Papers by Keyword: Sintering

Abstract: Co additions to titanium aluminides were assessed to decrease the typically high sintering temperatures necessary for the densification of intermetallics. Compositions based on the binary Ti-45Al with ternary Co variations between 1-10 at.% were investigated. The specimens were cylinders with 8 mm diameter prepared using blended elemental powders followed by cold uniaxial pressing. Sintering was carried out under an argon atmosphere at different temperatures ranging from 1100 to 1400 °C for 2 hours in a tube furnace. The results indicated that there was a systematic increase in densification with Co additions. The relative density of the reference material Ti-45Al was approximately 53%, however, Co addition of 10% led to densifications in the order of 80%. A strong effect of decreasing the sintering temperature was achieved with Co additions. The microstructure changed from fully lamellar with 1 at.% Co sintered at 1400 °C to duplex with higher Co additions sintered at 1200 °C. Besides the γ-TiAl and α₂-Ti₃Al equilibrium phases, the formation of a CoAl₂Ti intermetallic was identified. The addition of 7% Co led to the highest hardness of approximately 450 HV.

Abstract: Ideal physical and mechanical properties and lightweight materials are the main requirements in today's transportation and automotive industries. This research aims to determine variations in Mg composition and sintering temperature of aluminum matrix composites using moulds with a powder metallurgy process on the properties and microstructure of the composite. Magnesium particles with a size of 250 μm were added to the Al-Cu-Mg-matrix at different volume ratios (1%, 1.5%). The mixture of Al, Mg, and reinforcement (Cu, ) powder was mixed at 1,500 rpm for 2 hours for homogeneous dispersion. The mixed powder is compacted at 200 MPa and sintered at different temperatures (500°C, 550°C, 600°C) and then allowed to cool slowly in the furnace. Composite character research was then done by testing density using the Archimedes principle, porosity, microhardness, wear rate, SEM characterization, quantitative analysis and EDS mapping. The optimal composite condition is characterized by a relative density of 57.45%, the lowest porosity ratio measured at 7.48%, a microhardness level of 52.1 HV and the lowest wear rate of 0.58 /m in the Al-Cu-Alumina composite with the addition of 1.5% Mg and sintered at a temperature of 600°C. This composite character is supported by the results of microstructure observations using SEM-EDS. The use of micro-in the Al-Cu-Mg composite supports the optimization of physical and mechanical characteristics as a composite worthy of being considered as the material of choice for components of transportation and automotive modes.

Abstract: This research synthesized a composite ceramic material base CaCO₃/Al₂O₃, CERMET, with possible biomedical applications. Eggshell was used as raw material to obtain CaCO_3, and it was reinforced with silver nanoparticles to improve the structural and mechanical properties of the ceramic system. The addition of silver nanoparticles promotes the formation of two phases. The first is a continuous phase called a matrix formed of CaAl₂O₄ (calcium aluminate). The second is a dispersed phase known as reinforcement made up of silver nanoparticles. The composite ceramics were synthesized using the solid-state synthesis technique from a chemical mixture of CaCO₃ and Al₂O₃ powders in the following chemical ratio: 49.5% CaCO₃ + 50.5% Al₂O₃, with silver nanoparticles added at different percentages (1%, 5%, 10%, 15%). The powder mixture was made in a high-energy mill for homogenization. After that, the mixture was compressed into cylindrical samples for their consolidation by sintering in a high-temperature muffle with a controlled atmosphere, using heating ramps. The sintered samples were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, and microhardness, including fracture toughness studies. In addition, the Archimedes method determined the sintered samples' density. The results showed a clear relation between the mechanical properties of the CaAl₂O₄ ceramic base and the incorporated silver nanoparticles since these increased as the percentage of silver nanoparticles increased. In addition, it was observed that the porosity of the samples could be controlled, making the composite material suitable for biomedical applications.

Abstract: In this work, the Fe-Cr-Mo-V-W-C-MoS₂ composites were fabricated using the powder metallurgy process. The uniaxial cold compaction was used to produce green specimens with the density of 6.3 g/cm³. Subsequently, the specimens were sintered at temperatures of 1150 and 1200 °C for 45 min in a vacuum furnace. Sintered specimens were cooled down in the furnace with N₂ at a cooling rate of 0.1 °C/s. The influence of MoS₂ addition on the density, hardness and microstructure were investigated. Density and hardness of composites were improved due to MoS₂ addition, especially, 5 wt.% MoS₂ addition and sintering at 1200 °C. The dissociation of MoS₂ contributed to the formation of sulfide phases and hard carbide particles within the composites. Sulfide phases such as FeS, CrS and other sulfides were detected by x-ray diffraction analysis. The reciprocating wear test was used to study the effect of MoS₂ addition on friction and wear resistance of composites. The synergy of FeS and CrS contained in the compacted layer and hard carbide particle formation within the matrix were expected to enhance tribological properties of composites by decreasing friction coefficient and improving wear resistance.

