Grinding Mechanism And Recrystallization Of Nickel-Based Single Crystal Superalloys

Nickel-based single crystal superalloys have good high-temperature strength and fatigue resistance because they eliminate the grain boundaries that are prone to crack sources,and are widely used in hot-end parts of aerospace engines,thermal steam turbines and other equipment.Grinding is a high-precision machining method.It is often used as the last process in the processing of nickel-based single crystal materials.However,due to the extremely poor thermal conductivity and small specific heat capacity of single crystal materials,the temperature in the grinding zone is high,which is easy to cause.The surface of the workpiece is easy to cause burns and recrystallization of nickel-based single crystal superalloys,and the recrystallization layer will seriously affect its high-temperature service performance.In order to study the grinding mechanism of nickel-based single crystal superalloy and the effect of grinding technology on its recrystallization evolution behavior during high temperature service,the grinding mechanism,grinding force and Grinding temperature and high temperature recrystallization after machining.The main findings are as follows:(1)Based on the structural characteristics of nickel-based single crystal superalloys,the FCC crystal structure and elastic-plastic anisotropy were firstly analyzed,and Abaqus was used to complete the simulation of single-grain grinding,and a suitable single-crystal material was established.The Hill constitutive model was used to analyze the distribution of the stress field and temperature field when the abrasive particles removed the material,and then the effects of different grinding parameters and anisotropy on the grinding force and grinding temperature were studied through single-factor simulation experiments.The results show that the maximum stress area is located at the contact position between the workpiece and the rake face of the abrasive grains,up to 1580MPa;the highest temperature field is located at the contact position between the workpiece and the rake face of the abrasive grains at the initial stage of grinding,and with the grinding progress,the highest temperature The grinding area gradually moves to both sides,and the grinding temperature increases with the grinding time;the grinding force decreases with the increase of the grinding speed,and increases with the increase of the grinding depth,and the normal force on the(001)surface is the smallest,but the tangential force is the largest;with the increase of grinding speed and grinding depth,the grinding temperature increases,and the grinding temperature of the(111)surface is higher than that of the(110)and(001)surfaces.(2)A test platform for single-grain cutting of nickel-based single crystal superalloys was constructed,and the grinding force in the simulation results was experimentally verified.The influence law is consistent with the simulation results.The normal grinding force in the test is 1-2N larger than the simulation results,and the tangential grinding force is about 1-3N smaller than the simulation results.(3)The effects of grinding depth and heat treatment conditions on the recrystallization morphology and thickness were explored by vacuum heat treatment of the ground single crystal alloys under different holding conditions.The results show that the material produces a plastic deformation layer after grinding without recrystallization;cellular recrystallization occurs after heat treatment at 1000℃/4h,and equiaxed recrystallization occurs when the heat treatment temperature is above1200℃.The thickness of the recrystallized layer increases with the increase of the heat treatment temperature,about 17 μm at1250°C,and the thickness of the recrystallized layer increases with the increase of the grinding depth.The processed sample with a grinding depth of 40 μm is kept at 1100°C for 4 hours and the recrystallized thickness is about 12 μm.The grinding depth has no effect on the recrystallized morphology.