With its advantages of high specific strength and good heat resistance, Ti-6A1-4V titanium alloy is widely used in aerospace, petrochemical, food and medical fields, accounting for 75%~85% of the total use of titanium alloy, becoming the trump card alloy in titanium alloy. However, the performance defects such as low hardness, poor wear resistance, and poor high temperature oxidation resistance greatly limit the further development of Gr.5 titanium alloy.
There are many surface modification technologies for Gr.5 titanium alloy, including traditional modification technologies represented by thermochemical oxidation, electroplating, and electroless plating, as well as modern material surface treatment technologies such as vapor deposition, ion implantation, micro-arc oxidation, and glow surface treatment.
(1) Chemical heat treatment
Gr.5 Titanium alloy has active chemical properties and can react with a variety of elements at different temperatures, and chemical heat treatment methods such as oxidation, ammonia and carburizing can prepare a hard ceramic layer on the surface of the alloy to improve the surface resistance and heat resistance of titanium alloy. The ceramic layer obtained by thermochemical method can also effectively inhibit the formation of cracks and prevent crack propagation, so that the cavitation resistance of Gr.5 titanium alloy can be significantly improved.
Using low-pressure vacuum ammonia infiltration treatment technology, TiN and TiAIN coatings can be obtained with good combination with the substrate, the depth of the hardened layer is 50~60um, and the surface hardness is 1000-1100HV. The TiN/TiN wear-resistant coating on the surface of Gr.5 alloy can be significantly improved by plasma ammonia infiltration method, which can significantly improve the surface hardness and wear resistance of the alloy. At low temperature (950°C), the modified layer of 3~15.4um can be prepared on the surface of the alloy for 5~40h of boron permeability of Gr.5, and the hardness is increased by about 5 times compared with the matrix, and the surface wear resistance coefficient is reduced to 0.2~0.3, and the wear resistance has been significantly improved.
(2) Vapor deposition
Vapor deposition is to condense the vapor of the material to be deposited on the substrate material under vacuum conditions to obtain a thin film that meets the requirements, and the thin film protective coating with excellent performance can be obtained on the surface of Gr.5 alloy by physical vapor deposition (PVD) or chemical vapor deposition (CVD) and derivatization methods of both methods.
The infrared broadband anti-reflection coating can be prepared on the surface of Gr.5 by chemical vapor deposition, and the broadband pass rate of the alloy surface reaches 3~12um, so that the infrared stealth performance of Gr.5 alloy can be improved. Diamond thin films can be prepared on the surface of Gr.5 by microwave plasma chemical deposition and hot filament chemical deposition. Micro diamond and nano diamond films with high purity CH, H2 and Ar as raw materials can be obtained on the surface of Gr.5 alloy by hot filament chemical vapor deposition. The diamond-like coating has good biocompatibility, excellent physical and chemical properties and excellent wear resistance, which is of great significance for the further application of titanium alloy in the medical field.
