Low Energy Mechanical Alloying Research Articles

Effect of milling energy on phase transformation of Ti-Ni powders during mechanical alloying

ABSTRACT The effect of milling energy on the phase evolution of mechanically alloyed Ti–Ni powders is reported. Alloys were produced by low-energy and high-energy mechanical alloying (LEMA and HEMA, respectively). Powders milled for different times were characterised by X-ray diffraction and scanning electron microscopy. The phase transformations of powders milled by LEMA and HEMA before amorphisation are presented. During LEMA, TiNi, TiNi3, Ti3Ni4, and Ti2Ni were formed at 50 and 100 h. At these times, the results were consistent with the Ti–Ni equilibrium phase diagram. Up to 7.27 wt% of TiNi with a crystallite size of 32.63 ± 0.01 nm appeared at 50–75 h. During HEMA, iron contamination inhibited the formation of the TiNi phase at short milling times, and up to 47.9% of Fe0.2Ni4.8Ti5 was generated. These results indicate that amorphisation and heat treatment are not the only methods of promoting phase transformation in Ti–Ni alloys.

Production of biodegradable Mg-based alloys by mechanical alloying

Mg has several attractive characteristics that make Mg-based materials potentially used for bio-engineering applications. In this work, a ternary Mg-Zn-Ca alloy was manufactured using low energy mechanical alloying (MA) followed by a sintering process under a controlled atmosphere. The aim of this work was to study the effect of milling time on ternary magnesium-zinc-calcium (Mg-Zn-Ca) alloys produced by mechanical alloying. The Mg base alloys were synthesized in a planetary ball mill under an argon atmosphere using stainless steel containers and balls with a milling regimen of 400 rpm for 2, 5 and 10 hours. The alloyed powders obtained by MA at different milling times were characterized by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). These results suggest that Mg65Zn30Ca5 and Mg70Zn25Ca5 alloys can be synthesized by mechanical alloying.

Temperature Dependent Mechanical Behavior of ODS Steels

An oxide dispersion strengthened (ODS) ferritic steel with nanometric grain size has been produced by means of low-energy mechanical alloying (LEMA) of steel powder (Fe-14Cr-1W-0.4Ti) mixed with Y2O3 particles (0.3 wt%) and successive hot extrusion (HE). The material has equiaxed grains (mean size of 400 nm) and dislocation density of 4 x 1012 m-2, and exhibits superior mechanical properties with respect the unreinforced steel. The mechanical behavior has been compared with that of ODS steels prepared by means of the most common process, high-energy mechanical alloying (HEMA), consolidation through hot isostatic pressing (HIP) or hot extrusion (HE), annealing around 1100 °C for 1-2 hours, which produces a bimodal grain size distribution. The strengthening mechanisms have been examined and discussed to explain the different behavior.

Synthesis of Pure NiTiSn by Mechanical Alloying: An Investigation of the Optimal Experimental Conditions Supported by First Principles Calculations

Synthesis of NiTiSn by a mechanical alloying process followed by a high temperature thermal annealing was studied. Experiments were conducted varying parameters like the provided energy, the mechanical alloying reaction time, as well as the annealing temperature and duration. Based on the careful investigation of the phases present in the samples by systematic X-ray diffraction (after mechanical alloying and after annealing) and selected microscopy analyses, a reaction mechanism is proposed supported by theoretical calculations at the DFT (Density Functional Theory) level. An energy window to prepare directly NiTiSn has been evidenced. Highly pure NiTiSn has also been obtained by conversion from a multicomponent precursor obtained by low energy mechanical alloying.

Development of a novel TiNbTa material potentially suitable for bone replacement implants

A novel (β+γ)-TiNbTa alloy has been developed by a combined low energy mechanical alloying (LEMA) and pulsed electric current sintering process (PECS). Microstructurally, this material presents interesting characteristics, such as a submicrometric range of particle size, a body-centered phase (β-TiNbTa) and, mainly, a novel face-centered cubic Ti-based alloy (γ-TiNbTa) not previously reported. Related to mechanical performance, the novel (β+γ)-TiNbTa shows a lower E (49±3GPa) and an outstanding yield strength (σy>1860MPa). This combination of original microstructure and properties makes to the (β+γ)-TiNbTa a novel material potentially suitable as biomaterial to fabricate bone replacement implants, avoiding the undesirable and detrimental stress-shielding problem and even the usual damage on the mechanical strength of Ti-based foams biomaterials.

