Cu单元素基合金表面激光高熵合金化的研究
发布时间：2018-12-21 20:56
【摘要】：高熵合金是目前发展起来的含有五种以上主要元素且呈现出FCC和BCC结构的固溶体相合金，其具有高硬度、高强度，较好的耐磨性、耐腐蚀性能以及优异的抗氧化性能。激光表面改性技术可以实现在低成本的金属材料表面，制备出高性能的涂层。本课题采用Nd:YAG固体脉冲激光器、半导体、CO2及光纤激光器分别在纯铜表面进行系列激光高熵合金化层的制备，研究激光辐照工艺对高熵合金化层的成形质量、显微组织、性能的影响规律。利用金相显微镜、扫描电镜、能谱仪、X-射线衍射仪、显微硬度仪、纳米压痕仪及往复摩擦实验机对合金化层组织形貌、成分、相结构及性能进行系统研究。 试验结果表明：激光快速成形四元FeCoCrAl合金是由BCC和两种金属间化合物组成，利用Nd:YAG激光辐照可使FeCoCrAl四元合金粉末在纯Cu表面反应合成制备FeCoCrAl/Cu五元高熵合金化层，合金化层具有简单固溶体结构。随Nd:YAG激光器电流增大，合金化层组织由颗粒状向胞状转变。热力学分析表明，FeCoCrAl/Cu激光高熵合金化层满足形成固溶体的条件。由于固溶强化和晶粒细化作用使高熵合金化层硬度明显提高。 采用半导体、CO2及光纤激光合金化技术制备的FeCoCrAlNix/Cu（x=0，0.5，1，1.5）高熵合金化层，随Ni元素的加入，合金化层的相组成由FCC+BCC逐渐转变成单一FCC结构，其硬度呈下降趋势。分别加入Mo和Ti元素的合金化层除了含有简单固溶体相外还出现其他相，而加入Si元素的合金化层仍为简单固溶体，且成形性较好。 往复磨损试验表明，FeCoCrAlNix/Cu（x=0，0.5，1，，1.5）激光合金化Ni含量变化时，耐磨性与硬度变化规律并不一致，FeCoCrAlNi/Cu合金化层由于经络状组织的存在，耐磨性较好。此外，FeCoCrAlSi0.5/Cu合金化层磨损表面仍较平滑，无明显的黏着，只出现少量黑色颗粒，磨损量较小。 由于激光功率密度以及材料对不同波长的激光吸收率的差异，不同的激光合金化层显微组织各异，经计算，Cu对不同波长激光吸收率及合金化过程中激光能量密度依次为：CO2激光＜光纤激光＜半导体激光。结合激光高熵合金化宏观成形性、组织、性能及制备工艺，利用光纤激光在Cu基材表面实现高熵合金化为最优方法。
[Abstract]:High entropy alloy is a kind of solid solution alloy which contains more than five main elements and presents the structure of FCC and BCC. It has high hardness, high strength, good wear resistance, corrosion resistance and excellent oxidation resistance. Laser surface modification technology can be used to fabricate high performance coatings on low cost metallic materials. In this paper, Nd:YAG solid-state pulse laser, semiconductor, CO2 and fiber laser were used to prepare series of laser high-entropy alloying layers on the surface of pure copper, and the forming quality and microstructure of high-entropy alloying layer by laser irradiation were studied. The influence law of performance. The microstructure, composition, phase structure and properties of alloyed layer were systematically studied by metallographic microscope, scanning electron microscope, energy spectrometer, X-ray diffractometer, microhardness tester, nano-indentation instrument and reciprocating friction tester. The experimental results show that the quaternary FeCoCrAl alloy is composed of BCC and two intermetallic compounds. The FeCoCrAl quaternary alloy powder can be synthesized by Nd:YAG laser irradiation on the surface of pure Cu to prepare FeCoCrAl/Cu quaternary high entropy alloying layer. The alloying layer has a simple solid solution structure. As the current of Nd:YAG laser increases, the alloying layer changes from granular to cellular. Thermodynamic analysis shows that the FeCoCrAl/Cu laser high entropy alloying layer meets the condition of forming solid solution. The hardness of high entropy alloying layer is improved obviously because of solid solution strengthening and grain refinement. The high entropy alloying (FeCoCrAlNix/Cu) layer prepared by semiconductor, CO2 and optical fiber laser alloying technology was used. With the addition of Ni element, the phase composition of the alloying layer gradually changed from FCC BCC to single FCC structure. Its hardness shows a downward trend. The alloying layer with Mo and Ti elements has other phases except simple solid solution phase, while the alloying layer with Si element is still simple solid solution, and the formability is good. The results of reciprocating wear test show that the wear resistance of FeCoCrAlNix/Cu (x0. 0. 5%) laser alloyed Ni is not consistent with the change of hardness. The wear resistance of FeCoCrAlNi/Cu alloying layer is better because of the existence of meridian structure. In addition, the wear surface of FeCoCrAlSi0.5/Cu alloying layer is still smooth, no obvious adhesion, only a small amount of black particles appear, and the amount of wear is small. Due to the difference of laser power density and the absorptivity of materials to different wavelengths, the microstructure of different laser alloying layers is different. The order of laser energy density in the process of laser absorption and alloying by Cu is as follows: CO2 laser < fiber laser < semiconductor laser. Combined with the macroscopic formability, microstructure, properties and preparation process of laser high entropy alloying, the optimal method of high entropy alloying on the surface of Cu substrate is achieved by using optical fiber laser.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.4
