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切削液过滤加工方法简析

  • 发表时间:2020-08-24 09:40:02
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  1概述
 
  钛合金具有低密度(约4.5g/cm3)、高强度和耐腐蚀性(如酸、碱、海水和大气)等一系列优良的机械和物理性能。因此,它被广泛应用于航空航天、核能、化工、石油、冶金、医疗设备等行业。
 
  (1)钛合金分类。钛是一种熔点为1720℃,异构化温度为882℃的同分异构体。当温度低于882℃时,钛的结构为六角形,称为α-钛。当温度高于882℃时,它具有体心立方晶格结构,称为β钛。根据上述两种组织的不同特点,加入不同的合金元素,逐步改变相变温度和相含量,得到不同组织的钛合金。
 
  钛合金在室温下有三种基本结构,可分为以下三种类型。①α钛合金。由α固溶体组成的单相合金。其耐热性比纯钛高,结构稳定,抗氧化性强,强度仍保持在500~600℃,抗蠕变能力强,但热处理不能强化。等级为ta4-ta8。硬度为240-300hb,抗拉强度σB为340-981mpa,延伸率δ为10%-25%,冲击值AK为(29.43-58.86)×104j/m2,导热系数к为7.54-10.47w/m·K。②β钛合金。由β相固溶体组成的单相合金。该合金未经热处理,具有较高的强度。淬火时效后,合金进一步强化,但热稳定性差,不适合在高温下使用。等级为tb1和TB2。硬度为240-300hb,抗拉强度σB为1079-1373mpa,延伸率δ为18%,冲击值AK为29.43×104j/m2,导热系数为6.28w/m·K。③α+β钛合金。它由α和β双轴组成。同时存在α稳定元素和β稳定元素,如Cr、Co、Fe、Ni和Mn,它们稳定了β相。Sn和Zr在α相和β相中都有相当大的固溶度,是有效的增强剂。该合金组织稳定,高温变形性能好,韧性和塑性好,可以通过淬火和时效来强化。热处理后的强度比退火态提高50%-100%。高温强度高,可在400-500℃长期工作。其热稳定性仅次于α钛合金。等级为tc1-tc10。结果表明,该材料的硬度为210~365hb,抗拉强度σB为589~1059mpa,延伸率δ为10%~15%,冲击值AK为(29.43~44.15)×104j/m2,导热系数κ为5.44~9.63w/m·K。
 
  在三种钛合金中,α钛合金的切削加工性能较好,其次是α+β钛合金,β钛合金的切削性能最差。其中最常用的是α-钛合金和α+β钛合金。
 
  (2)钛合金的性能和特点。
 
  ①比强度高。钛合金密度低,强度高,比强度(σB/ρ)大于超高强度钢。
 
  ②热强度高。钛合金具有良好的热稳定性和高温强度,能在500℃下长时间工作,而铝合金只能在200℃以下工作。在300~500℃下,钛合金的强度比铝合金高10倍左右。
 
  ③良好的耐腐蚀性。它的耐海水腐蚀性比钛合金钢长时间的耐腐蚀性要好得多。具有较强的耐点蚀、耐酸腐蚀和应力腐蚀性能。对碱、氯化物、氯、有机氯、硝酸、硫酸有良好的耐腐蚀性。然而,钛对还原氧和铬酸盐介质的耐蚀性较差。
 
  ④它具有很高的化学活性。钛与大气中的氧、氮、氢、一氧化碳、二氧化碳、水蒸气和氮气发生强烈反应。当碳含量大于0.2%时,钛合金中会形成硬质tic。当温度较高时,与n的相互作用形成tin硬表面,当温度高于600℃时,钛能吸收氧气,形成硬度较高的硬化层。如果氢含量增加,也会形成硬化层。表面硬脆层深度可达0.1~0.15mm,钛的硬度比基体高20%~30%。钛的化学亲和力也很大,很容易与摩擦表面结合
 
  1.Overview
 
  Titanium alloy has a series of excellent mechanical and physical properties,such as low density(about 4.5 g/cm3),high strength and corrosion resistance(such as acid,alkali,seawater and atmosphere).Therefore,it has been widely used in aviation,aerospace,nuclear energy,chemical industry,petroleum,metallurgy and medical equipment industries.
 
  (1)Classification of titanium alloys.Titanium is an isomer with a melting point of 1720℃and an isomerization temperature of 882℃.When the temperature is below 882℃,the structure of titanium is hexagonal,which is calledα-titanium.When the temperature is above 882℃,it has a body centered cubic lattice structure,which is calledβtitanium.According to the different characteristics of the above two structures,different alloy elements are added to change the phase transformation temperature and phase content gradually,so as to obtain titanium alloys with different structures.
 
