【摘要】：本文選擇Zr50.7Cu28Ni9Al12.3塊體非晶合金作為研究對(duì)象,結(jié)合非晶合金在實(shí)際成形和應(yīng)用方面面臨的實(shí)際應(yīng)力條件問(wèn)題,分別進(jìn)行氣體自由脹形和單邊缺口梁法三點(diǎn)彎曲試驗(yàn),系統(tǒng)研究了Zr基非晶合金在高溫和室溫下處于復(fù)雜應(yīng)力和應(yīng)變狀態(tài)時(shí)的變形過(guò)程。通過(guò)控制變形溫度、氣體壓力和加壓時(shí)間三個(gè)參數(shù)研究了不同因素對(duì)非晶合金氣體自由脹形過(guò)程的影響。借助金相顯微鏡(OM)對(duì)非晶合金脹形高度和厚向應(yīng)變進(jìn)行研究。結(jié)果表明,隨著變形溫度和氣體壓力的增加,非晶合金的變形能力增強(qiáng),脹形高度和厚向應(yīng)變?cè)黾?但是由于材料的流變導(dǎo)致其厚度不均勻程度加劇。在壓力為2 MPa時(shí)非晶合金脹形件容易發(fā)生破裂失效。借助差示掃描量熱儀(DSC)和透射電子顯微鏡(TEM)研究了非晶合金脹形過(guò)程中的結(jié)構(gòu)演變規(guī)律。研究發(fā)現(xiàn),隨著變形溫度的升高和加壓時(shí)間延長(zhǎng),非晶合金的晶化程度加劇,同時(shí)在非晶合金脹形件的不同部位也出現(xiàn)明顯的晶化程度的差異,這是由于應(yīng)變誘發(fā)晶化導(dǎo)致的,非晶合金脹形件越接近其脹形最高點(diǎn),所受到的應(yīng)變?cè)酱?晶化程度亦相應(yīng)增加。借助TEM觀察了非晶合金脹形件的微觀結(jié)構(gòu),結(jié)果表明,在變形溫度較低時(shí),晶化相以塊狀存在,隨著變形溫度的升高晶化相尺寸逐漸增加。當(dāng)溫度繼續(xù)升高到一定程度時(shí)從非晶基體中析出針狀晶化相,這將導(dǎo)致非晶合金的強(qiáng)度和塑性等力學(xué)性能的顯著下降。借助數(shù)字圖像相關(guān)方法(DIC)研究了單邊開(kāi)不同寬度U型缺口的非晶合金彎曲試樣在三點(diǎn)彎曲過(guò)程中缺口附近的應(yīng)變場(chǎng)的變化規(guī)律。彎曲試驗(yàn)的載荷-位移曲線表明,在三點(diǎn)彎曲過(guò)程中,Zr基非晶合金并沒(méi)有出現(xiàn)明顯的屈服現(xiàn)象,隨著缺口尺寸減小,非晶合金三點(diǎn)彎曲的最大載荷和最大彎曲位移逐漸減小,這是由于應(yīng)變集中程度增加導(dǎo)致韌性下降。利用DIC得到的缺口附近的應(yīng)變場(chǎng)分布結(jié)果表明,缺口附近區(qū)域的線應(yīng)變和切應(yīng)變均出現(xiàn)應(yīng)變集中現(xiàn)象,且應(yīng)變值隨著時(shí)間的增加呈現(xiàn)逐漸增加的趨勢(shì)。隨著缺口尺寸減小,應(yīng)變集中現(xiàn)象更加明顯,但缺口寬度的減小會(huì)造成缺口附近區(qū)域最大應(yīng)變值的減小。利用掃描電子顯微鏡(SEM)觀察了缺口附近區(qū)域和斷口兩側(cè)的剪切帶分布特征。剪切帶增殖和擴(kuò)展是局部切應(yīng)變超出彈性應(yīng)變極限造成的,研究發(fā)現(xiàn),隨著缺口尺寸減小,缺口附近區(qū)域剪切帶尺寸和數(shù)量減小。借助SEM對(duì)非晶合金彎曲試樣斷口進(jìn)行觀察,分析發(fā)現(xiàn),彎曲試樣斷口存在裂紋擴(kuò)展區(qū)和快速斷裂區(qū)兩個(gè)截然不同的區(qū)域。隨著缺口尺寸減小,應(yīng)變集中程度增加,非晶合金彎曲試樣的韌性下降,因此裂紋擴(kuò)展區(qū)的寬度和快速斷裂區(qū)的韌窩狀微觀結(jié)構(gòu)的尺寸均呈逐漸下降的趨勢(shì)。
[Abstract]:In this paper, Zr50.7Cu28Ni9Al12.3 bulk amorphous alloy is chosen as the object of study. Combined with the actual stress conditions of the amorphous alloy in actual forming and application, the gas free bulging test and one-sided notched beam three-point bending test are carried out, respectively. The deformation process of Zr based amorphous alloy in complex stress and strain state at high temperature and room temperature was systematically studied. The effect of different factors on the gas free bulging process of amorphous alloy was studied by controlling deformation temperature, gas pressure and pressure time. The bulging height and thick strain of amorphous alloy were studied by metallographic microscope (OM). The results show that with the increase of deformation temperature and gas pressure, the deformation ability of amorphous alloy increases, the bulging height and thick strain increase, but the thickness inhomogeneity is aggravated due to the rheology of the material. When the pressure is 2 MPa, the bulging part of amorphous alloy is prone to fracture failure. By means of differential scanning calorimeter (DSC) and transmission electron microscope (TEM), the structure evolution of amorphous alloy during bulging was studied. It is found that the crystallization