【摘要】：在提高金屬材料強(qiáng)度方法方面，晶粒細(xì)化是在不影響材料韌性的情況下提高金屬強(qiáng)度的最有效方法之一。在諸多通過劇烈塑性變形的晶粒細(xì)化工藝方法中，等徑角通道擠壓技術(shù)（ECAE, Equal Channel Angle Extrusion）作為一種典型有效的方法，已被廣泛應(yīng)用于各種金屬材料的晶粒細(xì)化。純銅作為一種在各個(gè)領(lǐng)域被廣泛使用的材料，其晶粒細(xì)化一直受到研究者的關(guān)注。 在本文工作中，為了揭示通過ECAE制備的超細(xì)晶Cu的劇塑性流變行為及其本構(gòu)關(guān)系，首先對超細(xì)晶Cu在不同應(yīng)變率下的力學(xué)特性進(jìn)行了研究，然后結(jié)合納米壓痕技術(shù)對超細(xì)晶銅在不同道次下的硬度進(jìn)行研究分析，研究了不同道次對純銅熱激活體積和應(yīng)變率敏感性的影響性，對變形機(jī)理進(jìn)行分析，最后為了對這種超細(xì)晶Cu的塑性流動(dòng)本構(gòu)關(guān)系進(jìn)行研究，首先基于金屬塑性流動(dòng)的熱激活位錯(cuò)滑移機(jī)理，以典型鋼DH36等金屬材料塑性流動(dòng)本構(gòu)關(guān)系研究為基礎(chǔ)，再結(jié)合超細(xì)晶銅Cu的劇塑性流變的特點(diǎn)，獲得了DH36鋼和超細(xì)晶Cu的塑性流動(dòng)本構(gòu)關(guān)系，本論文研究內(nèi)容如下： （1）為了測試超細(xì)晶Cu在不同應(yīng)變率下的劇塑性變形力學(xué)特性，利用MTS試驗(yàn)機(jī)與分離式Hopkinson壓桿技術(shù)對超細(xì)晶Cu材料分別了進(jìn)行10-3/s和約4,000/s應(yīng)變率下的力學(xué)特性進(jìn)行了測試，結(jié)果表明在10-3/s應(yīng)變率下，隨著擠壓道次數(shù)的增加，Cu的流動(dòng)應(yīng)力呈現(xiàn)先增大而后逐漸減小至穩(wěn)定狀態(tài)的趨勢，而在約4,000/s應(yīng)變率的動(dòng)態(tài)加載下，隨著擠壓道次數(shù)的增加，材料的流動(dòng)行為則表現(xiàn)為逐漸增大進(jìn)而穩(wěn)定的趨勢。 （2）為了研究超細(xì)晶Cu硬度與擠壓道次、應(yīng)變率的關(guān)系，基于納米壓痕技術(shù)，通過應(yīng)變率階躍試驗(yàn)，獲得材料在不同應(yīng)變率下的硬度隨著道次增加的變化關(guān)系，通過對其應(yīng)變率敏感性以及熱激活體積進(jìn)行分析發(fā)現(xiàn)，隨著變形的增加，超細(xì)晶Cu的應(yīng)變率敏感性呈現(xiàn)增加的趨勢，而熱激活體積則是先減小而后趨于穩(wěn)定的趨勢。 （3）為了揭示超細(xì)晶Cu晶界取向?qū)α鲃?dòng)應(yīng)力的影響，文中基于Gourdet的再結(jié)晶以及晶界遷移理論的三參數(shù)本構(gòu)模型推導(dǎo)出流動(dòng)應(yīng)力與晶界取向演化、亞晶內(nèi)位錯(cuò)密度以及晶粒尺度的關(guān)系式，揭示了隨著大角晶界比例的增加，材料的屈服應(yīng)力下降，進(jìn)而對應(yīng)變率敏感性以及熱激活體積的變化趨勢進(jìn)行理論解釋。 （4）為了研究不同擠壓道次下材料的微觀結(jié)構(gòu)，基于背散射電子衍射（EBSD, electronbackscattering diffraction）技術(shù)，，對4種代表道次的試樣進(jìn)行了微觀分析，結(jié)果顯示，隨著擠壓道次增加到32道次，大角晶界的比例增加到41%，晶粒尺度下降到341nm；而對于具有相同等效變形的試樣，晶粒尺度以及大角晶界的比例會(huì)嚴(yán)重影響材料的力學(xué)性能。 （5）為了獲得超細(xì)晶Cu的劇塑性流動(dòng)本構(gòu)方程，首先基于物理概念塑性流動(dòng)本構(gòu)理論，結(jié)合系統(tǒng)試驗(yàn)與唯象本構(gòu)方法，對典型金屬材料DH-36鋼等幾種材料的塑性流動(dòng)本構(gòu)關(guān)系進(jìn)行了系統(tǒng)研究。然而，通過對這類模型進(jìn)行理論分析發(fā)現(xiàn)，這類物理概念模型并不適用于材料劇塑性變形。為此，文中作者借鑒了這些金屬的塑性流動(dòng)本構(gòu)關(guān)系研究思路和方法，基于納米壓痕試驗(yàn)結(jié)果，建立了應(yīng)變率耦合下的劇塑性變形流動(dòng)本構(gòu)關(guān)系，通過與試驗(yàn)數(shù)據(jù)對照，模型預(yù)測結(jié)果與試驗(yàn)結(jié)果吻合良好。
[Abstract]:Grain refinement is one of the most effective methods to improve the strength of metal without affecting the toughness of the material. In the process of grain refinement through severe plastic deformation, ECAE, Equal Channel Angle Extrusion, as a typical effective method, has been used as a typical and effective method. Grain refinement is widely used in all kinds of metal materials. Pure copper is widely used as a material in various fields. Its grain refinement has been paid much attention by researchers.
