Mechanical Alloying Products Research Articles

Effect of metastable Cr(Mo)s/Cr(Mo)a powders on mechanical alloying the immiscible Cu–Mo–Cr system

Metastable-state alloy powders are usually synthesised by milling and occur as products of mechanical alloying (MA), but they are rarely used as starting materials for other MA processes. In this work, metastable-state alloy powders, including supersaturated solid-solution Cr(Mo)s and amorphous Cr(Mo)a were prepared in advance. Then, the Cr(Mo)s/Cr(Mo)a powder mixture was mechanically alloyed with elemental Cu to form Cu–Mo–Cr alloy. The effects of the metastable-state powder Cr(Mo)s/Cr(Mo)a on MA of the immiscible Cu–Mo–Cr system were evaluated. Phases and microstructures of the milled powders were analysed by XRD and TEM, respectively. The results show that amorphous Cu-60wt.%Cr(Mo) and supersaturated solid-solution Cu-20wt.%Cr(Mo) alloy powders can be synthesised by MA. It is concluded that MA of the Cu–Mo–Cr ternary alloy system is significantly promoted when elemental Cu powder is milled with metastable-state alloy powder Cr(Mo)s/Cr(Mo)a. Furthermore, the promoting effect of amorphous Cr(Mo)a on MA the Cu–Mo–Cr alloy system is much greater than that of supersaturated solid-solution Cr(Mo)s, during the milling process.

Nanocrystalline Al3Ni2 alloy with high hardness produced by mechanical alloying and high-pressure hot-pressing consolidation

An elemental powder mixture corresponding to Al3Ni2 phase stoichiometry was subjected to mechanical alloying. A metastable nanocrystalline AlNi intermetallic phase with the mean crystallite size of 12 nm was formed upon milling. Heating of the synthesised powder in a calorimeter up to 720 °C caused phase transformation into an equilibrium Al3Ni2 intermetallic phase with the mean crystallite size of 41 nm. The product of mechanical alloying was consolidated at 1000 °C under the pressure of 5 GPa and 7.7 GPa. During consolidation, a phase transformation analogous with the one observed in the course of heating in the calorimeter took place. Both bulk materials have nanocrystalline structure with mean crystallite size of 67 nm and 58 nm, the smaller one in the sample consolidated under the higher pressure. The hardness of the produced Al3Ni2 intermetallic is 8.81 GPa (898 HV1) and 8.72 GPa (887 HV1), while the specific yield strength, estimated using the Tabor relation, is 624 kNm/kg and 617 kNm/kg for the sample hot-pressed under 5 GPa and 7.7 GPa respectively. On the basis of the obtained results, we can assume that the quality of consolidation with preserving a nanocrystalline structure is satisfactory and the hardness as well as the estimated specific yield strength of the produced materials are relatively high.

Microstructure and mechanical properties of nano-Y2O3 dispersed ferritic alloys synthesized by mechanical alloying and consolidated by hydrostatic extrusion

The present study reports synthesis of 1.0wt% nano-Y2O3 dispersed high strength ferritic alloys with nominal compositions of 83.0Fe–13.5Cr–2.0Al–0.5Ti (alloy A), 79.0Fe–17.5Cr–2.0Al–0.5Ti (alloy B), 75.0Fe–21.5Cr–2.0Al–0.5Ti (alloy C) and 71.0Fe–25.5Cr–2.0Al–0.5Ti (alloy D) (all in wt%) by mechanical alloying using planetary ball mill followed by consolidation of alloyed powders by hydrostatic extrusion at 1000°C and 550MPa pressure with a strain rate ~10−1s−1. The products of mechanical alloying and extrusion have been characterized by X-ray diffraction, scanning and transmission electron microscopy, energy dispersive spectroscopy and image analysis. Mechanical properties in terms of hardness, compressive strength, yield strength and Young's modulus have been determined using nano-indenter and universal testing machine. The present ferritic alloys record significantly high levels of compressive strength (850–2226MPa) and yield strength (525–1505MPa), Young's modulus (240–265GPa) and hardness (14.7–17.8GPa) with an impressive true level of strain (5.0–22.5%). These superior mechanical properties measure about 1.5 times greater, albeit with a lower density (~7.4Mg/m3) than that of standard oxide dispersion strengthened ferritic alloys (<1200MPa). Furthermore, the extent of plastic strain before failure in the present routine surpasses all previous attempts of identical synthesis but different consolidation routes for the same set of ferritic alloys. In general strength is higher along transverse than longitudinal direction of extrusion. Thus, it is concluded that uniform dispersion of nanometric (10–20nm) Y2O3 (ex-situ) or Y2Ti2O7 (in-situ) in high volume fraction along boundaries and within the grains of high-Cr ferritic matrix is responsible for this unique combination of high strength and ductility in the present alloys developed by powder metallurgy route.

