钛合金表面激光熔覆陶瓷Ti-Al-Si复合涂层的组织结构与耐磨性

发布时间：2018-04-28 11:17

  本文选题：钛合金 + 激光熔覆　； 参考：《山东大学》2016年博士论文

【摘要】：钛合金具有高的强度,低的密度和优良的耐蚀性,已被应用于航空航天、石油化工等领域,但是由于硬度低、耐磨性能较差,限制了其在工业领域的应用。因此,利用表面改性技术在钛合金表面制备高硬度耐磨涂层成为钛合金表面强化领域的研究热点之一。激光熔覆技术与传统的表面改性技术相比,具有高的效率,熔覆层与基体之间的结合为冶金结合,涂层结构细小与涂层对基体的稀释作用小等优点。本论文对工业领域中应用最广泛的Ti-6A1-4V钛合金进行激光熔覆,采用理论与试验相结合的方法,以Ti-Al-Si作为钛合金表面激光熔覆层的预置材料,获得与基体呈冶金结合的金属陶瓷复合涂层。由于涂层中原位生成了Ti5Si3,Ti7Al5Si12和Ti3AlC2等主要强化相,以及TiAl,Ti3Al和Al3 Ti等辅助强化相,熔覆层的硬度和耐磨性得到了大幅度提高。通过预置涂层材料设计和工艺参数调整,控制熔覆层中原位生成陶瓷相的种类、含量与分布特征,减小涂层脆化倾向；分析熔覆层的形貌、物相、组织结构、硬度和耐磨性,阐述了熔覆层中物相的原位形成机制和熔覆层的界面结构,研究了熔覆层的强化机理,揭示了陶瓷TiC(或B4C)与Y2O3对熔池凝固过程的影响规律及作用机理。研究表明,采用Ti,Al和Si作为熔覆材料,在开放的氩气环境下对Ti-6Al-4V钛合金表面进行激光熔覆,能够制备出与基体呈现冶金结合的高硬度耐磨复合陶瓷涂层；涂层中原位生成了Ti5Si3,Ti7Al5Si12,Ti3AIC2,Ti3Al,TiAl和TiAl3等多种硬质强化相,在熔池凝固过程,这些强化相的生长相互抑制,避免了组织粗化,有利于获得组织细小致密的熔覆层;预置涂层材料配比和激光熔覆上艺参数均会对熔覆层的质量、微观组织和性能产生影响,在本论文试验条件下,当预置涂层粉末的质量分数为Ti-35Al-15Si、Ar气的压力为0.2～0.3MPa、激光功率为950～1100W、扫描速度为5mm·s-1时,熔覆层的硬度和耐磨性最优。将TiC(或B4C)陶瓷加入预置涂层中,B4C和Ti发生原位反应生成TiC,TiB和TiB2等陶瓷强化相,有利于进一步提高熔覆层的硬度和耐磨性,但是当TiC(或B4C)含量过高时,熔覆层中含有过量的陶瓷相,不利于熔覆层整体硬度和耐磨性能的提高。研究表明,当TiC(或B4C)的添加量为20wt.%(或10wt.%)时,制备的熔覆层表现出最高的硬度和最优的耐磨性能。稀土氧化物Y2O3可以显著细化熔覆层的微观组织,其作用机制概括如下：在熔池中,未熔化分解的Y2O3可作为晶体生长的异质形核核心；一部分Y2O3会分解为Y与O2,Y作为表面活性元素,容易在晶界或相界偏聚,阻碍晶界或相界移动。然而,Y2O3的添加量过多会使熔覆层的脆性增加,不利于熔覆层耐磨性能的提高。本文的研究表明,在熔覆材料中添加2wt.%Y2O3时,获得的熔覆层耐磨性能最优。在熔覆材料中同时加入适量的TiC(或B4C)和Y2O3,制备出的熔覆层微观组织细小致密,表面硬度较高,耐磨性能优异。在熔覆材料中添加20wt.%TiC(或10wt.%B4C)与2wt.%Y2O3时,制备的熔覆层的硬度约提高为Ti-6A1-4V合金硬度的5倍,耐磨性能较好。在800℃温度下高温磨损试验后,熔覆层试样表面均生成一层氧化膜,其主要由Al2O3,TiO2和SiO2组成。随着温度升高,熔覆层的摩擦系数升高,磨损量也增大。随着载荷的增大,摩擦系数减少,磨损量反而增大。成分不同的熔覆层的磨损量为：基体(501πmm3)Ti-45Al-15Si (485πmm3)Ti-35Al-15Si(4507πmm3) Ti-25Al-15Si(4327πm3)(Ti-35Al-15Si)-1Y2O3(421πmm3)(Ti-35Al-15Si)-20TiC (408πmm3)(Ti-35Al-15Si)-10B4C(396πmm3)(Ti-35Al-15Si)-20TiC-1Y2O3(385π mm3)(Ti-35Al-15Si)-20B4C-1Y2O3(381πmm3),熔覆层的磨损机制为氧化磨损、剥落磨损和粘着磨损,基体的磨损机制为氧化磨损和粘着磨损。本论文利用激光熔覆技术在Ti-6A1-4V钛合金表面制备出高硬度耐磨复合陶瓷涂层,阐述了熔覆层中物相的原位形成机制和熔覆层的界面结构,揭示了陶瓷相TiC(或B4C)与稀土氧化物Y2O3对熔池凝固过程的影响规律及作用机理,为激光熔覆技术在钛合金机械传动件制备领域的应用提供试验依据与理论基础。
[Abstract]:Titanium alloy has high strength, low density and excellent corrosion resistance. It has been applied to aerospace, petrochemical and other fields. But because of low hardness and poor wear resistance, it restricts its application in industry. Therefore, the surface modification technology is used to make the high hardness and wear-resistant coating on the surface of titanium alloy to become the field of titanium alloy surface strengthening. Compared with the traditional surface modification technology, laser cladding technology has high efficiency, the combination of cladding layer and matrix is metallurgical bonding, the coating structure is small and the coating has little dilution to the matrix. The laser cladding of the most widely used Ti-6A1-4V titanium alloy in this paper is used in this paper. The method of combining theory and experiment with Ti-Al-Si as the preset material on the laser cladding layer on the surface of the titanium alloy to obtain a metal ceramic composite coating that is metallurgical bonding with the matrix. The hardness and resistance of the cladding layer are the main strengthening phase, such as Ti5Si3, Ti7Al5Si12 and Ti3AlC2, as well as the auxiliary strengthening phase such as TiAl, Ti3Al and Al3 Ti. Through the design of the prefabricated coating material and the adjustment of the process parameters, the types of in situ formed ceramic phase in the cladding layer, the content and the distribution characteristics, the tendency of the coating embrittlement are reduced, the morphology, phase, structure, hardness and wear resistance of the cladding layer are analyzed, and the in-situ formation mechanism and melting of the phase in the cladding layer are expounded. The strengthening mechanism of cladding layer is studied, and the influence rule and mechanism of the ceramic TiC (or B4C) and Y2O3 on the solidification process of the molten pool are revealed. The study shows that the laser cladding of the surface of the Ti-6Al-4V titanium alloy in an open argon environment by using Ti, Al and Si as cladding material can produce metallurgy with the