Nb-Ti-Si-Cr基合金表面含Zr和Y的硅化物渗层的组织及性能

发布时间：2018-06-08 11:34

本文选题：Nb-Ti-Si-Cr基超高温合金 + 硅化物渗层　；参考：《西北工业大学》2016年博士论文

【摘要】：Nb-Si基多元超高温合金由于具有熔点高、密度低、高温强度和室温断裂韧性好等一系列优点而具有巨大的应用潜力。但该合金较差的高温抗氧化性能严重制约了其实际应用。多元合金化虽然能够有效提高该合金的高温抗氧化性能,但过量添加合金化元素有时会降低合金的综合性能如高温强度和熔点。与合金化不同,表面涂层在改善合金抗氧化性能的同时对合金自身力学性能的影响较小。因此,在合金化的基础上制备表面涂层以提供高温有氧环境下的保护,是Nb-Si基多元超高温合金取得实际应用的有效手段。本文依据上述思路,采用Si-Zr-Y扩散共渗和磁控溅射Zr膜+Si-Y扩散共渗两种方法,在新型Nb-Ti-Si-Cr基多元超高温合金表面分别制备了Si-Zr-Y共渗层和ZrSi_2-NbSi_2复合渗层。采用XRD、SEM和EDS等测试手段分析了渗层的相组成、微观形貌和成分分布。同时,本文针对所制备渗层的特点,研究了Si-Zr-Y共渗层的高温抗氧化性能、摩擦磨损及固体粒子冲蚀性能和ZrSi_2-NbSi_2复合渗层的高温抗氧化性能,并对其高温抗氧化机理、摩擦磨损和固体粒子冲蚀机制进行了讨论,主要结果如下:(1)采用扩散共渗方法在Nb-Ti-Si-Cr基多元超高温合金表面制备了Si-Zr-Y共渗层。揭示了催化剂种类(NaF,NH4F,NH4Cl,NaBr和NaCl)和含量(1~8wt.%)、共渗温度(1100~1350℃)、渗剂中Zr粉含量(5~15wt.%)以及共渗时间(0~12h)对共渗层组织的影响规律。采用不同种类催化剂经1250℃保温8h所制备的Si-Zr-Y共渗层由外至内均由(Nb,X)Si2(X代表Ti,Cr,Zr和Hf)外层、(Ti,Nb)5Si4中间层和富Al,Y的(Nb,X)5Si3内层组成。其中,采用NaF为催化剂时制备的共渗层较厚且组织致密,共渗层内Zr和Y的含量也较高。渗剂中的NaF含量不会明显改变共渗层的组织结构,但当NaF的含量由1wt.%增加到5wt.%时,共渗层的厚度逐渐增加且致密性得到改善,而进一步增加NaF含量至8wt.%时,共渗层的厚度反而有所降低。共渗温度对渗层的组织结构和生长速率均有显著影响:1150和1200℃保温8h所制备的共渗层与1250℃保温8h所制备的共渗层具有相似结构,但1300和1350℃保温8h所制备的共渗层中出现了疏松多孔的(Ti,Nb)5Si4最外层;同时,共渗层的厚度及渗层内Zr和Y元素的含量均随共渗温度的升高而增加。增加渗剂中Zr粉含量会相应地导致渗层内Zr含量的增加,但会明显抑制共渗层的生长速率,同时,渗剂内Zr粉含量过高(15wt.%)还会导致共渗层表面出现富Zr的(Ti,Nb)5(Si,Al)4最外层。共渗层的厚度随共渗时间的延长呈抛物线规律增加,表明共渗层的形成由扩散控制,但共渗时间的延长不会明显改变共渗层的组织结构。(2)选取渗剂组分为10Si-10Zr-3Y2O3-5NaF-72Al2O3(wt.%),经1250℃保温8h所制备的共渗层进行1250℃恒温氧化、室温及800℃摩擦磨损及固体粒子冲蚀实验。结果表明,所制备的Si-Zr-Y共渗层具有优异高温抗氧化性能,其在1250℃时的恒温氧化速率常数较基体合金低约3个数量级。氧化后所形成的氧化膜主要由较薄的TiO2外层和致密的SiO2内层组成,该氧化膜能够在1250℃的空气中保护基体合金长达200h。但经200h氧化后的氧化膜在局部出现开裂和剥落。Si-Zr-Y共渗层的硬度显著高于Nb-Ti-Si-Cr基体合金。在相同的摩擦载荷下,Si-Zr-Y共渗层无论在室温还是800℃时的摩擦磨损抗力均优于基体合金,原因为在共渗层试样的磨损表面形成了由SiO2组成的氧化产物,可对磨损面起到有效保护。与基体合金相比,Si-Zr-Y共渗层在30°小攻角冲蚀状态下具有更高的耐冲蚀抗力,但在90°大攻角冲蚀状态下的耐冲蚀抗力较低。(3)采用先在合金表面磁控溅射Zr膜,然后Si-Y扩散共渗的方法,在Nb-Ti-Si-Cr基多元超高温合金表面成功制备了ZrSi_2-NbSi_2复合渗层。揭示了沉积Zr膜的厚度(2~10μm)及Si-Y共渗温度(1150~1350℃)对渗层组织的影响规律。发现不同Zr膜厚度和Si-Y共渗温度所制备的渗层具有相似的结构,均主要由ZrSi_2外层,(Nb,X)Si2(X代表Ti,Cr,Zr和Hf)中间层和(Ti,Nb)5Si4内层组成,共渗层的厚度随着共渗温度的升高显著增加,过高的Si-Y共渗温度(1350℃)还会导致共渗层中各层界面处产生裂纹。选取Zr膜厚度为10μm,再经1250℃/4h Si-Y共渗所制备的渗层进行1250℃恒温氧化实验。结果表明,ZrSi_2-NbSi_2复合渗层具有较好的高温抗氧化性能。氧化后在渗层表面形成了由SiO2,ZrSiO4,ZrO2,Al2O3,TiO2和Cr2O3混合组成的致密氧化膜,该氧化膜能够在1250℃的空气中保护基体合金100h以上。氧化膜的形成过程包括ZrSi_2外层的氧化和保护性内氧化膜的生长两个阶段。其中,ZrSi_2外层的氧化较为迅速,此时氧化膜的生长主要由O的内扩散控制,随着保护性内氧化膜的形成和生长,氧化膜的生长逐渐由O的内扩散占优转变为Si,Ti,Cr和Al的外扩散占优。
[Abstract]:Nb-Si based superalloy has great potential for application because of its high melting point, low density, high temperature strength and good fracture toughness at room temperature. However, the poor high temperature oxidation resistance of the alloy seriously restricts its practical application. The addition of alloying elements can sometimes reduce the comprehensive properties of the alloy, such as the high temperature strength and melting point. Unlike alloying, the surface coating has little effect on the alloy's mechanical properties while improving the antioxidant properties of the alloy. Therefore, the surface coating is prepared on the basis of alloying to provide protection under the high temperature and aerobic environment, which is the Nb-Si base. Based on the above thought, the Si-Zr-Y co impermeable layer and ZrSi_2-NbSi_2 