Study For Pulse Vacuum Nitriding Titanium Alloy And The Kinetics

Due to titanium alloy has the excellent properties, has been widely used in fields of national defense, chemistry, energy, aerospace and biological engineering. However, there are a large number of drawbacks limit it to be practicle, like low surface hardness, poor wear resistance and fatigue resistance, which lead to narrow the scope of its application. As a result, we hope to modificate the titanium alloy with a surface layer combined with high strength and hardness gradient change, good abrasion resistance, excellent chemical stability and good biological compatibility leading to extend its service life. In light of the defects of traditional surface treated method, we proposed a gas pulse method to improve its performances. The relationship between process parameters and vaies properties has also been studied. Moverover, we also studied the mechanism of the nitriding conditions and kinetics properties. The main contents and results are as follows:(1) We modificated the surface of tatitum alloy by the pulse vacuum technology and also explored the effect of the nitriding temperature and nitriding pressure, nitrogen and argon mixing different experimental parameters to its surface properitties. The morphology of surface organization, element distribution, phase composition, hardness,wear resistance and corrosion resistance after nitriding have been analysied. Firstly, influence of temperature: it can be found that the a more stable surface phase that composited with TiN0.3 generated after treated under 750-900 ℃ by pulse vacuum nitriding approach. TA2 nitriding layer and bulky organization thickness increased along with the rise of temperature. It increased two orders of magnitude compared with theuntreated samples. Hence, Nitriding temperature has a little influence on corrosion resistance of the nitriding layer. Secondly, pressure influence:the nitriding pressure affect the phase composition of TA2 nitriding layer,negative pressure is advantageous to the N atom vacuum infiltration. So,the influence of pressure for nitriding layer is smaller than that of temperature. Thirdly, the influnece of nitrogen and argon mixture: the lower nitrogen content is benefit for N atom diffusion treated the TA2 nitrogen argon ratios. However, the less effective against penetration of active N atomic density and thickness increase. We also observed that nitriding layer surface became denser with the increase of nitrogen partial pressure, resulting in that the N diffusion become harder.(2) In light of the issuses of single gas nitriding method, this paper puts forward a new kind of carbonitriding process. after processing technique of carbon and nitrogen compound permeability The surface performances of TA2 titanium alloy treated with this method aresignificantly better than those of the samples treated with single gas nitriding method. The surface phases of modified samples transformed from pure titanium nitride to titanium carbonitride composite phase(TiN0.3, C0.7 N0.3 Ti, TiN/TiC). The new surface is more uniform and has a good hardness gradient, which leads to the improvement in esistance and corrosion resistance of TA2 titanium alloy.(3) Kinetics of the nitriding process has also been studied.Titanium alloy gas nitriding is a typical gas-solid reaction. Ideally,gas-solid reaction kinetics under certain conditions effect by surface diffusion and surface infiltration. And in the actual experiment,infiltration during the process of nitriding varies with the increase of reaction time speed. From nitriding titanium alloy and carbonitriding methods, infiltration kinetics of gas-solid reaction is put forward a new kind of compound control dynamics model, setting n control coefficient in the model used to determine diffusion control for dominanting role or penetration control of leading role.The dynamics model of titanium nitride dynamics has beeb fittted with the test data. The results show that the means of control of titatum alloy in the process for nitriding speed will be different with the differebt nitriding methods.