Fundamental functions of physical and chemical principles in the polishing of titanium alloys: mechanisms and problems

Titanium alloys have excellent specific strength, outstanding corrosion resistance, and good biocompatibility, which are widely used in mechanical and medical fields such as compressor disc, blade, stator, and hip and knee joint. Titanium alloy workpieces must be machined to obtain specific shapes. However, the machining marks inevitably exist on the titanium alloy surface, which have a poor effect on the performance of workpieces. Therefore, polishing is scheduled at the subsequent process to remove the machining marks. Because titanium alloys are typically difficult-to-polish materials, the polishing surface quality and efficiency require to be improved further. To have an in-depth and comprehensive understanding of the polishing technology of titanium alloys, this paper reviews systematically the material’s polishing mechanisms and processes. To date, various fundamental mechanisms, including mechanics, heat, optic, electricity, magnetism, ultrasound, and chemistry, are employed to polish titanium alloy surface. On this basis, four types of polishing techniques were developed (i.e., mechanical polishing, high-energy beam polishing, chemical polishing, and compound polishing) to improve the high surface integrity of titanium alloys. Furthermore, the advantages and disadvantages of each polishing technique are discussed in detail from the views of model, optimization, equipment, efficiency, surface quality, and cost. Finally, this paper proposes the future development directions of the polishing techniques of titanium alloys.