Abstract
By restricting the dilated deformation, surface modification can stimulate multiple shear banding and improve the plasticity of bulk metallic glasses (BMGs). Aimed at modifying the surface of BMGs by thin layers, a crystalline Ni coating with ultrafine grains was coated on the surface of a Ti-based BMG by electroless plating. With a thickness of about 10 μm, the prepared thin coating could effectively limit the fast propagation of primary shear bands and stimulate the nucleation of multiple shear bands. As a result, the compression plasticity of the coated Ti-based BMG was improved to about 3.7% from near 0% of the non-coated BMG. Except for a small amount of Ni coating was adhered to the BMG substrate after fracture, most of the coatings were peeled off from the surface. It can be attributed to the abnormal growth of some coarse grains/particles in local region of the coating, which induces a large tensile stress at the interface between the coating and the BMG substrate. It is suggested that, for electroless nickel plating, improving the adhesive bonding strength between the coating and the substrate has a better geometric restriction effect than simply increasing the thickness of the coating.
Highlights
Titanium-based bulk metallic glasses (BMGs) are rapidly developing glassy alloy systems in recent years due to the requirement of lightweight metals in modern industries [1,2,3]
The thickness of the inner coating is relatively smaller than the outer coating and the coating is adhesive to the surface of BMG rod, even after removing the outer coating
The traditional electroless Ni plating is introduced to the study on plasticity improvement of Ti-based BMGs at room temperature
Summary
Titanium-based bulk metallic glasses (BMGs) are rapidly developing glassy alloy systems in recent years due to the requirement of lightweight metals in modern industries [1,2,3]. BMGs, especially the alloys with compositions within the range of best GFA in each alloy system, often show brittle deformation behaviors and the compression plasticity at room temperature is poor. Among Ti-Zr-Be-Fe-Cu BMG alloys, the GFA of Ti37.31 Zr22.75 Be25.48 Fe5.46 Cu9 BMG is the best one, and the critical size of as-cast rod with full glassy structure is >32 mm in diameter, but its plasticity is relatively poor (less than 1%) [12]. For high strength structural materials, certain plasticity usually is required not Metals 2017, 7, 562; doi:10.3390/met7120562 www.mdpi.com/journal/metals
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