Disordering of the Ni3Si intermetallic compound by mechanical milling

The ordered f c c intermetallic compound Ni₃Si was mechanically milled in a high-energy ball mill. The severe plastic deformation produced by milling induced transformations with increasing milling time as follows: ordered f c c disordered f c c nanocrystalline f c c. The structural and microstructural evolution with milling time was followed by X-ray diffraction, TEM, hardness tests, and differential scanning calorimetry (DSC). Complete disordering occurred at milling times of 2 h and kept the saturated H of the DSC peak in the range of estimated enthalpy even after 60 h milling. The structural development during milling of the f c c solid solution for Ni₃Si was presumably dominated by the formation and refinement of a dislocation cell structure into microcrystallites which eventually reached nanometre dimensions.     

Synthesis of the CaAl2O4 nanoceramic compound using high-energy ball milling with subsequent annealing

Monocalcium aluminate, CaAl₂O₄, is the main constituent of calcium alumina cements which have found wide applications in refractory industries. In the present work, CaAl₂O₄ nanoceramic compound was produced by high-energy ball milling of the oxide powders followed by annealing. The phase evolution and microstructural changes of the powders during the process were investigated by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that no CaAl₂O₄ was formed during ball milling even after 100 h. By subsequent annealing, the nucleation and growth of CaAl₂O₄ took place at 1000 °C after 2 h. Depending on milling time, the amount of CaAl₂O₄ increased with increasing annealing temperature. The CaAl₂O₄ single phase was obtained by milling the sample for 100 h and subsequently annealing at 1200 °C for 2 h. The quantitative phase analysis was used to measure CaAl₂O₄ phases in these processes. The average particle diameter of the sample milled for 100 h and annealed at 1200 °C was found to be less than 100 nm as measured by transmission electron microscopy.     

Metallothermic reduction of zinc sulfide induced by ball milling

Stoichiometric mixtures of ZnS + Al and ZnS + Mg were milled for different times in a planetary ball mill. The XRD traces of the as-milled samples showed the presence of zinc, MgZn₂, and MgS after 30-min milling in the ZnS–Mg system. The traces of MgZn₂ disappeared after 1-h milling and the reduction reaction seemed to have been completed after 5-h milling. The ZnS–Al system was somewhat different with only slight reduction to zinc after 1 h and ZnS peaks still present after 10 h of milling. Isothermal heating under argon atmosphere of 3-h-milled samples showed the presence of hexagonal ZnAl₂S₄ and mixtures of MgS and Zn_0.68Mg_0.32S in the ZnS–Al and ZnS–Mg systems, respectively. These results show that the reaction in the ZnS–Al system progressed gradually during milling. The decrease in the crystallite size of reactants materials (especially ZnS) during milling operation led to decrease in the formation temperature of hexagonal ZnAl₂S₄ phase and decrease in the transformation temperature of sphalerite (ZnS) to hexagonal wurtzite.     

Solidification behavior of Al-Si-Fe alloys and phase transformation of metastable intermetallic compound by heat treatment

Solidification behavior of Al-20 wt% Si-8 wt% Fe and Al-30 wt% Si-5 wt% Fe alloys during cooling with a cooling rate of 10 K/min has been studied using optical microscopy, X-ray diffractometry, differential thermal analysis, scanning electron microscopy and energy dispersive X-ray spectroscopy. In Al-20Si-8Fe alloy, metastable -Al₄FeSi₂ phase with tetragonal structure formed first from melt, followed by primary Si precipitation and then remaining liquid solidified finally into ternary eutectic of -Al, Si and phases. However, in Al-30Si-5Fe alloy, primary Si formed first, followed by the phase precipitation and then eutectic solidification. During isothermal heat treatment of as-solidified alloys, phase transformation from the phase to equilibrium phase began at the interface between phase and -Al matrix and progressed toward the inside of phase with co-precipitation of Si particles due to the difference in composition between -Al₄FeSi₂ and -Al₅FeSi phases.     

Solid-state transformation in nanocrystalline Ti induced by ball milling

In the current study, we report for the first time a new Ti rhombohedral (trigonal) structure induced by HEBM and subsequent sintering. During ball milling of Ti powder, solid-state transformation does not only depend on the grain refinement but also on the successful deformation of the nano-sized crystallites due to high energy ball impacts. Thermal stability of Ti-nanocrystalline in FCC allotrope was investigated. Upon sintering, the unstable FCC restored back to the rhombohedral phase rather than to HCP. The appearance of HCP Ti after sintering could suggest that prolonged milling leads to dispersion of hard particles (HCP) into more ductile particles belonging to allotropic phases, and hence possibility of resurfacing on sintering.     

