本文選題：鈦合金 + 電火花沉積��； 參考：《河南科技大學》2015年碩士論文

【摘要】：鈦合金擁有密度小、比強度高、耐熱性好、抗疲勞和蠕變性能好等優(yōu)點,在航空、航天、航海、能源化工、汽車、冶金和核工業(yè)等領域都有重要應用。鈦及鈦合金的硬度較低,摩擦系數(shù)較大,耐磨性差,性質(zhì)非�；顫�,制約了其應用。采用電火花沉積技術,對鈦及鈦合金進行表面改性,可以改善其表面性能。利用DZ-4000III電火花沉積/堆焊機在TA2基體上制備了Ni Cr、Co Cr、WC改性層,對改性層組織、性能以及結合機理進行了研究。研究表明:隨著沉積電壓增大,改性層質(zhì)量顯著降低,改性層表面及內(nèi)部出現(xiàn)的裂紋等缺陷增多;改性層厚度并不是隨著沉積時間增加而持續(xù)增加;改性層與基體之間的主要元素發(fā)生了擴散。三種改性層中,CoCr改性層質(zhì)量較差,改性層表面微裂紋較多。WC改性層顯微硬度最高可達950.7HV200g,Co Cr改性層次之,Ni Cr改性層最低;隨著與改性層表面距離的增大,改性層顯微硬度逐漸降低;硬度變化趨勢表明,改性層與基體間存在過渡區(qū)。WC改性層厚度太薄(僅為25μm左右),且與基體熔合較差,應用受到限制。制備的Zr/WC復合改性層(鋯做中間層),硬度可達960.5HV200g,厚度可達50μm。探索了在TC11合金基體上制備ZrTi改性層,改性層厚度可達200μm,改性層顯微硬度可達700HV200g以上;改性層與基體之間的主要元素發(fā)生了擴散,且與基體結合很好,改性層內(nèi)部有少量氣孔,未發(fā)現(xiàn)微裂紋等缺陷,較好實現(xiàn)了TC11的表面改性。顯微分析表明,電火花改性層與基體材料之間屬于冶金結合。改性層自身具有較好的強度,NiCr改性層強度可達580MPa,Co Cr改性層強度可達350MPa。改性層中殘余應力分布不均勻,既有拉應力,也有壓應力。殘余壓應力會提高改性層疲勞強度,抑制疲勞裂紋的產(chǎn)生,而且可以通過增加裂紋的閉合效應來降低疲勞裂紋的擴展速率,殘余拉應力則相反。電火花沉積放電機理為接觸放電。采用高速攝影觀測了電火花沉積起弧直至形成飛濺的整個過程。電火花沉積過程中存在電極材料的損失,隨著電壓增大,電極對基體的熔敷率有所降低。
[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.
【學位授予單位】：河南科技大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TG174.4

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本文編號：1990509