Papers by Keyword: Powder Metallurgy

Abstract: In cold bulk metal forming, coatings based on zinc phosphate are commonly used for lubrication. This has a negative impact on the environment, negatively affects human health, and requires significant pre-and post-surface treatments. Powder metallurgical (PM) components are a promising alternative to zinc phosphate coatings due to the process related porosity of the workpiece which acts as lubricant reservoir. During the forming process, the lubricant stored in the pores is released and lubricates the tool and workpiece surfaces. For an efficient process design of such components, finite element method (FEM) is an effective tool to analyse forming and friction behaviour. To this end, a realistic material model is essential for accurate simulation results. Hence, in this work, the flow behaviour of PM semi-finished products is characterised by means of compression and tensile tests. The results indicate that the material exhibits different behaviour under compression and tension. In compression, the material demonstrates higher yield strength and flow stresses compared to tension. Additionally, inhomogeneity of the material distribution can be observed, characterised by a denser core and more porous outer regions. The porous outer regions make it suitable for storing lubricant for application in forming processes.

Abstract: In this study, CoCrFeNiTi high entropy alloy (HEA) powder was treated by ball milling (BM) for up to 50 hours and sintered compacts were fabricated by spark plasma sintering (SPS). XRD analysis confirmed that the BM powder formed a single BCC solid solution phase after 25 hours, and a nanocrystalline structure was obtained due to the reduction in crystallite size and increase in dislocation density. Meanwhile, after sintering, the main phase changed to FCC, and secondary phases such as CoTi₂, CrFe, and TiC were precipitated. Carbon analysis by EMIA and EPMA showed that the carbon content in the powder and sintered compact increased with increasing BM time, which is considered to be the cause of TiC formation. Micro-Vickers hardness tests showed maximum hardness at the initial state, decreased at 5 hours, and then recovered after 15 hours due to the effect of secondary phase precipitation and microstructure. The effects of BM treatment and sintering conditions on phase structure, microstructure, element distribution, and mechanical properties were clarified, suggesting that it is an effective method for controlling the properties of HEA.

Abstract: A mathematical model of the shaping processes of structurally inhomogeneous porous materials has been developed. Generalized relations of the theory of elastic-visco-plasticity for dispersed materials are used for rigid-plastic and elastic-plastic of the material solid phase models. The procedures of projection-grid methods for solving boundary value problems were used. It has been performed in form of step by step calculation. The special algorithm is used to consider some types of plastic deformation, including rigid plastic behaviour, elastic – plastic case and some other rheological behaviour of matrix materials. The algorithm procedures were realized in a form of numerical model. Some elements of this model were implemented in modern finite element software versions. The results of calculations, aimed at manufacturing of main and responsible parts are presented in article.

Abstract: To investigate the effect of the oxygen amount involved in mechanical alloying (MA) of Al and Y₂O₃ powders on the phase evolution of the alloy powders, two types of MA were performed: MA with low and high oxygen content in the MA atmosphere. Analyses of the lattice parameter and composition of the Al matrix by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy, respectively, and the integrated intensity of Y₂O₃ indicated that in the low-oxygen MA, the driving force for Y₂O₃ precipitation was small and Y and O dissolved into the matrix, producing supersaturated solid solution powder, while in the high-oxygen MA, the driving force for Y₂O₃ precipitation was large, resulting in the formation of Y₂O₃-precipitated powder.

Abstract: In recent years, AlCoCrFeNi High-Entropy Alloy (HEA) has attracted attention because it is expected to be a next-generation aerospace engine material because it has specific strength, excellent corrosion and wear resistance. However, the influence of microstructure of the material synthesized via spark plasma sintering (SPS), a powder metallurgy technique, on high temperature mechanical properties, in particular, creep features, has rarely been reported. In the study, to investigate the abovementioned issue, the HEAs using powder mean size of 14.6, 41.9 and 82.4 μm synthesized via SPS at 1273 K and 1373 K were prepared. Creep tests were conducted at 973 K. The obtained results indicated that HEAs SPSed at 1373 K exhibited higher creep strength than those of synthesized at relatively low temperature, because the microstructure of the former is different from those of the latter. In addition, FCC/B2 phase boundary fracture was observed for HEA synthesized at 1373 K. By contrast, powder boundary fracture was observed for the remaining HEAs. Moreover, the Monkman-Grant relation can be employed to predict creep rupture time for all types of HEAs on one master curve.

Abstract: A FeCoNiCu high-entropy alloy was synthesized via mechanical alloying using elemental powders. The structural evolution during milling and the effects of subsequent sintering were investigated. X-ray diffraction confirmed the formation of a single-phase FCC solid solution with nanocrystalline structure. SEM and EDS analyses showed homogeneous element distribution without segregation. Microhardness testing revealed an average value of 105.47 HV1, indicating sufficient mechanical performance. The results demonstrate the potential of FeCoNiCu HEAs for structural applications.

