Conventional Powder Metallurgy Research Articles

Production and Characterization of Hybrid Al6061 Nanocomposites

Aluminum-based hybrid nanocomposites, namely the Al6061 alloy, have gained prominence in the scientific community due to their unique properties, such as high strength, low density, and good corrosion resistance. The production of these nanocomposites involves incorporating reinforcing nanoparticles into the matrix to improve its mechanical and thermal properties. The Al6061 hybrid nanocomposites were manufactured by conventional powder metallurgy (cold pressing and sintering). Ceramic silicon carbide (SiC) nanoparticles and carbon nanotubes (CNTs) were used as reinforcements. The nanocomposites were produced using different reinforcement amounts (0.50, 0.75, 1.00, and 1.50 wt.%) and sintered from 540 to 620 °C for 120 min. The characterization of the Al6061 hybrid nanocomposites involved the analysis of their mechanical properties, such as hardness and tensile strength, as well as their micro- and nanometric structures. Techniques such as optical microscopy (OM) and scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD) were used to study the distribution of nanoparticles, the grain size of the microstructure, and the presence of defects in the matrix. The microstructural evaluation revealed significant grain refinement and greater homogeneity in the hybrid nanocomposites reinforced with 0.75 wt.% of SiC and CNTs, resulting in better mechanical performance. Tensile tests showed that the Al6061/CNT/SiC hybrid composite had the highest tensile strength of 104 MPa, compared to 63 MPa for the unreinforced Al6061 matrix. The results showed that adding 0.75% SiC nanoparticles and CNTs can significantly improve the properties of Al6061 (65% in the tensile strength). However, some nanoparticle agglomeration remains one of the challenges in manufacturing these nanocomposites; therefore, the expected increase in mechanical properties is not observed.

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.

Insights on the electrical conductivity enhancement mechanisms of carbon polymer dots (CPDs) reinforced Cu composites

Carbon polymer dots (CPDs) has represented unique potential in reconciling the incompatible properties of strength and electrical conductivity (EC) in copper matrix composites, while the mechanisms underlying EC improvement remain to be fully elucidated. 0.2CPDs/Cu composites prepared by conventional powder metallurgy processes achieves excellent mechanical and electrical conductivity simultaneously. Compared to pure Cu, CPDs not only participated in the construction of a better electronic transport pathway, but accelerated the twinning forming behavior, leading to outstanding strength(~423 MPa) and electrical conductivity(95%IACS). Here the conductive behavior of CPDs/Cu composites was revealed through characterizing the intrinsic electrical properties of CPDs and composites microstructure evolution. CPDs not only participated in the construction of a better electronic transport pathway, but accelerated the twinning forming behavior. Increased twinning domain leads to the remarkable amelioration of grain boundary resistance, meanwhile, the intragranular CPDs made a significant contribution on the enhanced mechanical strength via Orowan strengthening. This work makes up the lack of understanding on the mechanical and electrical enhancement mechanism in our prior research.

Magnetron sputtered ß-Ti coatings for biomedical application: A HiPIMS approach to improve corrosion resistance and mechanical behavior

This work presents the surface modification of commercially pure Ti specimens (c.p.-Ti) prepared by conventional powder metallurgy by depositing a thin film of a ß-Ti alloy (Ti-35Nb-7Zr-5Ta, wt. %, TNZT). Two types of pulsed technologies: conventional (p-DC) and high-power impulse magnetron sputtering (HiPIMS), with and without bias assistance (−60 V) under similar power conditions (250 W) were applied on titanium specimens and silicon substrates leading to different film morphologies and functional properties. Microstructural, X-ray diffraction, nanoindentation, surface wetting, XPS and electrochemical impedance measurements were done to characterize their functionality. All the coatings presented a reduced Young’s Modulus (E ≤ 80GPa) compared to the bulk Ti, representing a reduction of more than 30 %. This decrease can significantly contribute to the reduction of the stress-shielding effect, mitigating the risk of implant loosening and failure. The hardness values of TNZT coatings, slightly lower than c.p.-Ti substrate, range from 4.1 to 4.7 GPa. XPS analysis shows a passivation layer of TiO2, Nb2O5, and ZrO2, which offers high impedance and excellent corrosion resistance. The best compromise between mechanical and corrosion properties is achieved with the HiPIMS technology, thanks to its compact film microstructure with high electrical resistance, despite its limited thickness of about 1 μm.

