Effect of hot isostatic pressing on mechanical properties of Fe₄₁Cr₁₅Mo₁₄C₁₅B₆Y₂Co₇ BMG

Abstract

Fe-based bulk amorphous rods of 3 mm in diameter and a composition of Fe₄₁Cr₁₅Mo₁₄C₁₅B₆Y₂Co₇ were produced by copper mold casting. The as-cast amorphous rods contain a small (2%) fraction of pores. To close the pores, samples cut from the amorphous rods were hot isostatically pressed (hipped) at 863 K, which is in the supercooled liquid temperature range between the glass transition temperature and the crystallization temperature of the amorphous phase, and under a pressure of 200 Mpa. Microstructure examination of the hipped samples shows that hipping results in an increase of the density of the samples from 7.9 g/cm³ to 8.0 g/cm³, and a decrease of the porosity level from 2% to 1%, and that a very small fraction of unknown crystalline phase form. As a result of these microstructure change caused by hipping, the average room temperature compressive fracture strength of the bulk metallic glass (BMG) decrease from 3500 Mpa to 3000 MPa, while the strain to fracture changes little from 1.5% to 1.4%. The mechanisms of the effect of hipping on microstructure and mechanical properties of the Fe-based BMG are discussed.