本文编号：2389451
[Abstract]:High entropy alloy is a kind of solid solution alloy which contains more than five main elements and presents the structure of FCC and BCC. It has high hardness, high strength, good wear resistance, corrosion resistance and excellent oxidation resistance. Laser surface modification technology can be used to fabricate high performance coatings on low cost metallic materials. In this paper, Nd:YAG solid-state pulse laser, semiconductor, CO2 and fiber laser were used to prepare series of laser high-entropy alloying layers on the surface of pure copper, and the forming quality and microstructure of high-entropy alloying layer by laser irradiation were studied. The influence law of performance. The microstructure, composition, phase structure and properties of alloyed layer were systematically studied by metallographic microscope, scanning electron microscope, energy spectrometer, X-ray diffractometer, microhardness tester, nano-indentation instrument and reciprocating friction tester. The experimental results show that the quaternary FeCoCrAl alloy is composed of BCC and two intermetallic compounds. The FeCoCrAl quaternary alloy powder can be synthesized by Nd:YAG laser irradiation on the surface of pure Cu to prepare FeCoCrAl/Cu quaternary high entropy alloying layer. The alloying layer has a simple solid solution structure. As the current of Nd:YAG laser increases, the alloying layer changes from granular to cellular. Thermodynamic analysis shows that the FeCoCrAl/Cu laser high entropy alloying layer meets the condition of forming solid solution. The hardness of high entropy alloying layer is improved obviously because of solid solution strengthening and grain refinement. The high entropy alloying (FeCoCrAlNix/Cu) layer prepared by semiconductor, CO2 and optical fiber laser alloying technology was used. With the addition of Ni element, the phase composition of the alloying layer gradually changed from FCC BCC to single FCC structure. Its hardness shows a downward trend. The alloying layer with Mo and Ti elements has other phases except simple solid solution phase, while the alloying layer with Si element is still simple solid solution, and the formability is good. The results of reciprocating wear test show that the wear resistance of FeCoCrAlNix/Cu (x0. 0. 5%) laser alloyed Ni is not consistent with the change of hardness. The wear resistance of FeCoCrAlNi/Cu alloying layer is better because of the existence of meridian structure. In addition, the wear surface of FeCoCrAlSi0.5/Cu alloying layer is still smooth, no obvious adhesion, only a small amount of black particles appear, and the amount of wear is small. Due to the difference of laser power density and the absorptivity of materials to different wavelengths, the microstructure of different laser alloying layers is different. The order of laser energy density in the process of laser absorption and alloying by Cu is as follows: CO2 laser < fiber laser < semiconductor laser. Combined with the macroscopic formability, microstructure, properties and preparation process of laser high entropy alloying, the optimal method of high entropy alloying on the surface of Cu substrate is achieved by using optical fiber laser.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.4
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