Coarse-grained WC–6Co hardmetals with dual-scale and plate-like WC structures fabricated by convention powder metallurgy process

In this work, coarse-grained WC–6Co hardmetals featuring dual-scale and plate-like structures were successfully fabricated via conventional powder metallurgy process using W, ultrafine WC, Co and carbon black as raw materials. The investigation focuses on the effects of two critical factors, sintering temperature and ultrafine WC powder content, on the microstructures, densities, and mechanical properties. The results demonstrate that increasing the sintering temperature accelerates the growth of WC grains via 2D nucleation growth mechanism, thus enhancing the plate-like structure of WC grains. The addition of ultrafine WC powder reduces the mean WC grain size and eliminates the preferential orientation of WC grains because of its separating effect on coarse WC grains. Moreover, the dual-scale and plate-like structures can be achieved with sufficient ultrafine WC content (≥ 20 wt%) and adequate sintering temperature (≥ 1500 °C). Notably, the coarse-grained WC–6Co alloy sintered at 1550 °C with the addition of 20 wt% ultrafine WC powder exhibits good comprehensive mechanical properties: hardness of 1493 ± 7 HV30, transverse rupture strength of 2698 ± 58 MPa and fracture toughness of 16.93 ± 0.65 MPa·m1/2.

Effects of YH2 dopant on densification behavior, microstructure and mechanical properties of Ti–6Al–4V alloys

Ti6Al4V-xYH2 (x = 0, 0.1, 0.2, and 0.3 wt%) was produced in this research employing conventional powder metallurgy methods (cold pressing and sintering). The densification behavior, microstructure and mechanical properties of Ti6Al4V alloy caused by the addition of YH2 were systematically studied. The outcomes indicated that the Ti6Al4V containing 0.1 wt% YH2 has received a synergistic increase in ductility and strength (Ultimate tensile strength: 976.4 MPa; Elongation: 9.3 %), which is mainly attributable to the combined effect of grain refinement and purification of impurity oxygen. The study provides an economical approach for employing low-cost, high-oxygen HDH Ti powder to produce high-performance Ti material.

Rapid, Micron-Resolution 3D Printing of Nd:YAG Ceramic with Optical Gain.

Polycrystalline yttrium aluminum garnet (YAG) ceramic doped with neodymium (Nd), referred to as Nd:YAG, is widely used in solid-state lasers. However, conventional powder metallurgy methods suffer from expenses, time consumption, and limitations in customizing structures. This study introduces a novel approach for creating Nd:YAG ceramics with 3D free-form structures from micron (∼70µm) to centimeter scales. Firstly, sol-gel synthesis is employed to form photocurable colloidal solutions. Subsequently, by utilizing a home-built micro-continuous liquid interface printing process, precursors are printed into 3D poly(acrylic acid) hydrogels containing yttrium, aluminum, and neodymium hydroxides, with a resolution of 5.8µm pixel-1 at a speed of 10µm s-1. After the hydrogels undergo thermal dehydration, debinding, and sintering, polycrystalline Nd:YAG ceramics featuring distinguishable grains are successfully produced. By optimizing the concentrations of the sintering aids (tetraethyl orthosilicate) and neodymium trichloride (NdCl3), the resultant samples exhibit satisfactory photoluminescence, emitting light concentrated at 1064nm when stimulated by a 532nm laser. Additionally, Nd:YAG ceramics with various 3D geometries (e.g., cone, spiral, and angled pillar) are printed and characterized, which demonstrates the potential for applications, such as laser and amplifier fibers, couplers, and splitters in optical circuits, as well as gain metamaterials or metasurfaces.

