發(fā)布時間：2018-05-05 18:06

  本文選題：粉末冶金 + 表面滾壓　； 參考：《華南理工大學》2016年博士論文

【摘要】：鐵基粉末冶金零部件在汽車等行業(yè)有廣泛的應用。但是常規(guī)方法生產(chǎn)的粉末冶金零件制品中殘留一部分孔隙,導致材料強度不足。而表面滾壓強化技術能夠低成本地顯著提高材料的表面密度和性能。因此本文結(jié)合高密度粉末冶金零部件制造的發(fā)展趨勢,針對目前國內(nèi)外對鐵基粉末冶金燒結(jié)材料和零件表面致密化技術的基礎研究的不足,圍繞鐵基粉末冶金材料的表面致密化行為展開系統(tǒng)深入的研究,采用自行研制的滾壓工具和裝備研究粉末冶金材料表面致密化的過程和機理,以及材料的摩擦磨損性能和滾動接觸疲勞性能,為高密度鐵基粉末冶金材料和零件的應用提供可靠的理論依據(jù)和技術保障。具體研究成果如下:發(fā)明了一種粉末冶金滾壓工具和滾壓設備及其方法,其通過夾持固定在車床上實現(xiàn)滾壓力的精確控制和滾壓過程中滾壓力的測量。滾壓過程中通過縱向進給對材料表面施加一定的滾壓力,對材料進行表面滾壓加工,實現(xiàn)了粉末冶金材料自表面向心部形成一定的密度梯度,發(fā)現(xiàn)滾壓力在較短時間內(nèi)即停止降低,滾壓加工塑性變形主要發(fā)生在滾壓初始階段。滾壓力是影響滾壓效果的主要參數(shù),隨著滾壓力增加,表面致密層厚度和表面硬度增加明顯。主軸轉(zhuǎn)速是影響滾壓效果的次要參數(shù),隨著主軸轉(zhuǎn)速的增加,材料表面致密層厚度和表面硬度變化較小。材料燒結(jié)密度對滾壓致密化效果的影響隨著滾壓力的增加而減弱。對表面硬化層厚度進行解理分析,發(fā)現(xiàn)硬化層厚度與滾壓力成正比,與材料的屈服強度成反比,并且硬化層與材料的相對密度和泊松比相關。當滾壓力達到2800 N后,致密層厚度達到335μm,表面硬度達到315 HV0.1。滾壓材料抗拉強度達到444 MPa,提高了75%。滾壓材料的塑性也有所提高,延伸率達到4.5%。對滾壓材料拉伸端口分析發(fā)現(xiàn)表面層等軸韌窩增多,同時材料表面存在大約10μm厚度的長條狀的白亮撕裂棱薄層。對滾壓材料截面微觀組織分析發(fā)現(xiàn)孔隙的形貌隨著表面致密層深度的增加從球形向線條狀轉(zhuǎn)變。表面層珠光體層片間距變小,并且其層片方向產(chǎn)生了明顯的彎曲,傾向于平行表面分布;鐵素體沿著滾壓的方向發(fā)生塑性變形被拉長,發(fā)生明顯細化。對滾壓面進行分析發(fā)現(xiàn)珠光體的形貌與其層片方向和滾壓方向的夾角有關,夾角較大時,珠光體形成波浪狀或褶皺裝,甚至發(fā)生破碎,形成顆粒狀;夾角較小時,珠光體會形成網(wǎng)絡狀形貌。滾壓加工能夠提高材料的滑動摩擦磨損性能。干摩擦條件下,滾壓加工材料的摩擦系數(shù)和磨損體積明顯低于未滾壓材料。通過對接觸表面的應力分析,發(fā)現(xiàn)滾壓材料在表面和表面下形成的切應力較未滾壓試樣顯著降低。滾壓加工材料的磨損機理主要是磨粒磨損的犁溝作用和少量鱗片剝落,粘著磨損程度較未滾壓試樣顯著降低。油潤滑條件下,滾壓加工能夠提高材料在高載荷時的摩擦磨損性能,其在高載荷時的摩擦系數(shù)和磨損體積明顯低于未滾壓材料。滾壓材料表面的滑動摩擦性能具有一定的方向性。干摩擦條件下,摩擦方向與滾壓加工方向相反時,材料摩擦系數(shù)和磨損體積數(shù)值略高于摩擦方向與滾壓方向相同的試樣,磨損程度較嚴重。油潤滑條件下,其在高載荷時的摩擦系數(shù)和磨損體積要明顯高于摩擦方向與滾壓方向相同的材料。滾壓材料的滾動接觸疲勞性能顯著提高。滾壓材料的滾動摩擦系數(shù)和磨損深度較未滾壓材料有顯著降低,降低幅度分別達到75%和50%。在低應力下,滾壓材料的磨損形式為犁溝和剝層磨損;在高應力下,滾壓材料的磨損形式為點蝕和剝層磨損。根據(jù)裂紋擴展模型,裂紋在一定時間內(nèi)擴展一定長度需要施加的剪切力正比于彈性模量。因而與未滾壓材料相比,滾壓加工使材料的磨損向剝落的轉(zhuǎn)變推遲到更高的載荷。滾壓材料磨損率顯著小于未滾壓材料,并且先于未滾壓材料進入穩(wěn)定階段。在低滾動周期,材料的磨損以犁溝和剝層磨損為主;在高滾動周期,材料的磨損形式為剝層磨損、點蝕和剝落。根據(jù)建立的裂紋擴展模型,裂紋擴展壽命正比于材料的彈性模量平方,反比于所受剪切應力平方。滾壓加工延長了裂紋的擴展壽命,延長了材料剝落產(chǎn)生的時間。滾壓材料的滾動接觸疲勞性能明顯提高。其額定壽命為未滾壓試樣的2.82倍。滾壓材料的失效形式主要為剝落和點蝕。其剝落坑較未滾壓材料明顯減少,剝層磨損程度與未滾壓材料相比較輕。
[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.

【學位授予單位】：華南理工大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TF125;TG306

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本文編號：1848750