In this work, in order to reveal the plastic rheological behavior and its constitutive relation of ultrafine crystal Cu prepared by ECAE, the mechanical properties of ultrafine crystal Cu under different strain rates were studied first, and then the hardness of ultrafine crystal copper under different channel times was studied by nano indentation technology, and the different channels were studied on pure copper. The effect of thermal activation volume and strain rate sensitivity is analyzed. Finally, in order to study the constitutive relationship of the plastic flow of this superfine crystal Cu, first based on the mechanism of the thermal activated dislocation slip of the metal plastic flow, based on the study of the plastic flow constitutive relation of the typical steel DH36 and other metal materials, then the superfine crystal is combined. The plastic flow constitutive relationship of DH36 steel and ultrafine grained Cu has been obtained by the plastic rheological behavior of Cu Cu.
(1) in order to test the mechanical and plastic deformation mechanical properties of superfine crystal Cu at different strain rates, the mechanical properties of ultra-fine crystal Cu materials under 10-3/s and 4000/s strain rate were tested by MTS test machine and separate Hopkinson pressure rod technique. The results showed that the flow of Cu under the 10-3/s strain rate, with the increase of the number of extrusion channels, the flow of Cu. The dynamic stress tends to increase first and then gradually decrease to the stable state, but under the dynamic loading of the strain rate of 4000/s, with the increase of the number of extrusion channels, the flow behavior of the material increases gradually and then the trend of stability.
(2) in order to study the relationship between the hardness of the superfine crystal and the strain rate of the extrusion channel and the strain rate, based on the nanoindentation technology, the strain rate step test was used to obtain the change of the hardness of the material at different strain rates with the increase of the channel. By analyzing the strain rate sensitivity and the thermal activation volume, the superfine crystal Cu was found to increase with the increase of the strain rate. The strain rate sensitivity showed an increasing trend while the thermal activation volume decreased first and then stabilized.
(3) in order to reveal the influence of the grain boundary orientation on the flow stress of the superfine crystal Cu, based on the recrystallization and the three parameter constitutive model of the grain boundary migration theory, the relationship between the flow stress and grain boundary orientation evolution, the intragranular dislocation density and the grain size are deduced, which reveals that the yield of the material increases with the increase of the grain boundary ratio in the large angle. A theoretical explanation is given for the variation of the force and the change trend of thermal activation volume.
(4) in order to study the microstructure of the material under different extrusion channels, the microanalysis of 4 representative sample samples was carried out based on EBSD (electronbackscattering diffraction) technology. The results showed that as the extrusion channel increased to 32 times, the proportion of the grain boundary in the large angle increased to 41%, and the grain size decreased to 341nm. For specimens with the same equivalent deformation, the ratio of grain size and large angle grain boundary will seriously affect the mechanical properties of the material.
(5) in order to obtain the plastic flow constitutive equation of superfine crystal Cu, based on the physical concept plastic flow constitutive theory and the system test and phenomenological constitutive method, the plastic flow constitutive relation of DH-36 steel, such as the typical metal material, is systematically studied. The physical conceptual model does not apply to the plastic deformation of the material. Therefore, the author draws on the research ideas and methods of the plastic flow constitutive relations of these metals. Based on the results of the nanoindentation test, the constitutive relation of the plastic deformation flow under the strain rate coupling is established. The model prediction results and the experimental results are compared with the experimental data. The fruit is in good agreement.
【學(xué)位授予單位】：西北工業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG146.11

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