不同溫度下激光沖擊TA2工業(yè)純鈦拉伸性能及微觀強化機理研究
發(fā)布時間：2018-11-05 13:20
【摘要】：鈦及鈦合金因其密度低、比強度高、機械性能好和耐腐蝕性強等優(yōu)點在航空航天、海洋開發(fā)和汽車工業(yè)等領域上的應用越來越廣泛。通常鈦及其合金結構件的中高溫服役環(huán)境在500°C以下,而傳統(tǒng)的表面處理方法無法滿足鈦及其合金結構件的中高溫強化要求。激光沖擊強化技術是一種新型的表面處理技術,廣泛應用于金屬材料的表面改性方面研究。目前尚未發(fā)現(xiàn)有關激光沖擊強化工業(yè)純鈦在不同溫度下的拉伸力學性能方面的研究,也未見關于激光沖擊強化工業(yè)純鈦在不同溫度下的微觀組織演變和塑性變形行為方面的報道。針對以上問題,本文以TA2工業(yè)純鈦為研究對象,開展了激光沖擊工業(yè)純鈦在不同溫度下的拉伸性能和斷口形貌特征,組織演化和顯微硬度分布特點,以及激光沖擊工業(yè)純鈦中高溫拉伸塑性變形行為微觀演變機制等方面的研究,具體研究內(nèi)容如下:(1)研究了激光沖擊TA2工業(yè)純鈦在不同溫度下的拉伸性能和斷口形貌特征,獲得了中高溫拉伸變形行為與斷口形貌演變的規(guī)律:對TA2工業(yè)純鈦拉伸試樣標距部分進行大面積激光沖擊強化處理,對未沖擊試樣和沖擊試樣在20°C、150°C、250°C以及350°C下進行拉伸試驗,結果表明工業(yè)純鈦抗拉強度隨溫度升高顯示出降低的趨勢。同一種溫度下激光沖擊試樣斷口頸縮現(xiàn)象比未沖擊試樣斷口要明顯,并且斷口形貌顯示激光沖擊試樣的塑性更好。溫度變化對TA2工業(yè)純鈦斷裂類型的影響非常明顯,常溫下TA2工業(yè)純鈦拉伸斷裂類型屬于脆性斷裂,當拉伸溫度逐漸提高時,工業(yè)純鈦表現(xiàn)出更加優(yōu)異的塑性性能,斷裂形式也逐漸轉變?yōu)榛旌蠑嗔押晚g性斷裂。(2)研究了激光沖擊TA2工業(yè)純鈦微觀組織和顯微硬度分布,以及微觀組織結構變化和顯微硬度變化的內(nèi)在聯(lián)系:對不同拉伸溫度的TA2工業(yè)純鈦斷口區(qū)微觀組織和顯微硬度進行了深入的研究,結果表明激光沖擊后的TA2工業(yè)純鈦晶粒細化明顯,有大量變形孿晶、位錯和“透鏡狀”相變馬氏體??產(chǎn)生。激光誘導產(chǎn)生的馬氏體相比于鋼鐵中的要細小很多,且性質(zhì)不穩(wěn)定。當溫度逐漸升高至350°C后,晶內(nèi)相變馬氏體發(fā)生?→??逆相變,并且隨著溫度的升高逐漸消失。發(fā)現(xiàn)?晶粒都有不同程度的變大,但是幅度不是很均勻,亞晶粒長大較為明顯。激光沖擊強化處理顯著提高了TA2工業(yè)純鈦的硬度,隨著拉伸溫度的提高硬度有所降低,但是幅度不是很大。又因為拉伸斷裂產(chǎn)生嚴重塑性變形后,塑性變形過程中流動應力不斷增加,并且有大量位錯和形變孿晶產(chǎn)生,位錯相互作用,在流動應力的作用下彌散速度加大,釘扎效應增強,又會有新的位錯源產(chǎn)生導致顯微硬度提高。因此,溫度升高晶粒變大引起的軟化和拉伸機械變形引起的硬化兩者共同作用,使得硬度變化不是很大。(3)研究了激光沖擊工業(yè)純鈦拉伸試樣在不同溫度下塑性變形微觀演變機制以及同一試樣不同區(qū)域位置的塑性變形演變機制:對激光沖擊TA2工業(yè)純鈦拉伸試樣在不同溫度下拉伸區(qū)的TEM圖像微觀組織進行了全面的研究,研究發(fā)現(xiàn)不同溫度下拉伸試樣的變形行為模型可用位錯分步激活和孿晶解體模型來解釋。激光沖擊使得TA2工業(yè)純鈦生成孿晶,由于工業(yè)純鈦的層錯能低,中高溫和變形外力對位錯有激活作用,孿晶中積塞的位錯被激活,不斷穿過孿晶界,當溫度和外力到達某個臨界值,孿晶界基本解體,孿晶消失,積塞的位錯彌散均勻分布。在這個過程中,孿晶界會吸納其反應物——不全位錯,從而提高材料塑性性能。當溫度升高到350°C以上時,塑性變形行為的位錯分步激活和孿晶解體模型基本結束,這段變形行為中位錯的形核及運動在塑性變形過程中成為主要機制。不同斷口區(qū)域的微觀組織的不同,主要是孿晶界造成的結果,嚴重塑性變形區(qū)域的TA2工業(yè)純鈦內(nèi)部生成大量孿晶簇,孿晶界的存在阻礙了受外應力激活位錯的運動。
[Abstract]:Titanium and titanium alloy have the advantages of low density, high specific strength, good mechanical property, strong corrosion resistance and the like in the fields of aerospace, marine development and automobile industry. Generally, the high-temperature service environment of titanium and its alloy structural parts is below 500 擄 C, and the traditional surface treatment method can not meet the requirement of high-temperature strengthening of titanium and its alloy structural parts. Laser shock peening is a new kind of surface treatment technology, which is widely used in surface modification of metallic materials. At present, it has not been found that the research on the tensile mechanical properties of pure titanium under different temperatures has not been found in the laser shock peening industry, but it has not been reported on the microstructure evolution and plastic deformation behavior of pure titanium under different temperatures. Aiming at the above problems, this paper takes TA2 industrial pure titanium as the research object, and develops the characteristics of tensile properties and fracture morphology, microstructure evolution and microhardness distribution of pure titanium at different temperatures. The results are as follows: (1) The tensile properties and fracture morphology of pure titanium in laser shock TA2 industrial pure titanium at different temperatures are studied. The rule of the evolution of high temperature tensile deformation behavior and fracture morphology is obtained: a large area laser impact strengthening treatment is carried out on a TA2 industrial pure titanium tensile sample standard distance part, and the unimpact sample and the impact sample are subjected to a tensile test at 20 DEG C, 150 DEG C, 250 DEG C and 350 DEG C, The results show that the tensile strength of pure titanium decreases with the increase of temperature. At the same temperature, the fracture neck shrinkage of the laser impact specimen is obviously lower than that of the non-impact specimen, and the fracture morphology shows that the plastic of the laser impact specimen is better. The effect of temperature change on the fracture type of pure