Titanium and titanium alloys are widely utilized in aerospace, petrochemical, and medical industries due to their non-toxic nature, lightweight properties, high strength-to-weight ratio, and excellent biocompatibility. However, limitations in hardness, poor wear resistance, and inadequate high-temperature oxidation performance hinder the further advancement of titanium alloys. To overcome these drawbacks, chemical heat treatment, also known as chemical modification, has emerged as an effective means of enhancement.
Chemical heat treatment involves altering the surface chemical composition and microstructure of metal components using chemical reactions, sometimes combined with physical methods, to achieve improved performance compared to homogeneous materials. Common chemical heat treatment methods for titanium and its alloys include nitrogen diffusion, carbon diffusion, boron diffusion, and metal diffusion.
Nitrogen diffusion treatments create high-hardness nitrides (such as TiN and Ti2N) on the surface of titanium alloys, providing excellent corrosion resistance and wear properties. Various nitrogen diffusion techniques include salt bath nitriding, gas nitriding, ion implantation nitriding, double glow ion nitriding, surface laser nitriding, and vacuum nitriding. Carbon diffusion treatments result in carbides on the surface, enhancing hardness and wear resistance.
Boron diffusion treatments form borides on the titanium alloy surface, further increasing hardness and corrosion resistance, suitable for applications requiring high hardness and wear resistance. Compounds such as TiB and TiB2 are formed through boron diffusion techniques, which encompass solid, liquid, and gas methods.
Metal diffusion involves permeating other metal elements onto the titanium alloy surface to create composite materials, thereby improving performance. The selection of pre-diffused metal elements should exhibit good solubility with titanium alloys. Factors influencing metal solubility include atomic size, chemical affinity, crystal structure, and relative atomic valence.
In conclusion, the diverse chemical heat treatment methods for titanium alloys each offer unique advantages, and the choice of technique should align with specific requirements. Currently, nitrogen and carbon diffusion technologies are prevalent. As titanium and titanium alloy technologies continue to evolve, surface treatments hold significant potential for enhancing product performance.
