A Study On Laser Surface Modification Technology And Coating Characteristics On Titanium Alloys

Titanium alloys are used widely in aviation, national defence, automobile, medicine and other fields because of their advantages in lower density, excellent corrosion resistance, and good fatigue resistance etc. However, their high friction coefficient, high sensitivity to adhesive wear and fretting wear, as well as their weak resistance to wear and bad resistance to high temperature oxidation restricts the application of titanium alloys. Laser surface modification technique can change these surface defects of titanium alloys under the condition of keeping the virtues of titanium alloy substrate. For the reason, laser surface modification is one of effective, economic, appropriate and designable methods.In this paper, surfaces of Ti6A14V alloy were modified by CO₂ laser. Special composite metallurgy coatings, which have excellent wear resistance and high temperature oxidation resistance, were obtained directly on the surfaces of Ti6A14V alloy. Furthermore, the coatings showed good metallic combination with the substrate of titanium alloy.In order to carry out the laser surface modification process successfully, a coaxial powder feed nozzle with gas protection was designed at first. Through investigations of suitable technical parameters of the coaxial powder feed nozzle with gas protection, a higher duty factor of powder and better protection effect was obtained.Moreover, based on properties of the Ti6A14V alloy and characteristics of the laser surface modification, four types of coating were designed: laser cladding Ni-Ni base alloy gradient coating, laser cladding Mo-Ni base alloy gradient coating, laser surface in-suit formed TiC coating and laser surface in-suit formed TiC+TiB2 coating.Furthermore, the suitable technical parameters of laser surface modification for each type of coating above-mentioned were established. Influences of different technical parameters to the laser cladding Ni-Ni base alloy gradient coating had been investigated emphatically and the most suitable technical parameters had been obtained. By means of SEM and micro-hardness tester, microstructure of the coatings was investigated, and micro-hardness was measured. The results showed that the coatings appeared representative characteristics of quick solidification, the micro-hardness appeared gradient character clearly from deep substrate to surface and the stress distribution was improved effectively.At last, tribological characteristics and characteristics of high temperature oxidation resistance were tested. The results showed that laser surface modification could increase wear resistance and high temperature oxidation resistance of Ti6A14V alloy.