Abstract: The need for porous materials is rapidly increasing in different applications like electrolysis, direct vaporization, and fluid transport by capillary lift. Additional to a certain porosity between 30 and 60 vol.%, the surface quality, mechanical stability and easy machinability come more and more into focus. Further requirements are raw materials that are low cost and available for mass production and the possibility to select from different materials like titanium, nickel, iron and their alloys for the chosen manufacturing route. In this work, the authors show a powder metallurgical approach on sintered titanium sponge to create a porous structure that meets the above-mentioned requirements. The sintering combines a fast hot pressing by Spark Plasma Sintering with a stop-controlled densification. With this setup it is possible to sinter a titanium sponge to sheets or discs. The sintered titanium sponge was densified to a porosity of 25 and 53 vol.% without any addition of organic or other sintering agents and creating a material that is close as possible to the purity of the initial sponge powder. The shape of the top and bottom of the sintered titanium sponge adapts the surface of the used punches during sintering and can be flat or structured. The plates or sheets can be easily machined to the desired shape using water jet cutting, wire erosion or drilling or milling. Preliminary tests were carried out on porous structures for capillary lift and direct heating elements for vaporisation.

Abstract: Titanium alloys are widely used in aerospace applications due to their excellent strength-to-weight ratio, corrosion resistance, and high temperature performance. However, including nanoparticles as reinforcement in titanium alloys can further improve their mechanical properties, making them even more suitable for demanding aerospace applications. Titanium matrix composites (TMC) are titanium alloys typically reinforced with micron-sized ceramic particles. These reinforcements improve some properties, such as strength, but deteriorate others. However, reducing the size of reinforcements to the nanometer range allows for larger reinforcement effects to be obtained with much smaller volumetric fractions of reinforcement, which is less detrimental to fatigue, toughness, ductility, etc. This work focuses on the study of simple and safe manufacturing routes for nanoreinforced Ti alloys that increase the strength of the base material with a low negative effect on ductility. The selection of the compositions and treatment temperatures was carried out using binary phase diagrams and experimental results.

Abstract: This investigation focuses on the microstructural refinement of the γ-TiAl intermetallic alloy Ti-45Al-2Nb-2Mn (at.%) + 0.8 (vol.%) TiB2 (Ti4522XD) processed by powder metallurgy. The alloy powders were manufactured using the Electrode Induction-melting Gas Atomization (EIGA) process and subsequently consolidated through Hot Isostatic Pressing (HIP), resulting in a near-γ microstructure.The study further explores the effects of three distinct thermal treatments on the microstruc ture: 1) heating to 1300°C for 2 hours followed by furnace cooling (HT1), 2) heating to 1300°C for 2 hours, then water quenching and aging at 850°C for 8 hours before furnace cooling (HT2), and 3) heating to 1300°C for 2 hours, followed by water quenching and aging at 700°C for 8 hours before furnace cooling (HT3). These processes were tailored to promote the development of duplex (DP) and fully lamellar (FL) microstructures. Characterization was performed using X-ray diffraction (XRD) to identify phase distributions and scanning electron microscopy (SEM) to examine the surface morphology. Transmission elec tron microscopy (TEM) was used for a preliminary assessment of actual lamellar spacing. As a result, two different microstructures were obtained: DP for HT1 and near fully lamellar (NFL) for HT2 and HT3, but differences in the final actual lamellar spacing were observed for these last two cases. Additionally, the presence of microcracks of different morphologies was observed by SEM prior to any mechanical testing.

Abstract: TiAl alloy is a high-temperature structural material that is highly sensitive to microstructure. Different hot working or heat treatment processes can refine the grain, release stress, and adjust the phase type and distribution. This study investigates the effect of heat treatment and rolling on the microstructure of powder metallurgy TiAl alloys in detail, resulting in TiAl alloys with high plasticity achieved through hot pack rolling. The heat treatment temperature was set between 1290°C and 1330°C, with a temperature interval of 10°C, a holding time of 30 minutes, and cooling with the furnace. Spheroidization of the grains occurred at 1310°C. Phase analysis of the TiAl alloy was conducted after heat treatment at 1290°C, 1310°C, and 1330°C. The microstructure of the TiAl alloy after heat treatment at 1290°C still consisted of γ phase and B2 phase, with no significant change in the content of γ phase and B2 phase. After heat treatment at 1310°C, numerous α₂ phases abruptly emerged in the microstructure. The TiAl sheet exhibits an elongation of 3.6% at room temperature, which increases to 65% at 700°C. The study investigated the phase transformation process, grain morphology, and microstructure evolution of powder metallurgy TiAl alloy under different heat treatment temperatures and rolling. The relationship between microstructure and temperature of powder metallurgy TiAl alloy was established using electron backscattering diffraction.