The Glassy Structure Formation and Phase Evolution in Mechanically Alloyed and Spark Plasma-Sintered Al-TM-RE Alloys

Ram S Maurya,Tapas Laha

doi:10.1007/s11665-019-04505-1

Abstract

The present study deals with the comparative study of amorphization tendency of Al86Ni6Y6, Al86Ni6Y6Co2 and Al86Ni6Y4.5Co2La1.5 alloy powders via mechanical alloying performed at 300 revolution per minute with ball-to-powder ratio of 15:1 and subsequently the devitrification tendency of 300 °C and 500 °C spark plasma-sintered bulk amorphous alloys. Mechanically alloyed Al86Ni6Y6, Al86Ni6Y6Co2 and Al86Ni6Y4.5Co2La1.5 powders yielded nearly fully amorphous structure after 140, 170 and 200 h, respectively. The requirement of prolonged milling was attributed to the soft and ductile nature of aluminum with high stacking fault energy. Amorphous powders were consolidated via spark plasma sintering at 300 and 500 °C by applying a constant pressure of 500 MPa. X-ray diffraction was performed on the 300- and 500 °C-sintered samples. XRD patterns of the 300 °C-sintered alloys exhibited very-low-intensity nanocrystalline FCC-Al peak overlaying an amorphous hump evincing retention of a large amount of the amorphous phase. Enhanced devitrification tendency was reported in the 500 °C-sintered alloys; however, a major difference in the devitrification tendency of the 500 °C-sintered Al86Ni8Y6, Al86Ni6Y6Co2 and Al86Ni6Y4.5Co2La1.5 alloys was that the quinary alloy exhibited higher tendency of devitrification, which was also corroborated by performing HRTEM and analytical TEM experiment. This could be attributed to the higher probability of coupling of atoms by short-range atomic shuffling during spark plasma sintering. Vickers hardness, and relative density estimated via Archimedes’ principle, varied depending on the degree of free volume annihilation and crystallization during sintering.

Highlights

Bulk metallic glasses (BMGs), having outstanding mechanical, chemical and physical properties, could replace the presently used metallic materials in many structural and functional applications (Ref [1, 2])
Povstugar et al (Ref 29) reported formation of such intermetallic phases in the 50-h and 100-h milled Al85Y8Ni5Co2 powder. This Al-rich phase may form at any stages of milling; in this work, we report only a few interval milled powders as it would be tedious to analyze the instantaneous phase formation during milling
Various Al-based bulk alloys consolidated at 300 °C exhibited very few nanocrystalline FCC-Al distributed in amorphous matrix as confirmed by low-intensity FCC-Al peak overlaying broad XRD hump

Summary

Introduction

Bulk metallic glasses (BMGs), having outstanding mechanical, chemical and physical properties, could replace the presently used metallic materials in many structural and functional applications (Ref [1, 2]). The devitrification behavior of glassy alloys synthesized via powder metallurgy is reported to be dependent on the type and atomic size of the elements present in the alloy (Ref 15-20), sintering pressure (Ref 9, 21, 22), temperature (Ref 10, 12) as well as time (Ref 23). In this context, Huang et al (Ref 15) reported the dependence of crystallization behavior of Al-Ni-La amorphous alloys on Ni and La contents, fabricated via melt spinning. The effect of various alloying elements on amorphization tendency of the mechanically alloyed various Al-rich powders has been compared

Synthesis of Amorphous Powders Via Mechanical Milling

Results and Discussion

Role of Particle Morphology

Relative Density and Hardness of Consolidated Bulk Alloys

Conclusions