本文選題：層片結(jié)構(gòu)　切入點(diǎn)：軟硬微區(qū)　出處：《太原理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：對(duì)于材料而言,不管均勻結(jié)構(gòu)或不均勻結(jié)構(gòu),其最終目標(biāo)都是為了得到優(yōu)異的力學(xué)性能。根據(jù)霍爾-佩奇定律,納米晶材料的屈服強(qiáng)度極高,可塑性極低,會(huì)迅速頸縮失穩(wěn)。粗晶材料有很好塑性,但犧牲了強(qiáng)度。為了兼具高屈服強(qiáng)度和良好塑性,需要增加其應(yīng)變硬化能力。為此,已有研究報(bào)道了多種增強(qiáng)增塑的策略。其中,梯度納米結(jié)構(gòu)和層片納米結(jié)構(gòu)使材料應(yīng)變硬化能力提高很多,也獲得了很好的強(qiáng)度塑性。梯度結(jié)構(gòu)硬化的原因是存在應(yīng)變梯度,導(dǎo)致塑性應(yīng)變不相容,但缺乏細(xì)致的變形物理及微結(jié)構(gòu)研究,不適合工業(yè)化生產(chǎn)。層片納米結(jié)構(gòu)材料的特點(diǎn)是層片狀的納米級(jí)微觀結(jié)構(gòu),軟硬相差值很大,甚至幾個(gè)量級(jí)。對(duì)其變形機(jī)理雖提出了背應(yīng)力概念及背應(yīng)力測(cè)試方法,但研究者對(duì)其認(rèn)識(shí)及計(jì)算方法存在較大差異,對(duì)層片納米結(jié)構(gòu)的應(yīng)變硬化機(jī)理及微結(jié)構(gòu)關(guān)系研究不深入,還沒有系統(tǒng)性認(rèn)識(shí)其演化規(guī)律,故有必要對(duì)層片納米結(jié)構(gòu)進(jìn)行剖析。從微元法和微結(jié)構(gòu)角度看,梯度納米結(jié)構(gòu)相當(dāng)于是一層層納米層片結(jié)構(gòu)組合而成的,其微結(jié)構(gòu)機(jī)理是相通的。因此,探究并揭示層片納米結(jié)構(gòu)的力學(xué)行為及其應(yīng)變硬化機(jī)理便具有很高的學(xué)術(shù)意義和應(yīng)用價(jià)值。本文選取10號(hào)鋼和多層板作為模型材料。利用冷軋10號(hào)鋼板得到超細(xì)晶的層片結(jié)構(gòu)以及熱軋多層板,然后退火處理調(diào)控微觀結(jié)構(gòu),得到軟硬不均勻分布,晶粒大小不同的組織。通過單軸準(zhǔn)靜態(tài)拉伸測(cè)試、顯微硬度測(cè)試、加卸載測(cè)試、應(yīng)力松弛測(cè)試及應(yīng)變場(chǎng)測(cè)試等,研究并分析其力學(xué)行為、背應(yīng)力硬化、林位錯(cuò)硬化及局部應(yīng)變?cè)茍D演化;借助光學(xué)顯微鏡(OM)、掃描電子顯微鏡(SEM)及透射電子顯微鏡(TEM)表征微觀結(jié)構(gòu)組織和觀察斷口形貌,最后分析并闡明了層片納米結(jié)構(gòu)的變形行為及其應(yīng)變硬化機(jī)理。論文的主要結(jié)論如下:(1)不同退火處理的層片結(jié)構(gòu)10號(hào)鋼試樣中存在軟-硬微區(qū)結(jié)構(gòu),且硬度差值及硬度分布不均勻性越大,塑性應(yīng)變不相容越明顯,導(dǎo)致背應(yīng)力越大,從而使背應(yīng)力硬化顯著提高加工硬化能力。拉伸時(shí),軟-硬微區(qū)層片結(jié)構(gòu)試樣表面的局部應(yīng)變是不均勻的,存在局部應(yīng)變場(chǎng)及局部應(yīng)變速率場(chǎng)。不均勻的軟硬微區(qū)結(jié)構(gòu)能有效抑制塑性變形初期的應(yīng)變局域化,避免過早頸縮失穩(wěn)。(2)10號(hào)鋼層片組織的瞬態(tài)應(yīng)變硬化實(shí)質(zhì)是變形時(shí)非均勻軟硬微區(qū)的塑性應(yīng)變不相容,產(chǎn)生背應(yīng)力,使Kernel平均晶粒取向差變大,從而增加幾何必需位錯(cuò)密度,導(dǎo)致背應(yīng)力硬化。同時(shí),可動(dòng)位錯(cuò)密度增加,激活體積減小以及位錯(cuò)運(yùn)動(dòng)受阻,導(dǎo)致產(chǎn)生交滑移和多滑移,引起位錯(cuò)纏結(jié)或交割,從而形成位錯(cuò)墻或位錯(cuò)界面,導(dǎo)致位錯(cuò)交互作用增強(qiáng),繼而產(chǎn)生林位錯(cuò)硬化。背應(yīng)力硬化和林位錯(cuò)硬化共同影響變形時(shí)的加工硬化過程。(3)大尺度不均勻復(fù)合板的力學(xué)行為與層片結(jié)構(gòu)10號(hào)鋼的相似,即硬度差值越大,結(jié)構(gòu)越不均勻,應(yīng)變硬化能力可能越強(qiáng),從而得較好強(qiáng)度與塑性匹配。復(fù)合板界面處的晶粒尺度存在梯度分布,靠近界面處的晶粒較大,心部晶粒較小。多層板界面很穩(wěn)定,可能是影響力學(xué)性能的一個(gè)關(guān)鍵因素。
[Abstract]:For the materials, regardless of uniform structure or uneven structure, its ultimate goal is to obtain excellent mechanical properties. According to Holzer Paige's law, nanocrystalline materials of high yield strength, plasticity is very low, will quickly necking instability. Coarse grained materials have good plasticity, but the expense of strength. In order to both high yield strength and good plasticity, the need to increase the strain hardening ability. Therefore, researchers have reported a variety of enhanced plasticizing strategies. Among them, gradient nano structure and nano structure layer material strain hardening ability to improve a lot, also won the strength of good plastic. Cause hardening of the gradient structure is there is strain gradient plastic strain, resulting in inconsistent, but the lack of detailed physical deformation and microstructure study, not suitable for industrialized production. The characteristics of lamellar nanostructured materials is nanometer lamellar microstructure, soft hard phase difference A large, even several orders of magnitude. The deformation mechanism is put forward the concept of back stress and back stress testing methods, but there is a big difference on the understanding and Research on the calculation method