本文選題：難熔合金 + 高熵合金��； 參考：《哈爾濱工業(yè)大學(xué)》2016年博士論文

【摘要】：高熵合金打破傳統(tǒng)合金以一種或兩種元素為主元的合金設(shè)計思路,以五種及五種以上元素為主元,具有熱力學(xué)上的高熵效應(yīng)、動力學(xué)上的緩慢擴散效應(yīng)、結(jié)構(gòu)上的嚴重晶格畸變效應(yīng)及性能上的雞尾酒效應(yīng)等特性,合金具有簡單的組織結(jié)構(gòu)及優(yōu)異的綜合性能。為開發(fā)新型高溫結(jié)構(gòu)材料,本文根據(jù)高熵合金的設(shè)計理念,采用真空電弧熔煉技術(shù)制備以難熔金屬元素為主元的Mo-Nb-Hf-Zr-Ti難熔高熵合金體系,并分別添加金屬元素Al、Cr或非金屬元素Si、B、C調(diào)整合金性能,研究添加元素對合金組織和性能的影響規(guī)律及機制。首先采用Thermo-calc軟件結(jié)合TCNI-5數(shù)據(jù)庫相圖計算預(yù)測MoNbHf ZrTi合金相組成,試驗研究等摩爾MoNbHfZrTi合金的相組成、顯微組織、相穩(wěn)定性、力學(xué)性能及熱變形行為,并研究了MoNbHfZr Ti合金中五種組成元素含量變化對合金組織和性能的影響規(guī)律。研究發(fā)現(xiàn):相圖計算與試驗結(jié)果一致,MoNbHfZrTi合金由單相體心立方(BCC)固溶體相組成,熱分析(DSC)和熱處理結(jié)果表明該BCC相具有極高的結(jié)構(gòu)穩(wěn)定性,在1450 oC以下沒有發(fā)生任何相變。鑄態(tài)合金和均勻化態(tài)合金室溫下的屈服強度分別為1719 MPa和1575 MPa,合金壓縮斷口屬于典型的脆性斷裂。在ε?=0.1 s-1及T=1200 oC下,合金屈服強度仍能達到750 MPa。MoNbHfZrTi合金在900 oC及以上溫度熱變形時,應(yīng)力-應(yīng)變曲線呈現(xiàn)典型的動態(tài)再結(jié)晶特征,連續(xù)動態(tài)再結(jié)晶和不連續(xù)動態(tài)再結(jié)晶同時發(fā)生,其中不連續(xù)動態(tài)再結(jié)晶占主導(dǎo)地位,變形溫度的升高和應(yīng)變速率的增加將弱化連續(xù)動態(tài)再結(jié)晶機制。MoNbHf ZrTi合金中各組元含量在11.11~27.27at.%之間時,合金仍由單相BCC固溶體相組成,與等摩爾MoNbHfZrTi合金相比,合金強度和硬度均降低,但在非等摩爾Mo-Nb-Hf-Zr-Ti合金中,Mo含量增加合金強度提高,Hf、Zr和Ti含量增加合金強度降低,Nb含量變化對合金強度影響不大。綜合考慮強度、塑性、密度及成本等方面的因素,選取綜合性能較好的Mo0.5NbHf0.5ZrTi(Mo0.5Hf0.5)合金作為基體合金,分別添加Al或Cr元素研究合金組織和性能的變化規(guī)律。研究發(fā)現(xiàn)少量的Al或Cr元素可以固溶入基體相BCC1中,較多Al元素的添加合金將形成與BCC1晶格常數(shù)相近的新的固溶相BCC2相,基體相BCC1富集Mo和Nb元素,BCC2相富集Zr和Hf元素;Cr元素添加后合金中形成MgCu2型Laves相(Nb,Hf,Zr,Ti)-(Mo,Cr)2。Mo0.5NbHf0.5ZrTiAl0.3(Al0.3)和Mo0.5NbHf0.5ZrTiCr0.3(Cr0.3)合金熱處理后分別析出更多的BCC2相和Laves相。少量Al或Cr元素的添加可以提高合金強度同時改善合金塑性。隨Al元素含量增加合金強度有少量提高塑性降低,隨Cr元素含量增加合金強度逐漸提高,強度的提高主要歸因于Laves相的形成。非金屬元素B、Si或C元素添加到Mo0.5NbHf0.5ZrTi合金中形成了硼化物、硅化物或碳化物增強的Mo0.5NbHf0.5ZrTi難熔高熵合金。研究發(fā)現(xiàn):合金基體相仍為BCC固溶相,硼化物增強相為MB2相,其中M為Mo、Nb、Hf、Zr、Ti元素,硅化物增強相為M5Si3相,其中M為Mo、Nb、Hf、Zr、Ti元素,碳化物增強相為MC,其中M為Hf、Nb、Zr、Ti元素。B、Si或C與金屬元素之間的二元合金混合焓值越負即結(jié)合能越強所形成的硼化物、硅化物或碳化物中金屬元素的含量越高。少量B、Si或C元素的添加,合金的強度提高同時塑性也得到改善,塑性的提高主要歸因于細晶強化及基體相固溶強化度的降低,而較多B、Si或C元素的添加提高合金強度的同時降低了合金的塑韌性。研究同時添加Al、Cr、B、Si或C其中幾種元素后Mo-Nb-Hf-Zr-Ti合金的組織結(jié)構(gòu)發(fā)現(xiàn):同時添加多種合金化元素后Mo-Nb-Hf-Zr-Ti合金仍由BCC固溶相作為基體相,而其它相的形成種類和數(shù)量與加入的合金化元素的含量及合金化元素與基體合金組成元素的結(jié)合能有緊密的聯(lián)系。如在合金MoNb1.5Hf0.3Zr0.5Ti1.5Al0.2Cr0.2C0.05B0.05Si0.05中盡管Si、C、B三種元素的含量是相同的,但是C元素與Mo、Nb、Hf、Zr、Ti的結(jié)合能最強,因此合金中形成的第二相主要為碳化物相。
[Abstract]:High entropy alloy has broken the design idea of alloy with one or two elements as the main element, with five and more than five elements as the main element. The alloy has the characteristics of high entropy effect in thermodynamics, slow diffusion effect in kinetics, serious lattice distortion effect in structure and the effect of chicken tail wine on performance, and the alloy has simple tissue junction. In order to develop new high temperature structural materials, based on the design concept of high entropy alloy, this paper uses vacuum arc smelting technology to prepare Mo-Nb-Hf-Zr-Ti refractory high entropy alloy system with refractory metal elements as the main element, and to add metal elements Al, Cr or non-metallic element Si, B, C to adjust the alloy properties, and to study the addition of the alloy. The influence law and mechanism of elements on Microstructure and properties of alloy. First, the phase composition of MoNbHf ZrTi alloy was calculated and predicted by Thermo-calc software combined with TCNI-5 database phase diagram. The phase composition, microstructure, phase stability, mechanical properties and thermal deformation behavior of MoNbHf ZrTi alloy were tested and studied, and five groups of MoNbHfZr Ti alloys were studied. The effect of the change of the content of the elements on the microstructure and properties of the alloy. It is found that the calculation of the phase diagram is in agreement with the experimental results. The MoNbHfZrTi alloy is composed of the solid solution phase of the single phase body center cubic (BCC). The thermal analysis (DSC) and heat treatment results show that the BCC phase has a very high structural stability, and there is no