titanium in TA2 industry is very obvious. The tensile fracture type of pure titanium in TA2 industry belongs to brittle fracture at normal temperature. When the tensile temperature is gradually increased, the industrial pure titanium shows more excellent plastic property. The fracture form is also gradually transformed into mixed fracture and ductile fracture. (2) The inner relationship between microstructure and microhardness distribution of pure titanium in laser shock TA2 industrial pure titanium was studied. The microstructure and microhardness of TA2 industrial pure titanium fracture zone were studied deeply. The results show that the crystal grain refinement of TA2 industrial pure titanium after laser shock is obvious, and there are a large number of deformed columnar crystals and dislocations. "lenticular" Phase change martensite? Generates. Laser-induced martensite is much smaller and unstable than in steel. When the temperature gradually rises to 350 擄 C, the phase-change martensite in the crystal occurs? What's the matter? the inverse phase change and gradually disappears as the temperature increases. Discovery? The crystal grains have different degrees of change, but the amplitude is not very uniform, and the subgrain growth is obvious. Laser shock peening significantly improved the hardness of pure titanium in TA2 industry, but the hardness decreased with the increase of tensile temperature, but the amplitude was not very large. In addition, after severe plastic deformation is generated due to tensile fracture, the flow stress in the plastic deformation process is continuously increased, and a large number of dislocations and deformations are generated, dislocation interaction is generated, the dispersion speed is increased under the action of flow stress, and the pinning effect is enhanced, a new dislocation source may also result in an increase in microhardness. As a result, both the softening and stretching mechanical deformation caused by the large temperature increase grain function together so that the hardness variation is not large. (3) The mechanism of plastic deformation of pure titanium tensile specimen under different temperatures and the mechanism of plastic deformation evolution in different regions of the same specimen were studied. In this paper, a comprehensive study was conducted on the microstructure of TEM images of laser shock TA2 industrial pure titanium tensile test specimens at different temperatures. The results show that the deformation behavior model of tensile specimens under different temperatures can be explained by the dislocation step activation and the split-crystal breakdown model. The laser shock causes the TA2 industrial pure titanium to generate the polycrystalline silicon crystal, because the layer of the industrial pure titanium is low, the middle and high temperature and the deformation external force have an active effect on the dislocation, the dislocation of the product plug in the polycrystalline silicon crystal is activated, the crystal grain boundary is continuously passed, and when the temperature and the external force reach a certain critical value, the grain boundary of the polycrystalline silicon is basically disintegrated, the crystals disappear and the dislocation of the product plug is uniformly distributed. In this process, the grain boundary will absorb its reactant _ non-complete dislocation, thus improving the plastic property of the material. When the temperature rises above 350 擄 C, the dislocation step-by-step activation of plastic deformation behavior and the collapse model of crystal structure are basically finished, and the nucleation and movement of dislocations in this deformation behavior become the main mechanism during the plastic deformation process. The microstructure of different fracture zones is different, mainly because of the result of grain boundary, and a large number of crystal clusters are generated inside TA2 industrial pure titanium in severe plastic deformation area.
