Papers by Keyword: Powder Metallurgy

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 the present study, the production of aluminum foam was carried out using the powder metallurgy technique, specifically employing the sintering – dissolution process (SDP). The SDP method, which constitutes a sequential series of four well-defined steps, was employed to achieve the desired foam structure and properties. These steps involved carefully controlling the parameters and conditions throughout the process to ensure successful foam formation. Aluminum powder with a particle size of (1.99 μm) as a raw material was mixed with NaCl with a particle size between (150-425μm) used as a space holder at different ratio (25, 35, 45and 55 wt. %.). Obtained Al-foam with 45% NaCl demonstrated the most optimal structure. Some additives (Mg) added to the powder mixture, it was found that the mechanical and the tribological properties of the produced foam were improved. The introduction of metal’s micro-particles led to a notable enhancement in both compressive stress and micro-hardness, the compressive stress increased substantially from 15.2 MPa to 56.5 MPa for the foam containing 45% NaCl and 45% NaCl + Add., respectively. While the micro-hardness exhibited a noteworthy increase from 51.5 HV to 62.1 HV. Results also showed important reduction in the wear rate from (0.00000155 g/cm) to (0.00000079 g/cm) for the Al-samples of (45% NaCl) and (45% NaCl+ Additive) respectively, the lowest value recorded for the coefficient of friction was (0.15) for (Al-Foam with 45% NaCl + Additive) compare to (0.19) and (0.21) for (Al-foam with 45% NaCl) and (pure Al) respectively at 10 N applied load and 800 rpm.

Abstract: A powder metallurgical process has been applied to synthesize the FeNiCr+Y₂O₃ oxide dispersion strengthened (ODS) alloys. The composition of the reinforcing Y₂O₃ added into matrix was varied from zero to 2.0 percent weight. Raw powders were carefully weighed with a four-digit balance. Y₂O₃ powder was pre-linked into Fe powder as the dominant element in the matrix by manually ground for half an hour. Ni and Cr powders were then mixed evenly for the next a half hour to obtain FeNiCr+Y₂O₃ precursor. Avoiding agglomeration and grain coarsening, the precursor was uniformly homogenized by milling for 20 hours. The precursors were then compressed at an isostatic pressure of 100 kN to 12 grams of pellets each. To prevent sample erosion during smelting with an electric arc furnace (EAF), crystal growing mechanism by conventional sintering was performed at 900 °C for 2 hours. This strengthens the bonds between precursors in forming ODS alloys. The samples were then melt-casted in the arc by 4 times flips. As a result, the neutron diffraction analysis and SEM-EDS strongly reveal the austenitic crystal structure and Y2O3 oxide successfully dispersed in the cast-alloy respectively. The microstructures with Y2O3 oxide spread uniformly overall the cast-alloy surfaces.

Abstract: Sintered Ti6Al4V titanium alloys prepared from TiH₂/60Al40V powder blends under various technological conditions were studied. The microstructural evolution was investigated by X-ray diffraction, scanning electron microscopy, optical microscopy, and energy dispersive X-ray analysis. The corrosion resistance of sintered titanium alloy was evaluated by the static immersion test in 40 wt.% H₂SO₄ acid, according to ASTM standard G31-72(2004). Depending on powder metallurgy processing parameters (compaction pressure or sintering temperature), the Ti6Al4V alloy was obtained with various structural features (porosity and structural heterogeneity). It was shown that those structural features of sintered Ti6Al4V titanium alloy are a key microstructural factor that determines their corrosion resistance. For instance, an increase in porosity leads to enhanced corrosion resistance. Based on the current research, the optimal manufacturing regimes of powder metallurgy of Ti6Al4V titanium alloy ensure the achievement of characteristics sufficient for practical use in aggressive conditions of the chemical industry were obtained.

Abstract: Amongst biomedical metallic materials, titanium alloys are normally used as structural permanent implants due to their favourable combination of mechanical properties and biocompatibility. However, commonly implanted titanium alloys are expensive and, unless purposely surface treated, generally cannot prevent surgical infections related to bacteria. Specifically, bacterial infection in biomedical protheses leads to inflammation, obstruction of the healing process, prevention of osteogenesis and, eventually, premature failure of the implant. This work therefore analysis the development of new ternary Ti-based alloys with built-in antibacterial capability as pathogenic bacterial infection occurring during surgery is a raising issue of metallic biomedical implants. The new Ti-based alloys were designed to be manufactured via powder metallurgy, which permits to successfully produce chemically homogeneous materials, key for a uniform antibacterial response, at lower cost. It is found that, primarily due to the stabilisation of the beta phase, the amount of the selected β stabilising alloying elements directly increases the mechanical performance and the antibacterial capability. Consequently, new ternary Ti-based alloys are promising candidates for structural prosthesis functionalised with antibacterial capability.