High-energy ball milling of intermetallic Ti-Cu alloys for the preparation of oxide nanoparticles

Copper and titanium oxides in the nano-size range show unique chemical and physical properties and thus have been intensively considered for novel and smart applications. In this work, oxide nanoparticles were prepared by high-energy ball milling of Ti-Cu alloys followed by a controlled oxidation process. Alloys of the Ti-Cu system Ti-50Cu, Ti-57Cu, and Ti-65Cu (in wt.%) prepared by arc melting were selected considering they provide different starting brittle intermetallic phases before milling. Microstructural investigation indicated that Ti-50Cu was composed of Ti₂Cu and TiCu, while Ti-57Cu was single-phase TiCu. Ti-65Cu was dual-phase and consisted of Ti₃Cu₄ and Ti₂Cu_3. A mean particle size below 10 nm was achieved after high-energy ball milling for all compositions. The oxidation process was then investigated in two temperature ranges. At high oxidation temperatures of 700–800 °C, a complete oxidation took place leading to oxides TiO₂-rutile and CuO in all alloys. However, at a low oxidation temperature (350 °C), partial oxidation occurred and different oxides were obtained. Ti-50Cu was the most promising alloy and led to a mix of TiO₂ (rutile and anatase), CuO, Cu₂O, and Ti₃Cu₃O. After long exposure to thermal oxidation, the resulting oxides remained in the nanometric range with a particle size distribution showing a D50 of approximately 6 nm.     

Phase transformation of the intermetallic compound Al4Ca

By measurement of physical properties and microscopic examination it was found that the phase Al₄Ca undergoes a martensitic transformation with M _s130° C. The low temperature structure is monoclinic, a=0.6158 nm, b=0.6175 nm, c=1.118 nm, =88.9°. The Dl₃ structure ascribed to Al₄Ca hitherto is valid only above M _s. Orientation relationships indicate that the transformation proceeds by a shear of 1.1° on (1 1 0) planes of the Dl₃ structure.     

The influence of ball milling and subsequent calcination on the formation of LiFeO2

The influence of ball milling and subsequent calcination of a 1:1 molar mixture of -Fe₂O₃ and Li₂CO₃ on the formation of LiFeO₂ has been investigated. Pre-milling was found to lower the temperature of ferrite formation by ca. 200°C and a thermally stable -LiFeO₂ phase was found to form in the temperature range 500–600°C. Slow cooling of the pre-milled mixture calcined at higher temperatures resulted in the formation of some LiFe₅O₈.     

Solid-state reactions in the Al-Fe system induced by ball milling of elemental powders

Elemental aluminium and iron powders have been mechanically alloyed in the atomic AlFe ratios of 11 and 13. The structural evolution of the samples was followed by X-ray diffraction and differential calorimetry. Extended milling caused the formation of an almost completely disordered b c c solid solution instead of the equilibrium B2 and DO₃ compounds. Upon heating to 700 °C the formation of the B2 phase was observed in the equiatomic samples and no significant variation of the long-range state of order in the iron-rich samples. Upon heating of samples pre-milled for short or intermediate times, at about 400 °C, the nucleation and growth of Al₅Fe₂ was observed which, upon further heating to 700 °C, transformed to the B2 phase or to the b c c solid solution, depending on the sample composition. These results suggest that the solid-state reactions proceed through diffusion of iron atoms in the aluminium layers, and that for an iron concentration in these layers below about 50 at%, the Al(Fe) solid solution could be in a metastable phase.     

Carburising behaviour of low carbon steel with nanocrystalline surface layer induced by ball milling

Abstract

Ball milling, as a surface nanocrystallisation method, was employed to investigate the influence of severe plastic deformation on the carburisation treatment performed on low carbon steel. The results indicated an enhancement in the carburisation efficiency as a result of surface milling. This enhancement was attributed to the formation of a nanocrystalline layer in the surface of the treated samples. It was found that the main reasons for the accelerated kinetics of the carburisation process would be the considerable amounts of non-equilibrium defects and the finer austenite grains in the early and later stages of the treatment respectively, which facilitate the carbon diffusion.     

Investigating the effect of ball milling during the deep cryogenic heat treatment of the 1.2080 tool steel

The effect of attrition milling on the structure and hardness of the 1.2080 tool steel during the deep cryogenic heat treatment was investigated via the scanning electron microscope (SEM), X-ray diffraction (XRD) and microhardness and hardness evaluation. Some newly formed defects were produced during the attrition milling of the samples as a result of the surface contact between the balls and samples. These defects affect the carbides nucleation during the cryogenic heat treatment. Moreover, the surface impact produces a residual compressive stress on the samples surface. These phenomena lead to an increase in the hardness and percentage of the carbides. It was also observed that milling the samples before the cryogenic heat treatment is not beneficial due to austenite aging. Furthermore, some newly nano-sized carbides were also produced during the cryogenic heat treatment in the structure, increasing the hardness further.     