of depth of strain hardening, mechanism of lamellar nanostructure and microstructure studies, yet the evolution rules of the system knowledge. It is necessary to lamellar nanostructures were analyzed. From the micro element method and micro structure perspective, gradient nano structure is equivalent to a layer of nano lamellar structure formed by combining the micro structure mechanism is the same. Therefore, to explore and reveal the lamellar structure of the nanojunction mechanical behavior and strain hardening mechanism is very high the academic significance and application value. This paper selects 10 steel and plywood as model material. The use of cold rolled steel plate to be the No. 10 layer structure of ultra-fine grain hot rolling and multilayer board, then annealing microstructure control, get Soft and uneven distribution of grain size of different tissues. Through uniaxial quasi-static tensile test, microhardness test, loading test, stress relaxation test and strain field testing, research and analysis of its mechanical behavior, stress hardening, dislocation hardening and local Ying Bianyun forest graph evolution by means of optical microscope (OM); (SEM), scanning electron microscopy and transmission electron microscopy (TEM) microstructure and fractographic morphology characterization, finally analyzed and discussed the deformation behavior of lamellar nanostructure and strain hardening mechanism. Following the knot theory: (1) different annealing structure of 10 steel specimens are soft hard microstructure, hardness and hardness difference and uneven distribution of the larger plastic strain incompatibility is more obvious, leading to the back stress, so that the back stress hardening significantly improve work hardening ability. The tensile, soft hard micro layer The local strain surface sheet structure of the specimen is not uniform, the existence of local strain and local strain rate field. The uneven soft micro structure can effectively inhibit the plastic deformation of the initial strain localization, to avoid premature necking instability. (2) the transient strain No. 10 steel sheet of hard tissue is in essence uniform micro non deformation of soft and hard plastic strain incompatibility, produce back stress, the Kernel average grain misorientation increases, thereby increasing the density of geometrically necessary dislocations, resulting in hardening back stress. At the same time, the movable dislocation density increases and the activation volume decreases and the dislocation motion is blocked, resulting in cross slip and multiple slip. Delivery caused by entanglement or dislocation, thus forming dislocation walls or dislocation interface, resulting in enhanced dislocation interaction, and then generate the forest dislocation hardening back stress and hardening. Common dislocation hardening effect of hardening during deformation process. (3) a large scale The mechanical behavior of composite plate with uniform layer structure of 10 steel is similar to that of the hardness difference is bigger, the more uneven structure, strain hardening ability is stronger, and better strength and plasticity. The gradient distribution of grain size exists at the interface of composite plate, near the interface of grain is bigger, heart the grain is smaller. Multilayer interface is very stable, may be a key factor affecting the mechanical properties.

【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG142.1;TB383.1

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本文編號(hào)：1609276