J. Eckert

Glass‐forming range in mechanically alloyed Ni‐Zr and the influence of the milling intensity

Amorphous Ni‐Zr powders have been prepared by mechanical alloying from crystalline elemental powders. The glass‐forming range has been determined by x‐ray diffraction, differential scanning calorimetry and saturation magnetization measurements. From 27 to 83 at.u2009% Ni the powders become amorphous. This shows that deep eutectics do not play any role, contrary to amorphization by melt spinning. Crystallization temperatures, crystallization enthalpies, and wave numbers Qp, obtained from x‐ray diffraction investigations, are compared with the data received for rapidly quenched samples. In addition, the effect of the milling intensity on the glass formation has been studied for the first time. If the intensity is too high, crystalline intermetallic phases are formed. On the other hand, the powder needs an extended milling time to become completely amorphous if the milling intensity is too low. Conclusions on the actual temperature of the individual particle during mechanical alloying and on the glass‐forming pr...

Formation of quasicrystals by mechanical alloying

Quasi‐crystalline Al65Cu20Mn15 powder has been produced by mechanical alloying from crystalline elemental powders. The alloying process has been monitored by x‐ray diffraction, and the resulting product has been characterized by transmission electron microscopy. The quasi‐crystalline phase forms after about 90 h of milling. The crystallization temperature and enthalpy have been determined by differential scanning calorimetry. The results are compared with data for melt‐spun material.

Formation of quasicrystalline and amorphous phases in mechanically alloyed Al-based and TiNi-based alloys

Abstract The formation of quasicrystalline and amorphous powders by mechanical alloying from crystalline, elemental powder has been investigated for Alue5f8Cuue5f8M (M = v, Cr, Fe, Co, Ni) Alue5f8Mue5f8Si (M = Cr, Mn), Alue5f8M (M = V, Cr, Mn, Fe, Co), Tiue5f8Niue5f8Feue5f8Si, and Tiue5f8Niue5f8V alloy systems. The alloying process has been monitored by X-ray diffraction and differential scanning calorimetry, and the microstructure has been characterized by scanning electron microscopy. Quasicrystalline phases form directly during milling by a solid-state interdiffusion reaction from the crystalline starting materials for Alue5f8Cuue5f8Cr and Alue5f8Cuue5f8V. For Alue5f8Cuue5f8Fe the formation of the quasicrystalline phase is observed after additional annealing at elevated temperatures. Amorphous phase formation is achieved for the Tiue5f8Niue5f8Feue5f8Si, Tiue5f8Niue5f8V, Alue5f8Mue5f8Si (M = Cr, Mn), and Alue5f8M (M = V, Fe) alloy systems. For Tiue5f8Niue5f8Feue5f8Si and Alue5f8Crue5f8Si additional annealing results in an amorphous-to-quasicrystal transition. Finally, no alloying during milling has been obtained for binary Alue5f8Mn, Alue5f8Co, and Alue5f8Cr. Only for Alue5f8Cr the formation of a quasicrystalline alloy can be observed after isothermal annealing of the layered composite formed during milling. The results are compared with data for rapidly quenched material.

GLASS FORMATION AND EXTENDED SOLUBILITIES IN MECHANICALLY ALLOYED COBALT-TRANSITION METAL ALLOYS

Binary Co-TM (TM ≡ Mn, Cr, V) alloys have been prepared by mechanical alloying of elemental powders in a planetary ball mill and investigated by X-ray diffraction, differential scanning calorimetry and saturation magnetization measurements. For Co-V, an amorphous phase appears in the central composition range, whereas for Co-Cr and Co-Mn an extended solid solution can be obtained during mechanical alloying. The extent of the glass-forming range is discussed in terms of a thermodynamic approach. The larger the driving force for the interdiffusion reaction the wider the glass-forming range.

Synthesis of NiTi and FeTi alloys by mechanical alloying: formation of amorphous phases and extended solid solutions

