【作者】 陈莉；

【导师】 周宏；

【作者基本信息】 吉林大学 ， 材料加工工程， 2007， 博士

【摘要】 提高热作模具寿命是国内外众多企业急需解决的重大问题。生物经过亿万年的进化形成了特殊的具有优异功能的体表形状。通过对典型生物体表非光滑形状的分析,发现生物体表的非光滑特征是其表面耐磨的主要原因。因此本文利用激光模仿生物体表的非光滑形状,在模具钢表面加工出非光滑单元体,由它们和材料表面共同组成仿生非光滑表面,研究仿生非光滑表面模具的耐磨损性能。首先研究了模具钢表面上激光处理区的组织和结构,把因激光加热而组织发生变化的区域定义为激光处理的仿生非光滑单元体。讨论了激光参数、母材成分、母体组织及非光滑单元体成分等对非光滑单元体特征及非光滑表面试样磨损性能的影响,并在此基础上提出了仿生非光滑表面试样的磨料磨损机理。研究结果表明利用激光可以在模具钢表面制备出具有不同特征的类似生物体表的非光滑表面形状,使模具钢的磨损性能明显得到改善。非光滑表面试样磨损过程中,非光滑单元体起到阻碍磨损进行的作用。而决定非光滑表面试样磨损性能提高幅度的因素包括激光加工参数、非光滑单元体的形状、分布间隔、非光滑单元体成分、母材成分、母体组织等等。非光滑表面试样磨损时,磨料相当于在断续的平面上进行磨损,当磨料运动到非光滑单元体前沿时受到阻碍,犁、削深度变浅。当非光滑单元体较硬或磨料尖角被磨钝时,磨料在非光滑单元体上滚动,反之磨料则在非光滑单元体上滑动,且犁、削深度较浅,由此减轻磨损程度。如果非光滑单元体分布间隔适合,磨料可能越过相邻两非光滑单元体的中间基体材料部位而直接对下一非光滑单元体进行磨损,从而大大减小了材料的磨损几率,使非光滑表面试样的磨损性能明显提高。另外首次将生物体表的非光滑形状应用于压铸模具型腔和冲头表面,使生产汽车发动机罩盖的压铸模具使用性能明显提高,服役周期延长,冲头的在线工作时间延长至少两倍以上,经济效果显著,为制备具有高耐磨性的非光滑表面热作模具开辟了一条新途径。更多还原