degree of amorphous alloy increases with the increase of deformation temperature and pressure time, and there are obvious differences of crystallization degree in different parts of bulging part of amorphous alloy, which is caused by strain induced crystallization. The closer the bulging part of amorphous alloy is to its bulging peak, the greater the strain is and the degree of crystallization increases accordingly. The microstructure of bulging part of amorphous alloy was observed by TEM. The results show that the crystalline phase exists as a block when the deformation temperature is low, and the size of crystallization phase increases gradually with the increase of deformation temperature. When the temperature continues to rise to a certain extent, a needle-like crystallization phase is precipitated from the amorphous matrix, which will lead to a significant decrease in mechanical properties such as strength and plasticity of the amorphous alloy. By means of digital image correlation method (DIC), the variation of strain field near the notch in three point bending process of amorphous alloy bending specimens with different widths of U notches is studied. The load-displacement curve of bending test shows that there is no obvious yield phenomenon in Zr-based amorphous alloy during three-point bending. With the decrease of notch size, the maximum load and maximum bending displacement of three-point bending of amorphous alloy decrease gradually. This is due to an increase in strain concentration resulting in a decrease in toughness. The results of the strain field distribution near the notch obtained by DIC show that both the linear strain and the shear strain in the region near the notch show the phenomenon of strain concentration and the strain value increases gradually with the increase of time. With the decrease of the notch size, the strain concentration becomes more obvious, but the decrease of the notch width will result in the decrease of the maximum strain value in the region near the notch. The distribution characteristics of shear bands near the notch and on both sides of the fracture were observed by scanning electron microscopy (SEM). The propagation and propagation of shear band are caused by the local shear strain exceeding the elastic strain limit. It is found that the size and number of shear band near the notch decrease with the decrease of notch size. The fracture surface of amorphous alloy bending specimen was observed by SEM. It was found that there were two distinct zones of crack growth zone and fast fracture zone on the fracture surface of amorphous alloy. With the decrease of notch size and the increase of strain concentration, the toughness of amorphous alloy bending specimens decreases, so the width of crack growth zone and the size of dimple microstructure in fast fracture zone tend to decrease gradually.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG139.8

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