ti(С,N)-Based Cermets

Ti (C,N)-based cermets with varying WC additions (Ti (C0.6N0.4)-36Ni-12Mo-1C-xWC, x = 0, 3, 6 and 9 wt%) were prepared by conventional powder metallurgy techniques. The microstructure and mechanical properties of all four Ti (C,N)-based cermets were investigated. Isothermal oxidation of all four cermets were also investigated in air at 800°C up to 100 h using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction analysis (XRD). The grains of Ti (C,N)-based cermets became more homogeneous with the increase of WC content. The TRS and fracture toughness increased with the increase of WC content and then decreased when WC content exceeded 6wt%, but hardness decreased continuously with the increase of WC content. The oxide scales formed on the surface of all four samples during the oxidation process were porous and multi-layered, consisting of NiO outerlayer and TiO2 based innerlayer, respectively. The thickness of the oxide scales and oxidation rates increased with the increase of WC content, especially when the content of WC addition reached 9wt%. The cermet with 6wt% WC addition showed excellent mechanical properties and acceptable high temperature oxidation resistance.

Influence of S and Te substitutions on the thermoelectric properties of the cluster compound Ag3.8Mo9Se11

We report on a detailed study of the influence of S and Te substitutions for Se on the thermoelectric properties of the cluster compound Ag3.8Mo9Se11. Two series of polycrystalline samples Ag3.8Mo9Se11-ySy (0 ≤ y ≤ 0.5) and Ag3.8Mo9Se11-zTez (0 ≤ z ≤ 0.5) were synthesized by a combination of conventional powder metallurgy technique followed by spark plasma sintering. Powder X-ray diffraction and wavelength dispersive spectroscopy indicate that both S and Te successfully substitute for Se and exhibit a low solubility limit of y ≈ z ≈ 0.5. Measurements of the thermoelectric properties between 2 and 800 K show that S and Te substitutions tend to lead to a more pronounced heavily-doped character with respect to Ag3.8Mo9Se11. The very low lattice thermal conductivity of these compounds (κL≈ 0.5 W m−1 K−1) can be attributed to the large thermal displacement parameters of the Ag atoms. Despite the heavily-doped nature of the samples, the charge carriers conduct less heat than expected by the Wiedemann-Franz law resulting in significantly lower Lorenz numbers than predicted by the degenerate limit above 300 K. The combination of favourable electronic properties and low thermal conductivity leads to interesting dimensionless thermoelectric figures of merit ZT of 0.7 near 800 K.

Enhancement of structural and magnetic properties of M-type hexaferrite permanent magnet based on synthesis temperature

The main purpose of this research work is to develop the single domain magnetic particles of M-type barium hexaferrite (BaFe12O19) using oxide precursors employing conventional powder metallurgy technique. The phase formation and magnetic performance of the powders and magnets will be optimized by adjusting calcination and sintering temperatures. The synthesis of M-type barium hexaferrite was carried out in two sections. A series of four samples have been prepared by initial wet mixed powders calcined at different temperatures, i.e., 750, 850, 950 and 1050 °C. On the basis of structural analysis, the sample calcined at 950 °C has been selected and further divided into four parts to sintered them at 1100, 1150, 1200 and 1250 °C. The structural measurements depict the confirmation of M-type barium hexaferrite structure. SEM micrographs show the hexagonal-shaped grains. The abrupt decrease in coercivity for the sample sintered at 1250 °C has been seen which may be due to high sintering temperature, at which the particles have multi-domain properties.

Some Studies on the Bulging Characteristics of Cold-Upset Steel Preforms

Present investigation pertains to establish the bulging characteristics of sintered steel preforms under cold upsetting. Cylindrical preforms of Fe-0.8%C and with 1%Mo and 2%Mo of 86% initial theoretical density and 0.4 initial aspect ratio have been produced through conventional powder metallurgy techniques. These preforms were further subjected to secondary deformation, that is, cold upsetting under nil and zinc stearate lubricant conditions. The results obtained from this experiment were used to study the bulging characteristics with densification and hoop stress. An empirical equation is determined between these parameters and is found to follow a power law relationship.

