【作者】 常海威；

【导师】 雷明凯；

【作者基本信息】 大连理工大学 ， 材料表面工程， 2006， 博士

【摘要】 金属离子高温注入是一种重要的表面合金化工艺,是在大束流密度轰击或辅助热源加热条件下实现的高温基体注入工艺。较常规离子注入,高温注入具有更大的注入深度,并可在离子注入层中形成有利于改善表面层性能的金属间化合物。目前,对于金属离子高温注入的研究主要集中在注入工艺改进及表面改性层性能的评价方面,金属离子高温注入合金化的表面改性机理并不完全清楚。金属离子高温注入金属的特殊传质过程,金属间化合物产生及其转变规律显著影响改性层的成分和结构,决定改性层的性能。为完善和控制金属离子高温注入工艺及进一步发挥金属离子高温注入在表面合金化领域的重要作用,本论文针对金属离子高温注入金属靶的传质机制及金属间化合物形成及转变机制进行了理论分析和实验研究。 利用粒子与固体相互作用理论和辐照增强扩散理论,建立了金属离子高温注入金属靶的传质模型。采用动态Monte Carlo方法模拟离子注入过程,引入饱和浓度限模拟晶体靶局部饱和现象,采用基于辐照增强扩散的扩散方程描述注入粒子扩散过程,根据缺陷线性退火理论确定辐照增强扩散系数,结合杂质原子和非平衡空位扩散方程给出了注入粒子的浓度—浓度分布,在扩散方程中引入了空位源函数并考虑了离子溅射造成的表面退让效应。利用建立的金属离子高温注入金属靶传质模型计算了Cr-Al,Ni-Al,Fe-Al体系在注入温度为室温到700℃,注入能量为2-120 keV,注入剂量为2×10¹⁶-1×10¹⁸ions cm^-2的注入条件下注入粒子的浓度—深度分布,计算浓度—深度分布与实验测量结果相符,验证了所建立的传质模型的正确性,并通过计算分析讨论了计算与实验测量误差的成因,且讨论了注入温度,注入能量,注入剂量等因素对高温注入传质过程的影响。 针对金属离子高温注入金属的界面反应特性,借鉴二元薄膜热退火过程中化合物形成预测中的有效形成热概念,建立了金属离子高温注入金属的有效形成热模型。有效形成热是利用金属间化合物的标准形成热,与反应界面上控制元素的有效浓度和形成金属间化合物的控制元素浓度的比值之积计算,各种可能形成的金属间化合物中,有效形成热最小的金属间化合物为预测先形成化合物。采用有效形成热模型预测了金属Fe,Hf,Mo,Nb,Ni,Ta,Zr离子在注入温度300-600℃,注入能量50-140 keV,注入剂量10¹⁷-10¹⁸ions cm^-2,束流密度10-60 μA cm^-2条件下注入金属Al形成的金属间化合物Al₁₃Fe₄,HfAl₃,MoAl₁₂,NbAl₃,NiAl₃,TaAl₃,ZrAl₃,预测结果与文献报道结果相符。考虑到亚稳相形成,有效形成热模型合理预测了Cr离子高温注入金属Al,在400℃形成化合物Cr₁₄Al₈₆,高于400℃形成化合物Cr₂Al₁₃。考虑固态界面上金属间化合物的形核难易程度,有效形成热模型合理预测了金属V离子高温注更多还原