Abstract: The study investigates the impact of printing resolution on the dimensional change and microstructure of additive-manufactured parts, specifically dental crowns produced through binder jetting and sintering. Dental crowns are crucial for dental restoration, providing strength and support to damaged teeth. The additive manufacturing process involves digital scanning, 3D metal printing, sintering, and post-processing. The focus here is on the dimensional accuracy and microstructure of the sintered parts made from 17-4PH stainless steel powder. Two printing resolutions, 250 μm and 400 μm, are evaluated to observe their effects on the final properties. Results reveal that printed parts exhibit a significant enlargement (17-19%) due to allowances for binder removal during sintering. Sintered parts, while smaller than printed parts, still exhibit a 4-7% enlargement compared to the original CAD model. Microstructural analysis indicates the presence of ferrite and austenite matrix structures, with particles identified as silicon dioxide residue from the binder. The finer resolution (250 μm) shows greater particle area and count, leading to higher microhardness. These findings provide insights into the dimensional changes and microstructural features crucial for precision in dental applications utilizing additive manufacturing technology.

Abstract: In this work, the molecular dynamics simulation method is employed to understand the sintering behaviour and mechanical properties of the Invar alloy. The densification behaviour of Invar alloy nanoparticles with different sizes at a fixed sintering temperature is investigated. The influence of external pressure is also simulated. Finally, the uniaxial tensile test is employed to study the mechanical response of the sintered product. The results show a qualitative relationship between particle size, external pressure, densification, and mechanical properties. Smaller particle sizes and higher external pressure promote densification. The uniaxial tensile results show that the sintered structure has a lower Young’s modulus than the bulk crystal because of the porosity, and the sample with high porosity has a low value of mechanical strength.

Abstract: In this study, the phase formation, microstructure and microhardness of nickel-based superalloy fabricated using a spark plasma sintering technique were evaluated. The microstructure and microhardness of the nickel-based superalloy were explored at diverse sintering temperatures (600 °C - 1050 °C). The phase formations and volume fraction with respect to temperature were predicted by using CALPHAD-based software. The microstructure, phase constitution, and microhardness were evaluated via scanning electron microscope (SEM), X-ray diffraction (XRD), and Vickers hardness tester. The findings indicated that the spark plasma sintering technique enables the development and growth of the necking of particles, enhancing elemental bonding and alloy densification as the temperature increases. The hardness value increases at increasing temperatures, with a maximum value of 353 HV attained at a temperature of 1050 °C.

Abstract: This research investigated metal injection moulding of dental pins for orthodontics application. 316L stainless steel powder was selected as an alternative low-cost material in comparison to the more expensive titanium alloy counterpart. The feedstock was prepared at 60% solid loading using an environmentally friendly multi-component binder. Injection moulding was operated using a four-cavity mould. The effects of moulding temperature of 250-280 °C measured at the barrel on mouldability, and specimen properties were studied. After debinding, specimens were sintered at 1250 °C for 2 hours in a hydrogen atmosphere. Experimental results indicated that injection at moulding lower temperature of 250-260 °C gave better mouldability, providing less specimen distortion and demoulding difficulty. The green density was 5.49 g/cm³, giving 93.41% theoretical density. Injection at lower temperature of 250-260 °C also provided higher sintered density and slightly lower volume shrinkage. Sintered microstructure experienced densification with small degree of isolated porosity in specimen center, however with interconnected porosity along specimen edges, responsible for 6.87 g/cm³ sintered density (86.01% theoretical density).

Abstract: Hollow glass microspheres (HGM) have been employed in a wide range of applications such as thermal insulating coatings for construction and transportation applications and for acoustic insulation coatings. As such, it is expected for the HGM to exhibit an extremely high pressure tolerance in order to endure the harsh environment. In this present study, an effort has been made to investigate the mechanical properties of hollow glass microsphere. The glass sphere with diameters between 5-30 µm, 50-90 µm and 90-125 µm were used for this investigation. This study's objectives are to investigate the strength of HGM and gain an in-depth understanding of the mechanical characteristics of the sintered spheres.

Abstract: In this study to the authors knowledge 1^st time, Metal Injection Molding (MIM) technique was used to introduce the magnesium alloy WE43 into binder-based powder metallurgical (PM) processing. Towards later adoption to binder-based 3D-printing technologies, Fused Granular Fabrication (FGF) technique, respectively for biomedical application. Metal Injection Moulding (MIM) is a binder based economic near net shape prototyping technique for production of complex shaped parts in high number and high reproducibility, and hence perfect as a “gold standard” for the introduction of new Mg-alloys into binder passed PM processing. In doing so, dogbone shape tensile test specimen were manufactured by MIM, subsequently solvent debound and conventional sintered in argon atmosphere. Next to the as sintered specimens (asS), solid solution heat treatment (T4) and precipitation hardening heat treatment (T6) were performed on additional specimens. Tensile tests pointed out high strength and ductility of as sintered and heat treaded specimens of up to 226 MPa UTS at 7.6% elongation at fracture. The microstructure was investigated using SEM imaging technique equipped with energy disperse x-ray energy analysis (EDX) for secondary phase analysis. Hence, the magnesium alloy WE43 could be identified as a high strength and ductility alloy for binder based PM processing for future additive manufacturing approaches in biomedical applications of patient adapted implants.