Exploring the role of Fe in the wear and corrosion resistance of Ti-based alloys produced with conventional powder metallurgy

In this study, the Ti-6Al-XFe alloy was produced by conventional powder metallurgy at varying Fe contents (3.5, 7.0, 10.5, 14.0, 17.5, and 21.0 wt%) to investigate its potential as a substitute for Nb and V. The primary aim was to assess the impact of Fe content on the mechanical, tribological, and electrochemical properties of the alloys, focusing on their suitability for biomedical implants. XRD and SEM analyses revealed a decrease in the α-Ti phase and an increase in the β-Ti and FeTi phases with higher Fe content. The lowest porosity (0.8 %) and highest hardness (348.4 Hv0.2) were observed in the Ti-6Al-17.5Fe alloy. Tensile and flexural strengths peaked at 238.3 MPa and 680 MPa, respectively, in the 17.5Fe alloy. The Ti-6Al-14.0Fe alloy showed the smallest change in specific wear rate (0.274 × 10−6 mm3/N·m) under dry conditions, while the Ti-6Al-7.0Fe alloy had the smallest change (0.565 × 10−6 mm3/N·m) under wet conditions. The 7.0Fe alloy demonstrated the highest corrosion resistance, with the lowest Icorr (1.02 × 10−8 mm3/N·m) and corrosion rate (14.02 × 10−3 mpy), and the highest charge transfer resistance in EIS analysis.

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.

In Situ Fabrication of Ti-xNb Alloys by Conventional Powder Metallurgy

In Situ Fabrication of Ti-xNb Alloys by Conventional Powder Metallurgy

Using fused filament fabrication to improve the tribocorrosion behaviour of 17-4 PH SS in comparison to other metal forming techniques

Fused filament fabrication (FFF) is one of the additive manufacturing processes which has gained more interest because of its simplicity and low-cost. This technology is similar to the conventional metal injection moulding (MIM) process, consisting of the feedstock preparation of metal powder and polymer binders, followed by layer-by-layer 3D printing (FFF) or injection (MIM) to create green parts and, finally, debinding and sintering. Moreover, both technologies provide near-dense parts. This work presents an in-depth study of the processing method’s influence. The porosity, microstructure, hardness, corrosion, and tribocorrosion behaviour are compared for 17-4 PH SS samples processed from powder by additive manufacturing using FFF and MIM, as well as conventional powder metallurgy (PM) samples. MIM samples exhibited the highest macro and microhardness, while corrosion behaviour was similar for both MIM and FFF samples, but superior in comparison to conventional PM samples. However, the FFF-as fabricated samples displayed a significant improvement in tribocorrosion resistance that could be explained by the higher proportion of delta ferrite and retained austenite in their microstructure.

Compaction behaviours of 17-4 PH, 316L, and 1.4551 stainless-steel powders during cold pressing

Despite numerous recent technological developments, conventional powder metallurgy (CPM) remains the most commonly applied technique for fabricating stainless-steel products. However, the compressibility of stainless-steel powders is still a critical issue. Martensitic stainless-steel powders (i.e., 17-4 PH) are significantly harder than austenitic stainless-steel powders (i.e., 316L and 1.4551). Herein, three different stainless-steel (DSS) powders (i.e., 17-4 PH, 316L, and 1.4551) were investigated using a high cold pressing pressure (i.e., 1.6 GPa) and a relatively low sintering temperature of 1200 °C during CPM. Dimensional and Archimedes density measurements, volume and radial shrinkage calculations, optical and scanning electron microscopy analyses, and compressive strength measurements were conducted to investigate the physical and mechanical properties. Using 1.6 GPa resulted in a 10 % and 6 % increase in the relative green density of the 17-4 PH and 316L samples, compared with the reported literature. For the first time, relative sintering densities of approximately 97 % and 99 % were obtained for 316L and 1.4551 at a sintering temperature of 1200 °C, respectively. Despite the insufficient sintering process, the relative density of the 17-4 PH sample increased by 2 % compared with the literature values reported for higher sintering temperatures. The shrinkage ratios were much lower than those reported in the literature. Furthermore, the present 316L samples achieved 90 % of the compressive yield strength observed in cast 316L, a 25 % increase compared with that previously reported in the literature. This study extends the CPM procedure for enhancing green densities, employing low sintering temperatures, and reducing the shrinkage values of stainless-steel powders with differing hardness.

