Conventional Powder Metallurgy Techniques Research Articles

Large-Size and Ultrahigh Purity Tungsten with Enhanced Physical Properties via Chemical Vapor Deposition.

Conventional powder metallurgy techniques fail to meet the demands for ultrahigh purity tungsten (UHPW) and scalable component sizes required by the semiconductor industry. In this study, ultrahigh purity (99.999998 wt %) large-size tungsten parts, with an adjustable thickness and a diameter of 350 mm, were prepared via a chemical vapor deposition (CVD) method using ultrahigh purity (99.9999 wt %) tungsten hexafluoride (WF6) as the precursor. The microstructure and physical properties of the resulting CVD-UHPW were evaluated and compared with those of powder metallurgy tungsten (PM-W). The results indicate that CVD-UHPW displays a columnar grain microstructure with a lower dislocation density and internal strain, whereas PM-W shows an equiaxed grain microstructure. CVD-UHPW has a density of 19.17 g/cm3, closely matching the theoretical density of tungsten (19.35 g/cm3) and significantly higher than PM-W's density of 18.79 g/cm3. The specific heat capacities of CVD-UHPW, measured from 298 to 1473 K, range from 0.113 to 0.146 J/g·K, similar to PM-W's range of 0.120 to 0.151 J/g·K. CVD-UHPW shows improved electrical and thermal conductivities compared to PM-W, with values ranging from 1.68 × 106 to 1.78 × 107 S/m and 105.7 to 196.4 W/(m·K) from 298 to 1473 K. This study highlights the potential of the CVD method for the large-scale production of ultrahigh purity tungsten parts, emphasizing its significant applicability across various industries.

Tribology of Mg-B4C nanocomposites fabricated following powder metallurgy route

In this experimental work, magnesium nanocomposite reinforced with various percentage of boron carbide (0.5%, 1.0%, 1.5%, 2.0% by volume) is fabricated using conventional powder metallurgy technique. Characterisation and wear test of the fabricated composite have been performed using scanning electron microscopy, tribology test monitor respectively. It is observed that addition of B4C increases the hardness and wear resistance linearly. Addition of 2% B4C produces the hardness of the nanocomposites as high as 57.93 ± 4.9 Hv. Furthermore, the nanocomposites displayed improved wear resistance and lower friction coefficient compared to the base magnesium. The influence of sliding speed on these properties has been systematically presented. The paper provides an in-depth exploration of wear mechanisms through a meticulous analysis of SEM micrographs of worn surfaces. This work offers valuable insights into the microstructural characteristics and tribological behaviour of Mg-B4C nanocomposites. These findings underscore the potential application of Mg-B4C nanocomposites in the development of lightweight wear-resistant materials. The impact of incorporating minute amounts of nano-sized boron carbide into Mg, on its behaviour under small loads and repeated scratching has been investigated in this study. Moreover, introspection of the wear mechanisms and the effectiveness of the powder metallurgy technique in fabricating composite materials is presented.

Optimizing the Microstructure and Properties of Fe–Ni–Cu–Mo–C Sintered Steel by TiB2

The Fe–Ni–Cu–Mo–C powder metallurgy sintered steels with TiB2 reinforced were prepared by the conventional powder metallurgy techniques. This study explored the influence of incremental TiB2 additions, ranging from 0.1 to 0.6 wt.%, on the microstructure and properties of these steels. The results reveal that the microstructures primarily consist of martensite, Ni-rich austenite, Cu-rich pearlite, TiB2, and Ti–O rich nanoparticles. The latter form via a reaction between TiB2 and free oxygen. Notably, both the density and impact strength of the steels showed enhancement with increasing TiB2 content. The optimal values, 7.25 g/cm3 for density and 17.23 J/cm2 for impact strength, were observed at a TiB2 concentration of 0.5%. The hardness and ultimate tensile strength also increased steadily, reaching maxima of 38.7 and 1083.7 MPa at 0.6% TiB2, respectively. However, excessive TiB2 led to the formation of a net-like B-containing eutectic network, adversely affecting the steel properties. Steels with 0.5% TiB2 exhibited excellent wear resistance. At 200 rpm, the dominant failure mode was abrasive wear, which shifted to adhesive wear with oxidation at 400 rpm, followed by abrasive wear.

