GH4169合金電子束焊接頭組織及疲勞裂紋擴(kuò)展研究
發(fā)布時(shí)間：2018-07-29 20:23
【摘要】：本文以6 mm厚GH4169鎳基高溫合金為研究對(duì)象,采用電子束焊研究焊接接頭組織和焊縫疲勞裂紋擴(kuò)展。采用金相顯微鏡(OM)和掃描電子顯微鏡(SEM)對(duì)不同電子束流、掃描波形和熱處理狀態(tài)下的焊接接頭顯微組織進(jìn)行分析;采用三維散斑動(dòng)態(tài)應(yīng)變測(cè)量?jī)x(XTDIC)和拉伸試驗(yàn)機(jī)對(duì)焊縫拉伸變形過(guò)程進(jìn)行分析;采用疲勞裂紋擴(kuò)展試驗(yàn)機(jī)對(duì)焊縫疲勞裂紋擴(kuò)展速率進(jìn)行分析。研究的主要結(jié)論有:束流29 mA時(shí),能獲得成形最優(yōu)的焊縫,成形美觀無(wú)明顯缺陷,接頭橫截面呈上寬下窄的釘形。電子束流增大,熔深顯著增加,深寬比增大。加入掃描波形易導(dǎo)致焊縫背面未焊透,接頭橫截面中下部出現(xiàn)彎曲現(xiàn)象,呈不對(duì)稱性。焊接接頭熱影響區(qū)小,上部組織為朝熱源生長(zhǎng)的γ相,同時(shí)伴隨著二次枝晶形成,中部組織生長(zhǎng)方式由胞狀生長(zhǎng)變?yōu)橹鶢罹L(zhǎng)直到等軸晶生長(zhǎng),下部組織為細(xì)小的枝晶臂。電子束流對(duì)組織影響不大,而掃描波形會(huì)改變?chǔ)孟嗳∠蚍植?并減少二次枝晶數(shù)量,焊后熱處理焊縫晶粒細(xì)化,長(zhǎng)條狀枝晶數(shù)量減少。接頭硬度呈母材高、焊縫低的趨勢(shì)。電子束流增大,焊縫硬度升高。加入掃描波形不能提升焊縫硬度。熱處理后母材硬度提升了96 HV,焊縫硬度提升了111.5 HV。最優(yōu)工藝參數(shù)下焊縫抗拉強(qiáng)度達(dá)到母材的96.3%,熱處理后母材和焊縫的抗拉強(qiáng)度增加了281 Mpa和275 Mpa,延伸率達(dá)到36%和31%,性能顯著提升。XTDIC測(cè)試結(jié)果顯示,熱處理后母材和焊接試樣變形斷裂方式不同。熱處理母材試樣中心形成最大應(yīng)變場(chǎng)且無(wú)偏移,中心晶粒拉長(zhǎng)變形嚴(yán)重,裂紋于中心萌生,朝四周擴(kuò)展最后發(fā)生斷裂。焊后熱處理試樣初始最大應(yīng)變場(chǎng)分布于試樣左上角,隨后偏移到試樣右側(cè),整體應(yīng)變場(chǎng)呈從右到左依次減小的趨勢(shì)。發(fā)現(xiàn)右側(cè)晶粒拉長(zhǎng)變形嚴(yán)重,首先開裂,并朝左側(cè)擴(kuò)展最后發(fā)生斷裂。熱處理焊縫斷口較熱處理母材斷口韌窩較淺,塑性更差。焊后熱處理焊縫斷口存在熔合不良,氣孔等缺陷。GH4169合金母材、最優(yōu)參數(shù)焊縫、S形掃描焊縫及圓形掃描焊縫的疲勞裂紋擴(kuò)展符合Paris公式。不同焊縫抗裂紋擴(kuò)展能力均優(yōu)于母材,且最優(yōu)參數(shù)焊縫抗裂紋擴(kuò)展能力最好。估算母材和不同焊縫的疲勞裂紋擴(kuò)展門檻值,母材抗裂紋萌生能力優(yōu)于不同焊縫。加入圓形掃描波形有助于提升焊縫的抗裂紋萌生能力。GH4169合金疲勞裂紋擴(kuò)展斷口分為裂紋萌生區(qū)、裂紋擴(kuò)展區(qū)和瞬斷區(qū)。擴(kuò)展初期存在解理小臺(tái)階,為準(zhǔn)解理斷口。擴(kuò)展中期有明顯的疲勞條帶形成,同時(shí)伴隨著撕裂棱。擴(kuò)展快速區(qū)為撕裂棱、孔洞和二次裂紋構(gòu)成的微孔聚集形韌窩斷口。母材裂紋源萌生于中部區(qū)域,焊縫裂紋源主要萌生于近表面夾雜物及焊接缺陷處。最優(yōu)參數(shù)焊縫疲勞條帶之間有明顯的二次裂紋出現(xiàn),有助于釋放裂紋尖端能量,提高抗裂紋擴(kuò)展能力。圓形掃描焊縫裂紋擴(kuò)展斷口存在著更多的缺陷,裂紋擴(kuò)展速率快,疲勞條帶很淺。
[Abstract]:In this paper, the microstructure and fatigue crack propagation of welded joints were studied by electron beam welding (EBW) with 6mm thick GH4169 nickel-base superalloy. Metallographic microscope (OM) and scanning electron microscope (SEM) were used to analyze the microstructure of welded joints under different electron beams, scanning waveforms and heat treatment. The tensile deformation process of weld was analyzed by (XTDIC) and tensile testing machine, and the fatigue crack growth rate was analyzed by fatigue crack growth tester. The main conclusions are as follows: when the beam current is 29 Ma, the optimum weld can be obtained, and the shape of the joint has no obvious defects, and the cross section of the joint is a nail shape with the upper width and the lower width. When the electron beam current increases, the penetration depth and the aspect ratio increase significantly. The addition of scanning waveform can lead to the underside weld penetration and bending phenomenon in the middle and lower part of the cross section of the joint, which is asymmetric. The heat affected zone of the welded joint is small, the upper part of the joint is 緯 phase growing towards the heat source, accompanied by the secondary dendrite formation, the growth mode of the middle part of the joint changes from cellular growth to columnar crystal growth until equiaxed crystal growth, and the lower part of the joint is a fine dendritic