matrix. Combined with high hardness and wear-resistant composite ceramic coating, the coating produced a variety of hard strengthening phases, such as Ti5Si3, Ti7Al5Si12, Ti3AIC2, Ti3Al, TiAl and TiAl3, in the solidification process of the molten pool. The growth of these intensities inhibited each other, avoided the coarsening of the tissue, and was beneficial to the formation of fine and compact cladding layer; the preposition coating material ratio and laser On the condition of this paper, the hardness and wear resistance of the cladding layer are best when the mass fraction of the coated powder is Ti-35Al-15Si, the pressure of Ar gas is 0.2 to 0.3MPa, the laser power is 950 to 1100W and the scanning speed is 5mm s-1, and TiC (or B4C) pottery is used in this paper. In the pre coating of porcelain, the in-situ reaction between B4C and Ti generates TiC, TiB and TiB2 ceramic strengthening phase, which is beneficial to further improving the hardness and wear resistance of the cladding layer. But when the content of TiC (or B4C) is too high, the excess ceramic phase in the cladding layer is not conducive to the improvement of the hardness and wear resistance of the cladding layer. The study shows that TiC (or B4C) is not good. When the addition amount is 20wt.% (or 10wt.%), the prepared cladding layer shows the highest hardness and the best wear resistance. The rare earth oxide Y2O3 can significantly refine the microstructure of the cladding layer. The mechanism of its action is summarized as follows: in the molten pool, the Y2O3 can be used as the heterostructure core of the crystal growth; a part of Y2O3 will be decomposed. As Y and O2, Y as a surface active element, it is easy to segregate at grain boundary or phase boundary, impede the movement of grain boundary or phase boundary. However, the excessive addition of Y2O3 will increase the brittleness of the cladding layer, which is not conducive to the improvement of the wear resistance of the cladding layer. The study shows that the coating layer has the best wear resistance when adding 2wt.%Y2O3 to the cladding material. With the addition of appropriate amount of TiC (or B4C) and Y2O3 in the cladding material, the microstructure of the cladding layer is fine and compact, the surface hardness is high, and the wear resistance is excellent. When adding 20wt.%TiC (or 10wt.%B4C) and 2wt.%Y2O3 to the cladding material, the hardness of the prepared cladding layer is about 5 times that of the hardness of the Ti-6A1-4V alloy, and the wear resistance is better. The temperature of the cladding layer is at 800 C. After the high temperature wear test, a layer of oxide film is formed on the surface of the cladding layer, which is mainly composed of Al2O3, TiO2 and SiO2. With the increase of temperature, the friction coefficient of the cladding layer increases and the wear amount increases. With the increase of the load, the friction coefficient decreases and the wear amount is increased. The wear amount of the cladding layer with different components is 501 PI mm3 ) Ti-45Al-15Si (485 PI mm3) Ti-35Al-15Si (4507 PI mm3) Ti-25Al-15Si (4327 PI m3) (Ti-35Al-15Si) -1Y2O3 (421 PI mm3) (Ti-35Al-15Si) -20TiC (396 PI mm3) (385 PI) (381 PI), the wear mechanism of the cladding layer is oxidation wear, peeling wear and adhesion grinding. The wear mechanism of the matrix is oxidation wear and adhesion wear. In this paper, the high hardness and wear-resistant ceramic coating was prepared on the Ti-6A1-4V titanium alloy surface by laser cladding technology. The formation mechanism of the phase in the cladding layer and the interface structure of the cladding layer were expounded. The melting pool of ceramic ceramic phase TiC (or B4C) and the rare earth oxide Y2O3 was revealed. The influence rule and mechanism of solid process provide experimental basis and theoretical basis for the application of laser cladding technology in the preparation of titanium alloy mechanical transmission parts.

【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG174.4
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本文编号：1815059