Sintering behaviour of liquid phase sintered 90Mo-10(Ni–Cu) alloys

Molybdenum (Mo), a refractory material, boasts an elevated melting point of 2610 °C and is predominantly synthesised through powder metallurgy at high temperatures reaching 2000 °C, necessitating the use of liquid phase sintering (LPS) technique. This study investigates the LPS of Mo with varying proportions of Ni–Cu binders, aiming to understand the mechanism of intermetallic formation and to manufacture low-cost, dense, intermetallic-free and near-net-shape Mo-base alloys. Employing the manufacturing design paradigm for 90W-10(Ni–Cu) tungsten heavy alloys (WHAs) and utilising conventional powder metallurgy techniques, Mo-based 90Mo10(Ni–Cu) alloys were synthesised. Initial findings indicate that the densification of Mo-compacts increases with increasing the Ni–Cu ratio in the binder phase. However, an excess of Ni results in the loss of structural rigidity and geometric distortion during sintering. In Ni-rich alloys, two distinct liquid phases, Ni-rich and Cu-rich, emerge at sintering temperatures. These phases exhibit different solubilities for Mo and solidify into a dual-phase matrix. Intriguingly, in contrast to WHAs, 90Mo-10(Ni–Cu) alloys with a Ni-rich composition manifested irregular Mo particles, a dual-phase matrix, and δ-MoNi intermetallic compound formation. The formation of the intermetallic compound can be avoided by reducing the solubility of Mo in the Ni-rich liquid during sintering. Microstructural evolution and distortion are analysed using stereological quantification of various microstructural parameters. It reveals that alloys with low Mo solubility, high connectivity and high dihedral angle maintain their structural rigidity and resist distortion. Both micro-hardness and bulk hardness increased with increasing Ni–Cu ratios in the binder phase. Based on the present results, a mechanism for liquid phase sintering in the 90Mo-10(Ni–Cu) system in the presence of two liquid phases is postulated.

Improving Laser Powder Bed Fusion Printability of Tungsten Powders Using Simulation-Driven Process Optimization Algorithms.

This study applies numerical and experimental techniques to investigate the effect of process parameters on the density, structure and mechanical properties of pure tungsten specimens fabricated by laser powder bed fusion. A numerical model based on the simplified analysis of a thermal field generated in the powder bed by a moving laser source was used to calculate the melt pool dimensions, predict the density of printed parts and build a cost-effective plan of experiments. Specimens printed using a laser power of 188 W, a scanning speed of 188 mm/s, a hatching space of 80 µm and a layer thickness of 30 µm showed a maximum printed density of 93.2%, an ultimate compression strength of 867 MPa and a maximum strain to failure of ~7.0%, which are in keeping with the standard requirements for tungsten parts obtained using conventional powder metallurgy techniques. Using the optimized printing parameters, selected geometric artifacts were manufactured to characterize the printability limits. A complementary numerical study suggested that decreasing the layer thickness, increasing the laser power, applying hot isostatic pressing and alloying with rhenium are the most promising directions to further improve the physical and mechanical properties of printed tungsten parts.

Manufacturing Oxide Dispersion Strengthened (ODS) steel plate via cold spray and friction stir processing

Oxide dispersion strengthened (ODS) steels, traditionally fabricated by ball milling and conventional powder metallurgy techniques to achieve bulk form, followed by intricate rolling and thermal treatment steps to achieve plate or sheet form. Here, we present a novel processing route that combines cold spray (CS) with friction stir processing (FSP) to manufacture ODS steel plate directly from gas atomization reaction synthesis (GARS)-prepared powder, thus no rolling steps involved. Microstructural and mechanical characterizations were performed to assess the quality and properties of the resulting ODS steel plate. Our findings demonstrate that the slightly porous CS deposited layer was fully consolidated after FSP, yielding a fully dense ODS steel plate that exhibited a favorable tradeoff between strength and ductility upon extraction from the substrate. Furthermore, through microstructural analysis, we revealed the presence of an appreciable density (∼1022/m3) of nano-sized oxide particles, with the majority being smaller than 5 nm via the combined CS + FSP fabrication route. This work serves as a first proof-of-concept demonstration of the manufacturing approach described herein, offering a possible alternative route for producing ODS steel plates.

