Which surface finishes are available for titanium and titanium alloy sheets?
Titanium Plates are metal sheets made from titanium. As they are primarily made of titanium, they possess its properties, including being extremely lightweight yet highly durable and corrosion-resistant. Consequently, they are widely used in industries such as metallurgy, electronics, healthcare, chemicals, petroleum, pharmaceuticals and aerospace. Due to varying industry requirements, the surfaces of titanium plates supplied to different sectors undergo specialised treatment, resulting in differences in their properties.
Why is surface treatment necessary for Titanium Materials? The primary purpose is to enhance surface quality and mechanical properties, as well as corrosion and wear resistance. The two main types of surface treatment for titanium and titanium alloy materials are as follows:
I. Chemical treatment methods. This typically involves a two-stage process of alkaline and acid washing. Advantages include minimal metal loss, high efficiency and the elimination of the need for mechanical pre-treatment, resulting in high-quality surface treatment outcomes.
The alkali washing process for titanium and titanium alloys involves treating the surface in a molten alkali solution. The alkali washing solution is a sodium hydroxide solution containing 15–20% sodium nitrate. This solution reacts with the oxide scale on the titanium material's surface to form soluble titanates, thereby removing the oxide scale. The process involves immersing the titanium material in a molten alkali bath for treatment, followed by water quenching and rinsing with high-pressure water. Adding 5% sodium nitrate to the alkali washing process significantly reduces hydrogen absorption in pure titanium. It is also essential to strictly control the temperature of the alkali solution and the processing time. Excessively high temperatures can intensify the reaction between the metal and the solution, increasing metal loss and potentially causing the titanium material to catch fire. Optimising process parameters ensures processing quality while minimising metal loss.
Titanium materials usually need to be pretreated before acid washing, for example with molten alkali washing, mechanical scaling removal or sandblasting. Acid washing of titanium is essentially an electrochemical process that results in the formation of metal ions. When using mixed acid solutions containing hydrofluoric acid or fluorides for acid washing, special attention must be paid to the possibility of atomic or molecular hydrogen being generated by hydrogen ion reduction and penetrating the metal interior, which could cause hydrogen embrittlement. To prevent hydrogen absorption in titanium materials effectively, the ratio of nitric acid to hydrofluoric acid in the acid washing solution must be strictly controlled, ensuring the nitric acid content is at least five times higher than the hydrofluoric acid content. However, excessively high nitric acid concentrations can reduce reaction rates, impair production efficiency and generate large amounts of harmful fumes, thereby increasing operational complexity.
II. Physical treatment methods. Methods such as sandblasting (shot blasting) and grinding are primarily used to remove oxide scale, oxide films and gas-absorbed layers from the surfaces of titanium materials. They are also used to polish the surfaces of processed materials.
The basic principle of sandblasting is to use streams of sand or steel shot travelling at high speeds to impact the surface of the workpiece, thereby removing the oxide scale from its surface. Compared to chemical methods, sandblasting produces better surface results, but is less efficient in terms of production. It is also commonly used to remove defects or contaminants from the inner surfaces of tubes. Sandblasting of titanium alloys is divided into wet and dry methods. Water sandblasting significantly reduces dust levels in the workplace compared to dry sandblasting. This surface treatment is primarily used for castings, scrap materials and rolled materials, particularly flat materials and sheets. After sandblasting, sheets are usually acid-washed to remove metal dust.
Grinding is one of the primary auxiliary processes used to remove surface defects, such as cracks, folds and unevenness, as well as oxide scale, from workpieces using grinding tools. For certain titanium alloys that may undergo severe ageing during alkaline cleaning or hydrogen absorption during acid cleaning, grinding can be used to prevent these issues and achieve the desired surface finish. Sandbelt grinding can also be used to remove surface defects from finished tubes, bars and plates, thereby improving the final product's surface finish. Grinding does not affect the chemical composition of the processed material and residual stress in plates is minimal. Additionally, grinding equipment is highly automated and achieves high processing precision. However, grinding is relatively costly, requires the processed material to be flat, and the titanium dust generated during sanding is flammable, necessitating stringent safety precautions.
ProX Metal offers titanium plates in a range of grades, including GR1, GR2, GR3, GR4, GR5, GR7 GR9,GR12. various surface finishes are available. Plates with a bright surface have a lustre created by rolling the metal and are ideal for the conventional processing of GR1 and GR2 industrial-grade titanium. Sandblasted plates are particularly suitable for GR7 titanium-palladium alloys, as the rough texture they create enhances coating adhesion. Mirror-finished plates are primarily made from GR2 and GR5 materials, which are precision-polished to achieve a medical-grade smoothness. Anodised plates are ideal for GR12 titanium-molybdenum-nickel alloys, offering diverse colour options through electrolytic colouring.
Contact us to select the optimal solution for your corrosion-resistant titanium plate project, combining performance, quality, and surface finish.