Microstructural evolution during combustion reaction between CuO and Al induced by high energy ball milling

The product of the combustion reaction between CuO and Al induced by high energy ball milling has been characterised by using X-ray diffractometry and scanning electron microscopy. It has been observed that the combustion reaction can be ignited very easily by the ball milling. The reaction product consists of polycrystalline Cu in bulk and particle forms and a large number of nanometer sized spherical Al2O3 particles attached to the surface of the Cu. It has been demonstrated that this microstructure is evolved through rapid solidification of Cu and Al2O3 melts and rapid condensation of Cu vapour. Cu and Al2O3 phases are separated in the reaction product. The reason for this is mainly attributed to the large difference in their density and the shaking force of the ball mill.     

Nano-structured intermetallic compound TiAl obtained by crystallization of mechanically alloyed amorphous TiAl, and its subsequent grain growth

The amorphization process during mechanical alloying (MA) was investigated for the Al-50at%Ti and Al-50at%Ti-10vol%TiB₂ powder mixtures. Pure metallic powders of Al and Ti were finely mixed and transformed to the amorphous phase after being milled for about 2880 ks. In the case of Al-50at%Ti-10vol%TiB₂ powder, the amorphous alloys with a fine dispersion of TiB₂ particles could be obtained for a shorter milling times than that required for the powders without TiB₂ ceramics. As a result of heat treatment for the mechanically alloyed amorphous powders, a nanocrystalline intermetallic compound of TiAl () could be produced. Subsequent grain growth of the phase during heat treatment was investigated by estimating the grain-growth exponent and the activation energy for grain growth. It was found from this estimation that the grain growth was further suppressed as the powders were mechanically alloyed for longer times. Furthermore, the addition of the TiB₂ particles that could be dispersed during MA finely and homogeneously in the amorphous matrix was found to be effective for suppression of the grain growth especially at elevated temperatures as well as for a long annealing.     

Synthesis by ball milling and characterization of Al-Zn alloys

Mechanical ball milling is a useful technique for systems with positive enthalpy of mixing. With this technique solubility of a solute in a solid solution can be enhanced. Al-Zn system has positive heat of mixing. High energy ball milling has been employed to produce four alloys of Al with 2.5 to 10 wt% Zn. Powders of Al (1–125 m) and Zn (0.7–5.0 m) were mixed together in the desired proportion and milled with a powder to ball weight ratio of 1:20. The size and shape of the particles of as-received and alloy powders were examined in a scanning electron microscope (SEM) while their microanalysis was performed by energy dispersive system (EDS) attached with SEM. It has been observed that 120 h of milling of the powders produced homogeneous alloys. X-ray diffraction (XRD) patterns confirm complete solubility up to 10 wt% Zn in Al. Using the quasi-chemical theory of binary solid solutions, the enthalpy of mixing of 10 wt% Zn in Al has been determined to be 276 cals/mol. It is shown that stress exerted by very high density of dislocations, generated by mechanical milling, plays a major role in the enhancement of solubility. Hardness has been measured and it increases with increasing solute content.     

Bismuth redistribution induced by intermetallic compound growth in SnBi/Cu microelectronic interconnect

It was found that Bi particles, with a diameter of 100 nm, precipitated along Cu₃Sn/Cu interface and Bi crystallites dispersed in Cu₃Sn layer in 42Sn58Bi/Cu microelectronic interconnect, when it was aged at 120 °C for 7 days. The mechanism for Bi redistribution like this was discussed. Cu₆Sn₅ turned into Cu₃Sn by Cu diffusion that is dominant in Sn/Cu inter-diffusion during the aging process. Bi precipitation occurred in Cu₃Sn due to lower Bi solubility in Cu₃Sn than that in Cu₆Sn₅. The Bi precipitates can traverse the formed Cu₃Sn quickly toward the Cu₃Sn/Cu interface, attributed to the Kirkendall effect. They stayed and nucleated there to form particles, owing to their unwettability on Cu. The formed Cu₃Sn got oversaturated with Bi, when the joint cooled from 120 °C to room temperature. Then Bi crystallites precipitated dispersedly in Cu₃Sn layer.     

Improvement in oxidation resistance of the intermetallic compound titanium aluminide by heat treatment under a low partial pressure oxygen atmosphere

The improvement in oxidation resistance of an intermetallic compound TiAl was investigated by means of a new type of surface treatment: heat treatment under a low partial pressure oxygen atmosphere. The specimens treated by this method showed superior oxidation resistance compared with a nickel-base superalloy Inconel 713C during cyclic heating to a temperature of 1173 K in static air. The best conditions for the heat treatment under a low partial pressure oxygen atmosphere were found to be: pressure, 6.7 X 10-³ Pa; temperature, 1273 K; time, 7.2 ks (2 h) or more. It was presumed that the excellent oxidation resistance resulting from this method is due to preferential formation of a thin, strong Al₂0₃ surface layer.