Biomechanical behavior of a new design of dental implant: Influence of the porosity and location in the maxilla

The biomechanical performance of dental implants determines their clinical success. In this work, the stress and deformation distribution of a new implant design (dense and porous) was evaluated by the Finite Element Method. Furthermore, the effect of the location of the dental implant in the maxillary zone, as well as the mechanical response in the peri-implant maxillary tissue (cortical and trabecular) is discussed in detail. Before carrying out the computational study of the dental implant, Ti6Al4V cylindrical preforms obtained by conventional powder metallurgy and space-holder technique were characterized, to choose the most appropriate porosity (percentage and size) to achieve the biomechanical and biofunctional balance of the dental implant investigated. The novel porous dental implant under investigation exhibits 40% porosity in the region in contact with the trabecular bone, featuring inclined pores at 60 and 120° with a diameter of 200 μm. Our findings revealed that the cortical bone experienced the highest stress values, whereas the trabecular bone exhibited the highest levels of strain. Notably, the location of dental implants in the maxilla highlighted as the most influential factor affecting the maximum values of von Mises equivalent stress and strain. Furthermore, in the second molar location, the stress and strain levels exceeded the recommended thresholds for maintaining peri-implant bone density. Additionally, the porous implants generated significantly higher levels of stress and strain in the peri-implant trabecular bone than dense implants.

Supreme tensile properties in precipitation-hardened 316L stainless steel fabricated through powder cold-consolidation and annealing

One of the key goals of processing 316L stainless steel by powder metallurgy (PM) techniques is to achieve industrial-viable tensile properties without structural defects like poor densification, undesired phase transitions, and oxidation during high-temperature sintering. To address this, this study adopts high-pressure torsion to fabricate a fully dense structure at ambient temperature through cold consolidation. The samples fabricated by the present PM-based technique exhibits considerably enhanced tensile properties compared to counterparts processed by conventional PM techniques, with a remarkable yield strength of 1 GPa and total elongation of 46%. Additionally, the segregation of certain elements during subsequent annealing results in a unique microstructure with nano-scale sigma precipitates which induces dislocation pile-up, leading to improved yield strength and retarded dislocation motion. The results indicate that the present PM-based route is an applicable technique to achieve the strength-ductility synergy in 316L stainless steel.

Mechanical, wear and corrosion behavior of Ti–6Al–xNb (x = 3.5–21 wt%) alloys manufactured by powder metallurgy

In this study, Ti–6Al–xNb alloys with different Nb percentages (x = 3.5–21 wt%) were produced by the conventional powder metallurgy technique. After mixing and pressing the alloy powders in appropriate proportions, the green samples were sintered in a tube furnace under a vacuum atmosphere at 1200 °C for 2 h. The X-ray diffraction analysis (XRD) showed that all the alloys consist of α–Ti, TiNb (β–Ti) and AlNb2 phases. The results showed that the Ti–6Al–14Nb alloy among all alloys has the best mechanical properties, and the microhardness, tensile and flexural strength are 276.4 Vickers hardness (Hv0.2), 453 MPa and 1682 MPa, respectively. Tribological tests were carried out in both dry and wet conditions with Hanks' Balanced Salt Solution. While generally, the specific wear rates of the samples increased with Nb content up to 17.5 wt% under dry conditions, on the other hand, they increased with increasing Nb content under wet conditions. On the other hand, the specific wear rate increased with increasing the sliding distance. The best corrosion resistance alloy among all the samples was Ti–6Al–7Nb with −0.0968 V corrosion potential (Ecorr), 0.015 μA/cm2 corrosion current density (Icorr) values.