Mechanochemical synthesis of the low-temperature (B20) phase of FeGe

We have investigated solid-state reactions in an equiatomic mixture of Fe and Ge powders during ball milling in a water-cooled high-energy mill under an argon atmosphere. The mechanical alloying products have been characterized by x-ray diffraction, Mossbauer spectroscopy, and calorimetry. The observed sequence of phase formation correlates with the thermodynamic properties of the iron germanides involved. The alloy prepared by ball milling for 2 h consists entirely of nanocrystallites (≃15 nm) of the low-temperature, stable, cubic (B20) phase of FeGe.

Synthesis and characterisation of nanostructured FeCo alloys

Nanocrystalline Fe(1−x)Co x (x = 0.12, 0.5, 0.6) mixtures have been prepared by mechanical alloying using a planetary ball mill under several milling conditions. The alloying process between the elemental powders and the microstructure changes of the prepared samples have been investigated using X-ray diffraction (XRD) and 57Fe Mossbauer spectrometry. The XRD patterns refinement on the mechanical alloying products according to the Rietveld method (Maud software) reveals the allotropic transformation of Co from fcc to hcp form and the progressive dissolution of Co into the α-Fe lattice as a function of both Co concentration and milling conditions. The grain size values of the obtained powders reaches a nanometer scale of about 10 nm. Mossbauer results show that the beginning of the solid state reaction between Fe and Co elemental powders depends on the milling conditions. After 24 h of milling, the average hyperfine magnetic fields values of Fe88Co12, Fe50Co50 and Fe40Co60 mixtures are consistent with a disordered and an ordered FeCo solid solution, respectively.

Fundamental Formation Laws of Phase Composition, Structure and Properties of Aluminium Materials Manufactured by Mechanical Alloying

The present investigation objective is to develop the technological process for strengthened aluminium alloys formation of different density based on mechanical alloying. Standard aluminium and magnesium powders were used as initial materials. Lithium was introduced in free state and binded in hydroxide LiOH. Granulated composition with mean particle size 0.2 ... 0.3 mm is the product of mechanical alloying. Thermal treatment of granulated compositions and hot compaction of semiproducts initiate phase transformations which contribute to thermodynamic equilibrium state of the alloys. Alloy base is characterized by micro- or small crystalline structure and presents a solid solution of magnesium and lithium in aluminium strengthened by nanocrystalline inclusions of aluminium oxides, magnesium and aluminium carbides which results in high strength of said alloys at low and high temperatures.

Effects of ambient temperature and acceleration on various mechanical alloying products: MgAlZn quasicrystals, NiZr amorphous alloys and amorphous Se

In the present work, we employed a high-energy mill which is capable of milling with intensities up to 150 G (where G is the gravity of the earth) in ambient temperatures up to 300 °C. Phase transformation diagrams were constructed as functions of milling intensity and ambient temperature for three representative systems: Mg 48Al 15Zn 37, Ni 50Zn 50 and pure Se. The ambient temperature measured on the outer wall of the vial was found to coincide well with the true “annealing” temperature which the powdered sample experiences during milling. It is shown that both the milling intensity and ambient temperature affect substantially the formation rate of a quasicrystal in the MgAlZn system and that of an amorphous phase in both NiZr and Se. By choosing appropriate conditions, we found the shortest milling times to complete the formation of MgAlZn quasicrystals, amorphous NiZr alloy and Se to be 30 min, 3 h and 20 min respectively.