Showing papers on "Powder metallurgy published in 2019"

High-entropy alloys fabricated via powder metallurgy. A critical review

Abstract: High-entropy alloys (HEAs) have attracted a great deal of interest over the last 14 years. One reason for this level of interest is related to these alloys breaking the alloying principles ...

Wear and mechanical properties of Al6061/SiC/B4C hybrid composites produced with powder metallurgy

Abstract: This study investigates the production of various reinforced and non-reinforced composite materials using powder metallurgy (PM). It presents the new approach into optimize the mechanical properties of hybrid composites (Al-SiC-B4C) produced with powder extrusion process. A16061 powders are used as the matrix material and B4C and SiC powders are used as the reinforcement materials. Matrix and reinforcement materials are mixed in a three-dimensional mixer. The mixtures are then subjected to cold pressing to form metal block samples. Block samples are subjected to hot extrusion in an extrusion mold after being subjected to a sintering process. This produces samples with a cross-sectional area of 25 × 30 mm2. These extruded samples were subjected to T6 heat treatment. The composite materials produced are examined in terms of density, hardness, transverse rupture strength, tensile strength, and wear resistance. Furthermore, optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and XRD are performed to examine the microstructure, surface fractures, and surface abrasion. In this study, high density Al6061/B4C/SiC hybrid composite materials were successfully produced. After extrusion, some micro particles were found to crack. The highest hardness occurred in 12%B4C reinforced composites. The lowest hardness was obtained in Al6061 alloy without reinforcement. The highest tensile strength occurred in 12%SiC particle reinforced composite material. The highest wear resistance was obtained for 9%B4C+3%SiC samples due to the hardness of B4C and the good adhesion properties of the matrix and SiC.

Evaluation of the mechanical and wear properties of titanium produced by three different additive manufacturing methods for biomedical application

Abstract: Commercially pure titanium, as a widely used metallic biomaterial, was fabricated using dissimilar additive manufacturing (AM) methods, namely selective laser melting (SLM), laser engineered net shaping (LENS) and wire arc additive manufacturing (WAAM). Microstructures as well as mechanical and wear properties of the produced titanium samples were studied. Diverse microstructural features were related to the different linear energy densities and cooling rates induced by each AM method. Tensile testing evaluation indicated the highest yield and ultimate tensile strengths as well as elastic energy for titanium produced by SLM. However, the maximum ductility was obtained in the WAAM-fabricated titanium due to its larger grain size and slightly higher densification. All the mechanical properties obtained were either superior or comparable to those of cast and powder metallurgy produced titanium. Fracture surface analysis showed the presence of mainly coarse and fine dimples for WAAM and SLM-produced samples, respectively. This was consistent with the grain size of each sample. Wear performances and mechanisms were also examined and the results were in agreement with the values obtained from the hardness to elastic modulus ratios (H/E and H3/E2).

A review on recent developments in binder jetting metal additive manufacturing: materials and process characteristics

Abstract: Binder Jetting Metal Additive Manufacturing (BJ-MAM), known also as metal 3D-printing, is a powder bed-based additive manufacturing technology. It consists of the deposition of liquid binder drople...

The porosity, microstructure, and hardness of Al-Mg composites reinforced with micro particle SiC/Al2O3 produced using powder metallurgy

Abstract: In this study, Al-Mg metal matrix composite (MMC) materials reinforced with micro-sized SiC, Al2O3 particles were manufactured using powder metallurgy. SiC and Al2O3 particles with 1 μm size were added to the Al-Mg matrix at different volume ratios (15–30%). A mixture of Al, Mg, reinforcement (SiC, Al2O3) powders was mixed at a speed of 16 rpm over a 24 h-time period for a homogeneous dispersion. The mixed powders were pressed at 300 and 600 MPa. Composite materials produced at different pressures were sintered under for 30, 60, 90 min and at 300, 400, 500 °C and allowed to cool in the furnace. The microhardness, porosity, microstructure of Al-Mg/SiC and Al-Mg/Al2O3 composites were investigated and characterized. The highest porosity ratio for all test conditions was measured as being 17% in the Al-Mg composite reinforced with 15% SiC produced at 300 MPa and 400 °C for 90 min. The lowest porosity ratio was measured as being 5.4% in the Al-Mg composite reinforced with 15% SiC produced at 600 MPa and 500 °C for 90 min. In their microstructure studies, a generally homogeneous microstructure was observed.

Low-cost powder metallurgy Ti-Cu alloys as a potential antibacterial material.