STRUCTURE, MECHANICAL PROPERTIES, AND OXIDATION RESISTANCE OF MN-RICH FE-MN-AL ALLOYS

In this study, Mn-rich Fe-Mn-Al alloys with different Al content (Al = 0, 3, and 5 % by weight) were fabricated from ferromanganese lumps using a conventional powder metallurgy technique. The samples were compacted in 1 cm steel dies using a load of 8 tons and then sintered at 1100 °C for 2 h in a tubular furnace under a vacuum condition of around 0.5 mbar. To evaluate the effect of Al addition to Fe-Mn-Al alloy, the Archimedes principle and Vickers hardness were applied to estimate the density and hardness of the compact alloys. Moreover, the high-temperature oxidation resistance of the alloy was evaluated at 800 °C for 8 cycles. The structure of the alloy before and after oxidation was studied by means of X-Ray Diffractometer and SEM-EDS. The XRD analysis results show that the FeMn-0Al alloy is mainly composed Fe3Mn7 phase, the presence of FeAl phase at 3 wt% Al, and Al8Mn5 phase at 5 wt% Al. The density and hardness of Fe-Mn-Al alloys decreased with the increased Al content. Fe-Mn-Al alloy without Al addition exhibits poor oxidation resistance since the first cycle of the test. The results of microstructural analysis showed that although the alloy with the addition of 3 wt% Al showed less mass gain after being exposed for 8 cycles at 800 °C, the Fe-Mn-Al alloy with 5 wt% tended to be more resistant to oxidation and had no cracking defects. The structure of the oxide formed on the surface of the alloy is composed of two layers (ie; outer and inner layer) which are affected by each alloy composition.

A Comparative Study on Microstructure and Tribological Properties of Al/Gr Composites Prepared via Conventional and Flake Powder Metallurgy Techniques

A Comparative Study on Microstructure and Tribological Properties of Al/Gr Composites Prepared via Conventional and Flake Powder Metallurgy Techniques

Synergy of tensile strength-ductility in IN718/CoCrFeMnNi/IN718 multi-material processed by powder high-pressure torsion and annealing

Materials manufactured through conventional powder metallurgy (PM) techniques generally exhibit inferior tensile properties due to structural defects. Nevertheless, a recently proposed cold-consolidation technique using powder high-pressure torsion represents well-manufactured structures with ultra-high tensile properties in the absence of cracks or pores. This novel PM-based technique is utilized in the present investigation to fabricate a multi-material Inconel 718/CoCrFeMnNi/Inconel 718 layered structure. By a combination of uttermost high densification, ultra-fine-grained microstructure, and hetero-deformation induced strengthening effect, the present cold-consolidated multi-material exhibits tensile properties with yield strength of 1255.4 MPa, uniform elongation of 13.7%, and total elongation of 25.0%, overcoming monolithic Inconel 718 and CoCrFeMnNi systems. These findings shed light on the capability of the cold-consolidation technique to manufacture multi-layered and gradient multi-functional structures with excellent mechanical response under tensile stress.

Achieving high strength and high ductility in ZK60 alloy with a heterogeneous lamella structure

Heterogeneous structure emerges as a novel design philosophy for metal materials to break through the strength-ductility tradeoff. Here we present a heterogeneous lamella (HL) structure in ZK60 alloy that was fabricated by conventional powder metallurgy techniques, i.e., powder pretreatment and hot extrusion. The distinctive structure consists of soft coarse-grained (CG) lamella embedded in the hard ultrafine-grained (UFG) matrix. Compared to the homogeneous CG and UFG counterparts, the HL ZK60 alloy exhibits an excellent combination of tensile yield strength (404.4 MPa) and uniform elongation (13.5 %). This strength-ductility synergy can be attributed to the hetero-deformation induced (HDI) strengthening and HDI strain hardening as a result of the deformation incompatibility and mutual constraint between the hetero-zones.

Approach to the Fatigue and Cellular Behavior of Superficially Modified Porous Titanium Dental Implants.

