本文選題：鈦合金 + 激光熔覆�。� 參考：《山東大學(xué)》2016年博士論文

【摘要】：鈦合金具有高的強(qiáng)度,低的密度和優(yōu)良的耐蝕性,已被應(yīng)用于航空航天、石油化工等領(lǐng)域,但是由于硬度低、耐磨性能較差,限制了其在工業(yè)領(lǐng)域的應(yīng)用。因此,利用表面改性技術(shù)在鈦合金表面制備高硬度耐磨涂層成為鈦合金表面強(qiáng)化領(lǐng)域的研究熱點(diǎn)之一。激光熔覆技術(shù)與傳統(tǒng)的表面改性技術(shù)相比,具有高的效率,熔覆層與基體之間的結(jié)合為冶金結(jié)合,涂層結(jié)構(gòu)細(xì)小與涂層對(duì)基體的稀釋作用小等優(yōu)點(diǎn)。本論文對(duì)工業(yè)領(lǐng)域中應(yīng)用最廣泛的Ti-6A1-4V鈦合金進(jìn)行激光熔覆,采用理論與試驗(yàn)相結(jié)合的方法,以Ti-Al-Si作為鈦合金表面激光熔覆層的預(yù)置材料,獲得與基體呈冶金結(jié)合的金屬陶瓷復(fù)合涂層。由于涂層中原位生成了Ti5Si3,Ti7Al5Si12和Ti3AlC2等主要強(qiáng)化相,以及TiAl,Ti3Al和Al3 Ti等輔助強(qiáng)化相,熔覆層的硬度和耐磨性得到了大幅度提高。通過(guò)預(yù)置涂層材料設(shè)計(jì)和工藝參數(shù)調(diào)整,控制熔覆層中原位生成陶瓷相的種類、含量與分布特征,減小涂層脆化傾向；分析熔覆層的形貌、物相、組織結(jié)構(gòu)、硬度和耐磨性,闡述了熔覆層中物相的原位形成機(jī)制和熔覆層的界面結(jié)構(gòu),研究了熔覆層的強(qiáng)化機(jī)理,揭示了陶瓷TiC(或B4C)與Y2O3對(duì)熔池凝固過(guò)程的影響規(guī)律及作用機(jī)理。研究表明,采用Ti,Al和Si作為熔覆材料,在開(kāi)放的氬氣環(huán)境下對(duì)Ti-6Al-4V鈦合金表面進(jìn)行激光熔覆,能夠制備出與基體呈現(xiàn)冶金結(jié)合的高硬度耐磨復(fù)合陶瓷涂層；涂層中原位生成了Ti5Si3,Ti7Al5Si12,Ti3AIC2,Ti3Al,TiAl和TiAl3等多種硬質(zhì)強(qiáng)化相,在熔池凝固過(guò)程,這些強(qiáng)化相的生長(zhǎng)相互抑制,避免了組織粗化,有利于獲得組織細(xì)小致密的熔覆層;預(yù)置涂層材料配比和激光熔覆上藝參數(shù)均會(huì)對(duì)熔覆層的質(zhì)量、微觀組織和性能產(chǎn)生影響,在本論文試驗(yàn)條件下,當(dāng)預(yù)置涂層粉末的質(zhì)量分?jǐn)?shù)為Ti-35Al-15Si、Ar氣的壓力為0.2～0.3MPa、激光功率為950～1100W、掃描速度為5mm·s-1時(shí),熔覆層的硬度和耐磨性最優(yōu)。將TiC(或B4C)陶瓷加入預(yù)置涂層中,B4C和Ti發(fā)生原位反應(yīng)生成TiC,TiB和TiB2等陶瓷強(qiáng)化相,有利于進(jìn)一步提高熔覆層的硬度和耐磨性,但是當(dāng)TiC(或B4C)含量過(guò)高時(shí),熔覆層中含有過(guò)量的陶瓷相,不利于熔覆層整體硬度和耐磨性能的提高。研究表明,當(dāng)TiC(或B4C)的添加量為20wt.%(或10wt.%)時(shí),制備的熔覆層表現(xiàn)出最高的硬度和最優(yōu)的耐磨性能。稀土氧化物Y2O3可以顯著細(xì)化熔覆層的微觀組織,其作用機(jī)制概括如下：在熔池中,未熔化分解的Y2O3可作為晶體生長(zhǎng)的異質(zhì)形核核心；一部分Y2O3會(huì)分解為Y與O2,Y作為表面活性元素,容易在晶界或相界偏聚,阻礙晶界或相界移動(dòng)。然而,Y2O3的添加量過(guò)多會(huì)使熔覆層的脆性增加,不利于熔覆層耐磨性能的提高。本文的研究表明,在熔覆材料中添加2wt.%Y2O3時(shí),獲得的熔覆層耐磨性能最優(yōu)。在熔覆材料中同時(shí)加入適量的TiC(或B4C)和Y2O3,制備出的熔覆層微觀組織細(xì)小致密,表面硬度較高,耐磨性能優(yōu)異。在熔覆材料中添加20wt.%TiC(或10wt.%B4C)與2wt.%Y2O3時(shí),制備的熔覆層的硬度約提高為Ti-6A1-4V合金硬度的5倍,耐磨性能較好。在800℃溫度下高溫磨損試驗(yàn)后,熔覆層試樣表面均生成一層氧化膜,其主要由Al2O3,TiO2和SiO2組成。隨著溫度升高,熔覆層的摩擦系數(shù)升高,磨損量也增大。隨著載荷的增大,摩擦系數(shù)減少,磨損量反而增大。成分不同的熔覆層的磨損量為：基體(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),熔覆層的磨損機(jī)制為氧化磨損、剝落磨損和粘著磨損,基體的磨損機(jī)制為氧化磨損和粘著磨損。本論文利用激光熔覆技術(shù)在Ti-6A1-4V鈦合金表面制備出高硬度耐磨復(fù)合陶瓷涂層,闡述了熔覆層中物相的原位形成機(jī)制和熔覆層的界面結(jié)構(gòu),揭示了陶瓷相TiC(或B4C)與稀土氧化物Y2O3對(duì)熔池凝固過(guò)程的影響規(guī)律及作用機(jī)理,為激光熔覆技術(shù)在鈦合金機(jī)械傳動(dòng)件制備領(lǐng)域的應(yīng)用提供試驗(yàn)依據(jù)與理論基礎(chǔ)。
[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.

【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG174.4
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本文編號(hào)：1815059