【摘要】：隨著微納米加工技術(shù)的不斷發(fā)展,單晶鍺等脆性材料在紅外光學(xué)、微機(jī)電系統(tǒng)等高科技領(lǐng)域的應(yīng)用日益廣泛,這些領(lǐng)域?qū)Σ牧系谋砻婕庸ぞ纫呀?jīng)達(dá)到了納米量級(jí),這就需要超精密的加工理論和方法作為支撐。在納米加工過(guò)程中,為了使單晶鍺等脆性材料以塑性切削的方式去除從而獲得高質(zhì)量的光學(xué)表面,其關(guān)鍵是控制條件實(shí)現(xiàn)脆塑轉(zhuǎn)變,這往往需要把切削深度控制在納米量級(jí)。由于單晶鍺是硬脆材料并存在各向異性,確定脆塑轉(zhuǎn)變臨界切削厚度對(duì)實(shí)現(xiàn)脆塑轉(zhuǎn)變從而切削出一致光滑的表面至關(guān)重要。但單晶鍺等脆性材料的塑性域切削一直沒(méi)有形成統(tǒng)一的理論認(rèn)識(shí)和加工方法。本文借助分子動(dòng)力學(xué)仿真、納米壓痕和劃痕實(shí)驗(yàn)及理論分析等方法研究了單晶鍺不同晶面在切削過(guò)程中的塑性域切削機(jī)理。通過(guò)對(duì)單晶鍺脆塑轉(zhuǎn)變機(jī)理的研究,獲取了單晶鍺脆塑轉(zhuǎn)變臨界切削深度。這對(duì)于深入理解單晶鍺等脆性材料納米切削機(jī)理具有重要的理論意義和實(shí)用價(jià)值。首先對(duì)單晶鍺(100)、(110)和(111)晶面進(jìn)行納米壓痕仿真和實(shí)驗(yàn)研究。并建立了壓痕仿真模型。對(duì)不同晶面的微觀變形機(jī)理和力學(xué)特性進(jìn)行了深入探究。研究結(jié)果表明:單晶鍺(111)晶面相比于其它晶面具有較小的彈性模量和硬度值,這種現(xiàn)象實(shí)驗(yàn)和仿真結(jié)論基本一致。隨著壓入深度增加,單晶鍺各晶面的硬度與彈性模量都表現(xiàn)出尺寸效應(yīng)現(xiàn)象,并且在加載和卸載過(guò)程中有突進(jìn)和突退現(xiàn)象發(fā)生,劃分了單晶鍺在不同加載深度下對(duì)應(yīng)的不同變形階段。其次,對(duì)單晶鍺不同晶面進(jìn)行變深度切削的分子動(dòng)力學(xué)仿真,并建立了變深度切削模型,通過(guò)對(duì)仿真切削過(guò)程中切屑的形成和切削力的變化分析得到了單晶鍺彈性變形和塑性去除的兩個(gè)不同階段,并得到了彈塑性轉(zhuǎn)變的臨界切削厚度和切削力,(100)晶面發(fā)生彈性變形和塑性切削的臨界切削厚度和切削力分別為0.48nm和42nN。然后研究了不同的切削速度、切削厚度、切削晶面和刀具前角等加工參數(shù)對(duì)單晶鍺彈塑性變形和表面質(zhì)量的影響,從去除方式、原子變化、勢(shì)能和切削力變化的角度分析,得出了不同切削參數(shù)對(duì)單晶鍺內(nèi)部結(jié)構(gòu)變形和表面質(zhì)量的影響機(jī)制,以及不同晶面的各向異性差異。最后,通過(guò)單晶鍺納米刻劃實(shí)驗(yàn),確定了單晶鍺脆塑轉(zhuǎn)變的臨界切削深度和范圍及變化規(guī)律,并對(duì)切削過(guò)程中的影響因素進(jìn)行了分析。同時(shí)針對(duì)單晶鍺刻劃中的各向異性現(xiàn)象進(jìn)行了不同晶面的刻劃實(shí)驗(yàn),總結(jié)脆塑轉(zhuǎn)變臨界切削深度的各向異性。并對(duì)單晶鍺脆塑轉(zhuǎn)變臨界切削深度進(jìn)行了理論預(yù)測(cè)。結(jié)果表明:(100)晶面因其具有最小表面密度、最深脆塑轉(zhuǎn)變深度,在劃痕過(guò)程中發(fā)生脆塑轉(zhuǎn)變最晚,而且隨著劃痕速度的增加,脆塑轉(zhuǎn)變臨界深度和臨界載荷也相應(yīng)增加。
[Abstract]:With the development of micro and nano processing technology, brittle materials such as single crystal germanium have been widely used in infrared optics, micro electromechanical systems and other high-tech fields. The surface processing accuracy of these fields has reached nanometer order of magnitude. This needs the ultra-precision processing theory and the method as the support. In the process of nanocrystalline machining, in order to remove the brittle materials such as germanium by plastic cutting and obtain high quality optical surfaces, the key point is to control the conditions to achieve brittle plastic transition, which often requires the depth of cutting to be controlled in nanometer order. Because single crystal germanium is a hard brittle material and anisotropy exists, it is very important to determine the critical cutting thickness of brittle plastic transition to realize brittle plastic transition and to cut a uniformly smooth surface. However, the plastic domain cutting of single crystal germanium and other brittle materials has not formed a unified theoretical understanding and processing methods. In this paper, the plastic cutting mechanism of single crystal germanium in different crystal faces in cutting process has been studied by means of molecular dynamics simulation, nano-indentation and scratch experiments and theoretical analysis. The critical cutting depth of single crystal germanium brittle plastic transition was obtained by studying the mechanism of single crystal germanium