Papers by Keyword: Mechanical Alloying

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: Al₂₅Ni₂₅W₂₅Cr₂₀V₅ refractory high entropy alloy (RHEAs) was synthesised by mechanical alloying (MA) and its characterization study and mechanical behaviour of this prepared refractory high entropy alloy was investigated in this research work. After 18 hr of mechanical alloying, fine grained microstructure was obtained and homogeneous distribution of all metal elements was achieved. Crystallite size, lattice strain and phase analysis of prepared RHEAs powders were calculated through X-ray diffraction (XRD) techniques. Morphological study of prepared RHEAs powders was investigated through scanning electron microscopy (SEM). Aluminium, Nickel, Tungsten, Chromium and vanadium elements presented in the prepared RHEAs were identified through Energy dispersive spectrum analysis (EDAX). After milling, powders were compacted and sintered at two temperatures such as 600°C and 800°C. Density, porosity and Vickers micro hardness measurements were taken after sintered at 600°C and 800°C. The results indicate that the sintering environment and conditions will affect the mechanical properties of developed Al₂₅Ni₂₅W₂₅Cr₂₀V₅ refractory high entropy alloy.

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: 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: Biomaterials are significantly required for medical technology. Hydroxyapatite (HA) is a bioactive material and is an excellent candidate for use as a bone replacement or bone repair material. Because HA has similar properties to human bone. However, the disadvantage of HA is its low mechanical strength. Titanium (Ti) is the famous material used to strengthen the strength of HA. This is because Ti can be used in the human body without causing undesirable reactions. The development of Ti-HA composite materials provides a bioactive material with high-strength properties. The homogeneous microstructure of materials, which is essential for achieving the required properties, can be accomplished by using composite particles as the starting materials. This research aims to develop the Ti-HA composite particles by mechanical alloying method. The mixture of Ti and HA in a mass ratio of 70:30 (Ti:HA) was milled by using a high-energy mill, i.e., a vibration mill, at a speed of 750 and 1000 rpm for 30, 60, 120, 180 and 300 minutes without inert gas supply. The results show that the Ti-HA composite particles were produced by using a vibration mill. HA particles completely cover the surface of Ti. No phase change of Ti and HA was observed under all milling conditions except at 1000 rpm for 300 minutes. The tiny XRD peaks of TiO were observed. This study developed an effective and low-cost method for producing Ti-HA composite particles, which is advantageous to engineering and medical technology.

Abstract: In this study, the 2024 Al powder with different weight fractions of graphite is mechanically milled using a high-energy ball mill for 3 hours each in the nitrogen environment. The milled powder is compacted at an elevated temperature. X-ray diffraction is used to phase analysis of milled powder as well as compacted specimens. Optical microscopy is used for microstructural analysis and hardness measurements are done for the evaluation of mechanical properties. The hot compacted specimens are also tested for their wear properties. Results show that there is no new phase formed during mechanical milling. But, after hot compaction of the milled powder, Al₂Cu formed due to precipitation. No reaction is observed between the aluminum and the carbon (graphite) after milling as well as hot compaction. Microstructures of all hot compacted specimens are not showing pores, which, signifies full density after compaction. The formation of Al₄C₃ is not observed at any stage of processing. Therefore, graphite is uniformly distributed in all specimens, and the same is observed at grain boundaries of α-Al grains in the microstructures. Hardness increases with the addition of 1 wt.% graphite but it decreases with a further increase in graphite. The wear resistance of 2024 Al with 1 wt% graphite is the highest among all the compositions. The high hardness and wear resistance of 2024Al with 1 wt% graphite is the consequence of precipitation of Al₂Cu during hot compaction and the presence of graphite which creates hindrances in the metal matrix. The presence of free graphite in the vicinity of grain boundaries acts as a solid lubricant which improves wear resistance of 2024 Al.

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: Fe(Ni, Si) solid solutions were elaborated by high energy mechanical alloying from elemental Fe, Ni and Si powdersfor a milling time of 72 h. From X-ray diffraction (XRD) analysis, it has been shown that the Fe(Ni, Si) samples present a single phase in the whole range of Si content and exhibit a solid solution of disordered bcc α-Fe. The lattice parameter a (Å) of the new structures and the mean crystallitessize <D> (nm) were found to decrease with increasing Si contents. In contrast, the microstrain behaviour presents two different stages as the Si contents are increased. Scanning Electron Microscopy (SEM) images confirmed the behaviour of the mean crystallites size, where it can be seen that the addition of Si promotes the reduction of the size of powder particles. The saturation magnetization Ms was found to decrease by a factor of almost 1.4 and the coercively was found to increase by a factor of almost 2.4, when the Si content was increased from x= 0 % to x= 20 %. The Mössbauer spectroscopy confirmed the local in site crystal locations of Si and Ni as they diffuse into the matrix of the bcc α-Fe structure to form a solid solution.

Abstract: Laser diffraction, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Differential Scanning Calorimetry (DSC) were employed to characterize the particle size, morphology and structure of mechanically alloyed Ti₅₀Al₃₀Ni₂₀ alloy. Cyclic amorphous-crystalline-amorphous phase transformations were investigated during mechanical alloying, using high-energy ball milling technique. After 20 h of milling, an amorphous/nanocrystalline phase was obtained. This amorphous/nanocrystalline phase tended to transform into crystalline grains after 50 h of milling. In a cyclic phase transformation, the obtained crystalline phase is transformed into the amorphous phase after 70 h of milling. This amorphous phase crystallized through a single sharp exothermic peak at 590°C. On the basis of our results, the destabilizing effect of the defects created by the milling media (balls), which leads to the cyclic transformations, depends on the input energy and milling time.

Abstract: Nanoparticles Cu₂SnSe₃ alloys were synthesized by mechanical alloying from mixtures of pure crystalline Cu, Sn and Se powders using a low cost planetary ball milling process optimizing the milling duration and the rotational speed. The properties of Cu₂SnSe₃ (CTSe) thin films deposited by thermal evaporation from this powder on glass substrate at T_s = 400°C were investigated. Powders and films were analyzed by X-ray diffraction (XRD), scanning electron microscopy(SEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM), to determine their microstructure, morphology, chemical compositions and root-mean-square (RMS) roughness. XRD analysis revealed that all samples crystallize in polycrystalline nature with cubic structure and lattice parameter a = 5.68 Å. The optical measurements were carried out in the [500-2500nm] wavelength range and were determined from spectral transmission data. Optical measurements showed that the deposited layers had a relatively high absorption coefficient of 10⁴ cm^-1 and the direct energy band gap was found to be around Eg =1.29eV. The suitable p-type conductivity of CTSe thin films was confirmed by hot probe method. Other electrical parameters (carrier concentration n_p = 10.04x10¹⁸ cm^-3, electrical resistivity ρ = 30.49x10^-2 Ω cm and mobility μ_H = 94.33 cm²/V s) were measured at room temperature.