【作者】 李友生；

【导师】 邓建新；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2010， 博士

【摘要】 钛合金材料的导热系数小、高温化学活性大、弹性模量低、与其他金属材料摩擦系数大等特性使它成为一种典型的难加工材料。本文通过理论分析与试验研究相结合的方式,模拟和研究了切削加工钛合金(Ti-6Al-4V)时不同硬质合金刀具材料与工件材料的溶解-扩散情况,系统研究了硬质合金刀具材料与钛合金之间的化学性能相互匹配关系。最后,通过Ti-6Al-4V钛合金的铣削实验,验证并分析了在切削加工Ti-6Al-4V时不同硬质合金刀具的氧化磨损和溶解-扩散磨损,建立了硬质合金刀具材料与钛合金之间的化学性能匹配关系,从而为选择合适刀具材料切削加工钛合金提供了依据。利用热力学溶液理论,计算了硬质合金刀具材料中的WC、TiC和Co在Ti中的溶解度。刀具材料中的WC、TiC和Co在Ti中的溶解度都受温度的影响较大：温度越高,其在Ti中的溶解度越大。通过对菲克扩散定律的分析,得到了适合硬质合金刀具材料和Ti-6Al-4V之间的元素溶解-扩散浓度表达式和扩散通量表达式。根据元素溶解-扩散的浓度表达式,进一步得到了计算刀具材料和钛合金之间各元素扩散系数的方法,从而为合理解释和分析溶解-扩散试验的结果提供了理论依据。同时,对硬质合金刀具材料与Ti-6Al-4V之间元素扩散的微观机理进行了探讨。利用物质吉布斯自由能函数法对硬质合金刀具材料和Ti-6Al-4V钛合金可能发生的氧化反应进行了热力学计算,从理论上对氧化反应能否发生及其氧化产物进行了分析。温度为1000 K时的热力学计算结果表明：硬质合金刀具材料和Ti-6Al-4V在空气中都能发生氧化反应,其中刀具材料中的WC、TiC和Co分别被氧化成WO3、TiO2和CO3O4；而钛合金中的Ti、Al、V也会被氧化并生成相应的氧化产物；钛合金中的Ti与刀具材料中的WC会发生置换反应,生成TiC和W。选用YT5、YT15、YG6、YG6X和YG8五种硬质合金刀具材料与Ti-6Al-4V进行元素溶解-扩散试验。通过试验,全面分析了在相同溶解-扩散条件下不同刀具材料与Ti-6Al-4V的元素溶解-扩散,系统考察了扩散温度和扩散时间对元素溶解-扩散的影响。试验表明：相同扩散条件下,YT类硬质合金刀具材料与Ti-6Al-4V之间的元素溶解-扩散程度比YG类的严重；Co含量多的YG类硬质合金刀具材料与Ti-6Al-4V的元素溶解-扩散程度严重；细晶粒的刀具材料与Ti-6Al-4V的元素溶解-扩散程度轻微；五种硬质合金刀具材料与Ti-6Al-4V之间的元素溶解-扩散剧烈程度按由大到小的顺序排列为：YT15>YT5>YG8>YG6>YG6X；扩散温度对元素溶解-扩散的影响很大,温度越高,刀具材料与钛合金之间的元素溶解-扩散越剧烈；扩散时间对元素溶解-扩散影响表现为：溶解-扩散时间越长,元素的溶解-扩散深度越大,当扩散时间达到1.5 h左右时,溶解-扩散基本达到一个稳定的状态,即使继续延长扩散时间,元素的扩散深度增加很小。对元素扩散后的刀具材料进行了硬度测试,试验得出：未发生溶解-扩散的刀具硬度基本没有变化；发生溶解-扩散的刀具硬度有明显变化,在靠近扩散界面处,刀具的硬度值明显低于其正常硬度值,远离扩散界面一定距离后,刀具的硬度逐渐恢复至正常水平。虽然刀具材料与钛合金之间的元素溶解-扩散深度只有几个微米,但元素的溶解-扩散流失对刀具材料硬度的影响深度超过几十个微米。通过五种硬质合金刀具材料的氧化试验,系统研究了不同硬质合金刀具材料的抗氧化性能好坏。研究表明：温度为800 K时,硬质合金刀具材料在空气中开始发生氧化反应；温度为900 K时,刀具材料中的WC已经被部分氧化成WO3,Co元素被氧化成CO3O4；刀具材料中的TiC,在温度达到1300 K时才发现其氧化产物TiO2；YT类硬质合金刀具的抗氧化性一般比YG类的好；刀具成分相同时,晶粒尺寸是影响刀具抗氧化性能的关键因素,晶粒越小,刀具的抗氧化性能越好。通过Ti-6Al-4V的氧化试验,可以得出：在1100K时,Ti与空气中的02和N2发生氧化反应,生成Ti02和Ti4N3。在相同切削参数下进行Ti-6Al-4V的铣削实验,实验结果显示：YT类硬质合金刀具的磨损程度远远大于YG类刀具的磨损程度,溶解-扩散磨损和氧化磨损是刀具的主要磨损机理；五种硬质合金刀具的氧化磨损程度按由强到弱的顺序排列为：YT15>YT5>YG6>YG8>YG6X;切削加工过程中,钛合金切屑容易粘结在刀具表面并在高温和元素浓度梯度作用下与刀具材料发生元素的溶解-扩散,五种刀具材料的溶解-扩散磨损程度按由强到弱顺序排列为：YT15>YT5>YG8>YG6>YG6X。通过理论分析和试验研究相结合的方法,对上述五种不同硬质合金刀具材料与Ti-6Al-4V钛合金进行化学性能匹配研究,得出：细晶粒的YG类刀具材料与Ti-6Al-4V之间的元素溶解-扩散程度最小；在Ti-6Al-4V钛合金的铣削实验中,细晶粒YG类刀具的氧化磨损和溶解-扩散磨损程度最低；从刀具材料与工件材料的化学性能匹配分析,细晶粒YG类硬质合金刀具最适合Ti-6Al-4V钛合金的切削加工。更多还原

