Research Progress on Wear-resistant PVD Coatings on Titanium Alloy Surfaces and Their Preparation Technologies

Titanium and titanium alloys have the advantages of low density, high specific strength and good corrosion resistance, and are widely used in aerospace, energy and chemical engineering, biomedicine and other fields. However, titanium alloys have low hardness and poor tribological properties. They are characterized by high and unstable friction coefficients, severe adhesive wear, and strong sensitivity to fretting wear, which limits their application in the field of wear.

The tribological properties of titanium alloys can be effectively improved through surface modification. Common surface modification techniques include micro-arc oxidation, electroless plating, laser cladding, thermal spraying, chemical heat treatment, ion implantation technology, electroplating, and physical vapor deposition (PVD), etc. The oxide layer prepared by micro-arc oxidation technology has good corrosion resistance and certain load-bearing capacity and wear resistance under high loads. However, this technology has problems such as high noise and high energy consumption. The chemical coating is uniform in thickness and highly dense, but the solution required for this technology is too expensive. Laser cladding technology has the advantages of a small heat-affected zone and high energy density, but it also has problems such as coating cracking and organizational defects. Thermal spraying has the advantages of lightweight equipment, flexible process and controllable coating thickness, but the coating has problems such as micro-pores and low strength. Chemical heat treatment has the advantages of simple equipment, convenient operation and low cost. It can significantly improve surface hardness and wear resistance. However, its infiltration rate is slow, the infiltration layer is difficult to control, and the efficiency is low, which has certain limitations. Ion implantation technology can precisely control the type, dosage and depth of implanted ions, thereby achieving specific surface properties. However, it has some shortcomings, such as high equipment cost, low processing efficiency, limited ion implantation depth and great difficulty in processing complex three-dimensional shaped workpieces. Electroplating can form a uniform, continuous and thickth-controllable metal coating on the surface of conductive materials. The process is relatively simple and the cost is low. However, for non-conductive materials such as plastics and ceramics, special pretreatment is required before electroplating can be carried out, and some electroplating processes can cause environmental pollution. PVD technology uses glow, arc discharge or heating evaporation methods in a vacuum chamber to evaporate the target material into gas molecules, which are then deposited onto the substrate surface to form a coating. It features uniform and dense coating, good adhesion, controllable thickness, high repeatability, no need for thermal activation, and good adhesion. It is suitable for large-scale industrial assembly line production. It is a highly promising surface modification technology for titanium alloys. At present, although there are numerous studies on PVD coatings on titanium alloy surfaces, systematic summaries and generalizations are relatively few.