钛合金表面稀土改性化学镀厚镀层及其性能

Preparation and Properties of Rare Earth Modified Electroless Plating Coating on Titanium Alloy Surface

目的在钛合金表面化学镀镍磷厚镀层,并研究稀土的引入对镀层性能的影响。方法使用SEM及EDS对化学镀层的厚度及成分进行测试;使用XPS对镀层中的稀土元素价态进行分析;使用XRD对不同热处理方式的镀层进行组成分析;使用显微硬度仪测试经热处理的镀层的硬度;通过电化学测试对钛合金及经热处理的镀层进行耐蚀性分析。结果经稀土改性的厚镀层由70μm厚的Ni-P层和30μm厚的Ni-P-Ce层组成。镀层由Ni、P及Ce三种元素组成,其各自的质量分数分别为89.94%、10.03%和0.03%,且铈由+4、+3和0三种价态构成。随着热处理温度的升高,镀层逐渐由非晶态转变为晶态,该转变发生于200~300℃,且成分也发生了变化;镀层的硬度增加,经400℃热处理的镀层硬度大约为1000HV。镀层的存在可以有效提升钛合金基材的耐蚀性,但是随着热处理温度的增加,耐蚀性大幅降低,最佳热处理温度为200℃(其腐蚀电流密度和极化电阻分别为0.2445μA/cm^2、155.464 k?)。结论经稀土改性的镀层为100μm厚的厚镀层。稀土元素铈与镍、磷在钛合金上发生了共沉积。热处理温度对镀层的结晶方式和成分都有影响,对镀层硬度具有明显的影响,对镀层的耐蚀性能影响较大。

The work aims to prepare electroless Ni-P coating on titanium alloy surface and study effect of rare earth on properties. SEM and EDS were used to test thickness and composition of chemical plating; XPS was adopted to analyze valence state of rare earth element in plating coating; XRD was taken to analyze composition of plating coating through different heat treatments; microhardness tester was used to test hardness of plating coating through heat treatment; and electrochemical test was conducted to characterize corrosion resistance of titanium alloy and plating coating through heat treatment. Rare earth-modified thick coating was composed of a 70 μm NiP layer and a 30 μm Ni-P-Ce layer. The coating was formed by three elements including Ni, P and Ce with respective mass fraction of 89.94%, 10.03% and 0.03%. The element Ce was composed of three valence states of ＋4, ＋3 and 0. With the increase of heat treatment temperature, the coating gradually changed from amorphous to crystalline. The transformation occurred at 200-300 ℃ and the composition also changed. The hardness of coating increased and reached 1000HV after heat treatment at 400 ℃. The coating could effectively improve the corrosion resistance of titanium alloy substrate, but the corrosion resistance dropped dramatically as the heat treatment temperature in- creased. The optimum heat treatment temperature was 200 ℃ （the corrosion current density and polarization resistance were 0.2445 μA/cm^2 and 155.464 kΩ respectively）. The coating modified by rare earth was 100 μm thick plating coating. Rare earth cerium, nickel andphosphorus are co-deposited on the titanium alloy due to reaction. The heat treatment temperature has obvious influence on crystallization mode, composition and hardness, especially corrosion resistance.