铁基烧结材料表面滚压致密化技术及其摩擦磨损和滚动疲劳性能

发布时间：2018-05-05 18:06

本文选题：粉末冶金 + 表面滚压　；参考：《华南理工大学》2016年博士论文

【摘要】：铁基粉末冶金零部件在汽车等行业有广泛的应用。但是常规方法生产的粉末冶金零件制品中残留一部分孔隙,导致材料强度不足。而表面滚压强化技术能够低成本地显著提高材料的表面密度和性能。因此本文结合高密度粉末冶金零部件制造的发展趋势,针对目前国内外对铁基粉末冶金烧结材料和零件表面致密化技术的基础研究的不足,围绕铁基粉末冶金材料的表面致密化行为展开系统深入的研究,采用自行研制的滚压工具和装备研究粉末冶金材料表面致密化的过程和机理,以及材料的摩擦磨损性能和滚动接触疲劳性能,为高密度铁基粉末冶金材料和零件的应用提供可靠的理论依据和技术保障。具体研究成果如下:发明了一种粉末冶金滚压工具和滚压设备及其方法,其通过夹持固定在车床上实现滚压力的精确控制和滚压过程中滚压力的测量。滚压过程中通过纵向进给对材料表面施加一定的滚压力,对材料进行表面滚压加工,实现了粉末冶金材料自表面向心部形成一定的密度梯度,发现滚压力在较短时间内即停止降低,滚压加工塑性变形主要发生在滚压初始阶段。滚压力是影响滚压效果的主要参数,随着滚压力增加,表面致密层厚度和表面硬度增加明显。主轴转速是影响滚压效果的次要参数,随着主轴转速的增加,材料表面致密层厚度和表面硬度变化较小。材料烧结密度对滚压致密化效果的影响随着滚压力的增加而减弱。对表面硬化层厚度进行解理分析,发现硬化层厚度与滚压力成正比,与材料的屈服强度成反比,并且硬化层与材料的相对密度和泊松比相关。当滚压力达到2800 N后,致密层厚度达到335μm,表面硬度达到315 HV0.1。滚压材料抗拉强度达到444 MPa,提高了75%。滚压材料的塑性也有所提高,延伸率达到4.5%。对滚压材料拉伸端口分析发现表面层等轴韧窝增多,同时材料表面存在大约10μm厚度的长条状的白亮撕裂棱薄层。对滚压材料截面微观组织分析发现孔隙的形貌随着表面致密层深度的增加从球形向线条状转变。表面层珠光体层片间距变小,并且其层片方向产生了明显的弯曲,倾向于平行表面分布;铁素体沿着滚压的方向发生塑性变形被拉长,发生明显细化。对滚压面进行分析发现珠光体的形貌与其层片方向和滚压方向的夹角有关,夹角较大时,珠光体形成波浪状或褶皱装,甚至发生破碎,形成颗粒状;夹角较小时,珠光体会形成网络状形貌。滚压加工能够提高材料的滑动摩擦磨损性能。干摩擦条件下,滚压加工材料的摩擦系数和磨损体积明显低于未滚压材料。通过对接触表面的应力分析,发现滚压材料在表面和表面下形成的切应力较未滚压试样显著降低。滚压加工材料的磨损机理主要是磨粒磨损的犁沟作用和少量鳞片剥落,粘着磨损程度较未滚压试样显著降低。油润滑条件下,滚压加工能够提高材料在高载荷时的摩擦磨损性能,其在高载荷时的摩擦系数和磨损体积明显低于未滚压材料。滚压材料表面的滑动摩擦性能具有一定的方向性。干摩擦条件下,摩擦方向与滚压加工方向相反时,材料摩擦系数和磨损体积数值略高于摩擦方向与滚压方向相同的试样,磨损程度较严重。油润滑条件下,其在高载荷时的摩擦系数和磨损体积要明显高于摩擦方向与滚压方向相同的材料。滚压材料的滚动接触疲劳性能显著提高。滚压材料的滚动摩擦系数和磨损深度较未滚压材料有显著降低,降低幅度分别达到75%和50%。在低应力下,滚压材料的磨损形式为犁沟和剥层磨损;在高应力下,滚压材料的磨损形式为点蚀和剥层磨损。根据裂纹扩展模型,裂纹在一定时间内扩展一定长度需要施加的剪切力正比于弹性模量。因而与未滚压材料相比,滚压加工使材料的磨损向剥落的转变推迟到更高的载荷。滚压材料磨损率显著小于未滚压材料,并且先于未滚压材料进入稳定阶段。在低滚动周期,材料的磨损以犁沟和剥层磨损为主;在高滚动周期,材料的磨损形式为剥层磨损、点蚀和剥落。根据建立的裂纹扩展模型,裂纹扩展寿命正比于材料的弹性模量平方,反比于所受剪切应力平方。滚压加工延长了裂纹的扩展寿命,延长了材料剥落产生的时间。滚压材料的滚动接触疲劳性能明显提高。其额定寿命为未滚压试样的2.82倍。滚压材料的失效形式主要为剥落和点蚀。其剥落坑较未滚压材料明显减少,剥层磨损程度与未滚压材料相比较轻。
[Abstract]:Iron based P / M parts are widely used in automotive industries. However, some pores in the powder metallurgy parts produced by conventional methods lead to insufficient strength of the materials. The surface rolling strengthening technology can significantly improve the surface density and performance of the materials. Therefore, this paper combines high density powder metallurgy zero. In view of the shortage of basic research on the surface densification of iron based powder metallurgy sintered materials and parts at home and abroad, the surface densification behavior of iron based powder metallurgy materials is systematically studied. The surface densification of powder metallurgy materials is studied by the rolling tools and equipment developed by ourselves. The process and mechanism, as well as the friction and wear properties of the material and the rolling contact fatigue properties provide reliable theoretical basis and technical support for the application of high density iron based powder metallurgy materials and parts. The concrete research results are as follows: a powder metallurgy rolling tool and rolling equipment and its method are invented, which are fixed to the lathe by clamping. In the process of rolling pressure, the rolling pressure is applied to the surface of the material, and the surface rolling process is carried out. The density gradient of the powder metallurgy material is formed from the surface to the heart, and the rolling pressure is stopped to stop in a short time, and the rolling pressure is stopped in a short time. The plastic deformation of rolling process mainly occurs in the initial stage of rolling pressure. The roll pressure is the main parameter affecting the rolling effect. With the increase of rolling pressure, the thickness of surface dense layer and the surface hardness increase obviously. The spindle speed is the secondary parameter affecting the rolling effect. With the increase of the spindle speed, the thickness of the dense layer and the surface hardness of the material surface change. The effect of the sintered density on the effect of roll densification decreases with the increase of the rolling pressure. The thickness of the hardened layer is analyzed. It is found that the thickness of the hardened layer is proportional to the rolling pressure, and is inversely proportional to the yield strength of the material, and the hardened layer is related to the relative