THE INFLUENCE OF SiC PARTICLE SIZE ON MECHANICAL PROPERTIES OF ALUMINIUM MATRIX COMPOSITES

The main aim of this study was to determine the influence of SiC particle size on the mechanical properties of aluminum matrix composites. The reinforcing phase was introduced into the aluminum matrix in two different particle sizes: a coarse fraction with particle size ranging from 40 to 60 μm, and a fine fraction with particle size of less than 2 μm. The SiC particles were added in various quantities equal to 2.5, 5, 7.5, and 10 wt% in order to determine the influence of different contents of the reinforcing phase on the density, hardness, and compressive strength of the obtained composite materials. By using scanning electron microscopy (SEM), the microstructure observations were performed and allowed for defining the influence of matrix/reinforcement particle size ratio (PSR) on the distribution of reinforcement particles in the matrix. The Al-SiC composites were prepared through the conventional powder metallurgy technique, including compaction under a pressure of 300 MPa and a sintering process in a nitrogen atmosphere at 600°C. Applying the reinforcing phase with the particle size (40–60 μm) similar to matrix (<63 μm) allowed us to obtain a more-uniform distribution of SiC particles in the matrix than after introducing the fine fraction of reinforcement (2 μm). The mechanical properties of the Al-SiC composites increased with increases in the weight fraction of the reinforcing phase, wherein this effect is more visible for composites reinforced with SiC particles of finer gradation.

Shaping Strategies for Porous Ti Fabrication throughout Colloidal Chemistry

Aimed by reducing the total cost of products, powder metallurgy (PM) processing of Ti is a subject of high interest. However, using of conventional PM techniques presents difficulties due to the intrinsic characteristics of Ti, like low strain ability, and high reactivity, which lead to low compressibility. Moreover, Ti powders with small particle size are difficult to process by conventional PM techniques as they present a lower compressibility and also a poor flowability. On the other hand, the colloidal processing has been used for long in ceramics to achieve green bodies with high densities, complex shapes and homogeneous microstructures, but they are rarely used to shape metal powders because of its high density and high surface reactivity. However, the possibility to process fine particles makes these techniques interesting for metals with low density like Ti.The colloid-chemistry control of metallic powders in aqueous slurries is proposed as a way to prepare Ti porous parts with small particle size, throughout the formulation of aqueous slurries with solid contents as high as 50 vol.%. The chemical and chemical-physic stability of Ti powders 10 μm in size was determined by measuring the zeta potential as a function of pH, and dispersant concentration, while the later optimization of Ti slurries and their adequation for the use of different colloidal techniques, were studied in terms of rheology and the addition of the processing additives, such as gel or foaming agents. Techniques such as thermal gelling, foaming, and impregnation of exo-templates or robocasting were used to build Ti parts with random and/or tailored macroporosity. The shaped pieces made on Ti were sintered in vacuum at 1100 oC for 30 minutes, and their microstructure and mechanical properties were determined and compared with dense materials shaped by combining PM and colloidal techniques in previous works

Design, Processing and Characterization of Materials with Controlled Radial Porosity for Biomedical and Nuclear Applications