Analysis of Strengthening Mechanisms in Nano-ODS Steel Depending on Preparation Route

Oxide dispersion strengthened (ODS) steels are promising materials for high temperature applications, in particular in fission and fusion nuclear reactors. In comparison to common reduced activation ferritic/martensitic steels they exhibit better resistance to neutron irradiation and creep owing to an uniform dispersion of nano-oxides particles (~5 nm) and a very fine grain structure (~500 nm). ODS steels are commonly prepared by high-energy mechanical alloying (HEMA) of a mixture of steel powder and Y2O3 particles followed by a consolidation stage consisting of hot extrusion (HE) or hot isostatic pressing (HIP). The samples are then submitted to annealing around 1100°C for 1-2 hours. Recently, the present authors proposed a novel method based on low-energy mechanical alloying (LEMA). In general ODS microstructure is quite complex and several mechanisms contribute to the mechanical strengthening with different effects depending on the temperature. The present work analyses the role played by each single mechanism at increasing temperature by considering the specific microstructural features. ODS steels prepared through different routes and process parameters display different grain size distribution and homogeneity of particles dispersion, factors which strongly affect the mechanical properties. Yield stress values measured in tensile tests performed at increasing temperature up to 700°C, either taken from literature or achieved by authors, have been examined and the following strengthening mechanisms have been considered to fit the experimental data: (i) solid solution; (ii) Bailey-Hirsch; (iii) Hall-Petch; (iv) Orowan; (v) Coble creep and (vi) Arzt-Rősler-Wilkinson. The analyses evidence advantages and drawbacks of different preparation routes and suggest some criteria for further improving the mechanical properties of these materials.

Mechanical Characterization of a Nano-ODS Steel Prepared by Low-Energy Mechanical Alloying

An oxide dispersion strengthened (ODS) ferritic steel with nanometric grain size has been produced by low-energy mechanical alloying (MA) of steel powder (Fe-14Cr-1W-0.4Ti) mixed with Y2O3 particles (0.3 wt %) and successive hot extrusion (HE). The material exhibits superior mechanical properties with respect to the unreinforced steel up to 400 °C; then such differences tend to progressively decrease and at 700 °C yield stress (YS) and ultimate tensile strength (UTS) values are very close. The microstructure and mechanical behaviour have been compared with those of ODS steels prepared by the most common process, high-energy MA, consolidation through hot isostatic pressing (HIP) or hot extrusion (HE), annealing around 1100 °C for 1–2 h. The main strengthening mechanisms have been examined and discussed to explain the different behaviour. In addition, heat treatments in the range 1050–1150 °C were carried out and a microstructural evolution with a relevant hardness decrease has been observed. TEM observations evidenced defect recovery and partial grain coarsening owing to the not perfectly homogeneous distribution of oxide particles.

Determination of milling parameters useful on the formation of CoSb3 thermoelectric powders by low-energy mechanical alloying

In this paper, CoSb3 polycrystalline powders were prepared from the raw material powders of Co and Sb using a combined process of mechanical alloying and heat treatment. Ball milling parameters: weight ratio of ball to powder (BPR) and milling times (tM) in the low energy planetary ball mill of CoSb3 powder were optimized. The milled samples were characterized through X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, dynamic light scattering, Raman spectroscopy and heat capacity. By using a simplified model, the mechanical milling parameters as collision duration, contact radius, compression of the balls, average maximum impact pressure on the contact surfaces and temperature of collision, were calculated. We have attempted to quantify the energy transferred per impact and per unit of mass for the formation of CoSb3. Our results predict that the optimum cumulative kinetic energies required for mechanical activation of the first trace of CoSb3 powder by grinding media was found to 10 kJ/g for BPR 80:1 with tM = 5 h. A close relation between this energy and the enthalpy of formation was observed.

Effect of Al2O3 Particles on Mechanical Properties of Al-(0-40%)Al2O3 Composite Foams Produced by Low Energy Mechanical Alloying

In this study, at first Al-Al2O3 composite powders having different volume fractions of Al2O3 (0, 10, 20, 30 and 40 vol.%) were produced by low energy mechanical alloying, which were used as foam materials. Then, composite foams with 50, 60, and 70 percent of porosity were produced by space-holder technique. Spherical carbamide particles (1-1.4 mm) were used to achieve spherical porosities. In order to investigate the compressive behavior of foams, the compression test with strain rate of 10 S was performed on the foam samples. The results showed that the compressive properties depended on the volume fraction * پ تابتاکم لوئسم یکینورتکلا تس : m_mirzaee1355@yahoo.com

Scheme of thermal compression of hydrogen (TCH) using MmNi4.25Al0.75 recovered with ethyl alcohol and handled under non protective atmospheres

