【作者】 王修春；

【导师】 李木森；

【作者基本信息】 山东大学 ， 材料学， 2007， 博士

【摘要】 用自行研制的机械能助渗装置,对机械能助渗铝的渗剂配方、温度、时间、滚筒转速、渗剂装入量、滚筒直径、渗剂粒度、冲击粒子等工艺因素对机械能助渗铝速度的影响进行了试验研究。应用金相分析、电子探针、X射线衍射仪、透射电镜等现代分析方法,研究和分析了机械能助渗铝层的组织结构、形貌、化学成分分布;分析了机械能对试样基体微观缺陷的影响。利用化学反应的热力学函数,研究分析了机械能助渗铝化学反应过程的方式、步骤;考察了机械能助渗铝过程中渗剂反应、活性原子吸附、扩散三个主要环节的热力学和动力学机制,从而确定了整个助渗过程的控制环节和非控制环节;在此基础上,建立了机械能助渗铝机制的理论模型。分析测试了机械能助渗铝层的显微硬度、耐腐蚀性、抗高温氧化性等性能以及机械能助渗铝层对基体抗拉强度、延伸率等力学性能的影响。结论表明:1、选择适宜的供铝剂、催渗剂和填充剂,机械能助渗可以在500-650℃的低温下得到厚度均匀、组织致密的渗铝层,渗铝层厚度可以达到250μm;渗速可以达到,甚至超过粉末高温渗铝（900℃以上）的速度。但渗层中形成疏松孔洞的倾向较大。2、渗铝温度越高,渗速越快。如果填充剂颗粒较细,当渗铝温度大于650℃时,铝粉熔化,渗剂流动性差,渗铝速度反而下降。因此机械能助渗铝温度应控制在500-650℃。如果填充剂颗粒较粗,铝粉熔化基本不影响渗剂流动性。在700℃机械能助渗铝渗速很快,08F钢渗铝层厚度达到500μm,但渗剂中的铝粉粘结成很大的铝球,浪费铝粉。渗层厚度与保温时间基本成抛物线关系。滚筒转速在8r/min、滚筒内空隙达到1O%时,渗速最快。3、渗铝层内部组织主要是由Fe₂Al₅相构成,Fe₂Al₅相呈柱齿状向基体内生长。渗铝层中还存在少量FeAl、Fe₃Al等铁铝化合物及非晶态合金相,在Fe₂Al₅相和基体之间没有FeAl、Fe₃Al等独立成层的低铝相区,没有形成晶粒粗大的含铝α-Fe相过渡区。4、渗铝层表面组织是在Fe₂Al₅相表面断续分布着Al₂O₃、FeO以及（FeO）_n·（Al₂O₃）_m等氧化物颗粒;这些氧化物颗粒先于Fe₂Al₅相生成。5、随着碳含量的增加,渗铝层厚度下降;1Cr18Ni9不锈钢、金属钛、镍表面机械能助渗铝也能得到渗铝层,渗铝速度远低于低碳钢;在铜表面机械能助渗铝未能得到渗铝层;在镁表面机械能助渗铝得到的渗铝层很脆,容易剥落。6、在500-700℃,粉末渗铝过程在热力学上是自发过程;在反应、吸附、扩散三个过程中,渗铝剂中反应产生活性铝原子的过程是反应控制的主要过程。7、机械能助渗的机制是由于渗剂颗粒之间相互冲击、摩擦提高了供铝剂的化学活性,增加了渗剂各组分之间、供铝剂与渗件表面之间的接触机会,加速了渗剂反应,使活性铝原子浓度大大提高。渗剂和渗件之间的相互冲击、摩擦使表面氧化膜变得不连续,净化了渗件表面,有利于活性原子吸附,也有提高渗速的作用。8、催渗剂NH₄Cl产生的HCl并不能完全清除试样表面的氧化铁薄膜,活性铝原子首先进入Fe₂O₃薄膜中夺取氧原子生成Al₂O₃,铁元素被还原,但铁原子并没有与铝结合为铁铝化合物,而是以FeO的形式存在,在渗层表面形成了（FeO）_n（Al₂O₃）_m氧化物颗粒。9、机械能渗铝层的显微硬度达到980HV_0.1;具有良好的耐NaCl、H₂S、H₂SO₃、HNO₃等腐蚀介质腐蚀的性能和高的抗高温氧化性。材料经过机械能助渗铝后,基体仍然可以保持良好的机械性能;工件变形小,可以应用于形状复杂的工件。因此机械能助渗铝工艺具有良好的应用前景。更多还原

