| Wear,corrosion and fatigue are the three most important forms for the failure of mechanical parts or components.Surface modification treatment technology is an effective means to solve this problem.Thermal reaction diffusion process,a kind of surface hardern treatment technology,is characterized by low cost,easy operation and excellent properties of as-obtained coating layers.Titanium composite film is widely used in the surface strengthening of the material due to its excellent physical and chemical properties,thus improving the microhardness,wear resistance and corrosion resistance of the material.At present,using Thermal reaction diffusion process to prepare the titanium composite film needs to be studied and improved further as some issues still need to be resolved with respect to the volatility and oxidation of the salt bath.In this study,we proposed to solve the issue by pre-carburizing and nitriding the steel matrix for the purpose of reducing the processing temperature and shortening the reaction time.In present work,the pre-carburized 20 steel and pre-nitrided 45 steel were titanized in the salt bath.Besides,thier microstructure and properties were investigated.The main conclusions are listed as follows:1.In the carburizing process of 20 steel,the cementite and pearlite microstructure were formed,creating thicker carburized layer in the outermost near surface region.As for the nitrided 45 steel,the typical three layer structure was distinguished.From top to bottom they were the compound layer,the diifusion layer and the core substrate,respectively.The main phse constitusion of the copmpound layer were the ?-Fe2-3N and y'-Fe4N.In addition,a loose layer with limited thickness was formed as well.2.Compared with TiO2,Ti-Fe alloy powder seems to be a more disered source of titanium for the salt bath titanizing.Considering the volatility and liquidity of the salt bath in addition to the quality of as-received coating,900 ?×3 h was a relative ideal processing condition under the given condition of this experiment.3.After being titanized at 900? for 3 h,a dense TiC coating with a thickness of 7.5 ?m was formed on the outermost surface of the pre-carburized 20 steel.The interface of the TiC coating and the substrate was obvious.The corresponding bonding force was about 52 N,and the micro-hardness was of about 1870+134 HV.On the other hand,as for the pre-carburized 45 steel,after being titanized at 900 ? for 3 h,a dense TiCN coating with a thickness of 8.5 ?m containing Ti-Fe solid solution was formed on the outermost surface.The relative interface shows a typical sawtooth pattern with the binding force of 68 N,and the micro-hardness was of about 1685 ±112 HV.4.The wear resistance of 20 steel was effectively improved by carburizing and the carburizing + titanizing treatment with the following order:Carburized + titanized 20 steel>Carburized 20 steel>20 steel matrix.Their main wear mechanisms were abrasion mechanism + oxidation wear,abrasive wear and adhesive wear,respectively.Furthermore,nitriding treatment can effectively reduce the friction coefficient of the 45 steel,but larger change of friction coefficient was observed in the process of friction and wear.For comparision,the nitriding+titanizing treatment has little influence on the friction coefficient of the 45 steel.Fortunately,its friction coefficient was steady in the friction and wear process.The sequence of wear resistance was:Ntrided + titanized 45 steel>45 steel matrix>Ntrided 45 steel.Their main wear mechanisms were oxidation wear,abrasive wear and adhesive wear,respectively.In addition,TiCN coating presented more excellent friction and wear performance as compared with TiC coating.5.Both the carburizing and the carburizing + titanizing treatment can reduce the corrosion rate of sample to improve its corrosion resistance with the following order:Carburized 20 steel>Carburized+ titanized 20 steel>20 steel matrix.Besides,nitring treatment can effectively improve the corrosion resistance,but nitriding + titanizing treatment can not,as after being duplex treated,the corrosion resistance decreased slightly.However,the corrosion potential of TiCN coating is higher and the corrosion current smaller than TiC coating,thus TiCN coating exhibited more corrosion resistance. |
PDF Full Text Request