【Abstract】 The metal ion implantation into metal at elevated temperatures is an important surface alloying process. The metal ion is implanted into metal that is heated by ion bombardment with the large ion current density or auxiliary heater. Compared with conventional ion implantation, the implantation depth at elevated temperatures is deeper and intermetallics that are benefit to the improvement of surface performance can form during metal ion implantation into metal at elevated temperatures. At present, the researches about the metal ion implantation into metal at elevated temperatures concentrate on the improvement of implantation process and the properties of the implanted layer. However, the modification mechanisms of the implanted layer are not fully understood. The mass transfer and the rule of the intermatellics formation and transformation during metal ion implantation into metal target at elevated temperatures determine the composition and construction of the implanted layer, which affect the performance of the implanted layer significantly. To improve and control the process of metal ion implantation into metal and make a further use of the process of metal ion implantation into metal at elevated temperatures in the surface alloying, the mechanisms of mass transfer and the rules of intermetallics formation and transformation have been studied by the theory analysis and the experimental measurement.A mass transfer model has been built up for metal ion implantation into metal at elevated temperatures, based on the transport of ions in matter and the radiation enhanced diffusion theory. With the model, the ion implantation process at elevated temperatures is simulated by the Dynamics Monte Carlo method. Using a maximum allowed atomic fraction simulates the local saturation behavior in the crystal target. The radiation enhanced diffusion coefficient is obtained by taking into account the linear annealing defects. The concentration-depth profiles of the implanted species are determined from the diffusion equations for the implanted species and nonequilibrium vacancies. The nonequilibrium vacancy source function and the surface sputtering effects are introduced in the diffusion equations. The concentration-depth profiles of Cr, Ni, and Fe ions implantation into Al and Al ions implantation into Fe were calculated at the temperatures of room temperature to 700 ℃, at the implantation energy of 2-120 keV and with the implantation doses of 2×10~16—1 ×10~18 ions cm"". The calculated results are consistent with the experimental ones. The effects of temperature, implantation energy and implantation dose on the radiation enhanced diffusion are also discussed and the errors generated from calculations andexperiments are analyzed.Due to the characteristics of interface reaction during metal ion implantation into metal at elevated temperatures, the effective heat of formation model is built to predict intermetallics formation during metal ion implantation into metal at elevated temperatures by introducing the conception of effective heat of formation. The effective heat of formation is calculated by the standard heat of formation of the intermetallics predicted to form multiplying the ratio of the concentration of the limiting element at the reaction interface and the concentration of the limiting element in this intermetallics. The intermetallics Al^Fe^ HfAb, MoAln, NbAls, NiAl3, TaAh and ZrAls are reasonably predicted to form during metal Fe, Hf, Mo, Nb, Ni, Ta and Zr ions implantation into metal Al at the implanted temperature of 300-600 °C, at the implanted energy of 50-140 keV, at the current density of 10-60 uA cm"2, with the implanted dose of 10I7-1018ions cm"2 and the prediction results are consistent with the experimental results. Considering the metastable phase formed during metal ion implantation into metal at elevated temperatures, the effective heat of formation model predicts formation of the intermetallics CrnAlge at the temperature of 40fr °C, and C^Alu at above 400 °C. By taking the nucleation barrier at solid state reaction interface into account, intermetallics VAI3 is predicted to form by the effective heat of formation model. The biphase M0AI12, M0AI5 and TiA^, TiAl formed during the metal Mo and Ti ion implantation into metal Al at above 600 °C, respectively, where the effective heat of formation model is not valid.Al ions with the implanted energy of 120 keV are implanted into Fe at the temperatures of room temperature to 500 °C to the implanted doses of 5><10i6 ions cm"2 and lxlO17 ions cm"2 by using the 400 keV accelerator and Al ions with the implanted energy of 45 keV are implanted into Mg alloy AZ31 at the temperatures of RT and 300 °C to the implanted doses of 2><1016-lxl017 ions cm’2 ions by using MEVVA source. The concentration-depth profiles of implanted species are obtained from Rutherford Backscattering Spectrometry (RBS) and the phase structure of samples is analyzed by X-ray diffraction analysis (XRD). And the concentration-depth profiles and the phase formation are calculated by the mass transfer model and effective heat of formation model given in this dissertation, respectively. The results of measurement and simulation show that with the implantation dose of 5x1016 ions cm"2, at 250 °C, the maximum concentration of the implanted Al in Fe samples is 6 at.% with a implantation depth of 160 nm; with the implantation dose of 1 xlO17 ions cm"2, with the temperature increasing from 250 °C to 500 °C, the maximum concentration of the implanted Al in Fe keeps constant of 10 at.% and the implantation depth increases from 180 nm to 200 nm; the intermetallics could be detected at 250 °C, with the implantation dose of lxlO17 ions cm"2 and at 500 °C, with the implantation doses of 6x1016 ions cm"2 and l><1017 ions cm"2; at room temperature and 300°C, with the implantation dose of l*10!7 ions cm"2, the maximum concentration of implanted Al in Mg alloy is 10 at.% and 8 at.%, the implantation depth is 840 nm and 1200 nm, respectively; at room temperature, with the implantation dose of l><1017 ions cm"2, intermetallics Al^Mgn starts to precipitate, while at 300 °C, with the implantation dose of2*1016 ions cm"2, the intermetallics Al^Mgn begins to precipitate; the calculated concentration-depth profiles and the prediction of phase formation by using the mass transfer model and effective heat of formation model are consistent with the experimental results.更多还原