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1、摘要本文采用天津大學(xué)材料加工系研制的TJUH.I型超聲表面納米加工處理裝置對(duì)以40Cr鋼為主的金屬材料進(jìn)行滾壓加工處理。利用高分辨透射電子顯微鏡(HRTEM)對(duì)滾壓加工后的樣品表層不同深度的微觀結(jié)構(gòu)進(jìn)行分析,采用X.射線衍射儀(XRD)測(cè)定了沿加工影響層深度方向的殘余應(yīng)力分布,用高精度電感式粗糙度儀對(duì)加工后的樣品表面粗糙度進(jìn)行測(cè)定,用顯微硬度計(jì)分析滾壓加工后樣品的硬度隨厚度方向的變化關(guān)系。前端固定的加工頭被可以自由滾動(dòng)的硬質(zhì)合金球替代,這樣以來(lái),加工頭的滑動(dòng)摩擦就被滾動(dòng)摩擦和較小程度上的滑動(dòng)摩擦代替,加工頭的磨損速率就可以顯著
2、降低。本文所得主要結(jié)果如下:(1)經(jīng)超聲表面滾壓加工處理后,在40Cr鋼的表層一定深度形成了等軸納米晶結(jié)構(gòu),晶粒取向呈隨機(jī)分布,并且在靠近表面的區(qū)域觀察到納米晶周圍被不定形態(tài)結(jié)構(gòu)包圍。加工后的試樣初始晶粒尺寸得到了很大程度的細(xì)化,表面晶粒尺寸為4.65.7.39nm,而納米層的厚度達(dá)到1509m。(2)經(jīng)超聲表面滾壓加工處理后,40Cr鋼的表層形成光潔的表面,表面質(zhì)量明顯提高,表面粗糙度降低至納米級(jí)。(3)經(jīng)超聲表面滾壓加工處理后,40Cr鋼的表面硬度與心部相比顯著提高,且硬度值隨著距表面距離的增大而減小。(4)經(jīng)過(guò)超聲表面滾
3、壓加工,試樣表面被引入了較大值的殘余應(yīng)力,其中在表層較大深度范圍內(nèi)以殘余壓應(yīng)力為主,在靠近表面的區(qū)域壓應(yīng)力的大小遠(yuǎn)超過(guò)簡(jiǎn)單拉伸試驗(yàn)的屈服強(qiáng)度。這種現(xiàn)象的出現(xiàn)與材料的力學(xué)性能,應(yīng)力狀態(tài)密切相關(guān)。關(guān)鍵詞:納米材料超聲表面滾壓加工x.射線衍射殘余應(yīng)力ABSTRACTInourresearch.theTJUH_Iultrasonicsurfacerollingextrusion(USRE)processingtreatmentequipmentthatwasinventedbyourselveswasappliedtothetreat
4、mentsof40Crsteelandtheotherkindsofmetal.Themicrostructuresofthesamplesurfaceandsub—surfacewerestudiedbyHRTEM.ThemeangrainsizeandresidualstressofthetreatedsamplewerecalculatedfromXRD.Ascanningelectronmicroscope(SEM)(XL30ESEM)wasusedtoexaminethemicro-structuraldevelop
5、mentalongthesectionperpendiculartOthetreatedsurfaceofthespecimen.Roughnessofthesurfacewasmeasuredbyhigh—resolutionsurfaceroughnessmeasuringinstrument.Micro-hardnesstesterwasusedtodeterminemicro.hardnessvariationaIongdepth.Frontfastentipwasimprovedbysintered.carbideb
6、allthatcanrollfreelvsothatthewearoftipcoulddiminishobviously.Ourworkdrawsthosefollowingconclusions:1)Anano—crystallisedlayerwhichis150p.mthickisrealizedonquenchedandtempered40Crbyultrasonicsurfacerollingextrusionprocessing(USRE).AfterUSREtreatment,theinitialcoarse—g
7、rainedstructureinthesurfacelayerwasrefinedintoequiaxedultrafinegrains(4.65—7.39nm)withrandomcrystallographicorientations.2)AfterUSREtreatment,thesurfaceroughnesscanreducetonano。scaleof50nm.Meanwhile,Micro·hardnesstestermeasurements’indicatethathardnessisenhancedinth
8、enano-crystallisedsurfacelayerrelativetothematrix。Asthedepthincreases,themicro-hardnessdecreasesdramatically.3)Thisprocessinduceslargeresi