Abstract Niue5f8Ti and Feue5f8Ti powders prepared by mechanical alloying of elemental crystalline powders in a planetary ball mill have been investigated by X-ray diffraction, differential scanning calorimetry and saturation magnetization measurements. The Niue5f8Ti powders become completely amorphous in the central composition range. For Ni 70 Ti 30 , the powder consists of an amorphous phase and crystalline intermetallic Ni 3 Ti. The Feue5f8Ti powders exhibit an amorphous phase from 30 to 70 at.% Fe and residual elemental α-Fe and Ti or crystalline intermetallic FeTi, respectively. The intermetallic phases form directly by milling, since the thermal conditions during extended processing are not sufficient for an in situ crystallization of amorphous powder. The coexistence of amorphous and intermetallic phases indicates that the mechanical alloying does not proceed under metastable equilibrium conditions. Outside the regime of the amorphous phase, mechanical alloying produces markedly extended solid solutions of at least 20 at.% Ti in Ni or Fe. The experimental results are compared with the glass-forming ability predicted by thermodynamic calculations. The amorphization depends strongly on a large negative enthalpy of mixing as a driving force for the interdiffusion reaction during milling. The enhanced solid solubility in both alloy systems can be explained by a small difference of the atomic radii of the individual components and a deformation-induced increase of the free enthalpy of the intermetallic phases.

Glass-forming ranges in transition metal-Zr alloys prepared by mechanical alloying☆

Abstract Amorphous TM-Zr (TM = Ni, Co, Mn, Cr or V) powders have been prepared by mechanical alloying from crystalline elemental powders. The glass-forming ranges have been determined by X-ray diffraction, differential scanning calorimetry and saturation magnetization measurements. For TM = Cr and V the powders do not become amorphous after 60 h of milling. For TM = Ni, Co and Mn an extended amorphous phase appears in the middle concentration range. Crystallization temperatures, crystallization enthalpies and superconducting transition temperatures are compared with the data received for rapidly quenched samples. The extent of the glass-forming ranges is discussed in terms of a thermodynamic approach. The larger the thermodynamic driving force for the interdiffusion reaction, the wider the glass-forming range.

Quasicrystal formation and phase transitions by ball milling

Abstract Quasicrystalline Alue5f8Cuue5f8Mn powder has been prepared by mechanical alloying. The quasicrystalline phase forms directly by milling via a solid-state reaction from the crystalline elemental powders. Single-phase quasicrystalline material is obtained for (15–25) at.% Cu and (10–20) at.% Mn. Besides, two-phase regions of quasicrystalline phase and crystalline material exist. The results are compared with data for melt-spun material. The milling conditions strongly affect the phase formation. For low milling intensity an amorphous phase instead of quasicrystalline material forms. High-intensity milling results in the formation of crystalline powder. The various phases can be transformed into each other by additional milling at higher or lower milling intensity. Possible mechanisms are proposed.

Amorphization reaction during mechanical alloying: influence of the milling conditions

Amorphous Ni-Zr powders have been prepared by mechanical alloying of elemental crystalline powders. The glass-forming range has been determined in detail at different milling intensities. Depending on the milling conditions, at least partial crystallization of the formerly amorphous material can occur from 66 to 75 at% Ni, due to a temperature rise during milling at high intensity. In comparison with isothermal annealing experiments at various temperatures on completely amorphous powder, a relation between milling temperature and milling time is shown. This confirms the similarity of the amorphization process during mechanical alloying with the solid-state interdiffusion reaction in alternating crystalline multilayers.

Glass-forming ranges of mechanically alloyed powders☆

Abstract The glass-forming ranges in mechanically alloyed TM-Zr alloys (where TM is a transition metal) have been determined by means of magnetization and crystallization experiments, by Mossbauer spectroscopy, and by investigating the superconducting properties. Glass formation by mechanical alloying is possible in the central composition range, i.e. from 30–78 at.% iron, 27–85 at.% nickel and 27–92 at.% cobalt. For TM-rich or zirconiumrich compositions, two-phase regions exist between the primary phases and the amorphous phase. It is shown that the measurement of the physical properties allows a more accurate determination of this than does X-ray diffraction.

Compositional dependence of quasicrystal formation in mechanically alloyed AlCuMn

Abstract Quasicrystalline Alue5f8Cuue5f8Mn powders have been prepared by mechanical alloying from crystalline elemental powders. The composition range of the quasicrystalline phase has been determined by X-ray diffraction. Single-phase quasicrystalline material forms in the ranges 15–25 at.% Cu and 10–20 at.% Mn. In addition, a twophase region of quasicrystalline phase and “solid solution” exists for 30 at.% Cu and 5–10 at.% Mn, and a mixture of quasicrystalline material and pure copper shows up for Al70Cu25Mn5. Alloys with low aluminium content exhibit a single-phase “solid solution”, and for aluminium-rich compositions the “solid solution” coexists with the pure elements. Crystallization temperatures, crystallization enthalpies and lattice parameters, obtained from X-ray diffraction investigations, are compared with the data obtained for rapidly quenched samples. Conclusions on the stability of the powders are drawn from these results.