phase transition below 1450 oC. The yield strength of gold and homogenized alloys at room temperature is 1719 MPa and 1575 MPa respectively. The alloy compression fracture belongs to typical brittle fracture. Under the epsilon =0.1 S-1 and T=1200 oC, the yield strength of the alloy can still reach the typical dynamic recrystallization characteristic of the stress strain curve when the temperature of 750 MPa.MoNbHfZrTi alloy is 900 oC and above the thermal deformation. Continuous dynamic recrystallization and discontinuous dynamic recrystallization occur simultaneously, in which the discontinuous dynamic recrystallization takes the dominant position. The increase of the deformation temperature and the increase of the strain rate will weaken the continuous dynamic recrystallization mechanism of the.MoNbHf ZrTi alloy. The alloy is still composed of the single-phase BCC solid solution phase. Compared to the mole MoNbHfZrTi alloy, the strength and hardness of the alloy decreased, but in the non equimormole Mo-Nb-Hf-Zr-Ti alloy, the Mo content increased the alloy strength, the Hf, Zr and Ti content increased the alloy strength, and the change of Nb content had little effect on the strength of the alloy. The comprehensive performance was selected by considering the factors such as strength, plasticity, density and cost. A good Mo0.5NbHf0.5ZrTi (Mo0.5Hf0.5) alloy is used as a matrix alloy, adding Al or Cr elements to study the change law of the microstructure and properties of the alloy respectively. It is found that a small amount of Al or Cr elements can be dissolved into the matrix phase BCC1, and the addition of Al elements will form a new solid solution phase BCC2 phase similar to the normal number of the BCC1 lattice, and the matrix phase is BCC1 rich. The concentration of Mo and Nb elements, BCC2 phase enrichment of Zr and Hf elements, and the addition of Cr elements to the formation of MgCu2 type Laves phase (Nb, Hf, Zr, Ti). Gold plasticity. With the increase of the content of Al elements, the strength of the alloy decreases slightly, and the strength of the alloy increases gradually with the increase of the content of the Cr element. The increase of the strength is mainly attributed to the formation of the Laves phase. The addition of the non metal elements B, Si or C elements to the Mo0.5NbHf0.5ZrTi alloy has formed a boron carbide, silicide or carbide enhanced Mo0.5NbHf0.5ZrTi. It is found that the matrix phase of the alloy is still BCC solid solution phase and the reinforced phase of boride is MB2 phase, in which M is Mo, Nb, Hf, Zr, Ti, and the silicide phase is M5Si3 phase, and M is Mo. The higher the binding energy, the higher the content of the metal elements in the borides, silicides or carbides. A small amount of B, Si or C elements are added, the strength of the alloy is improved and the plasticity is improved. The increase of the plasticity is mainly due to the refinement of the fine crystal and the decrease of the solid solution intensity of the matrix phase, and the addition of more B, Si or C elements to improve the alloy. The strength of the alloy reduces the ductility of the alloy at the same time. The structure of the Mo-Nb-Hf-Zr-Ti alloy after adding several elements of Al, Cr, B, Si or C is found. After adding a variety of alloying elements, the Mo-Nb-Hf-Zr-Ti alloy is still composed of the solid solution phase of BCC as the matrix phase, and the formation and quantity of other phases and the content of the alloying elements are added. The binding energy of the amount and alloying element to the matrix alloy is closely related. In the alloy MoNb1.5Hf0.3Zr0.5Ti1.5Al0.2Cr0.2C0.05B0.05Si0.05, although the content of the three elements of Si, C, and B is the same, the binding energy of C elements to Mo, Nb, Hf, Zr and Ti is the strongest, so the secondary phase formed in the alloy is mainly carbide phase.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG146.412

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