In this work, the fatigue and cellular performance of novel superficially treated porous titanium dental implants made up using conventional powder metallurgy and space-holder techniques (30 vol.% and 50 vol.%, both with a spacer size range of 100–200 µm) are evaluated. Before the sintering stage, a specific stage of CNC milling of the screw thread of the implant is used. After the consolidation processing, different surface modifications are performed: chemical etching and bioactive coatings (BG 45S5 and BG 1393). The results are discussed in terms of the effect of the porosity, as well as the surface roughness, chemical composition, and adherence of the coatings on the fatigue resistance and the osteoblast cells’ behavior for the proposed implants. Macro-pores are preferential sites of the nucleation of cracks and bone cell adhesion, and they increase the cellular activity of the implants, but decrease the fatigue life. In conclusion, SH 30 vol.% dental implant chemical etching presents the best bio-functional (in vitro osseointegration) and bio-mechanical (stiffness, yield strength and fatigue life) balance, which could ensure the required characteristics of cortical bone tissue.

Development and characterization of low metallic friction composites filled with brass chips

ABSTRACT This research is focused on investigating new low metallic non-asbestos organic friction composite materials obtained by conventional powder metallurgy techniques. Three different composite mixtures were prepared by varying brass concentrations 1.5, 2.0 and 2.5 wt-% using the glycerin as a plasticizer. The prepared brake pad materials were subjected to density, hardness, thermal stability, friction and specific wear rate analysis. Tribological properties of friction specimen were studied on pin-on-disc type friction testing machine model MMW-1 using nominal contact pressure 7.69 MPa, sliding velocity 1.74 m/s and 1.57 km sliding distance conditions. Microstructural characterization of worn surfaces was carried out using scanning electron microscopy. Obtained test results indicate that brass chips have an important effect on improving tribo-performance. Physical–mechanical characterization of friction composites showed that the use of glycerin improves the physical properties of materials by improving the powder compressibility and reducing the structural defects formed by brass chips.

Superlative room temperature and cryogenic tensile properties of nanostructured CoCrFeNi medium-entropy alloy fabricated by powder high-pressure torsion

Attaining decent tensile properties in materials fabricated by conventional powder metallurgy (PM) techniques has perennially been a pivotal challenge due to structural defects— typically pores. This work fabricates a nanostructured CoCrFeNi medium-entropy alloy with an uttermost relative density of 99.63% through PM, i.e., cold powder consolidation using high-pressure torsion followed by annealing. The cold-consolidated sample showed outstanding tensile strengths of 2.06 GPa and 2.81 GPa at room and cryogenic temperatures, respectively, which was never achieved in PM-processed materials. The enhanced cryogenic tensile properties can be associated with intensive mechanical twin activities. Additionally, engineering the microstructure through subsequent annealing leads to a desirable synergy of tensile strength and ductility, which are highly sought after in structural applications. The present findings pave the way to fabricate the parts with superior tensile properties for cryogenic applications through a PM-based approach.

Physical simulation of hot rolling of powder metallurgy-based Al/SiC composite by plane strain multi stage compression

The development of lightweight materials like Al/SiC metal matrix composite sheet is a challenge by different manufacturing processes for further application in the automobile and aerospace industries. In the present work, plane strain multistage compression was used to investigate the hot rolling of powder metallurgy-based Al/7vol.%SiC composite. The cuboids of dimension (80 mm × 45 mm × 15 mm) from this composite material were synthesized using a conventional powder metallurgy technique. Then, the plane strain samples were cut from these composite cuboids. After that, plane strain multistage compression tests were performed using a thermo-mechanical simulator, Gleeble-3800. The multistage compression consists of six stages of different strains and all stages were compressed at a constant strain rate (1 s−1) to achieve a final logarithmic strain of 1.5. All the plane strain stages were conducted at four different temperatures (350, 400, 450 and 500 °C). The flow curves obtained from the plane strain experiments show the initial hardening, then steady-state followed by final hardening. A constitutive equation for flow stresses has been developed and it predicts within the error of 2.62–6.18%. Then, the activation energy and dislocation densities are calculated and analyzed. Dislocation density is significantly high for this composite at the end of deformation as compared to the sintered one. After that, hot rolling experiments were conducted to make the Al/7vol.%SiC composite sheets. A comparative microstructural characterization has been examined using the optical image and electron backscatter diffraction. Recrystallized, deformed and sub-structured grains were observed in the hot-rolled sheet. The tensile fracture mechanisms are particle crack, void, growth and facet, whereas the edge crack in the plane strain samples due to particle crack and debonding. This study opens up the possible use of plane strain compression to design the hot rolling process in the industry for Al-metal matrix composites sheets.

