Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Mechanical Alloying And Milling

https://pure.uva.nl/ws/files/3824181/415_5054y.pdf

On the 4f-3d exchange interaction in intermetallic compounds

Magnetic interactions in R2Fe17-xAlx compounds (R = Ho, Y)

The 90 K superconductor, YBa 2 Cu 3 O δ (YBCO), has proved to be highly adaptable chemically as it can accommodate a wide variety of cationic and anionic substitutions. Indeed, the majority of the chemical elements, excluding noble gases and actinides, have been reported to substitute to some extent into the YBCO structure. This review covers the literature on such substitutions and their effect on the properties of YBCO. Reported solubility limits are given, together with crystal symmetry and trends in unit cell parameters with dopant concentration. The dopant site is considered; this is additionally complex in the case of copper substitution because of the two distinct copper sites in the crystal structure. The effect of the dopant on the critical temperature, T c , is reviewed; the literature is often contradictory due to the dual effects of variable oxygen content and the nature of the dopant. Preparation methods appear to have an effect on solubility limits, crystal symmetry and T c , Also, the methods used to determine solubility limits are often imprecise which can lead to contradictions. The magnetic properties of doped materials are reviewed; for some dopants, particularly the magnetic lanthanides, antiferromagnetism and superconductivity co-exist. The related RBa 2 Cu 3 O δ phases (R = lanthanide), their structure, properties and behaviour on doping are reviewed in a similar way. For the larger rare earths, the related systems R 1+ x Ba 2- x CU 3 O δ , are reviewed; as x increases, the transition temperature decreases and compositions R 1.5 Ba 1.5 Cu 3 O δ are semiconducting. The upper and lower solubility limit changes with R, and for R = Dy, the upper limit is x = 0 composition, LaBa 2 Cu 3 O δ , cannot be prepared in air since substitution of La onto the Ba site occurs, forming the Ba-deficient solid solutions. The discovery of superconductivity above liquid nitrogen temperatures in YBa 2 Cu 3 O 7 , has generated a vast quantity of research; to date, > 20 000 papers have appeared on the 123 materials (source: BIDS). This review, therefore, cannot be comprehensive, but attempts to highlight important substitutions, their effect on the properties of YBCO and any contradictions in the literature.

Crystal chemical substitutions and doping of YBa2CU3Ox and related superconductors

The magnetic properties of a series of Nd2Fe17−xAlx solid solutions, with x equal to 2.04, 4.01, 5.97, 7.94, and 9.06, have been studied by magnetic measurements, neutron diffraction, and Mossbauer spectroscopy. Magnetization studies indicate that the Curie temperature increases from 330 K in Nd2Fe17 to a maximum of ∼470 K at an x of 3.5. The compounds crystallize in the Th2Zn17 structure with lattice parameters and unit cell volumes which increase linearly with increasing aluminum content. The neutron diffraction results indicate that aluminum atoms are excluded from the 9d site, prefer the 18h site at low aluminum content, and prefer the 6c and 18f sites at high aluminum content. At 10 K the magnetic moments of the iron and neodymium atoms are collinear and take up a basal orientation at all aluminum contents. The moments decrease with increasing aluminum content and the magnetic moments per unit cell at 10 K are in excellent agreement with the 4.2 K saturation magnetization values. At 295 K the Nd2Fe17...

/pdf/a-magnetic-neutron-diffraction-and-mossbauer-spectral-study-q6jvsm341n.pdf

A magnetic, neutron diffraction, and Mössbauer spectral study of the Nd2Fe17−xAlx solid solutions

The free-powder magnetisation of RMn6-xCrxSn6 compounds has been measured for compounds with R = Y, Gd, Tb, Dy, Ho, Er in fields up to 38 T, and interpreted in terms of simple model, which is also outlined in this paper. From the measurements, estimates for the R-3d mean-field coupling constant (nRT) could be derived for the cases where R = Gd, Tb, Dy, Ho, Er. In turn, the nRT values can be related to the microscopic spin-coupling constant (JRT). In the case of YMn6Sn6 the high-field measurement presents evidence for a very weak antiferromagnetic coupling between the Mn layers. Furthermore, values for the Mn moments (μMn) were also derived from the magnetisation measurements. The estimated μMn values are of the order of 2.0μB.

/pdf/competing-exchange-interactions-and-their-relevance-for-the-23129tf2zy.pdf

Competing exchange interactions and their relevance for the magnetisation process in RMn6-xCrxSn6 powders (R=Y, Gd, Tb, Dy, Ho, Er)

A study of the crystal structure and the magnetic properties, especially the magnetocrystalline anisotropy of (Sm1−xYx)2Fe17Ny compounds (x=0, 0.2, 0.4, 0.6, 0.8, and 1.0, 2<y<3) has been performed. All the interstitially nitrided compounds preserve the same Th2Zn17- or Th2Ni17-type structure as the original compounds. The Curie temperatures decrease from 750 to 700 K as x increases from 0 to 1. The anisotropy field decreases linearly with increasing yttrium content. The spin reorientation has been investigated by means of high field magnetization measurements, AC-susceptibility measurements and thermomagnetic analysis, combined with X-ray diffraction. The anisotropy constants K1, K2 and K3 were derived by a phenomenological analysis, using magnetization curves measured in high fields, applied perpendicular to the alignment direction of the powder samples. A tentative spin phase diagram of the series is presented.

Magnetic anisotropy of (Sm, Y)2Fe17Ny compounds

The changes of the structural and magnetic properties of Co20Cu80 during mechanical alloying were studied as well as the structure and magnetic behaviour of mechanically alloyed Co24Cu76. The magnetic behaviour of the final products was compared to that of similar alloys prepared by different techniques. Clear evidence for superparamagnetism was found in the mechanically alloyed compounds.

Magnetic properties of mechanically alloyed Co-Cu

The magnetic interaction between the rare earth (R) and the Co moments in ferrimagnetic RCo 12 B 6 (R is heavy rare earth) intermetallic compounds, crystallizing in the hexagonal SrNi 12 B 6 , has been studied by means of high-field magnetisation measurements on fine (single-crystalline) power particles. Magnetisation curves were measured at 4.2 K in the high-field facility at the University of Amsterdam up to 38 T. Field-induced magnetic transitions which reflect changes in the configuration of the R and Co magnetic moments have been observed. The measured magnetisation curves were analysed with a mean-field model. The magnetic coupling constants J RCo between the R and Co moments in the Hamiltonian H =-2 Σ RCo J RCo S R S Co were determined and compared with those derived from the analysis of the compensation temperature and of the magnetic susceptibility measured at the compensation point.

G.F. Zhou

Papers

Competing exchange interactions and their relevance for the magnetisation process in RMn6-xCrxSn6 powders (R=Y, Gd, Tb, Dy, Ho, Er)

Magnetic anisotropy of (Sm, Y)2Fe17Ny compounds

Magnetic properties of mechanically alloyed Co-Cu

Field-induced transitions in RCo12B6 compounds

The Role of Enthalpy in Structural and Property Changes of Intermetallic Compounds