composite layer were prepared on the surface of the new Nb-Ti-Si-Cr based multivariable superalloy by using the two methods of Si-Zr-Y diffusion co permeation and magnetron sputtering Zr film +Si-Y diffusion co permeation. The methods of XRD, SEM and EDS were used. The phase composition, microstructure and composition distribution of the impermeable layer were analyzed. At the same time, the high temperature oxidation resistance, friction and wear, solid particle erosion and high temperature oxidation resistance of the Si-Zr-Y composite layer were studied, and the high-temperature oxidation resistance mechanism, friction and wear and solid particles were also studied. The main results are discussed. The main results are as follows: (1) Si-Zr-Y co permeation layer was prepared on the surface of Nb-Ti-Si-Cr based multicomponent superalloy by diffusion diffusion method. The types of catalysts (NaF, NH4F, NH4Cl, NaBr and NaCl) and content (1~8wt.%), CO infiltration temperature (1100~1350), Zr powder content (5~15wt.%) and co infiltration time (0~12h) in the permeation agent (0~12h) were revealed. The effect of the co permeable layer on the microstructure of the co permeable layer. The Si-Zr-Y Co layer prepared by different kinds of catalysts at 1250 C for 8h is made up of the outer layer (Nb, X) Si2 (X representing Ti, Cr, Zr and Hf), and (Ti, Nb) intermediate layer and the rich inner layer. The content of Zr and Y in the layer is also higher. The NaF content in the permeable agent does not obviously change the structure of the co permeable layer, but when the content of NaF increases from 1wt.% to 5wt.%, the thickness of the co permeable layer is gradually increased and the densification is improved, while the thickness of the co permeable layer decreases when the NaF content is increased to 8wt.%. The fabric structure and growth rate have significant influence: the co permeable layer prepared by 8h at 1150 and 1200 C is similar to the co permeable layer prepared at 1250 C for 8h, but the porous (Ti, Nb) 5Si4 layer appears in the co permeable layer prepared at 1300 and 1350 C, and the thickness of the co permeable layer and the content of the Zr and Y elements in the infiltration layer are all in the same time. With the increase of CO permeation temperature, the content of Zr powder in the permeating agent will lead to the increase of Zr content in the permeable layer, but it can obviously inhibit the growth rate of the co permeable layer. At the same time, the high content of Zr powder (15wt.%) in the permeating agent will lead to the appearance of Zr (Ti, Nb) 5 (Si, Al) 4 in the surface of the co permeable layer. The thickness of the co permeable layer is prolonged with the prolongation of the co permeation time. The increase of parabolic law shows that the formation of the co permeable layer is controlled by diffusion, but the prolongation of the co permeation time will not change the structure of the co permeable layer. (2) the permeation agent is selected as 10Si-10Zr-3Y2O3-5NaF-72Al2O3 (wt.