L-PBF Ti6Al4V的表面氮化处理及腐蚀磨损性能研究

Surface Nitriding Treatment and Tribocorrosion Properties of L-PBF Ti6Al4V

目的钛合金的耐蚀性能好,但耐磨损性能较差,大大限制了钛合金在许多工业及医学领域的应用。通过对L-PBF Ti6Al4V和轧制态Ti6Al4V合金在高纯氮气环境下进行氮化处理,探究氮化处理温度和原始组织差异对氮化处理结果及耐腐蚀磨损性能的影响。根据实验结果讨论不同氮化处理工艺下Ti6Al4V合金的组织演变,以及组织与腐蚀磨损的关系。方法对轧制Ti6Al4V和L-PBF Ti6Al4V分别进行不同温度下的气体氮化处理,通过显微组织分析、力学性能测试、SEM、CLSM、腐蚀磨损测试等方法系统地研究氮化处理工艺对其耐腐蚀磨损性能的影响。结果随着温度的升高,氮化物层和扩散层的厚度逐渐增加,氮化物主要由TiN和Ti2N组成。经氮化处理后,L-PBF Ti6Al4V和轧制态Ti6Al4V合金的氮化物层厚度分别达到10.2、8.23μm,显微硬度分别达到1251HV0.2、1290HV0.2。合金的腐蚀磨损性能得到大幅提高,磨损与腐蚀之间的协同作用加速了材料的损失。未处理的Ti6Al4V合金的磨损类型以磨粒磨损为主,而经氮化处理后合金的磨损机制变为磨粒磨损与黏着磨损的组合。结论轧制态Ti6Al4V中较多的β相促进了N的扩散,因而在试样中获得了更宽的固溶区;L-PBF Ti6Al4V中高含量α'相的存在促进了氮化物层的形成,使得L-820和L-920试样的氮化物层更厚。

Titanium alloys are widely used in biomedicine because of their excellent corrosion resistance,biocompatibility,and other properties.Among them,Ti6Al4V is often used as orthodontic materials and bone application implants.In biomedicine,the alloy is always processed into various complex shapes to meet the needs of different fields,but the current traditional processing methods are difficult to meet the needs of mass production.Laser powder-laying additive manufacturing(L-PBF)is a new additive manufacturing technology,which has the unique advantages of fast,near-shape machining and a high degree of design freedom.This technology determines the shape data of the sample by software modeling,then melts the metal powder with high-energy laser beams,and accumulates the shape layer by layer from bottom to top to obtain the desired shape,which solves the problems of long processing cycle and low material utilization rate in traditional forging and other manufacturing methods.However,the tribological properties of titanium alloy are poor,and there are serious adhesive wear and fretting wear in the application process,which greatly limits the application of titanium alloy in many industrial fields such as drive transport parts.On the basis of the good corrosion resistance of titanium alloy,surface modification to improve the wear resistance and hardness of titanium alloy surface have become a common method.The nitriding treatment of titanium alloy can form a hard compound layer of TiN and Ti2N on the surface of the alloy to enhance the properties of titanium.The work aims to investigate the effect of nitriding temperature and original microstructure differences on nitriding results and wear and corrosion resistance of L-PBF Ti6Al4V and rolled Ti6Al4V alloys by heat treatment under high purity nitrogen environment.According to the experimental results,the microstructure evolution of Ti6Al4V alloy under different nitriding processes and the relationship between microstructure and tribocorrosion resistance were discussed.It was found that the nitride layers of L-PBF Ti6Al4V and rolled Ti6Al4V alloys were 10.2μm and 8.23μm,respectively.The moreβphases in the rolled Ti6Al4V promoted the diffusion of N and thus obtained a wider solution zone in the sample;and the existence of highα'phase in L-PBF Ti6Al4V promoted the formation of nitride layer.The solution strengthening effect caused by the solid solution of N element inα-Ti also played a significant role in the improvement of the hardness,and the microhardness reached 1251HV0.2 and 1290HV0.2,respectively.After nitriding,the wear properties of L-PBF Ti6Al4V and roll Ti6Al4V alloys were greatly improved.After nitriding at 920ºC,the wear rate of roll Ti6Al4V was the lowest under tribocorrosion and pure mechanical wear,which was(0.055±0.003)mm/a and(0.041±0.0004)mm/a,respectively.The electrochemical test results show that the oxide layer and nitride layer produced by the nitriding process provided better corrosion resistance of the alloy.The corrosion current densities of the two alloys under tribocorrosion conditions were only 6.47×10^(−9)A/cm^(2)and 0.08×10^(−9)A/cm^(2).The wear mechanism of untreated Ti6Al4V alloy is mainly abrasive wear,while the wear mechanism of nitriding alloy is transformed into the combination of abrasive wear and adhesion wear.