Abstract: This proposal aims at structural characterization of Ti-Fe-Si-B alloys produced by high-energy ball milling and subsequent sintering. In this study, quaternary alloys were prepared from raw materials of high purity: Ti (99.9 wt-%), Fe (99.8 wt-%), Si (99.999 wt-%) and B (99.5 wt-%). The milling process of the Ti-2Fe-22Si-11B and Ti-7Fe-22Si-11B (at-%) powders was carried out in a planetary Fritsch P-5 ball mill. Subsequently, the Ti-Fe-Si-B powders milled for 600 min were sintered (1100 ° C for 240 min) under vacuum to obtain equilibrium structures. The characterization of as-milled powders and sintered alloys was performed by means of X-ray diffraction, scanning electron microscopy, and electron dispersive spectrometry. Extended solid solutions were formed during the initial milling times while that the brittle Ti5Si3 phase was formed for longer milling times in both the quaternary powder mixtures. This fact contributed for reducing the particle sizes. Homogeneous samples containing a small amount of pore were obtained after sintering at 1100°C for 4h. Results have indicated that the iron addition favored the formation of different binary phases of the Ti-Si system, and the formation of the Ti6Si2B compound was inhibited from the Ti-Fe-Si-B powder mixtures.
Abstract: This work aims to discuss on the phase transformation in mechanically alloyed and hot-pressed Ti-2Nb-22Si-11B and Ti-6Nb-22Si-11B powder mixtures. The milling process was conducted in a planetary ball milling using stainless steel vials (225 mL) and balls (19 mm diameter), rotary speed of 300 rpm, and a ball-to-powder weight ratio of 10:1. Hot pressing of mechanically alloyed Ti-Nb-Si-B powders was performed under vacuum at 1100°C for 1h. The as-milled and hot-pressed Ti-Nb-Si-B samples were evaluated by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. XRD results of milled Ti-Nb-Si-B powders indicated that the peaks of Nb and Si were reduced for longer milling times, suggesting that Nb and Si atoms were dissolved into the Ti lattice to form extended solid solutions. Iron contamination close to 6 at% was detected by EDS analysis. Hot pressing produced dense and homogeneous samples containing a small amount of Ti6Si2B.
Abstract: The work reports on the phase transformation in mechanically alloyed and hot-pressed Nb-4Si-8B and Nb-8Si-16B (at-%) alloys. Elemental powder mixtures were processed in a planetary ball mill under argon atmosphere using 300 rpm, stainless steel balls (19 mm diameter) and vials (225 mL), and a ball-to-powder weight ratio of 10:1. After dry milling for 7h, wet milling with isopropyl alcohol for more 20 min was adopted to increase the recovering of previously cold-welded Nb-4Si-8B powders. To obtain the equilibrium structures the as-milled powders were hot-pressed under vacuum at 1200oC for 1 h. The as-milled powders and hot-pressed samples were characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. XRD results revealed the presence of metastable phases in as-milled Nb-Si-B powders. The hot pressing has produced dense Nb-Si-B samples, which were formed by the Nbss, Nb3B2 and Fe2Nb phases beside of other unknown Si-rich phase.
Abstract: The milling process of elemental Ti-2Ta-22Si-11B and Ti-6Ta-22Si-11B (at-%) powder mixtures were performed in a planetary Fritsch P-5 ball mill using stainless steel vials (225 mL) and hardened steel balls (19 mm diameter). Ball-to-powder weight ratio of 10:1 and a rotary speed of 300 rpm were adopted, varying the milling time. Wet milling (isopropyl alcohol) for 20 more minutes was used to increase the yield powder in to the vial. Following the Ti-Ta-Si-B powders milled for 600 min were heat-treated at 1100°C for 1 h in order to obtain the equilibrium structures. The milled powders and heat-treated samples were characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. Supersaturated Ti solid solutions were formed during ball milling of Ti-Ta-Si-B powders while that the Ti5Si3 phase was formed after milling for 620 min of the Ta-richer powder mixture only. The particles sizes were initially increased during the initial milling times, and the wet milling provided the yield powder into the vials. A large amount of pores was found in both the sintered samples which presented the formation of the TiSS,(ss-solid solution) Ti6Si2B and TiB.