%), the co permeable layer prepared by 8h at 1250 C is oxidized at 1250 C, and the friction and wear of the solid particles and the solid particles at room temperature and 800. The results show that the prepared Si-Zr-Y co permeable layer has excellent high temperature oxidation resistance, and the constant temperature oxidation rate constant at 1250 C is about 3 orders lower than that of the matrix alloy. The oxide film formed mainly by the thinner TiO2 outer layer and the dense SiO2 inner layer, and the oxide film can be protected in the air of 1250 degrees C. The hardness of the matrix alloy as long as 200h. but the oxidation film after 200H oxidation is significantly higher than that of the Nb-Ti-Si-Cr matrix alloy. The friction and wear resistance of the Si-Zr-Y co permeable layer at room temperature or 800 C is better than that of the base alloy under the same friction load. The reason is the wear of the specimen in the co permeable layer. The surface formed an oxidation product composed of SiO2, which can effectively protect the wear surface. Compared with the matrix alloy, the Si-Zr-Y co permeable layer has a higher erosion resistance at 30 degrees of attack angle and erosion, but the resistance to erosion is lower at the 90 degree of attack angle. (3) the magnetron sputtering Zr film on the alloy surface and then the Si-Y diffusion are used. The ZrSi_2-NbSi_2 composite layer was successfully prepared on the surface of Nb-Ti-Si-Cr based multivariable superalloy. The influence of the thickness of the Zr film (2~10 mu m) and the Si-Y co infiltration temperature (1150~1350 C) on the layer tissue was revealed. It was found that the layers of different Zr film thickness and Si-Y co permeation temperature have similar structure, all of which are mainly Zr. The Si_2 outer layer, (Nb, X) Si2 (X represents Ti, Cr, Zr and Hf) in the middle layer and (Ti, Nb) 5Si4 inner layer, the thickness of the co permeable layer increases significantly with the increase of the co permeation temperature. The exorbitant permeation temperature (1350 degrees C) will lead to the crack in the interface of the layers of the co permeable layer. The thickness of the membrane is selected and then the layer prepared by the infiltration of 1250 degrees Celsius is carried out. The experimental results show that the ZrSi_2-NbSi_2 composite layer has good oxidation resistance at high temperature. After oxidation, a dense oxide film composed of SiO2, ZrSiO4, ZrO2, Al2O3, TiO2 and Cr2O3 is formed on the surface of the permeable layer. The oxide film can protect the matrix alloy 100h above the base alloy in the air of 1250 C. The formation process of the oxide film is wrapped. Including the two stages of the growth of the oxide and protective inner oxide film on the outer layer of ZrSi_2, the oxidation of the outer layer of the ZrSi_2 is more rapid. At this time, the growth of the oxide film is mainly controlled by the internal diffusion of O. With the formation and growth of the protective inner oxide film, the growth of the oxide film is gradually transformed from the internal diffusion of O to Si, and the external diffusion of Ti, Cr and Al is superior.
【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG174.4

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