Abstract: Ti and Ti alloys are extensively used in biomedical applications due to their excellent biocompatibility and mechanical properties but their high-cost of production is still a limiting factor. It has been reported that the addition of Cu to Ti enables the creation of Ti alloys exhibiting antibacterial properties. Therefore, in this study Ti-Cu alloys (Cu = 0.5, 2.5 and 5 in wt.%) with potential antibacterial activity were fabricated by powder metallurgy (i.e. cold press and vacuum sintering) to reduce the production costs. As many biomaterials are employed as structural components, the Ti-Cu alloys were also subjected to β forging in order to improve their mechanical properties. It is found that the studied Ti-Cu alloys have superior mechanical properties to other commonly used Ti-based materials and are, thus, potential candidate for biomedical applications. Moreover, among the tested materials, the β forged Ti-5Cu alloys has tensile strength of 904 MPa, elongation of 6.7%, and Vickers hardness of 302 HV, which are comparable to those of the Ti-6Al-4V, and comprises the Ti2Cu phase (confirmed by the XRD) as microstructural feature, which is fundamental to guarantee antibacterial properties.

Structural, mechanical and thermal characteristics of Al-Cu-Li particle reinforced Al-matrix composites synthesized by microwave sintering and hot extrusion

Abstract: In this study, Al-Cu-Li (5, 10 and 15 vol%) alloy particles reinforced Aluminum matrix composites were synthesized by powder metallurgy route incorporating microwave sintering and hot extrusion processes. The effects of novel Al based alloy reinforcement on the microstructure, mechanical and thermal characteristics of the Al/Al-Cu-Li composites were investigated. Uniformly distributed Al-Cu-Li alloy particles were observed in the microstructure of the composites. The synthesized materials were characterized for microhardness, co-efficient of thermal expansion, tensile and compressive properties. The results reveal that, hardness, Young's modulus, ultimate compression strength, ultimate tensile strength, yield strength and elongation of Al/15Al-Cu-Li composite improved by ∼186%, 53%, 42%, 47%, 41%, and 48%, respectively in comparison to pure Al. This increase in strength and hardness values is attributed to the distribution of hard and brittle aluminum-based alloy phases in the ductile Al matrix. Furthermore, coefficient of thermal expansion of composites revealed the better thermal stability behavior for Al/15Al-Cu-Li composite compared to pure Al. The results of the present study suggest that the Al/15Al-Cu-Li composite is a very promising candidate for aerospace applications, which are extremely demanding in terms of both comprehensive mechanical properties and lightweight.

Development of Wire + Arc additive manufacture for the production of large-scale unalloyed tungsten components

Abstract: The manufacturing of refractory-metals components presents some limitations induced by the materials' characteristic low-temperature brittleness and high susceptibility to oxidation. Powder metallurgy is typically the manufacturing process of choice. Recently, Wire + Arc Additive Manufacture has proven capable to produce fully-dense large-scale metal parts at relatively low cost, by using high-quality wire as feedstock. In this study, this technique has been used for the production of large-scale tungsten linear structures. The orientation of the wire feeding has been studied and optimised to obtain defect-free tungsten deposits. In particular, front wire feeding eliminated the occurrence of pores and micro-cracks, when compared to side wire feeding. The microstructure, the occurrence of defects and their relationship with the deposition process have also been discussed. Despite the repetitive thermal cycles and the inherent brittleness of the material, the as-deposited structures were free from internal cracks and the layer dimensions were stable during the entire deposition process. This enabled the production of a relatively large-scale component, with the dimension of 210 × 75 × 12 mm. This study has demonstrated that Wire + Arc Additive Manufacture can be used to produce large-scale parts in unalloyed tungsten by complete fusion, presenting a potential alternative to the powder metallurgy manufacturing route.

Experimental investigations on wear and friction behaviour of SiC@r-GO reinforced Mg matrix composites produced through solvent-based powder metallurgy

Abstract: In the present study, wear and friction behaviour of Magnesium(Mg) Metal Matrix Composite(MMC) reinforced with Silicon carbide(SiC) doped reduced graphene oxide (r-GO) nanosheets is carried over. In addition, a mathematical model is developed to predict the influence of various control factors of the Mg composites fabricated through Solvent-based powder metallurgy process. Herein SiC is doped with varying wt. % (10, 20, 30) into r-GO nanosheets and its effect over dry sliding wear is studied at constant control parameters like that of load (10N), sliding distance (1000m) and sliding velocity (1 m/s). Optimal parameter for specific wear rate (SWR) is attained by Taguchi method and the mathematical model was developed using Artificial Neural Network in order to understand the wear behaviour of developed MMC under varying parametric condition. Analysis of variance result reveals that wt.% of r-GO have major influence on SWR and sliding velocity have least effect. Occurrence of delamination wear could also be notified over the worn out surface.

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

Abstract: 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.

Mechanical properties and microstructure of Ti-Mn alloys produced via powder metallurgy for biomedical applications.