【Abstract】 The effects of agent formulation, temperature, time, speed of the cylinder, proportion of the permeability agent, diameter of the cylinder, particles size of permeability agent, impact particles on the mechanical aided aluminized speed are studied. The metallographic analysis, microhardness tester, electron probe and TEM are used to investigate the structure, morphology and chemical composition distribution of the aluminized layer, and the influence of mechanical energy on the microscopic flaw of the sample substrate are studied.By using the chemical reaction thermodynamic functions, the process and steps of mechanical energy aided chemical reaction are analyzed. The thermodynamics and kinetics mechanism of infiltration agent reaction, the adsorption and diffusion of active atomic in the mechanical energy aided aluminized process are studied. So we can ascertain the control step and the non-control step of the aided process. On this basis, a mechanical energy aided aluminized theoretical model is established.We test the microhardness, corrosion resistance, high temperature oxidation resistance, and the influences of the aluminized layer on the substrate tensile strength, elongation and other mechanical properties. Then we obtain the follow conclusions:1. Choosing suitable aluminum provider, catalytic agent and stuffing, uniform and compact alumimzed layer with the thickness more than 250μrn would be obtained at the low temperature of 500-650℃. By this method, the aluminized speed could reach the speed of the high temperature powder aluminizing （above 900℃）. Loosen structure is apt to be formed in the layer.2. The higher the aluminized temperature, the faster the aluminized speed. If the stuffing particles are small, the Al powder will dissolve when the aluminized temperature is higher than 650℃, because the fluid of the permeability agent is poor, the thickness of aluminized layer will decrease. So the temperature of mechanical energy aided aluminizing should be controlled between 500℃and 650℃. If the stuffing particles is coarser, the fluid of permeability agent will be finer, mechanical energy aided aluminized speed is fast at 700℃, 08F steel with the aluminized thickness 250μm can be obtained. However, Al powder of permeability agent bonds into big balls, so it is caused waste. The thickness of aluminized layer related to holding time is in a parabola form. The aluminized speed is the fastest when the rotational speed of cylinder is 8r/min and the performed gap of cylinder is 10%.3. The internal organization of aluminized layer is mainly composed phase, which grow in columnar form into the substrate. A little of FeAl, compound and amorphous alloy phase are formed in alumimzed layer. The low Al phase region of FeAl, Fe₃Al are not formed between Fe₂Al₅ and substrate, the transition phase ofα-Fe containing Al do not form coarse grain size.4. The gains of Al₂O₃, Fe₂O₃ and FeO·Al₂O₃ oxide are discontinuously distributed on the surface of Fe₂Al₅ phase in the surface texture of aluminized layer. The oxides is formed earlier than Fe₂Al₅ phase.5. The thickness of aluminized layer decreases along with the increase of carbon content. By mechanical energy aided aluminizing, the aluminized layer can be also obtained on the surface of 1Cr18Ni9 stainless steel, Ti and Ni, but the permeability speed is much slower than low carbon steel. The aluminized layer can not be obtained on the Cu surface by mechanical energy aided aluminizing. The aluminized layer obtained on Mg surface is crisp and easily flaking.6. At the temperature of 500℃to 700℃, the powder aluminized process is a thermodynamic spontaneous process. The agents produced active atomic is the control step during the process of reaction, adsorption and diffusion.7. Mechanical energy aided alumimzed mechanism is mainly because of agents vibration and friction, which can enhance internal defect density and the surface activity of the permeability agents, increase the contact chance of different component of agents, permeability agents and samples surface, so the aluminized reaction is accelerated, the concentration of active aluminum atoms is increased remarkably. The relative shift between agents and samples and mutual friction make the surface oxide film of samples become discontinuous, so the samples surface are purified, which would be benefit to adsorb active atom and enhance the aluminized speed too. 8. HCl generated from catalystic agent NH₄Cl can not remove all the FeO film on the surface of samples. The active Al atoms come into Fe₂O₃ film firstly, and grab the oxygen atoms and generate Al₂O₃, the Fe element is deacidized, but Fe and Al atoms do not combine into Fe-Al compounds, Fe is existed in the form of FeO. The oxide particles of （FeO）_n（Al₂O₃）_m are formed on the surface of aluminized layer.9. The microhardness of aluminized layer reach 980HV_0.1 by mechanical energy aided aluminizing. Mechanical aided aluminized layer has excellent corrosion resistance to NaCl, H₂S, H₂SO₃, HNO₃ and high temperature oxidation resistance. The substrate could maintain high mechanical properties after mechanical energy aided aluminizing, and this method could be applied to the workpieces with complex shapes, so the mechanical energy aided process has a good prospect.更多还原