Abstract: The mechanical alloying of Mo-Cu powders allows the production of highly homogeneous sintered pieces, with very thin Mo particles and good dispersion of Mo particles in the ductile Cu phase, allowing the development of a route for the preparation of Mo-Cu simple composite powders, environmentally sustainable and able to increase the sinterability of the material without causing damage to their properties of thermal conductivity and electrical. Was used the precursor powders of molybdenum (Ammonium heptamolybdate) plus Cu, where two samples were prepared by mixing processes. For mechanical alloying, and by mixing manually, and both reduced and sintered in a resistive furnace with hydrogen gas. The materials were analyzed by optical microscopy, XRD and density measurements. The results confirm the effect of mechanical alloying on the increasing in high density of the sintered samples and thereby producing superior properties to those shown by the mixing manually sample.
Abstract: This work presents the results on the high-energy ball milling and hot pressing of Ni-48Ti-2Sn and Ni-45Ti-5Sn (at-%) powder mixtures. The milling process was performed in a planetary ball mill using stainless steel vial (225 mL) and hardened steel balls (19 mm diameter), rotary speed of 300 rpm, and a ball-to-powder weight ratio of 10:1. Samples were collected into the vial after different milling times: 60, 180 and 300 min. In the sequence, wet milling (isopropyl alcohol) was adopted up to 720 min in order to increase the powder yield into the vials. The as-milled and hot-pressed samples were characterized by X-ray diffraction, electron scanning microscopy, and energy dispersive spectrometry. Results indicated that the ductile particles were promptly cold-welded during the initial milling times. XRD patterns of the Ni-48Ti-2Sn powder mixture indicated that the peaks of Ni, Ti and Sn disappeared after milling for 3h. Following, peaks of NiTi and Ni4Ti3 were preferentially formed during milling of Ni-Ti-Sn powders. A large amount of fine powders was yielded into the vial after wet milling for 720 min only. No significant carbon or oxygen contamination was detected by EDS analysis. Hot pressing produced homogeneous and dense samples which presented microstructures containing a large amount of the NiTi compound.
Abstract: The present work investigate the possibility of obtainment by mechanical alloying of Ni superalloys based on the Ni-Cr-Nb-C system strengthened by γ”(Ni3Nb), since γ”(Ni3Nb) as γ’ (Ni3Al) are typical coherent phase strengthening mechanisms in nickel superalloys. In order to evaluate this possibility, a composition with 71,65wt%Ni, 7,90wt%Cr, 20,00wt%Nb and 0,45wt%C was processed in a SPEX mill by 8 hours, consolidated and sintered at different temperatures (1200oC, 1250oC and 1300oC). The powder processed by MA and the sintered products were characterized by x-ray diffraction, SEM and EDS.
Abstract: The processes of high-energy milling and gained importance among the unconventional methods. In this work, we seek to compare the power supply two types of high energy mills (vibratory mill (SPEX) and planetary mill) with the variation of the milling power. The millings were carried out with a mixture of chromium oxide and aluminum metalic. The reduction of chromium oxide does not occur instantaneously, but gradually as the progress of milling with mechanical activation of powders, this mechanical activation occurs leading to the solid state reaction occurs. The results were obtained for thermal analysis of the samples. The energy released varies, exhibiting a maximum mechanical activation for the range of powers milling studied. The correlation between the energy mills can be made by identifying the milling power is reached at which the maximum in each mechanical activation mill and quantifying this activation.
Abstract: In the present paper a preliminary study was performed on the influence of mechanical milling on the synthesis of niobium nitrade. The niobium metal powder sample, passing # 635 mesh sieve, was processed by mechanical milling in SPEX mill for 8 hours using a ball-to-powder ratio of 7:1 and a nitrogen atmosphere. The powder was annealed at different temperatures, 900 °C, 1000 °C, 1100 °C and 1200 °C for 1 hour in a hydrogen and argon atmosphere to study their crystallization, which then were formed into blanks for analysis of the compressibility curves. These samples were also subjected to X-ray diffraction and the data were compared between the annealing temperatures. The compressibility curves of niobium samples with and without grinding were also evaluated, showing high compacting capacity. These samples were subjected to X-ray diffraction and X-ray fluorescence. As the formation of nitrides (Nb2N) was observed in SPEX type mill, the interest in studying the synthesis of nitrides came up, using mechanical milling in Attritor type mill. Same previous results of Attritor processing indicate a Nb2N and NbN synthesis after annealing treatments.