【作者】 王金刚；

【导师】 林树忠； 林成新；

【作者基本信息】 河北工业大学 ， 机械制造及其自动化， 2006， 博士

【摘要】 Fe-Mn-Si形状记忆合金在受到外部机械力作用时,通过应力诱发马氏体相变及其贡献的附加变形来适应外界宏观应力的变化,这种特性称为应力自适应特性。Fe-Mn-Si形状记忆合金的应力自适应特性与力学性能之间具有紧密的关系。研究发现,虽然该合金的硬度较低,但在一定的条件下却具有良好的耐磨性、良好的抗应变、应力疲劳特性,主要原因是该合金具有应力自适应特性。出现这种特性的主要原因是它具有的不全位错的可逆运动和相变伪弹性。应力自适应特性受以下因素的影响:(1)应力、应变值的大小;(2)温度的高低;(3)合金本身各种成分的含量及其组合。通过滑动摩擦磨损试验和应变疲劳试验研究了4种不同成分的Fe-Mn-Si形状记忆合金的耐磨性及其应变疲劳特性;使用该合金制造了某汽车变速器中的惰轮并进行了复杂应力作用下的疲劳试验;设计制造了压力试件并进行了压缩试验;借助X射线衍射定性定量分析(XRD)、电子扫描电镜(SEM)和透射电镜(TEM)观察等手段研究了该合金的摩擦磨损和疲劳过程中的相变机制及其微观机理。研究发现,干摩擦时,Fe-Mn-Si形状记忆合金具有一般奥氏体材料的摩擦磨损特性,磨损机理为粘着磨损;油润滑时,该合金具有良好的摩擦磨损特性,磨损机理为磨粒磨损,其磨损量不随着载荷的增加而增大,而是存在一个较佳载荷,在这个载荷下,磨损量最小。Fe-Mn-Si形状记忆合金具有良好的应变疲劳特性,在应变幅值±3%时的弯曲循环疲劳寿命可达1302次,远远高于不锈钢在相同条件下的80次;在应变幅值±1.5%时的拉压循环疲劳寿命达到1300次,远远高于U71Mn重轨钢在相同条件下的120次。该合金弯曲疲劳断裂后的ε马氏体含量几乎占到100%,断口类型为准解理断裂。XRD分析、SEM和TEM观察表明,油润滑磨损、弯曲循环以及拉压循环时该合金的应力自适应特性导致出现了γ→ε马氏体正逆相变,降低了应力集中,抑制了塑性滑移变形,降低了微裂纹的形成和扩展速度从而提高了耐磨性和疲劳寿命等力学性能。Fe-Mn-Si形状记忆合金具有较好的机械加工性,用该材料制造了某汽车变速器中的惰轮并进行了复杂应力作用下的疲劳试验证明,该惰轮的疲劳寿命是同条件下1Cr18Ni9Ti奥氏体不锈钢惰轮的11倍;对用该合金制造的试件的压缩试验及计算证明,当温度在-50℃～+50℃之间变化时,只要在钢轨中按照3%的比例焊接Fe-Mn-Si形状记忆合金,就可使钢轨中的温度应力降低11%,再一次证明了这种合金的应力自适应特性是其具有良好力学性能的根本原因。更多还原

【Abstract】 Fe-Mn-Si shape memory alloy (Fe-Mn-Si SMA) occurs martensitic transformation and transformation distortion in order to adapt change of macroscopical force in the condition of exerting outside mechanical stress. This characteristic is called the stress self-accommodation characteristic.The stress self-accommodation characteristic of Fe-Mn-Si SMA is close relative to mechanics property. It’s found that the Fe-Mn-Si SMA possess good wear-resisting performance, anti-strain and anti-stress fatigue characteristic in despite of its lower rigidity in some condition, because of having stress self-accommodation characteristic.The main reason for appearing this characteristic is that it has the partial dislocation reversible movement and transformation pseudoelasticity. The factors effected the stress self-accommodation characteristic are: (1) the value of stress and strain;(2)the surface temperature value ;(3) ingredient content and proportion component of Fe-Mn-Si SMA.The wear-resisting performance and the strain fatigue characteristic in four kinds of Fe-Mn-Si SMA with different components are investigated by sliding friction test and strain fatigue test; Some automobile transmission gearbox idler is made using the alloy and carried on fatigue tests under the complex stress condition; Pressure specimen designed and manufactured is carried on compression test ; The transformation and microcosmic mechanism of the SMA during the processes of wear abrasion and strain fatigue are respectively studied by X-ray diffraction(XRD),scanning electron microscope(SEM) and transmission electron microscopy (TEM) etc.It’s found that the Fe-Mn-Si SMA has the friction and wear characteristic of the common austenitic metal material in the dry friction, and the wear mechanism is adhesive wear; but it has good friction and wear characteristic and the wear mechanism is abrasive wear in lubrication. Moreover, Fe-Mn-Si SMA wear mass losses does not increase along with increasing the load ,while there is a better load that in which, the wear mass losses is the least in lubrication.Fe-Mn-Si SMA shows good strain fatigue resistance with cyclic bending fatigue life of 1302 times under the strain amplitude of±3% much better than stainless steel with 80 times in the same test conditions. And its cyclic tension-compression fatigue life is 1300 times under the strain amplitude of±1.5%, also much better than U71Mn heavy rail steel with 120 times. The bending-fatigue fractured section of Fe-Mn-Si SMA specimen possesses nearly 100%εmartensite with quasi-cleavage rupture type.It is indicated that from the analysis of XDR, the observations of SEM and TEM, in the conditions of lubrication, bending and tensile compression cycle, the stress self-accommodation characteristic of the alloy results in the appearance ofγ→εmartensitic positive and reverse transformation, reduces the stress concentration,suppresses the plastic slipping deformation and reduces the rate of microcrack’s formation and expansion.Consequently it improves the mechanics property of the wear-resisting performance and fatigue life.The Fe-Mn-Si SMA possess better machining property.According to the fatigue test of some automobile transmission gearbox idler made of this material under the complex stress condition , it is proved that, in the same condition, the fatigue life of this idler is 10 times more than that of 1Cr18Ni9Ti austenitic stainless steel idler; The compression test and calculation to specimen made of the alloy proves that, when the temperature changes between -50℃and +50℃, the temperature stress in rail can be reduced 11% as long as welding Fe-Mn-Si SMA according to 3% proportion in rail, so it is proved again, the stress self-accommodation characteristic of the alloy is the basic reason for its good mechanics property.更多还原