基于电火花沉积钛及钛合金表面改性层微观组织及性能研究

发布时间：2018-06-07 08:20

本文选题：钛合金 + 电火花沉积　；参考：《河南科技大学》2015年硕士论文

【摘要】：钛合金拥有密度小、比强度高、耐热性好、抗疲劳和蠕变性能好等优点,在航空、航天、航海、能源化工、汽车、冶金和核工业等领域都有重要应用。钛及钛合金的硬度较低,摩擦系数较大,耐磨性差,性质非常活泼,制约了其应用。采用电火花沉积技术,对钛及钛合金进行表面改性,可以改善其表面性能。利用DZ-4000III电火花沉积/堆焊机在TA2基体上制备了Ni Cr、Co Cr、WC改性层,对改性层组织、性能以及结合机理进行了研究。研究表明:随着沉积电压增大,改性层质量显著降低,改性层表面及内部出现的裂纹等缺陷增多;改性层厚度并不是随着沉积时间增加而持续增加;改性层与基体之间的主要元素发生了扩散。三种改性层中,CoCr改性层质量较差,改性层表面微裂纹较多。WC改性层显微硬度最高可达950.7HV200g,Co Cr改性层次之,Ni Cr改性层最低;随着与改性层表面距离的增大,改性层显微硬度逐渐降低;硬度变化趋势表明,改性层与基体间存在过渡区。WC改性层厚度太薄(仅为25μm左右),且与基体熔合较差,应用受到限制。制备的Zr/WC复合改性层(锆做中间层),硬度可达960.5HV200g,厚度可达50μm。探索了在TC11合金基体上制备ZrTi改性层,改性层厚度可达200μm,改性层显微硬度可达700HV200g以上;改性层与基体之间的主要元素发生了扩散,且与基体结合很好,改性层内部有少量气孔,未发现微裂纹等缺陷,较好实现了TC11的表面改性。显微分析表明,电火花改性层与基体材料之间属于冶金结合。改性层自身具有较好的强度,NiCr改性层强度可达580MPa,Co Cr改性层强度可达350MPa。改性层中残余应力分布不均匀,既有拉应力,也有压应力。残余压应力会提高改性层疲劳强度,抑制疲劳裂纹的产生,而且可以通过增加裂纹的闭合效应来降低疲劳裂纹的扩展速率,残余拉应力则相反。电火花沉积放电机理为接触放电。采用高速摄影观测了电火花沉积起弧直至形成飞溅的整个过程。电火花沉积过程中存在电极材料的损失,随着电压增大,电极对基体的熔敷率有所降低。
[Abstract]:Titanium alloys have many advantages, such as low density, high specific strength, good heat resistance, good fatigue and creep resistance, and have important applications in the fields of aviation, aerospace, navigation, energy and chemical industry, automobile, metallurgy and nuclear industry. Titanium and titanium alloys have low hardness, high friction coefficient, poor wear resistance and very active properties, which restrict their application. The surface properties of titanium and titanium alloy can be improved by EDM. The Ni-Cr-Co Cr-WC modified layer was prepared on the TA2 substrate by DZ-4000III EDM / surfacing machine. The microstructure, properties and bonding mechanism of the modified layer were studied. The results show that with the increase of deposition voltage, the quality of the modified layer decreases significantly, and the defects such as cracks on the surface and inside of the modified layer increase, and the thickness of the modified layer does not increase continuously with the increase of deposition time. The main elements between the modified layer and the matrix were diffused. Among the three kinds of modified layers, the quality of CoCr modified layer is poor, and the microhardness of modified layer with more micro-cracks on the surface of WC layer can reach the lowest of 950.7 HV200g / Co modified layer with the increase of the surface distance between the modified layer and the modified layer. The microhardness of the modified layer decreases gradually, and the change trend of hardness indicates that the thickness of the modified layer is too thin (only about 25 渭 m), and the fusion with the matrix is poor, so the application is limited. The prepared Zr/WC composite modified layer (zirconium as intermediate layer) has a hardness of 960.5 HV200g and a thickness of 50 渭 m. The preparation of ZrTi modified layer on the substrate of TC11 alloy was investigated. The thickness of the modified layer was up to 200 渭 m and the microhardness of the modified layer could reach to more than 700HV200g. The main elements between the modified layer and the matrix were diffused and bonded well with the matrix, and there were a few pores in the modified layer. No defects such as microcracks were found and the surface modification of TC11 was well realized. Microscopic analysis shows that the EDM modified layer and the matrix material belong to metallurgical bonding. The strength of NiCr modified layer can reach 580MPA / a and the strength of CoCr modified layer can reach 350 MPA / a. The residual stress distribution in the modified layer is uneven, both tensile and compressive stress. The residual compressive stress can increase the fatigue strength of the modified layer and inhibit the fatigue crack formation. Moreover, the fatigue crack growth rate can be reduced by increasing the crack closure effect, while the residual tensile stress is opposite. The discharge mechanism of EDM deposition is contact discharge. The whole process of electric spark deposition from arc to spatter was observed by high speed photography. The electrode material is lost in the process of EDM deposition, and the deposition rate of the electrode to the substrate decreases with the increase of the voltage.
【学位授予单位】：河南科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.4

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