density of the material and the Poisson's ratio. When the rolling pressure reaches 2800 N After that, the thickness of the dense layer reached 335 m, the surface hardness reached 315 HV0.1. and the tensile strength of the rolling material reached 444 MPa, and the plasticity of the 75%. rolling material increased. The elongation reached 4.5%. and the tensile port of the rolling material found that the surface layer of the surface layer increased and the surface of the material had a long strip of about 10 mu thickness. The microstructure analysis of the cross section of rolling material shows that the pore morphology changes from spherical to line with the increase of the depth of surface dense layer. The surface layer of pearlite layer is smaller, and the direction of the layer produces obvious bending, which tends to parallel surface distribution, and the ferrite occurs plastic deformation along the direction of rolling. The morphology of the rolling surface is related to the angle of the lamellar direction and the angle of the rolling direction. When the angle is larger, the pearlite forms a wave or folds, and even breaks and forms a granular form. The angle of the pearlite is small, and the pearlite will form a network shape. Rolling processing can improve the material. The friction coefficient and wear volume of the rolling material are obviously lower than those of the non rolling material under dry friction. Through the stress analysis on the contact surface, it is found that the shear stress of the rolling material is significantly lower than that of the non rolling material on the surface and surface. The wear mechanism of the rolling material is mainly abrasive wear. In the condition of oil lubrication, rolling process can improve the friction and wear properties of the material at high load, and the friction coefficient and wear volume of the material at high load are obviously lower than that of the non rolling material. The sliding friction property of the surface of the rolling material is certain. In the dry friction condition, when the friction direction is opposite to the rolling direction, the friction coefficient and the wear volume value of the material are slightly higher than the friction direction and the rolling direction, and the wear degree is more serious. Under the oil lubrication, the friction coefficient and the wear volume at high load are obviously higher than the friction direction and rolling direction. The rolling contact fatigue properties of rolling materials are significantly improved. The rolling friction coefficient and wear depth of rolling materials are significantly lower than those of non rolling materials. The reduction range is 75% and 50%. under low stress respectively. The wear form of rolling material is furrow and peeling wear. Under high stress, the wear form of rolling material is in the form of high stress. According to the crack propagation model, the shear force that the crack is extended to a certain length in a certain time is proportional to the modulus of elasticity. Therefore, the rolling process makes the wear of the material deferred to a higher load compared to the non rolling material. The wear rate of the rolling material is significantly smaller than that of the non rolling material. In the low rolling period, the wear of the material is dominated by furrow and peeling wear. In the high rolling period, the wear form of the material is peeling wear, pitting and peeling. The crack propagation life is proportional to the square of the modulus of elasticity of the material, and is inversely proportional to the square of the shear stress. Rolling process prolongs the propagation life of the crack and prolongs the time of the material exfoliation. The rolling contact fatigue performance of the rolling material is obviously improved. The rated life of the rolling material is 2.82 times as high as that of the non rolling specimen. The failure form of the rolling material is mainly spalling and pitting. Its peeling pit is less obviously less than the rolling material, and the degree of strip wear and tear is not rolled. The pressure material is lighter.

【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TF125;TG306

【参考文献】