arm. The electron beam has little effect on the microstructure, but the scanning waveform will change the orientation distribution of 緯 phase and decrease the number of secondary dendrites. The grain size of weld after heat treatment will be refined, and the number of long stripe dendrites will be decreased. The hardness of the joint shows the trend of high base metal and low weld seam. The hardness of weld increases with the increase of electron beam current. The addition of scanning waveforms does not improve weld hardness. After heat treatment, the hardness of base metal increased 96 HVV, the hardness of weld increased 111.5 HV. The tensile strength of weld metal reached 96.3Mpa. after heat treatment, the tensile strength of the base metal and weld increased 281 Mpa and 275Mpa. the elongation reached 36% and 31%. The deformation and fracture modes of base metal and welding specimen are different after heat treatment. The maximum strain field is formed in the center of the sample and no deviation is found in the center of the heat treatment sample. The center grain is elongated and deformed seriously, the crack initiation occurs in the center, and the fracture occurs at the end of the propagation. The initial maximum strain field was distributed in the upper left corner of the specimen and then shifted to the right side of the specimen. The whole strain field decreased from right to left. It is found that the right grain elongated and deformed seriously, first cracked, and then extended to the left side, finally fracture occurred. The fracture surface of heat treated weld is lighter and the plasticity is worse than that of base metal. The weld fracture surface of post-weld heat treatment has some defects, such as bad fusion, porosity and other defects. The fatigue crack propagation of the optimal parameters of the S-scan weld and circular scanning weld conforms to the Paris formula. The crack propagation resistance of different welds is better than that of base metal, and the optimum parameters are the best. The fatigue crack propagation threshold of base metal and different weld is estimated, and the resistance of base metal to crack initiation is better than that of different weld. The fatigue crack propagation fracture of alloy GH4169 can be divided into crack initiation zone crack propagation zone and transient fracture zone. At the beginning of expansion, there are small steps of cleavage and quasi-cleavage fracture. There are obvious fatigue bands in the middle stage of propagation, accompanied by ripping edges. The rapid propagation zone is composed of tear edges, holes and secondary cracks, which are formed by micropore aggregate dimple fracture. The source of the base metal crack originates in the middle region and the weld crack source mainly originates in the near surface inclusions and welding defects. There are obvious secondary cracks between the fatigue bands of weld seam with optimal parameters, which is helpful to release the energy of crack tip and improve the anti-crack propagation ability. There are more defects in the crack propagation fracture of circular scanning weld, the crack growth rate is fast, and the fatigue band is very shallow.