Effect of B content on microstructure and properties of powder metallurgy Ti-2Mn-2Sn alloy

Ti-2Mn-2Sn-xB (x = 0, 0.3, 0.5, 1, and 2 wt%) was produced in this research employing conventional powder metallurgy methods (cold pressing and sintering). The densification behavior, microstructure, and mechanical properties of Ti-2Mn-2Sn alloy caused by the addition of B were systematically studied. The outcomes indicated that the inclusion of B element can inhibit the densification behavior of Ti-2Mn-2Sn alloy. The morphology of microstructure eventually shifts from plate to equiaxial with the inclusion of B element. When the B element is less than 2 wt%, the strength of the sample exhibits an upward trend, which is mainly attributable to the combined effect of grain refinement and the presence of small amounts of TiB.

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.

A comparative study of electric current-assisted and conventional sintering of Inconel 718 superalloy

In this study, In718 powder mixtures prepared from elemental powders following stoichiometric composition and supplied as a commercial product were produced by conventional powder metallurgy (1300 °C/4 h) and electric current-assisted sintering (ECAS)(1700-2300A/10 min) methods and followed by a double-aging heat treatment. The characterization studies determined that the best results were the sample produced by the ECAS method using the elemental powder mixture. The targeted precipitate γ′, γ″, and δ phases were obtained after the heat treatment, and a hardness value of 344 ± 41 HV0.5 and a relative density of 98.96% were achieved. The sample preserved its surface integrity by exhibiting high corrosion resistance from hot corrosion studies in the temperature range of 650–850 °C and NaSO4 + 60%V2O5 environment. The corrosion rate of the sample, which was subjected to electrochemical corrosion tests in 3.5% NaCl and 10% NaNO3 solutions, was determined as 45.59 mpy and 10.56 mpy, respectively.

Microstructure and mechanical properties of Ti-Nb alloys: comparing conventional powder metallurgy, mechanical alloying, and high power impulse magnetron sputtering processes for supporting materials screening

At the interface of thin film development and powder metallurgy technologies, this study aims to characterise the mechanical properties, lattice constants and phase formation of Ti-Nb alloys (8–30 at.%) produced by different manufacturing methods, including conventional powder metallurgy (PM), mechanical alloying (MA) and high power impulse magnetron sputtering (HiPIMS). A central aspect of this research was to investigate the different energy states achievable by each synthesis method. The findings revealed that as the Nb content increased, both the hardness and Young’s modulus of the PM samples decreased (from 4 to 1.5 and 125 to 85 GPa, respectively). For the MA alloys, the hardness and Young’s modulus varied between 3.2 and 3.9 and 100 to 116 GPa, respectively, with the lowest values recorded for 20% Nb (3.2 and 96 GPa). The Young’s modulus of the HiPIMS thin film samples did not follow a specific trend and varied between 110 and 138 GPa. However, an increase in hardness (from 3.6 to 4.8 GPa) coincided with an increase in the β2 phase contribution for films with the same chemical composition (23 at.% of Nb). This study highlights the potential of using HiPIMS gradient films for high throughput analysis for PM and MA techniques. This discovery is important as it provides a way to reduce the development time for complex alloy systems in biomaterials as well as other areas of materials engineering.Graphical abstract

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.

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.