Study On Microstructure And Tribologocal Behaviors Of Pack Boronized Inconel625 Ni-Based Alloys

Ni-based alloys have an irreplaceable position in the aerospace industry due to its unique high temperature and corrosion resistance.However,the low hardness and poor wear resistance limit the alloy's further development and application.Surface treatment is one of the main ways to improve the hardness and wear performance of Ni-based alloys.Solid boriding is a surface modification process with advantages of simple operation and high hardness of the layer.It has been used to improve the hardness and wear resistance of the metal surface.In this paper,Inconel 625 nickel-based alloy was boronized at different temperatures?900°C,950°C and 1000°C?and time?4h,6h and 8h?using a solid granular boronizing agent.The effect of boronizing parameters on the microstructure,friction and wear properties of boronized layers and the wear mechanism were studied.The influence of rare earth on the microstructure and friction and wear properties of the boronized layer when the rare earth Ce was added to the boriding reagents was investigated.The catalysis mechanism of rare earth to boronizing process was analyzed.The experimental results can be used to guide the surface treatment and application of Inconel 625 and other nickel-based alloys.The main results are as follows:1.A stable multi-phase boriding layer was formed on the surface of Inconel625 Ni-based alloy after solid boriding.The upper layer was a dense chromium-boron compound layer,mainly containing Cr₂B,CrB₂,Cr₅B₃,CrB compound phases.A fine needle-like nickel-boron compound layer containing Ni₃B and Ni₂B phases was formed in the sublayer.With the increase of boronizing temperature,the thickness of boronizing layer increases,but when the temperature reaches1000?,silicified layer and diffusion layer appear.2.Solid boriding can significantly improve the surface hardness of Inconel625 nickel-based alloy.The sample after boriding at 950°C for 6h shows the highest hardness(1239HV_0.3),which is 4.1 times higher than that of the substrate.3.Under normal temperature friction condition,the friction coefficient of the boronized Inconel 625 nickel-base alloy decreases significantly compared with the matrix,and the wear amount decreases greatly.The room temperature wear resistance of Inconel 625 nickel-base alloy is effectively improved by boronizing.With the lowest friction coefficient and the smallest wear rate,the sample after boronizing at 950?for 6h shows the best wear resistance.4.After solid boronizing,the friction coefficient of Inconel 625 nickel-based alloy shows a trend of stabilizing,then increasing and finally stabilizing under the condition of high temperature friction and wear at 500?.The finally stabilized friction coefficient decreases obviously compared with the matrix,and the wear rate also reduces greatly.The friction coefficient and wear rate of the sample after boronizing at 950?for 6h are the smallest.Its wear resistance at high temperature is the best.5.The boronizing layer presents a multipeaked mountain like morphology after adding 5%rare earth to the boriding reagents.Compared with the boronized sample without adding rare earth,the surface of boronized sample becomes rougher and the boronized layer is more compact.No obvious layered structure appears as mentioned before.The thickness of boronizing layer with rear earth in boriding reagents is obviously increased,and the surface hardness of the sample is improved.The phases composition of sample with rear earth has not changed compared with that without adding rare earth.However,the peak strength of chromium-boronizing phase is increased after adding rare earth.The friction coefficient of boronizing layer with rare earth decreases both in the room temperature and high temperature?500??wear condition.The wear rate of the samples with rear earth was decreased by 0.44 times at room temperature and 0.21times under high temperature wear condition comparing that without rear earth.This indicates that the tribological properties of boronizing layer are obviously improved by adding rare earth to the boronizing reagents.