A MmNi4.25Al0.75 intermetallic was obtained by low energy mechanical alloying and low temperature heating at 600 °C for 24 h under Ar. The intermetallic was recovered from milling chamber using ethyl alcohol, dried, stored and handled under air at room conditions. Structure was characterized by XRD. A maximum stability temperature of 160 °C was obtained from non-isothermal DSC measurement under air. The kinetics of oxidation at 200 °C was analyzed. A maximum reaction degree (α = 0.1) was obtained after 2500 s of treatment. The hydrogen sorption properties of samples were studied by volumetric measurements. Hydrogen maximum mass percent capacity (mass %) was reached in less than 300 s. The thermodynamic sorption properties were measured. Values of ΔHf = −29 ± 2 kJ mol−1 and ΔSf = 197 ± 10 J mol−1 K−1 were obtained for absorption process and ΔHd = 28 ± 2 kJ mol−1 and ΔSd = 189 + 10 J mol−1 K−1 were obtained for desorption process. From these results, a one-stage of thermal compression of hydrogen is proposed with a standard compression ratio (Rc) of 5.71 in the 25–80 °C range.

Evolution of the phase stability of Ni–Al under low energy ball milling

Low energy mechanical alloying of Ni–35at.%Al and Ni–40at.%Al material was performed and the resulting structures were investigated by XRD and TEM. The final intermetallics observed consist of two phases, NiAl(B2) and Ni3Al while 7R and 3R martensite was observed in post-annealed samples. Different integrated milling times were associated to the intermetallic consolidation and initial blend dissociation.

Synthesis of Al-containing MmNi5 by mechanical alloying: Milling stages, structure parameters and thermal annealing

In this work, intermetallics of MmNi5−xAlx composition (Mm = mischmetal = La0.25Ce0.52Nd0.17Pr0.06) where x stands for 0.5 and 1 were synthesized by low energy reactive alloying. Minor structures present on the sample were identified. Structural parameters were calculated. Four stages of milling were characterized as a function of the integrated milling time (tim). The stages were characterized as Initial, Intermediate, Final and Completion. Initial stage ranges from 0 to 20 h. Intermediate and Final range from 20 to 50 h and from 50 to 120 h, respectively. Completion stage occurs at tim > 120 h. From these results, an optimum milling time was estimated. Energy consumption experiments at laboratory scale were done to optimize annealing parameters and to compare this low energy mechanical alloying–low temperature annealing method with high temperature traditional ones. The optimization was correlated to the structural parameters obtained on the structure. From these results, an improvement on the milling time-annealing process was proposed.

Improvement of as-milled properties of mechanically alloyed LaNi 5 and application to hydrogen thermal compression

LaNi 5 was obtained from raw materials by low energy mechanical alloying. Hydriding properties of as-milled intermetallic were improved by annealing. Pressure-composition isotherms showed flat plateaus when annealing temperature was 600 °C, this value is at least 300 °C lower than the synthesis and annealing temperature of standard equilibrium methods. This low energy mechanical alloying – low temperature annealing procedure reduces the number of intermediate stages needed to scale up the fabrication of the intermetallic. After cycling this material in hydrogen, its hydriding properties were studied in the 25–90 °C range. From these results, we propose a one-stage hydrogen thermal compression scheme working between 25 °C (absorption) and 90 °C (desorption) with a compression ratio of 2.5 and a useful capacity of 1.0 mass %.

SYNTHESIS OF AMORPHOUS/NANOCRYSTALLINE Ni–Ti POWDERS BY USING LOW ENERGY MECHANICAL ALLOYING

An amorphous/nanocrystalline 50 Ni –50 Ti powder was produced from elemental Ti and Ni powders by solid state synthesis utilizing low energy mechanical alloying with times up to 100 h. The morphology, microstructure, and phase composition of the milling products were evaluated by using scanning electron microscopy and X-ray diffraction analysis. The results indicated that there was no chemical reaction between the elements during the milling process, which led to the direct formation of an amorphous/nanocrystalline structure without any intermediate phase (intermetallic and/or solid solution phase) formation. It seems that the second kind of amorphization process proposed by Weeber and Bakker is governed. It was shown that the formation of amorphous phase was started after 80 h and developed during the milling for 100 h.

PHASE TRANSFORMATIONS DURING HEATING OF AMORPHOUS/NANOCRYSTALLINE Ni–Ti POWDERS

Amorphous/nanocrystalline 50 Ni –50 Ti powders were synthesized from elemental Ti and Ni powders by solid state synthesis utilizing low energy mechanical alloying with times up to 100 h. The produced powders were investigated by X-ray diffraction and differential scanning calorimetry to study phase transformations that occurred during heating in the calorimeter. It was found that at the first stage of the heating process, a disordered NiTi phase was formed at temperature of about 400°C. Further investigations indicated that this phase transformed into the Ni 3 Ti and Ti 2 Ni intermetallic compounds after heating at a temperature of about 800°C.

