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钛基梯度功能材料激光快速成形技术研究
Alternative TitleFabrication of TiMatrix FGMUsing Laser Metal Deposition Technique
杨光1,2
Department装备制造技术研究室
Thesis Advisor刘伟军 ; 王维
ClassificationTG302
Keyword钛合金 激光快速成形 碳化铬 原位合成 碳化钛 耐磨 功能梯度材料
Call NumberTG302/Y27/2010
Pages135页
Degree Discipline机械电子工程
Degree Name博士
2010-11-25
Degree Grantor中国科学院沈阳自动化研究所
Place of Conferral沈阳
Abstract功能梯度材料是为适应航天航空等领域的需要,满足极限环境下能反复地正常工作而发展起来的一种新型功能材料。其成分和结构呈连续的梯度变化,从而使材料的力学、热学和化学性能等按照设计呈连续地变化。本文研究FGM激光快速成形制备技术。通过精确控制多种粉末的输送和相应的工艺可以实现材料组成、微观组织结构和性能的梯度分布及多种材料的集成。 本文选择Ti6Al4V和纯Ti作为成形层材料主要成分可以有效提高与基体浸润性,实现成形层与基体的良好过渡。强化相选择和钛合金密度相近的TiC,有利于使粉末混合均匀,成形后成分分布均匀。在添加方式上选择原位自生的方法,即在成形粉末中添加Cr3C2陶瓷粉末,通过与Ti反应得到TiC。强化相在FGM中被设计成幂函数形式分布,并对FGM的弹性模量、泊松比、热膨胀系数、密度以及热导率等物性参数进行估算。有限元计算表明,钛基功能梯度材料单层厚度为1mm,最少层数为6层,形状分布因子为P=0.5时所设计的FGM热应力缓和最明显。 通过混合粉末激光快速成形实验,获得最优参数组合,根据实验数据制订激光快速成形FGM工艺规范及工艺参数图表。 FGM宏观和微观形貌分析表明成形层与基体结合良好,成形层组织均匀致密,没有气孔、裂纹等缺陷。显微硬度从成形层到基材的显微硬度呈现梯度下降,成形层硬度最高,大约是基材的3倍。 摩擦磨损试验在SRV-3摩擦磨损试验机上进行,试验条件为室温大气干滑动摩擦磨损,对磨副为GCr15钢球,计算体积磨损量,并采用扫描电镜观察磨损表面形貌,以此评价梯度成形层的磨损性能。基材的摩擦系数平均为0.9,FGM的摩擦系数为0.9~1.0之间,基材的体积磨损量为0.127mm3,成形层体积磨损量为0.002723mm3,基材的体积磨损量是成形层的46.6倍。磨损机制分析表明FGM以磨粒磨损为主,存在少量的粘着磨损,基材以氧化磨损和磨粒磨损为主。 高温滑动磨损试验在GW/ML-MS型高温销盘摩擦磨损试验机上进行,采用摩擦磨损试验机自带的标准附件记录摩擦系数,在表面形貌仪上测定试件的磨痕,计算磨损体积,并用扫描电镜观察磨损表面形貌。500℃高温下,Ti6Al4V和成形层的磨擦系数分别为0.32和0.37,Ti6Al4V的磨损量明显比成形层的磨损量大,磨损体积比为2.86。高温下摩擦系数较室温时有明显的降低,表明高温下摩擦表面形成氧化膜具有减摩效果。在500℃高温干摩擦条件下,成形层与基材磨损体积比为1/2.8。因为钛的氧化物减磨作用,摩擦系数较室温下较有大幅下降,成形层中TiC强化相的“骨架”是抵抗磨损的主要原因。
Other AbstractFunctionally Graded Materials (FGM) is now widely used by the materials community for a class of materials exhibiting spatially inhomogeneous microstructures and properties. Graded materials in themselves are not something new, but what is exciting about them is the realization that gradients can be designed at a micro-structural level to tailor specific materials for their. Laser Metal Deposition(LMD) processes have drawn much attention lately  because of their ability to form small quantities of functional prototypes and structural parts at very low cost to the buyer.LMD processes are similar in that a three-dimensional part in a computer-aided design file is sliced into layers which, in turn, define laser scan trajectories. A high-power laser is used to heat and melt metal powder, which solidifies to form a fully dense layer. The addition of multiple layers will produce a three-dimensional, fully dense part having net or near-net shape. This paper mainly focused on the application of Laser metal deposition technology to fabricate FGMs. That is to say FGMs with gradient distribution of material composition, microstructure and properties could be achieved by precisely controlling the delivery of a variety of materials. Then the intelligent manufacturing technology can be developed with the function of material design, preparation, processing. Laser metal deposition system is the most important part for fabrication of titanium matrix functionally gradient material, also in the field of technology research and industrial application. Experimental set-up consists of high-power CO2 laser source and control system including laser beam delivery system, vacuum chamber and vacuum acquiring system, powder feeding system and powder delivery nozzle, positioning devices and CAM software. Titanium and titanium alloy react easily with impurity in the air such as oxygen, nitrogen, carbon etc. During the fabrication, molten pool and its heat affected zone are easily oxidized under high temperature, which lead to low property of the coating. So vacuum chamber is the key part of the system. Among the effects of Laser metal deposition of titanium-matrix FGM factors, the cladding layer material system is a major factor, it is directly related to the cladding layer of service performance. In this paper, pure Ti and Ti6Al4V powder are used as the main components of coating materials which can gain the good wetting cladding and achieve the gradient cladding layer ,further more which can  improve wear resistance while maintaining titanium excellent features such as low density, high specific strength. The experiment tried to lead in TiC-reinforced phase to titanium matrix and fabricated FGM. Density of TiC is closed to Ti, which made them mix evenly and the component in FGM distribute uniformly. TiC and Ti have the nearly coefficient of thermal expansion, so that the cooling process does not produce significant stress, prevent cracks ,and improve the quality of fabricated material. This paper reports the investigations in-situ synthesis TiC reinforced layer on Ti6Al4V alloy by LMD using Cr3C2 and Ti powders mixtures. Mixtures of Cr3C2 powder and pure Ti powder were thoroughly mixed by ball milling in an argon atmosphere. The powder has a mesh size of -100/+325(the particle size between 45 and 150μm).The powder was exsiccated in drying vacuum