  At room temperature,titanium alloys have three basic structures,which can be divided into the following three types.①αtitanium alloy.Single phase alloy composed ofαsolid solution.Its heat resistance is higher than that of pure titanium,its structure is stable,its oxidation resistance is strong,its strength is still maintained at 500-600℃,and its creep resistance is strong,but it can not be strengthened by heat treatment.The grades are ta4-ta8.The hardness is 240-300hb,tensile strengthσB is 340-981mpa,elongationδis 10%-25%,impact value AK is(29.43-58.86)×104j/m2,thermal conductivityкis 7.54-10.47w/m·K.②βtitanium alloy.Single phase alloy composed ofβphase solid solution.The alloy has higher strength without heat treatment.After quenching and aging,the alloy is further strengthened,but the thermal stability is poor,so it is not suitable to be used at high temperature.The grades are tb1 and TB2.The hardness is 240-300hb,tensile strengthσB is 1079-1373mpa,elongationδis 18%,impact value AK is 29.43×104j/m2,thermal conductivityкis 6.28w/m·K.③α+βtitanium alloy.It is composed ofαandβbiaxially.There are bothαstable elements andβstable elements,such as Cr,Co,Fe,Ni and Mn,which stabilize theβphase.Both Sn and Zr have considerable solid solubility inαandβphases and are effective strengthening agents.This kind of alloy has stable structure,good high temperature deformation,toughness and plasticity,and can be quenched and aged to strengthen the alloy.The strength after heat treatment is 50%-100%higher than that of annealed state.It has high strength at high temperature and can work at 400-500℃for a long time.Its thermal stability is second only to that ofα-titanium alloy.The grades are tc1-tc10.The results show that the hardness is 210-365hb,tensile strengthσB is 589-1059mpa,elongationδis 10%-15%,impact value AK is(29.43-44.15)×104j/m2,thermal conductivityкis 5.44-9.63w/m·K.
 
  Among the three kinds of titanium alloys,the machinability ofαtitanium alloy is relatively good,followed byα+βtitanium alloy,and the worst isβtitanium alloy.Among them,the most commonly used areα-titanium alloy andα+βtitanium alloy.
 
  (2)The properties and characteristics of titanium alloy.
 
  ①High specific strength.Titanium alloy has low density and high strength,so its specific strength(σB/ρ)is greater than that of ultra-high strength steel.
 
  ②High thermal strength.Titanium alloy has good thermal stability,high temperature strength and can work at 500℃for a long time,while aluminum alloy can only work below 200℃.The strength of titanium alloy is about 10 times higher than that of aluminum alloy at 300-500℃.
 
  ③Good corrosion resistance.Titanium alloy can work in humid atmosphere and seawater for a long time,and its corrosion resistance is much better than that of stainless steel.It has strong resistance to pitting corrosion,acid corrosion and stress corrosion.It has excellent corrosion resistance to alkali,chloride,organic compound of chlorine,nitric acid and sulfuric acid.However,titanium has poor corrosion resistance to reducing oxygen and chromate media.
 
  ④It has high chemical activity.Titanium reacts strongly with O,N,h,Co,CO2,water vapor and nitrogen in the atmosphere.When the carbon content is more than 0.2%,hard tic will be formed in titanium alloy.When the temperature is higher,the tin hard surface will be formed by the interaction with n.When the temperature is above 600℃,titanium can absorb oxygen and form a hardened layer with higher hardness.If the hydrogen content increases,the hardening layer will also be formed.The depth of hard and brittle surface layer can reach 0.1-0.15mm,and the hardness of titanium is 20%-30%higher than that of base.The chemical affinity of titanium is also large,and it is easy to bond with the friction surface.
 
  ⑤The thermal conductivity is low and the elastic modulus is small.The thermal conductivity of titanium is very low,which is 15.24 w/m·K,1/4 of nickel,1/5 of iron and 1/4 of aluminum.However,the thermal conductivity of various titanium alloys is lower,which is generally 50%of that of titanium.For example,theкof TC4 is 7.95 w/m·K,and that of TC9 is 7.12 w/m·K.The elastic modulus E of titanium and titanium alloy is 110 000 MPa,which is about 1/2 of that of general steel,so it has poor rigidity and easy deformation.⑥Low temperature performance is good.Titanium alloy remains its mechanical properties at low and ultra-low temperatures(-100~-253℃),which is an important low-temperature structural material.
 
  2.Cutting characteristics of titanium alloy
 
  The melting point of titanium is high(1720℃),the activation energy is large,and the lattice atoms are not easy to get out of their equilibrium position.Therefore,the energy consumed in cutting into chips is large.The more alloying elements are added,the higher the strength and hardness of the alloy,and the more difficult it is to cut.The results show that when the hardness of titanium alloy is higher than 350 Hb,the machining is more difficult.When the hardness is less than 300hb,it is easy to stick the tool and it is difficult to cut.The best cutting hardness of titanium alloy is 300~350hb.The reason why titanium alloy is difficult to cut is not only hardness,but also other mechanical,physical and chemical properties.Its cutting characteristics are as follows.
 
  (1)The deformation coefficient is small.The chip deformation coefficient of cutting titanium alloy is slightly less than 1 or close to 1,which is a significant feature of cutting titanium alloy.The reason for the small plastic deformation and chip shrinkage is that titanium transforms fromαtoβat high cutting temperature,and the volume ofβtitanium increases,which leads to chip growth.Under the action of high temperature,titanium chips absorb
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