【學(xué)位授予單位】：南昌航空大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG456.3
本文編號(hào)：2153903
[Abstract]:In this paper, the microstructure and fatigue crack propagation of welded joints were studied by electron beam welding (EBW) with 6mm thick GH4169 nickel-base superalloy. Metallographic microscope (OM) and scanning electron microscope (SEM) were used to analyze the microstructure of welded joints under different electron beams, scanning waveforms and heat treatment. The tensile deformation process of weld was analyzed by (XTDIC) and tensile testing machine, and the fatigue crack growth rate was analyzed by fatigue crack growth tester. The main conclusions are as follows: when the beam current is 29 Ma, the optimum weld can be obtained, and the shape of the joint has no obvious defects, and the cross section of the joint is a nail shape with the upper width and the lower width. When the electron beam current increases, the penetration depth and the aspect ratio increase significantly. The addition of scanning waveform can lead to the underside weld penetration and bending phenomenon in the middle and lower part of the cross section of the joint, which is asymmetric. The heat affected zone of the welded joint is small, the upper part of the joint is 緯 phase growing towards the heat source, accompanied by the secondary dendrite formation, the growth mode of the middle part of the joint changes from cellular growth to columnar crystal growth until equiaxed crystal growth, and the lower part of the joint is a fine dendritic arm. The electron beam has little effect on the microstructure, but the scanning waveform will change the orientation distribution of 緯 phase and decrease the number of secondary dendrites. The grain size of weld after heat treatment will be refined, and the number of long stripe dendrites will be decreased. The hardness of the joint shows the trend of high base metal and low weld seam. The hardness of weld increases with the increase of electron beam current. The addition of scanning waveforms does not improve weld hardness. After heat treatment, the hardness of base metal increased 96 HVV, the hardness of weld increased 111.5 HV. The tensile strength of weld metal reached 96.3Mpa. after heat treatment, the tensile strength of the base metal and weld increased 281 Mpa and 275Mpa. the elongation reached 36% and 31%. The deformation and fracture modes of base metal and welding specimen are different after heat treatment. The maximum strain field is formed in the center of the sample and no deviation is found in the center of the heat treatment sample. The center grain is elongated and deformed seriously, the crack initiation occurs in the center, and the fracture occurs at the end of the propagation. The initial maximum strain field was distributed in the upper left corner of the specimen and then shifted to the right side of the specimen. The whole strain field decreased from right to left. It is found that the right grain elongated and deformed seriously, first cracked, and then extended to the left side, finally fracture occurred. The fracture surface of heat treated weld is lighter and the plasticity is worse than that of base metal. The weld fracture surface of post-weld heat treatment has some defects, such as bad fusion, porosity and other defects. The fatigue crack propagation of the optimal parameters of the S-scan weld and circular scanning weld conforms to the Paris formula. The crack propagation resistance of different welds is better than that of base metal, and the optimum parameters are the best. The fatigue crack propagation threshold of base metal and different weld is estimated, and the resistance of base metal to crack initiation is better than that of different weld. The fatigue crack propagation fracture of alloy GH4169 can be divided into crack initiation zone crack propagation zone and transient fracture zone. At the beginning of expansion, there are small steps of cleavage and quasi-cleavage fracture. There are obvious fatigue bands in the middle stage of propagation, accompanied by ripping edges. The rapid propagation zone is composed of tear edges, holes and secondary cracks, which are formed by micropore aggregate dimple fracture. The source of the base metal crack originates in the middle region and the weld crack source mainly originates in the near surface inclusions and welding defects. There are obvious secondary cracks between the fatigue bands of weld seam with optimal parameters, which is helpful to release the energy of crack tip and improve the anti-crack propagation ability. There are more defects in the crack propagation fracture of circular scanning weld, the crack growth rate is fast, and the fatigue band is very shallow.
【學(xué)位授予單位】：南昌航空大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG456.3
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