【學位授予單位】：江蘇大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.23;TG665
本文編號：2312217
[Abstract]:Titanium and titanium alloy have the advantages of low density, high specific strength, good mechanical property, strong corrosion resistance and the like in the fields of aerospace, marine development and automobile industry. Generally, the high-temperature service environment of titanium and its alloy structural parts is below 500 擄 C, and the traditional surface treatment method can not meet the requirement of high-temperature strengthening of titanium and its alloy structural parts. Laser shock peening is a new kind of surface treatment technology, which is widely used in surface modification of metallic materials. At present, it has not been found that the research on the tensile mechanical properties of pure titanium under different temperatures has not been found in the laser shock peening industry, but it has not been reported on the microstructure evolution and plastic deformation behavior of pure titanium under different temperatures. Aiming at the above problems, this paper takes TA2 industrial pure titanium as the research object, and develops the characteristics of tensile properties and fracture morphology, microstructure evolution and microhardness distribution of pure titanium at different temperatures. The results are as follows: (1) The tensile properties and fracture morphology of pure titanium in laser shock TA2 industrial pure titanium at different temperatures are studied. The rule of the evolution of high temperature tensile deformation behavior and fracture morphology is obtained: a large area laser impact strengthening treatment is carried out on a TA2 industrial pure titanium tensile sample standard distance part, and the unimpact sample and the impact sample are subjected to a tensile test at 20 DEG C, 150 DEG C, 250 DEG C and 350 DEG C, The results show that the tensile strength of pure titanium decreases with the increase of temperature. At the same temperature, the fracture neck shrinkage of the laser impact specimen is obviously lower than that of the non-impact specimen, and the fracture morphology shows that the plastic of the laser impact specimen is better. The effect of temperature change on the fracture type of pure titanium in TA2 industry is very obvious. The tensile fracture type of pure titanium in TA2 industry belongs to brittle fracture at normal temperature. When the tensile temperature is gradually increased, the industrial pure titanium shows more excellent plastic property. The fracture form is also gradually transformed into mixed fracture and ductile fracture. (2) The inner relationship between microstructure and microhardness distribution of pure titanium in laser shock TA2 industrial pure titanium was studied. The microstructure and microhardness of TA2 industrial pure titanium fracture zone were studied deeply. The results show that the crystal grain refinement of TA2 industrial pure titanium after laser shock is obvious, and there are a large number of deformed columnar crystals and dislocations. "lenticular" Phase change martensite? Generates. Laser-induced martensite is much smaller and unstable than in steel. When the temperature gradually rises to 350 擄 C, the phase-change martensite in the crystal occurs? What's the matter? the inverse phase change and gradually disappears as the temperature increases. Discovery? The crystal grains have different degrees of change, but the amplitude is not very uniform, and the subgrain growth is obvious. Laser shock peening significantly improved the hardness of pure titanium in TA2 industry, but the hardness decreased with the increase of tensile temperature, but the amplitude was not very large. In addition, after severe plastic deformation is generated due to tensile fracture, the flow stress in the plastic deformation process is continuously increased, and a large number of dislocations and deformations are generated, dislocation interaction is generated, the dispersion speed is increased under the action of flow stress, and the pinning effect is enhanced, a new dislocation source may also result in an increase in microhardness. As a result, both the softening and stretching mechanical deformation caused by the large temperature increase grain function together so that the hardness variation is not large. (3) The mechanism of plastic deformation of pure titanium tensile specimen under different temperatures and the mechanism of plastic deformation evolution in different regions of the same specimen were studied. In this paper, a comprehensive study was conducted on the microstructure of TEM images of laser shock TA2 industrial pure titanium tensile test specimens at different temperatures. The results show that the deformation behavior model of tensile specimens under different temperatures can be explained by the dislocation step activation and the split-crystal breakdown model. The laser shock causes the TA2 industrial pure titanium to generate the polycrystalline silicon crystal, because the layer of the industrial pure titanium is low, the middle and high temperature and the deformation external force have an active effect on the dislocation, the dislocation of the product plug in the polycrystalline silicon crystal is activated, the crystal grain boundary is continuously passed, and when the temperature and the external force reach a certain critical value, the grain boundary of the polycrystalline silicon is basically disintegrated, the crystals disappear and the dislocation of the product plug is uniformly distributed. In this process, the grain boundary will absorb its reactant _ non-complete dislocation, thus improving the plastic property of the material. When the temperature rises above 350 擄 C, the dislocation step-by-step activation of plastic deformation behavior and the collapse model of crystal structure are basically finished, and the nucleation and movement of dislocations in this deformation behavior become the main mechanism during the plastic deformation process. The microstructure of different fracture zones is different, mainly because of the result of grain boundary, and a large number of crystal clusters are generated inside TA2 industrial pure titanium in severe plastic deformation area.
【學位授予單位】：江蘇大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.23;TG665
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