brittle plastic transition. It has important theoretical significance and practical value for further understanding the mechanism of nanoscale cutting of single crystal germanium and other brittle materials. At first, the nanocrystalline indentation simulation and experimental study of single crystal germanium (100), (110) and (111) crystal face were carried out. A simulation model of indentation is established. The microscopic deformation mechanism and mechanical properties of different crystal planes were studied. The results show that the values of elastic modulus and hardness of single crystal germanium (111) crystal face are smaller than those of other crystal masks, which is consistent with the experimental and simulation results. With the increase of indentation depth, the hardness and elastic modulus of each plane of single crystal germanium show the phenomenon of size effect, and during loading and unloading, the phenomenon of breakout and sudden retreat occurs. The different deformation stages of single crystal germanium at different loading depths were divided. Secondly, the molecular dynamics simulation of variable depth cutting on different crystal faces of single crystal germanium was carried out, and the model of variable depth cutting was established. Two different stages of elastic deformation and plastic removal of single crystal germanium were obtained by analyzing the formation of chip and the change of cutting force in the process of simulated cutting. The critical cutting thickness and cutting force of elastic-plastic transformation are obtained. The critical cutting thickness and cutting force of (100) elastic deformation and plastic cutting are 0.48nm and 42 N, respectively. Then, the effects of different cutting speed, cutting thickness, cutting crystal plane and cutting tool front angle on the elastoplastic deformation and surface quality of single crystal germanium are studied. The changes of removal mode, atomic change, potential energy and cutting force are analyzed. The influence mechanism of different cutting parameters on the deformation and surface quality of single crystal germanium was obtained, and the anisotropy of different crystal planes was also obtained. Finally, the critical cutting depth and range of single crystal germanium brittle-ductile transition and its variation law were determined by the experiment of single crystal germanium nanocrystalline delineation, and the influencing factors in the cutting process were analyzed. At the same time, the anisotropy of single crystal germanium has been studied and the anisotropy of critical cutting depth of brittle plastic transition has been summarized. The critical cutting depth of single crystal germanium brittle plastic transition was predicted theoretically. The results show that: (100) because of its minimum surface density and the deepest depth of brittle plastic transition, the brittle plastic transition occurs late in the scratch process, and the critical depth and critical load of brittle plastic transition increase with the increase of scratch velocity.
【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TN304.11

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