Abstract: The density of green compact in powder metallurgy (PM) is a critical characteristic to determine the strength and tenacity of the product. Due to the fragility and sensitivity to the humidity of green compact, detection method triggers by knocking or immersion cannot be applied. Current inspection method for green compact is to use a densitometer with Archimedes Principle, which has to immerse green compact into water. This action considers a destructive test due to the porosity of the PM product, and the oxidation reaction of metal particles inside products cannot be controlled. Since the current detection method is destructive, most of the inspection on forming process of PM only complies after setup of compaction machine. The next non-destructive test is executed after sintering, such as Acoustic emission testing (AE) and Magnetic Testing (MT), which require a solid object for knocking or liquid immersion. To reduce defective compaction flow into the manufacturing process, a Non-destructive test in forming process is a prerequisite. Laser Doppler Vibrometer (LDV) takes advantage of measuring without damaging the test object and obtaining characteristic spectrum signal from the sample for further analysis, which is preferable for green compact of PM. The LDV test setup included a Polytec PSV-400 scanning laser vibrometer with a crystal resonator attached to the test product to generate reference vibration. Integrate spectrum in the frequency range 0 - 5000 Hz was recorded from 30 points of an annular pattern. Comparison of the spectrum and statistical analysis from defective specimens demonstrate that velocity increases within a specific frequency, which is different from with normal samples. Increases in velocity refer to uneven density distribution with an absence of particles inside product decline. The study approves the possibility of density detection in green compact using an LDV. Further studies aim to construct a relational model of specimen and compaction machine and determine a fundamental database for Advance Process Control (APC) of forming process in PM.

Abstract: Our research novel Ti-22Nb biomedical alloys made by powder metallurgy and analyze the effect of adding silicon at various weight ratios to the base alloy (0.4, 0.8, and 1.2 %at Si). In this work, the wear characteristics of Ti-Nb-Si alloys in dry conditions are examined, as well as the wear process. To measure the wear rate, a pin-on-disc wear testing apparatus was employed. The optical microstructure analysis showed that the microstructure had a mixture-like appearance and included only a small quantity of another phase. XRD results showed that the stability of the β phase increased with silicon concentration. The (Ti-22Nb) alloy's hardness and compressive strength both increased once silicon is added. Hardness also rises as the amount of silicon additions increases, with the maximum percentage (1.2 percent Si) resulting in the highest hardness and compressive strength

Abstract: In this paper, single-phase chemically homogeneous high-entropy ceramics (HEC) were synthesized from a mixture of pre-mechanically alloyed TiZrHfTaNb high-entropy alloy (HEA) powders and carbon. Mechanical alloying (MA) of a TiZrHfTaNb alloy with different process times made it possible to obtain a powder with uniform distribution of chemical elements and with the main phase in the form of a body-centered cubic (BCC) solid solution. HEC with the chemical formula MeC and space group Fm-3m begins to form at temperatures of about 1600 °C in the process of sintering a mixture of pre-mechanically alloyed HEA powders and carbon. A detailed study of the diffraction patterns revealed peaks of mixed zirconium-hafnium oxide (ZrHf)O₂, which is also confirmed by the microstructure analysis results and distribution elements. Increasing the process temperature to 2000 °C leads to the formation of a single-phase and chemically homogeneous (TiZrHfTaNb)C HEC.

Abstract: The research of deposition of a nitinol sample in an equiatomic ratio from a powder mixture of nickel and titanium 55Ni-45Ti (in wt.%) is aimed at studying the heterogenicity of the chemical composition in the cross-section of a thin-walled and multilayer (bulk) cylindrical sample. The main task of the study was to determine the presence or absence of the chemical composition deviation from layer to layer, and mechanical properties. Analysis on an optical microscope, EDS analysis, and microhardness measurement, a thin-walled sample was studied. A chemical gradient was detected in the sample from the base along with its entire height. An increase in the content of the Ti element and a decrease of the Ni element was detected with an increase in the number of layers and the height of the sample, and a change in the microstructure and hardness were found. The increase in hardness from the base to the top point of the sample reaches 50%. X-ray phase analysis (XRD) showed the presence of NiTi phases in the martensitic and austenitic state, the side phases of NiTi2 in a thin-walled sample, and the presence of the Ni4Ti3 phase and the TiO2 oxide phase in a cylindrical bulk sample. The chemical composition of the cylindrical bulk sample agrees with the chemical composition of the mixture loaded into the powder feeder 55:45 Ni and Ti in wt. %. To indirectly determine the shape memory effect of the final alloy, mechanical tests were carried out for compression of cylindrical samples with subsequent heating, which confirmed the presence of the shape memory effect with a degree of reversible deformation of about 40%.