Study on the preparation technology and fretting damage resistance property of coatings on titanium alloy

The activation process of electroless plating on titanium alloy TA7 was studied and an improved twice galvanizing technology was introduced, which could make sure to get good bonding coatings. The Ni-B coating with lead nitrate as stabilizer (common Ni-B coating) and the Ni-B coating with thallium sulfate as stabilizer (NTB coating) were prepared, which based on TA7 substrate. Surface morphology was observed with TM-1000 scanning electron microscope, and the fretting damage resistance property was tested on DELTALAB-NENE high-precision hydraulic servo fretting wear tester. The fretting test parameters are as follows: the ball of Ф40mm GCr15 was chose as fretting dual pieces, at 25±5°C and 60%±10%RH, with the dry friction, maximum displacement D=20µm, normal load Fn=100N, frequency f=3Hz, maximum cycles N=3000. The results show that friction coefficient of the NTB coating is 0.13 in running-in stage, which decrease 24% and 40% compared with TA7 substrate and the common Ni-B coating respectively. The NTB coating has outstanding fretting damage resistance property. The application of NTB coating could prolong the life cycle of the products and cuts the cost of reproducing significantly.