Phase Transformation and Morphology Evolution of Ti50Cu25Ni20Sn₅ during Mechanical Milling.

Dora Janovszky,Anna Sycheva,Ferenc Kristaly,Maria Sveda,Tomasz Koziel,Tamas Miko,Adam Racz

doi:10.3390/ma11091769

Abstract

Nanocrystalline/amorphous powder was produced by ball milling of Ti50Cu25Ni20Sn5 (at.%) master alloy. Both laser diffraction particle size analyzer and scanning electron microscope (SEM) were used to monitor the changes in the particle size as well as in the shape of particles as a function of milling time. During ball milling, the average particle size decreased with milling time from >320 µm to ~38 µm after 180 min of milling. The deformation-induced hardening and phase transformation caused the hardness value to increase from 506 to 779 HV. X-ray diffraction (XRD) analysis was used to observe the changes in the phases/amorphous content as a function of milling time. The amount of amorphous fraction increased continuously until 120 min milling (36 wt % amorphous content). The interval of crystallite size was between 1 and 10 nm after 180 min of milling with 25 wt % amorphous fractions. Cubic Cu(Ni,Cu)Ti2 structure was transformed into the orthorhombic structure owing to the shear/stress, dislocations, and Cu substitution during the milling process.

Highlights

Among the metallic elements of the periodic system, lightweight Ti occupies a special position due to its excellent high-temperature oxidation resistance and biocompatibility
The machined chips were fractioned to a particle size below 320 μm for planetary ball milling
A sample of 0.5 g was taken every 30 min to check the effect of the milling time on the particle size, shape, and amorphous content

Summary

Introduction

Among the metallic elements of the periodic system, lightweight Ti occupies a special position due to its excellent high-temperature oxidation resistance and biocompatibility. It has favorable mechanical properties, which—as in case of conventional crystalline materials—depend on the grain size (Hall–Petch relationship), with Ti-based amorphous alloys possessing ultrahigh strength and hardness [1,2,3]. The bulk amorphous alloys still do not display sufficient ductility for industrial applications. Users expect materials to have both high tensile strength and high tensile ductility. Materials usually have high strengths but low ductility, and it is very rare for both parameters to be high at the same time. The extreme enhancement in strength has been realized with ductility in nanocrystalline/amorphous alloys [4,5,6,7]

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