Effect of nano-phased bismuth-tin alloy surface coating on tribo-mechanical properties of basalt fiber reinforced composites

A novel method for coating basalt fiber with a eutectic bismuth-tin (Bi-Sn) mixture was developed. Bi-Sn nanoparticles were synthesized using a sol-gel process and deposited on basalt fiber by chemical vapor deposition, with the aim of evaluating the tribo-mechanical properties of the final epoxy-composite material. X-ray diffraction showed that the synthesized Bi-Sn alloy was highly polycrystalline with equal distribution of tetragonal and orthorhombic Bi-Sn polymorph phases with crystallite sizes between 17 and 55 nm. High-resolution electron microscopy revealed that the sample possesses highly fused, flake-stacked planar layers, with 50 nm-thick flakes of variable length. Elemental analysis determined that the alloy contains 57% Bi (at.wt%), and Raman spectroscopy confirmed the characteristic Bi-Sn fingerprint peaks of 148, 201, and 397 cm-1. Thermal analysis of the composites showed good thermal stability with only 4% mass loss at 700 °C. Furthermore, an increase in the Bi-Sn loading enhanced the tribo-tensile properties. It was found that at a Bi-Sn gravimetric loading of 0.2 g the composite yielded the highest ultimate tensile strength of 303 MPa compared to the reference (154 MPa), even as the Young's moduli showed a decrease in elasticity by up to 24.99%. Moreover, the tribology results showed a good friction coefficient (0.5), with a negligible wear rate (4.53 × 10-8 mm3/Nm) and relatively low wear volume (0.118 mm3). Thus, the proposed method resulted in alloy composites with improved tribo-mechanical properties, and has potential applicability in the development of lead-free solders.