The manufacture of graded materials has gained an enormous interest during the last decade due to the diversity of industrial and biological materials systems that require or are actually designed to implement that criterion; those natural or artificial materials offer multiple possibilities of applications. In this work, a novel uniaxial and sequential compaction device has been successfully designed and fabricated, in order to obtain samples with three different layers; this new device is suitable for both conventional and non-conventional powder metallurgy (PM) techniques. In addition, this device allowed us to use different combinations of powders and space-holder particles, irrespective of their nature, sizes, morphologies and proportions. It has no restriction about applying different compaction pressures for every layer, which may result in increasing or decreasing porosity. This compaction device is especially powerful if the aim is obtaining samples with radial graded porosity for biomedical applications (replacement of cortical bone involved in different joints and dental restorations) and nuclear applications (mimicking burnt used nuclear fuel). Specifically in this work, different samples with radial graded porosity were fabricated and then microstructurally and mechanically characterized: i) Commercially pure titanium (CP Ti) samples, starting from blends CP Ti with 20 vol.%, 40 vol.% and 60 vol.% of Sodium Chloride (NaCl) as space holder, which were placed in core, intermediate and external layers, respectively; processing conditions were 800 MPa of compaction pressure and 1250 °C for 2h in high vacuum of sintering; and ii) CeO2 samples, starting from blends CeO2 with 0.5 vol.%, 3.0 vol.% and 7.5 vol.% of Ethylene Bis Stearamide (EBS) as space holder, which were placed in core, intermediate and external layers, respectively; processing conditions were 460 MPa in external layer and 700 MPa in core and intermediate layers of compaction pressure, and 1700 °C during 4h in static air of sintering. This new device has proved to have unique advantages for solving problems of structural integrity in conventional PM manufacturing in a simple, economic and reproducible way.

Selective laser melting of Al-12Si alloy: Enhanced densification via powder drying

Unlike conventional powder metallurgy techniques, selective laser melting (SLM) is characterised by its fully melting process and very high heating and cooling rates and little has been known about the influence of powder surface state on the SLM process. In this study, the influence of low temperature powder drying on the surface chemistry of Al-12Si powder and its subsequent effect on SLM was investigated in detail by means of an in-depth X-ray photoelectron spectroscopy. An enhanced densification (relative density ≥99%) was achieved in the dried Al-12Si powder compared to the as-received powder. This has been attributed to the modification of powder surface by removing a moisture skin during the drying process, which prevents the formation of deleterious oxide and hydroxide during SLM. This study provides important information for achieving high relative density in SLM fabricated metal components from a powder drying aspect.

Submicron-porous NiTi and NiTiNb shape memory alloys with high damping capacity fabricated by a new top-down process

In this paper, submicron-porous NiTi and NiTiNb shape memory alloys were firstly fabricated by a new top-down process, including solidified phase controlling and etching process. These porous alloys possessed fine pore size (∼0.4 μm) and homogeneous pore distribution. The mechanical properties of these porous alloys were similar to those prepared by conventional powder metallurgy techniques or bottom-up process. However, the damping capacity of the submicron-porous NiTi was ∼0.07 and 40% higher than the counterparts produced by the conventional powder metallurgy techniques. The damping capacity of the submicron-porous NiTiNb was ∼0.18 and 50% higher than its dense counterpart. The internal friction value at austenite state for submicron-porous NiTiNb was ∼0.04 and 200% higher than its dense counterpart, 300% higher than submicron-porous NiTi. The high damping capacity of these submicron-porous shape memory alloys was considered to be caused partly by their fine pore structures, which enhanced the stress concentration and the microplastic deformation or collapse of thin nodes. These porous shape memory alloys exhibited moderate stiffness as well as high damping capacity and high specific strength, making them good candidate as practical engineering damping materials.

93W-5.6Ni-1.4Fe高比重合金放电等离子主烧结曲线的建立 *

Tungsten heavy alloys are used for a number of applications, including radiation shields, counter weights, electrical contacts, vibration dampeners and kinetic energy penetrators. The most common compositions consist of W along with some combination of Ni, Fe, or Cu. The alloys are usually fabricated by the conventional powder metallurgy technique, in which the elemental blended powders are first compacted and then followed by a high temperature sintering. An important processing goal for this alloy is to obtain a high density with fine grain size. It is therefore desirable to predict its densification behavior and final density. Recently, the master sintering curve (MSC) theory provides a better understanding of whole sintering process. In previous work, the densification and grain growth mechanisms during spark plasma sintering (SPS) of 93W-5.6Ni-1.4Fe heavy alloy were investi-