Fabrication Of In Situ TiC Particulate Reinforced Ni₃Al Surface Coating On Steel Substrate

Composite coating has its certain advantages,such as excellently comprehensive performance,low cost,easy recycling and so on,when comparing with the integrated composite. Consequently,it has drawn public concern all of the world.Ni₃AI intermetallic matrix composite reinforced by TiC particulate could exert the wear and heat resistance of intermetallic compound. So it is the best selection of the coating material.In this paper TiC-reinforced Ni3AI intermetallic matrix composite coating on steel was fabricated successfully using self-propagating High-temperature Synthesis in melt.The main reactions of the reaction of Ti-C-3Ni-AI system were forecasted through the thermodynamic analysis of Ti-C-3Ni-A1 system and testing by X-ray diffraction(XRD),scanning electron microscopy(SEM),energy-dispersive spectrum(EDS) and transmission electron microscopy(TEM).The Gibbs free energy and insulation temperature were calculated by Computer Programming confirmed that the final products of the system are TiC/Ni₃Al.Thermal explosion reaction conditions and process were also studied as well as the morphology of the product,the effect of active agent,the microstructure of coating, micro-hardness and wear resistance.The preliminary discussion of the composite coating on the surface of the formation mechanism was made.At the same time the study of thermodynamics and the thermal explosion of the system,the process simulation of self-propagating in melt was carried out by the use of software Procast in the computer;so as to get whole intuitive understanding of the process,as well as the impact of various parameters to the self-propagating process in melt.The experimental results showed that TiC and Ni₃Al were the most stable phases in Ti-C-3Ni-Al system.The exothermic reaction of nickel and aluminum created liquid and ignited the reaction of titanium and carbon.During reactions TiC was always in solid state and Ni₃Al in liquid state.Ingredients and thermal explosion temperature were found to have obvious influences on morphology and density of the products.In this study,the powder of prefabricated blocks was added into adequate magnesium and the results showed that the optimum content of magnesium is 2 percent and could promotes the reaction speed,shorten response time and lower the reaction-starting temperature.In addition, adding magnesium can reduce and destruct the oxide film on the forefront of fluid metal,as well as promoting heat transfer and infiltration between the liquid metal and prefabricated blocks.So the combination is metallurgical combine.TiC/Ni₃Al coating was formed on steel with metallurgical bond between the coating and steel substrate.The microstructure of the coating was presented to be 1～3μm of TiC particulates mounted in Ni₃Al.Interface morphology was varied with the TiC content of the coating.When content of TiC was less than 45wt%,the coating was integrated.When content of TiC is equal to or more than 45wt%,the coating was delaminated.Ni,Al,Ti,Fe and micro hardness were revealed to have graded distribution from the coating to the interface.The coating gave excellent wear resistance at room temperature and 400℃than H13 steel.