Study On Preparation Of Gradient Material For Self-Sharpening Cutters Based On Combustion Synthesis Melt-Casting Under Ultra-Gravity Field

With the rapid development of urbanization and the putting forward the strategy of Rural Revitalization,it has become a common understanding that there is no agricultural modernization without agricultural machinery modernization,and the important status of agricultural machinery modernization has become increasingly prominent.Cutting tool is the core part of modern agricultural machinery equipment,which directly affects the reliability of the whole machine.Compared with foreign countries,China has a large technical bottleneck in core materials and preparation process,so it is a real problem that needs to be solved in the development of high-end agricultural machinery.Based on the technology of high gravity combustion synthesis,Fe-based metal gradient materials were prepared in this paper.By optimizing the preparation process parameters,the hardness of the materials showed gradient distribution.The thickness ratio of the hardened layer of gradient aterial to 45 steel substrate was analyzed and designed.The self-grinding sharp cutter of rotary cutter of alfalfa harvester was designed and manufactured,as well as the field test was carried out.The microstructure and composition distribution of gradient material synthesized by hypergravity combustion were analyzed,the microhardness of gradient material layer was tested,and the forming mechanism of gradient material layer and its influence on properties were discussed.By comparing the field test of the new self-grinding sharp cutter with the market cutter,the conclusions are obtained as follows:1.The parameters of hypergravity combustion synthesis,such as composition of aluminothermic agent,particle size and so on,were determined by numerical analysis of the material through a multi-system adiabatic temperature.The influence of gravity coefficient on the velocity of multiphase separation is studied.The optimum technological parameters of hypergravity combustion synthesis are as follows:the hypergravity coefficient is 1000g,the adiabatic temperature is 3148.2K,the relative content of the aluminothermic agent component?mass fraction?:the content of Fe₃O₄/Al is 85%,the content of Cr-Fe is 5%,the content of Mo-Fe is 3%,the content of V-Fe is 3%and Mn-Fe content is 4%.This preparation process can form a uniform and dense gradient material layer.2.As a result,it was found that due to the different density of the diluent particles,the high-density carbide particles in the high-temperature iron melt are subjected to centrifugal force and are at the bottom of the gradient material,while the particles having a small density are distributed at the top of the gradient material.Due to the different hardness of the hard alloy particles in the diluent,the hardness of the gradient material gradually decreases in the direction of high gravity.3.The microstructure observation and hardness test of different parts of the gradient layer showed that the grain of the Fe based metal materials prepared by the supergravity combustion synthesis technology had a remarkable preferred orientation,and the matrix microstructure was columnar distribution along the direction of supergravity.The analysis shows that the gradient material is composed of carbide and eutectic structure,and the ceramic phase/metal phase is separated effectively under the action of super gravity field.The junction between carbide and Fe base,hardened layer and 45 steel matrix is metallurgical bonding.Within 0.7mm,the hardness gradually decreases from 768.8HV to 253HV in the direction of super gravity.The microstructure analysis showed that the gradient distribution was uniform,and the Mn element was further incorporated into the Fe matrix,which further strengthened the mechanical properties of the matrix.4.According to the size parameters specified by the national standard,the cutter of Alfalfa harvester cutter was prepared and field test was carried out.The experimental results show that compared with the national standard cutting knife,the new self sharpening cutting knife improves the cutting efficiency,reduces the smooth cutting stubble of the oil consumption,is beneficial to the crop regeneration,realizes the low damage cutting of alfalfa and the sharpness of the blade in a long time operation.The microstructure of the gradient material synthesized by hypergravity combustion is dense and the hardness changes slowly.The carbide particles and eutectic microstructure matrix,the hardened layer and 45 steel matrix are metallurgical,and the front tool face is worn evenly during the cutting process.The cutting tool prepared by the new material has good self-grinding performance.