【Abstract】 Grinding abrasion is a main die failure mechanism. Wear results in about 50 to 60% failure of hot die steel, which brings tremendous expense for commercial run. So prolonging the life-span of hot die is an important problem attracting many corporations, and a main target is to improve the wear-resistance of hot die to prolong life-span of die.Many researchers have made great effort in improving the wear-resistance of hot die and obtained greater advancement. However the earlier researches in enhancing wear-resistance of die were all focused in several ways including developing and explodering new wearable materials, designing the configuration aright and surface mortification technology. Cost arises because of explosering new wearable material and there is little effect. The means of improving configuration of is restricted by die. The whole surface is treated through traditional surface mortification technique, and there is only thinner hardening layer which is worn easily, so the protect action losses and the validity with various condition decreases. Thus it is necessary to creating new technique to preparation wearable hot die and seeks after wearing mechanisms of die for prolonging the life-span of die.According to the traditional idea, the smoother surface of object results the smaller fictional resistance during moving process. Thus improving the smoothness of wearable parts is seen as nessceray means to improve the wear-resistance of parts, and the working surfaces of the parts or the products that are needed to reduce the resistance of friction of material are all designed to be smooth. However the manufacturing cost arises and there is only little effect through the processing technique. Tribology and related research into bionics show that this kind of non-smooth biont surface can lower resistance of friction and wearing. The characteristic of biont that adapts to the survival environment has emerged gradually through hundreds of millions of years of evolution and optimizing. Practices indicate that not the surface is smoother to more excellent wear-resistance, but wear-resistance function of material with non-smooth shape excels on the contrary.The non-smooth shape was designed on several die steels through imitating the easy non-smooth shape of biont body based on the theory in the article. Some specimens with non-smooth surface in different characteristic are prepared by laser. The effects of laser parameter, the compositions of matrix, and the microstructure of matrix, the shape and distributing distance of non-smooth unit on the characteristic of non-smooth unit and on the wear-resistance of die steel with bionic non-smooth surface are discussed. The factors effecting properties of die steel with non-smooth surface are studied also. And bionic non-smooth units with enhancing particle are obtained by laser cladding. The effect of composition of non-smooth unit on die steel with non-smooth surface and the wear mechanism of material with non-smooth surface are discussed. And the non-smooth shape is applied on the surface of hot die for the first time. The wear-resistance of this kind of die is markedly improved, and the life-span of die is prolonged. So the economic effect is obvious.The wear resistances of non-smooth specimens with different laser parameters are all markedly better than that of the smooth specimen. The area ratio and volume of non-smooth unit increase, and the wear-resistances of non-smooth specimens improve, with the increasing of the laser power and pulse duration. The reason of the non-smooth material processed, respectively; with power 89.4 W and duration 20ms with better wear-resistance is that the results of the combination of area ratio, volume, and hardness of non-smooth unit.The shape and distributing distance of non-smooth unit influence the area ratio and volume of non-smooth unit, so effect the resistance of non-smooth unit on abrasive particle. The wear resistance of reticulate non-smooth specimen is the best, and then that of the striate non-smooth specimen takes second place and the cave pit is the worst, among studied several non-smooth shape specimens. The mumber, area ratio and volume of non-smooth unit increase, with the increasing of the distributing distance of non-smooth unit, the wear resistance of non-smooth specimen increases. However the wear resistance of smooth specimen wholly processed by laser is superior to that of non-smooth specimens whose distributing distance of non-smooth unit more than 2mm and inferior than that with less than 2mm.The different carbon content and alloy element of die steel results in different size, width, depth, area ratio and volume of non-smooth unit on die steel with non-smooth surface. The varying trend of the wear-resistance of the non-smooth the wear-resistance of three matrixes with non-smooth surfaces is the same whether the shape and distributing distance change or not. Namely, the wear-resistance of the non-smooth HD material is best, then that of the 3Cr2W8V and the H13 steel the worst.There is difference in the improving extent of wear resistance of non-smooth specimens with different microstructure than that of smooth specimen. The wear resistance of non-smooth specimen with tempered microstructure at 550℃, and then that of with quenched microstructure at 1100℃and at 650℃, and that of with annealed microstructure is the worst.The non-smooth unit processed by laser cladding makes up of laser cladding layer, melting zone and heat affect zone. The non-smooth unit includes a cladding layer than that of the non-smooth unit processed by laser remelting. The changing trend of wear-resistance is that of the cladding with WC best, than that of the cladding with Al2O3, laser remelting and that of the cladding with Ni60 worst among various means. The property of surface layer of material plays important role at the beginning of wear process, but the dept of non-smooth unit is major factor influencing the wear-resistance of non-smooth material at the behind of wear process.The characteristic of non-smooth unit influences the improving extent of wear-resistance of non-smooth material. The factors include laser parameter, the shape, distributing distance and composition of non-smooth unit, the composition and microstructure of matrix, which effect on the size, microstructure and hardness of non-smooth unit. The larger size, bigger volume and the higher hardness of non-smooth units result in the better wear-resistance of material with non-smooth surface.It is found that the wear-resistance of non-smooth specimens processed by laser imitating the shape of biont body is better than that of smooth specimen without processing by laser. The wear-resistance of some non-smooth specimens is ever better than that of specimens with smooth surface whole processed by laser remelting at different degree. The non-smooth unit plays a role in preventing wearing during wear process. Grinding abrasion of non-smooth specimen is equal to wearing on discontinuous plane. The ploughed dept of matrix changes shallowly when the abrasive particles move approaching the non-smooth unit because the baffling effect. There are two moving means of abrasive particle when it moves on the non-smooth unit. The abrasive particle turns to roll over from sliding when its hardness is higher or it is smooth and blunt, per contra, it slides on the non-smooth unit and the ploughing dept is shallow, so the wear extent decreases. The abrasive particle penetrates in shallowly and ploughing matrix continuously after it moves non-smooth unit, when the distributing distance of non-smooth unit is bigger, because of the baffling effect of non-smooth unit, and the next wear process begins. The abrasive particle maybe gets over the matrix part between two adjacent non-smooth units and wears the next non-smooth unit directly. Thus the wearing probability decreases and the wear-resistance of non-smooth specimen improves markedlyIt is found that the wear resistance of die processed to non-smooth surface by laser is markedly improved. This research is significant to improve the life-span of die. The means preparing bionic non-smooth surface material has characteristic of easy to operate, lowering cost and better wear-resistance, which exploits the researching extent about bionic research to metal material, and it develops a new technique for improving the wear-resistance of die.更多还原