激光熔覆Ni-WC的农用刀具磨损行为与自磨刃形成机制研究

Wear Behavior and Self-grinding Edge Formation Mechanism of Agricultural Tools Strengthened by Laser Cladding Ni-WC

摘要:

作物茎秆切割是机械化收获的关键环节，刀具材料直接影响刀具寿命和作物切割质量。本文采用激光熔覆Ni-WC制备自磨刃刀具，分析WC质量分数对熔覆层组织性能的影响。利用农机部件摩擦磨损试验机对刀具试样进行试验，结合偏光显微镜与二值化图像处理技术，定量分析了刃口磨损后的微观形貌，获得刀具磨损量和刃口钝圆半径演化规律。熔覆层耐磨性和厚度是刀具耐磨性及刃口锋利保持的主要影响因素。试验结果表明，当WC质量分数为20%~30%、熔覆涂层厚度为0.6~0.8 mm时，刀具在工作过程中能够形成自磨刃，并据此提出了自磨刃形成的判定标准和形成机制。研究结果为农用自磨刃刀具设计优化提供参考。

Abstract:

Crop stem cutting is a key step in mechanized harvesting, and the material design of the cutting tools directly affects their lifespan and the quality of crop cutting. The hardness and wear resistance of the integral cutting tools are low, and the tools is prone to chipping as the hardness increases. The self-sharpening edge technology can effectively solve this problem. The edge of cutting tool is composed of two or more materials, resulting in different wear resistance on two sides of the edge. During the operation a self-sharpening edge is formed, enabling the tool to remain sharp for a long time. However, systematic and quantitative analysis lacks on the mechanism of the self-sharpening edge formation. The reinforcement layer of Ni-WC was prepared on cutting tools by laser cladding to obtain self-sharpening. The microstructure, phase composition and hardness of the cladding layers were tested by using a metallographic microscope and X-ray diffraction. As the addition of WC the average hardness of the cladding layer increase, with the maximum reaching 979HV0.5. The tool samples were tested by using a friction and wear testing machine of agricultural machinery components. Then combining polarized light microscopy with binary image processing technology, the micromorphology of the worn cutting edge was quantitatively analyzed in order to obtain the evolution law of tool wear amount and cutting edge blunt radius. The wear resistance and thickness of cladding layer were two main influencing factors for the wear resistance and sharp edge retention of tools. When the WC content was 20%~30% and the cladding coating thickness was 0.6~0.8 mm, a self-sharpening edge can be formed. The field experiments were conducted to verify the results. Based on this, the criteria and formation mechanism for self-grinding edge were proposed. The research results can provide a reference for the design optimization of agricultural self-grinding edge cutting tools.