cabinet for 10 hours with the temperation of 150℃ and the substrate was preheated to 500℃ by home-made preheater. The TiC-reinforced phase has no pollution on its surface, and is well-bonded to the substrate, at the same time it is even distributed. Result of thermodynamic calculations show that the in-situ method is feasible. Distribution of reinforced phase in FGM shows power function relationship, and the following physical parameters were estimated: modulus of elasticity E, Poisson's ratio, thermal expansion coefficient, density and thermal conductivity λ .Then the finite element calculation showed that the thickness of single layer for Ti-matrix FGM is 1mm,the minimum number of layers is 6 ,and the thermal stress reduction in FGM is most obvious when the shape distribution factor P = 0.5 . The optimal parameters that can be obtained through the LMD process are laser power, scanning speed, powder delivery, focal length, ration of overlap etc. Then according to the experimental data FGM process specification and process parameters charts can be drawn, which can work as a guide to fabricate FGM. The results of analysis for FGM macrostructure and microstructure morphology showed that the layers are crack free and porosity free with low dilution and good metallurgical bond to the substrate and there exists a good compatibility of the reinforcement phase to the matrix material. X-ray diffraction analysis showed that the phase structure of FGM are mainly Ti, TiC and a small amount of TiCr2 phase, which indicates the in-situ reaction design rational. Microhardness analysis indicated that the hardness showed gradient descent from the cladding layer to the substrate ,and the coating hardness is about 3 times the substrate. Else the hardness of bonding zone is reduced for diffusing of substrate element. Gradient coating with stable hardness showed it has even mechanical properties in the region same thickness, which is good to maintain stability under the action of external force. Wear resistance of the coating was examined by means of SRV-3 Wear Tester. A sphere-on-flat geometry was used for the low amplitude oscillating dry sliding tests, in ambient conditions. the sample disk was in size 10mm×10mm×2.8mm with a surface polished down to emery paper of 1200 for the test. the coupled pin was a bearing ball of 7mm in diameter with hardness HRC60 made of GCr15 steel. The testing conditions were set at: load=20N, sliding frequency=10Hz,sliding distance=1mm,sliding time=0.5h.Thought the same test the following results were got: the substrate wear volume is 0.127mm3, and the coating wear volume is 0.002723 mm3.That is to say the wear resistance of the coating can be improved 46.6 times. Wear mechanism analysis showed that the main wear mechanism of substrate is oxidation wear and abrasive wear. and the coating is abrasive wear and few adhesive wear. and also the fretting test indicates the coating with Cr3C2 has high resistance to wear than subtract. GW/ML-MS pin-on-disk wear tester was used to examine wear resistance of the coating in temperature of 500℃.the sample disk was in size of Φ60mm×6mm with a surface polished down to emery paper of 1200 for the test. The coupled pin was a ceramic ball of 7mm in diameter made of Si3N4 ceramic, and the diameter of friction marks was 30mm,in addition the other fretting conditions were summarized as follows: the test load was 670g,revolving speed was 320r/min, wearing distance was 900m. A Talysurf-4 type profilometer was adapted to measure wearing profiles, from which the volume of wear out of the material was estimated. The morphologies of the wearing surface and also the debris were examined by SEM. The result of wearing test showed in the friction coefficient of Ti6Al4V substrate and coating were 0.32 and 0.37,else the Ti6Al4V substrate wear volume significantly higher than the wear volume of coating ,their wear volume ratio was 2.86.At 500℃temperature wear resistance of the coating is about 2.8 times of Ti6Al4V substrate. which is due to that the titanium oxide can reduce friction, so friction coefficient can decrease obviously than that at room temperature. In addition the action of Laser in-situ synthesis TiC hard phase is the main reason for better wear resistance.   This paper lays emphasis on the research of construction Laser metal deposition system, optimization fabrication process, FGM design and manufacturing technologies and performance analysis and testing, which is necessary for improving the performance of materials and has important military and economic significance.
Language中文
Contribution Rank1
Document Type学位论文
Identifierhttp://ir.sia.cn/handle/173321/9306
Collection智能产线与系统研究室
Affiliation1.中国科学院沈阳自动化研究所
2.中国科学院研究生院
Recommended Citation
GB/T 7714
杨光. 钛基梯度功能材料激光快速成形技术研究[D]. 沈阳. 中国科学院沈阳自动化研究所,2010.
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