Corrosion performance of HVOF and APS thermally sprayed NiTi intermetallic coatings in 3.5% NaCl solution

Amorphous/nanocrystalline Ni–Ti powders produced by low energy mechanical alloying were used as feedstock to deposit NiTi intermetallic coatings on 316L stainless steel substrate using high velocity oxy-fuel (HVOF) and air plasma spraying (APS) processes. Electrochemical impedance spectroscopy (EIS) and polarization tests indicated that the corrosion performance and passive behaviour of HVOF coating were far better than those of APS coating. The study also showed that the solution had penetrated through the coating microcracks and caused interior corrosion of APS coating, while the HVOF coating was immune from interior corrosion attack and consequently exhibited a good passive behaviour during long-term immersion.

A two-stage hydrogen compressor based on (La,Ce,Nd,Pr)Ni 5 intermetallics obtained by low energy mechanical alloying – Low temperature annealing treatment

La 0.67Ce 0.19Nd 0.08Pr 0.06Ni 5 was synthesized by low energy mechanical alloying. The AB 5 was milled up to completion stage to reach the final composition and appropriate particle size distribution and microstructure characteristics. Crystallite size, strain and sorption properties of as-milled samples were evaluated. After milling, La 0.67Ce 0.19Nd 0.08Pr 0.06Ni 5 and previously obtained LaNi 5 were annealed at 600 °C for 24 h. An improvement in both microstructural and hydrogen sorption properties was found. Equilibrium hydrogen sorption properties were obtained and quantified in the 25–90 °C range. From these results, a two-stage hydrogen compressor was proposed. In the first stage, hydrogen is absorbed by LaNi 5 at 575 kPa and 25 °C and desorbed at 1365 kPa and 90 °C. In the second stage, this fluid is absorbed by La 0.67Ce 0.19Nd 0.08Pr 0.06Ni 5 at 745 kPa and 25 °C and desorbed at 2100 kPa and 90 °C. As a result, a global compression ratio of 3.65 is reached using this scheme.

Magnesium influence in the electrochemical properties of La–Ni base alloy for Ni–MH batteries

The effect of the substitution of La by Mg in the hypo-stoichiometric La 1 - x Mg x Ni 3.8 Co 0.3 Mn 0.3 Al 0.4 ( x = 0.00 , 0.05, 0.10, 0.15 and 0.20) hydride alloys were metallurgically and electrochemically characterized in order to use them as negative electrodes in Ni–MH batteries. The Mg content was added to mother alloys by means of low energy mechanical alloying. The microstructure, composition and crystalline structure of the samples were analyzed by SEM, EDS and X-ray diffraction, respectively, and their electrochemical properties were analyzed by charge/discharge cycling stability and rate capability. The electrochemical results show that the alloy LaNi 3.8 Co 0.3 Mn 0.3 Al 0.4 reaches a maximum discharge capacity of 181.7 mAh/g. La 0.85 Mg 0.15 Ni 3.8 Co 0.3 Mn 0.3 Al 0.4 presents the best behavior in electrochemical cycling stability with a capacity decay of 4.4% after 50 cycles and a capacity reduction rate of 0.117 mAh/g per cycle. The alloy La 0.80 Mg 0.20 Ni 3.8 Co 0.3 Mn 0.3 Al 0.4 obtained the highest discharge capacity at high rate discharge.

Structural characterization and hydrogen sorption properties of nanocrystalline Mg 2Ni

The structure, chemical distribution, microstructure and thermal stability of a 2Mg–Ni mixture milled at different times in a low energy ball mill were investigated. After short time processing, a mixture of amorphous Mg-rich phase, nanocrystalline Mg and crystalline Ni was obtained. The crystallite size reduction and strain increment along with the formation of an amorphous phase was associated to the refinement of Mg at this stage. After long time milling, nanocrystalline Mg 2Ni was produced and both amorphous Mg-rich phase and Ni remained in the mixture as residual phases. Stable nanocrystalline Mg 2Ni was successfully synthesized by a combination of low energy mechanical alloying and further non-isothermal heating up to 300 °C. The reactivity and equilibrium features of Mg 2Ni were characterized by both hydrogen absorption/desorption and pressure–composition isotherm measurements. The nanostructured intermetallic showed a 3.0 wt% hydrogen storage capacity without activation and excellent hydrogen absorption/desorption kinetics.

Processing, microstructure and creep testing of Pt–Y 2O 3 composites

Two Pt–Y 2O 3 composites were prepared from recycled wastes by powder metallurgy technique using two different times (8 and 24 h) of low-energy mechanical alloying and their high temperature deformation behaviour was investigated by compressive creep testing at 1200 and 1573 K. The creep strain of the two materials was mutually compared and the role of the milling time was identified. The material milled for 24 h had superior creep resistance due to the better distribution of yttria particles. The microstructure of the Pt–Y 2O 3 system (material B) was analyzed by optical microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM).