Calorimetric and structural analysis of the new phase Al33Ni16Zr51 produced by direct synthesis and mechanical alloying

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Abstract

A new phase has been synthesized in the ternary phase diagram Al–Ni–Zr: its nominal composition is Al33Ni16Zr51. For the Al33Ni16Zr51 compound obtained by mixing the three components in suitable proportions, a study has been carried out by direct synthesis (calorimetry) and mechanical alloying in our laboratory. With the first method we know directly the enthalpy of formation of this alloy. For the amorphous alloys prepared by mechanical alloying we can determine the crystallisation enthalpy with the differential scanning calorimetry (DSC) method. So it is possible to determine a fundamental piece of information: the amorphous alloy formation enthalpy.

Introduction

Intermetallic compounds are of great interest both fundamentally and industrially for their remarkable high temperature, high strength, good ductility and corrosion resistance properties. New routes are used to prepare alloys from elements. Mechanical alloying [1], [2], [3], [4], [5] yields amorphous or nanocrystalline alloys. It is a technique which allows to monitor the microstructure of the alloy. In this study, amorphous Al–Ni–Zr alloys were investigated. The direct synthesis at high temperature yields crystalline alloys: it is an SHS type reaction (self-propagating high-temperature synthesis). A calorimetric study of Al33Ni16Zr51 was undertaken with the purpose of determining thermodynamic formation characteristics. Usual techniques like X-ray diffraction and microprobe analysis are also essential tools for a larger investigation of this type of alloy.

Section snippets

Experimental

The starting materials were aluminium powder (−325 mesh; 99.5% wt. pure), zirconium powder (−325 mesh; 99.7% wt. pure), both from Cerac, and nickel powder (−2500 mesh; 99.8% wt. pure) from Goodfellow.

Direct synthesis calorimetry: enthalpy of formation

For the following reaction 0.33Al (cfc)+0.16Ni (cfc)+0.51Zr (cc)→xAlNiZr+yAl2Zr3+zAl33Ni16Zr51+ΔfH (1010 K)with x+y+z=1 the formation enthalpy was, after five measurements: ΔfH (1010 K)=−54±2 kJ/mol.

Examination of the products by electron microprobe analysis showed the coexistence of three phases at room temperature: AlNiZr, Al2−xNixZr3 (fine scattered particles; 0.03≤x≤0.12) and the new phase Al33Ni16Zr51. Examination of the products by X-ray diffraction (Fig. 1) shows, apart from the AlNiZr,

Conclusion

A new phase with the following composition Al33Ni16Zr51 has been synthesized according to direct synthesis calorimetry and mechanical alloying. This phase has been characterized in the amorphous or crystalline state by XRD, EMPA and DSC.

One can underline that from the enthalpy results obtained by direct synthesis and differential calorimetry, a highly interesting piece of information has been deduced: the amorphous alloy formation enthalpy ΔfH (am).

The determination of the structure of this new

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