Study Of The Ion-Plasma Nitriding On Titanium And Titanium Alloys

The use of titanium and its alloys have been limited due to their poor wear properties and tend to corrosion in reducibility acid solution and strong oxidizing medium. So improving the surface property of titanium and its alloys has become the hotspot in the study of titanium and its alloys. The ion-plasma nitriding is a common method of surface modification. It has several advantages such as low cost, high speed of nitriding, little deformation, easy controlling. However, there are many influencing factors in ion-plasma nitriding on titanium and its alloy, and their interactions are very complicated. As a result, the process parameters of ion-plasma nitriding on titanium and its alloy are in need of systemic optimizing, if we want to get a good result.In this dissertation the orthogonal test was designed for plasma nitriding on pure titanium and TC4.Through the test, the influence of parameters such as the substrate temperature, gas medium, vacuum pressure and incubation time to the properties of plasma nitriding were studied. And optimal process parameters were got.Microstructure of the nitriding layer was analyzed using Zeiss Axiovert 25CA inverted microscope. Spectro GDA 750 Discharge optical emission spectrometer (GDOES) was used to describe the distribution of elements in the layer. Phase composition of the nitriding layer was characterized by D/Max 2500X-ray diffraction spectrometer. The micro-hardness was measured on the modified layer using a micro-hardness tester of Leco M-400-H1. corrosion tests were performed with a PS—168 corrosion tester.The results show that the substrate temperature was the main factor which influences the thickness of modified layer both for pure titanium and TC4.And optimal theoretical parameters obtained though the orthogonal test were validated. Studying the nitrogen content at 10um under the surface, the best experimental parameters wontents were: 87.06%, 77.56% for pure titanium and TC4. Analyzing ere: 950°C, NH₃+N₂, 80Pa and 6 hours for both. The highest nitrogen cthe results of XRD, nitriding products on pure titanium and TC4 at a relatively lower temperature 850°C were mainly low-concentration TiN and diffraction peak was low. As the temperature increased, the diffraction was strengthened .At 950℃and 1050℃, high-concentration TiN (δ) was the main products on the surface. The hardness of the samples after nitriding process has greatly improved compared with the substrate. Through the corrosion resistance measurement, holding time was the dominating factor which influences the corrosion properties. The optimal process parameters under which can get a good anticorrosion property were obtained after analyzing the orthogonal test and corrosion resistance measurement.