【Abstract】 Titanium alloy is well known as a typical difficult-to-machine material because of its low thermal conductivity, high chemical reactivity, low modulus of elasticity and high friction factor with other metal materials. This paper selected the wear mechanism of cutting tools in high-speed machining titanium alloy as an entry point, through theory analysis and experiment research, simulated the dissolution-diffusion process between cemented carbide tools and work-piece, systemically investigated the chemical performance matching relationship between cemented carbide tools and titanium alloy. At last, oxidation wear and dissolution-diffusion wear of different carbide tools were validated and analyzed through milling titanium alloy experiments, the chemical properties matching relationship were set up between carbide tools and titanium alloy, providing reliable bases for choosing suitable carbide tools in high-speed machining titanium alloy.Based on the thermodynamic theory of dissolubility, the solubility of WC, TiC and Co in Ti were calculated. The solubility of WC, TiC and Co in Ti were greatly effected by temperature, and the solubility in Ti increased as the temperature increased. Expression of element diffusion concentration and expression of diffusion flux that adapt to carbide tools and titanium alloy were obtained through Fick’s laws of diffusion analysis. Further more, based on the expression of element diffusion concentration, we got the method for calculating diffusion coefficients between carbide tools and titanium alloy, accordingly provided theoretical foundation for explaining and analyzing diffusion experiments logically. We also made primary discussion about microscopic mechanism in element diffusion between carbide tools and titanium alloy.Thermodynamic calculation of oxidation reaction between carbide tools and titanium alloy was got using Gibbs-Free Energy function, then oxidation reaction possibility and reaction products were analyzed theoretically. The results showed that at a temperature of 1000 K oxidation reaction would took place between carbide tools and titanium alloy in the air, WC, TiC and Co in carbide tools were oxidated into WO3, Co3O4 and TiO2 respectively, Ti, Al, and V in titanium alloy were also oxidated into corresponding oxidation products, Ti in titanium and WC in carbide tools turned into TiC and W through displacement reaction.Five carbide tools of YT5, YT15, YG6, YG6X and YG8 were chosen for element diffusion experiment with Ti-6Al-4V, element diffusion of different carbide tool materials with Ti-6Al-4V under the same diffusion condition was analyzed in detail, and the diffusion effect between tool material and workpiece material caused by diffusion temperature and diffusion time was reviewed systemically. The results showed that under the same condition, element diffusion of YT carbide tool materials with Ti-6Al-4V was serious than YG, YG carbide tool materials containing more Co had a more serious diffusion degree, and fine grain tool materials had a little diffusion with Ti-6Al-4V; dissolution-difusion degree between Ti-6Al-4V and the five carbide tools were as follows:YT15>YT5>YG8>YG6>YG6X; diffusion temperature greatly effected element diffusion, diffusion degree between carbide tools and titanium alloy increased as temperature increased; diffusion degree also increased as diffusion time increased, and reached a stable state after about 1.5 h, then it hardly increased even extend diffusion time.Tool hardness was tested after diffusion experiment, and the results showed that there was nearly no changes in tool hardness that carried no diffusion, but tool hardness that had carried diffusion greatly changed, hardness near the diffusion interface obviously decreased compared with normal tool hardness, and hardness far away form the interface reached a normal level gradually. Although it is only several microns took place between tool material and titanium alloy, the effect caused by diffusion was more than several tens of microns.Antioxygenic property of different tool materials was systemically analyzed by oxidation experiment using five carbide tools. Results showed that oxidation reaction of carbide tool materials took place when temperature reached 800 K, WC in tool materials was partly oxidated into WO3, and Co was oxidated into Co3O4 in the temperature of 900 K, TiC in tool materials was found oxidated into TiO2 when the temperature reached 1300 K, antioxygenic property of YT was better than YG, the main factor effect carbide tool oxidation was grain size when components and content were nearly the same, the smaller of the grain size, the better antioxygenic property. Through the oxidation reaction experiment of Ti-6A1-4V, we found that oxidation reaction took place at the temperature of 1100 K, Ti reacted with O2 and N2 in the air and resulting into TiO2 and Ti4N3.Milling experiment of Ti-6AI-4V was done under the same cutting parameters, and the results showed that wear degree of YT carbide tools was far more than YG carbide tools, dissolution-diffusion wear and oxidation wear were the main wear mechanism; the oxidation wear degree of the five carbide tools were as follows:YT15>YT5> YG6>YG8>YG6X; during the progress of cutting, titanium alloy chipping was clearly found bonded on tool surface, and made element diffusion easily took place with tool materials, dissolution-diffusion degree of the five carbide tools were as follows:YT15>YT5>YG8>YG6>YG6X.The chemical performance matching relationship between the five different carbide tools and Ti-6A1-4V was investigated through theory analysis and experiment research, and we concluded that:dissolution-diffusion degree of YG fine grain carbide tool was the least; YG fine grain tool had a smallest dissolution-diffusion wear and oxidation wear during practical cutting, so YG fine grain carbide tool material had a best chemical matching with Ti-6Al-4V.更多还原