Tribological Effects of 0.30% Titanium in NAB Alloy Post-Casting, Heat Treatment and Forging

Abstract

This study explores the effects of solution treatment, tempering, and forging on the microstructure and tribological properties of 0.30 % Ti-alloyed nickel–aluminum bronze. The modified NAB alloy exhibited a refined microstructure comprising a copper-rich α-phase, martensitic β-phase, and various intermetallic κ (kappa) phases. Titanium addition enhanced nucleation during solidification, reduced dendritic arm spacing, and promoted the formation of discrete κ phases, thereby improving grain refinement and phase uniformity. Notably, tempering the β-phase facilitated its partial decomposition into α and κ_III, with further precipitation of κ_IV and κ_II phases. Forging significantly altered the alloy's morphology, fragmenting dendritic arms into near-spherical forms and increasing the formation of secondary κ_IV phases while preserving the fundamental α, β, and κ phases. Hardness analysis revealed that Ti addition markedly improved hardness, with NAB-0.30 %Ti achieving 239.53 HB and 254.06 HB after heat treatment and forging, respectively. Enhanced hardness and improved wear resistance have been attributed to the presence of intermetallic κ phases, increased dislocation density, and grain refinement. Tribological testing confirmed that the forged NAB-0.30 %Ti alloy demonstrated the lowest friction coefficient (0.097), minimal weight loss (0.0035 g), and the best wear rate (1.17 × 10⁻⁸ g/N·m) over 10,000 meters of sliding distance. The findings highlight titanium’s role in refining microstructure and enhancing both hardness and tribological performance of NAB, making it a promising candidate for applications demanding superior wear resistance.