Study of Ti-7.5Si-22.5B alloys produced by powder metallurgy

Bruno Bacci Fernandes,Carlos De Moura Neto,Francisco Cristóvão Lourenço De Melo,Vinícius André Rodrigues Henriques,Alfeu Saraiva Ramos

doi:10.1590/s1516-14392014005000076

Abstract

Refractory alloys with silicides and borides have been used in high temperature applications because their elevated melting point, good oxidation resistance and high strength-to-weight ratio. The present study approaches the preparation of Ti-7.5Si-22.5B (at.-%) alloys through high-energy ball milling and sintering. The powders and compacts obtained in these processes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), density measurements, chemical analyses and Vickers hardness. It was verified that silicon and boron powders are dissolved in the titanium during milling with an iron contamination up to 6.0 at.-%. Furthermore, the use of short milling times and alcohol during the final stages of milling increases the powder yield. Such increasing was obtained even with a high rotary speed (300 rpm), which generally creates higher temperatures and consequently more sticking. After sintering of the as-milled powders, it was indentified mainly the Ti+Ti6Si2B+TiB+Ti5Si3 phases in the Ti-7.5Si-22.5B sintered alloys, which presented hardness values up to 800 HV. The materials produced by the present work can be employed in coating research as sputtering targets.

Highlights

The development of new compositions according to phase diagrams of the Ti-Si-B system is one of the main ways to obtain and investigate new titanium alloys with improved properties
High values of powder yield - around 86% in dry medium, reaching an accumulated of 96% after more 20 minutes in wet medium - were registered for the milling routes (MR) 2 probably due to the lower time used (1.3 hour) instead the lower pause frequency
Powder yield around 13% was registered after 30 hours of dry milling through the MR 1, which was increased to an accumulated of 65.9% due to the use of alcohol during 2 hours

Summary

Introduction

The development of new compositions according to phase diagrams of the Ti-Si-B system is one of the main ways to obtain and investigate new titanium alloys with improved properties. Analysis of thermomechanical treatments on composition, morphology and volume fractions of phases is fundamental to improve such development[1]. These titanium alloys have been used in structural applications at high temperatures and as a protective layer in drilling tools obtained through magnetron sputtering or other techniques[2,3,4]. High-energy ball milling (HEBM) has been used in the processing of complex materials instead conventional melting techniques. This solid-state technique allows phase transformations in non-equilibrium thermodynamic conditions, which modify the Gibbs’ free energy of the processed system[9,10]. Milling times must be chosen carefully to achieve an optimal level between dissolution/ amorphization and sticking of particles avoiding milling

Methods

Results

Conclusion