Effect of Silicon Carbide Weight Percentage and Number of Layers on Microstructural and Mechanical Properties of Al7075/SiC Functionally Graded Material

In this research, four different types of Al7075/SiC functionally graded materials (FGMs) are produced by varying the number of layers and weight percentages of silicon carbide(SiC). Each layer is fabricated with a predetermined configuration using the conventional powder metallurgy technique. The result of introducing different weight percentages of SiC particles in each layer and their effect on the functionally graded materials microstructure and mechanical properties are examined. The microstructural analysis clearly shows the uniform distribution of reinforcement material gradient from top to bottom and good interfacial bonding among the layers of FGMs. The functionally graded material’s density decreases with an increase in SiC weight percentage due to increased defects. The variation of hardness in each layer confirms the successful fabrication of Al7075/SiC functionally graded material with different layers. The mechanical properties of Al7075/SiC functionally graded materials mainly depend on the type of interfacial bonding between the layers, micro-cracks, pores, and SiC agglomerations. The prepared functionally graded materials exhibit extended mechanical and wear characteristics and are recommended in the manufacturing of gears, drive shafts, brake drums and bearings.

Fabrication and characterization of superficially modified porous dental implants

Abstract Stress-shielding and loosening compromise the success of dental implants under real-life service conditions. This work evaluates the mechanical behavior of superficially modified porous titanium dental implants fabricated by two different routes: conventional powder-metallurgy and space-holder techniques. A novel, feasible and repetitive protocol of micro-milling of the implant thread (before sintering), as well as surface modification treatments (after sintering) are also implemented. The discussion is conducted in terms of the influence of porosity and surface roughness on the stiffness and yield strength of implants. The macro-pores concentrate stress locally, and, at the same time, they could act as a barrier to the propagation of micro-cracks. Higher rugosity was observed for virgin implants obtained with spacer particles. Concerning superficially modified implants, while bioglass 1393 was the most effective coating due to its greater infiltration and adhesion capacity, chemical etching could improve osteoblast adhesion because modifies the roughness of the implant surface.

Design and characterization of Ti6Al4V/20CoCrMo−highly porous Ti6Al4V biomedical bilayer processed by powder metallurgy

Abstract The aim of this work was to develop a Ti6Al4V/20CoCrMo−highly porous Ti6Al4V bilayer for biomedical applications. Conventional powder metallurgy technique, with semi-solid state sintering as consolidation step, was employed to fabricate samples with a compact top layer and a porous bottom layer to better mimic natural bone. The densification behavior of the bilayer specimen was studied by dilatometry and the resulting microstructure was observed by scan electron microscopy (SEM) and computed microtomography (CMT), while the mechanical properties and corrosion resistance were evaluated by compression and potentiodynamic tests, respectively. The results indicate that bilayer samples without cracks were obtained at the interface which has no negative impact on the densification. Permeability values of the highly porous layer were in the lower range of those of human bones. The compression behavior is dictated by the highly porous Ti6Al4V layer. Additionally, the corrosion resistance of Ti6Al4V/20CoCrMo is better than that of Ti6Al4V, which improves the performance of the bilayer sample. This work provides an insight into the important aspects of a bilayer fabrication by powder metallurgy and properties of Ti6Al4V/20CoCrMo−highly porous Ti6Al4V structure, which can potentially benefit the production of customized implants with improved wear performance and increased in vivo lifetime.