Abstract: Titanium and especially its alloys are highly employed materials in biomedical applications because of their balanced mechanical properties and biocompatibility. Ti-Mn alloys (1, 5, and 10 wt%. Mn) were produced by powder metallurgy as a potential alternative material for biomedical applications. Two sets of samples were produced, one set as-sintered and the other was beta (β) forged. For the as-sintered samples with a content of up to 10 wt% Mn, the tensile strength ranged from 606 to 1070 MPa. On the other hand, for the β forged alloys the tensile strength ranged from 728 to 1224 MPa and the maximum value was for Ti-5Mn. Forged Ti-5Mn exhibits a good balance of mechanical properties such as ultimate tensile strength (1224 MPa), elongation (4.6%) and Vickers hardness (415 HV). The purely elastic properties of the Ti-10Mn alloy is attributed to the effects of the omega (ω) phase, the formation of which is due to the high amount of beta stabiliser added to Ti.

Microstructure and Mechanical Properties of Al–Co–Cr–Fe–Ni Base High Entropy Alloys Obtained Using Powder Metallurgy

Abstract: Four different compositions of high entropy alloys based on Al–Co–Cr–Fe and Al–Co–Cr–Fe–Ni systems were prepared using mechanical alloying and consolidation by spark plasma sintering. The chemical compositions of the studied alloys were experimentally selected to obtain a BCC solid solution and mixtures of BCC with FCC. The microstructure of the Al25Co25Cr25Fe25 (all in at%) high entropy alloy consisted of a matrix with a high concentration of Al, Co and Fe, in which spherical grains (50–200 nm) enriched in Cr were embedded. Both the matrix and grains had body centered cubic structures. The addition of nickel to a four-element system led to the formation of a multiphase composition. The microstructure of the Al20Co20Cr20Fe20Ni20, Al10Co30Cr20Fe35Ni5 and Al15Co30Cr15Fe40Ni5 HEAs consisted of fine grains measuring 50–500 nm composed of: AlNi-B2, BCC phase, FCC or BCC solid solutions and σ-sigma phase, respectively. The complex structure of the studied samples resulted in changeable mechanical properties. The highest compression strength of 3920 MPa was accompanied by an increased yield strength of 3500 MPa, and a low strain of 0.7%, for the Al25Co25Cr25Fe25 alloy. The addition of Ni led to the formation of plastic FCC phases responsible for a decrease in strength with increases in ductility, which, in the new non-equiatomic Al10Co30Cr20Fe35Ni5 high entropy alloy reached 6.3% at a yield strength of 1890 MPa and compression strength of 2230 MPa. The conducted abrasion studies revealed that non-equilibrium high entropy alloys have the highest abrasion resistance.

Breaking through the strength-ductility trade-off dilemma in powder metallurgy Ti–6Al–4V titanium alloy

Abstract: A novel approach was developed to fabricate low-oxygen powder metallurgy Ti–6Al–4 V (wt.%) titanium alloy with a highly desirable combination of ultrahigh tensile strength and good ductility. Using clean and unpassivated TiH2 based powder compact, together with cleaning effect of in-situ dehydrogenation during heating the powder compact resulted in a low oxygen content of 0.26% in final extrusion consolidated alloy. The nature of cleaning effect during sintering was proved to be a reduction reaction of TiO2 + 4[H] = Ti + 2H2O (g). Besides, solution & aging treatment produced a unique composite lamellar microstructure, which mainly consists of fine α platelets and β-transformed structures containing high number density of ultrafine acicular α precipitates. Such composite lamellar microstructure gave rise to extra geometrically necessary dislocations during tensile deformation and brought about significant dislocation hardening together with high global strain. Consequently, this Ti–6Al–4 V alloy exhibited a superior ultimate tensile strength of up to 1320 MPa and meanwhile a high elongation to fracture of not less than 12.5%.

Titanium-based matrix composites reinforced with particulate, microstructure, and mechanical properties using spark plasma sintering technique: a review

Abstract: The interest for lightweight and high-temperature materials for critical innovative applications is expanding in numerous modern industries. Reinforcing ceramic particles with micro/nano-scale sizes into titanium alloys is distinguished, thereby increasing the hardness and wear resistance. Alternatively, reduction in particles sizes also helps in increasing the strength, ductility, and creep resistance of the reinforced materials. Nano-ceramic has significant improvement in mechanical properties of a material, which makes it practically a good reinforcement in metal composites. Recent advancement in nanotechnology area demands innovative improvement in metal matrix composite for critical and functional applications. The effects of micro/nanomaterial dispersion in the metal matrix composite are spoken about and the formation of unexpected interfacial reaction on these properties. Powder metallurgy is a process where powder materials are being compacted or sintered in the furnace with the perspective of accomplishing higher densities. Spark plasma sintering techniques have a favorable condition over other sintering methods since it tends to decrease the sintering time with high temperatures, attaining higher densities, microstructural evolution, and the tendency to improve the mechanical properties of the material. This review focuses on the fabrication and mechanical properties of titanium alloy strengthening with micro/nano-ceramics.