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Research On Technology And Mechanism Of The Novel Surface Strengthening Method Combining Ultrasonic Impact Treatment With Electrospark Deposition

Posted on:2016-08-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y LiuFull Text:PDF
GTID:1221330485454380Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
Surface strengthening technology is an important mean to improve the surface or fatigue performance of material. However, a single traditional surface strengthening technology can not improve the surface and fatigue performance in the same time.Based on above reason, a novel surface strengthening technology combining ultrasonic impact treatment with electrospark deposition(Ultrasonic Impact Electrospark Treatment, UIET) was developed. The UIET coating with compressive residual stress was fabricated on metal material by developing the UIET equipment and a lot of process tests. The mechanism of UIET process was revealed by analyzing the impact signals and electrospark current signals of UIET. The microstructure of UIET coating was characterized using SEM, EDS, TEM, XRD and XPS techniques.The formation mechanism and performance of UIET coating were investigated.Using Ti-6Al-4V as base material, the mechanism of UIET process and formation of UIET coating were investigated. Results show that UIET is a sustainable process,and the UIET coating is formed by alloying reactions among base material, shock ball and ionized air or liquid. The grains of coating are fine because of rapid cooling and vibrating action.Using 45# steel and YG6 as base material and shock ball, respectively, the experimental research results show that the steady temperature and impact energy of shock ball are the major factors that affect the quality of UIET coating. The UIET coatings with uniform thickness and compressive residual stress are fabricated using the optimized parameters. The area under coating is hard to erode is call “white layer”.The hardness of surface is improved because of coating, while the hardness of white layer is improved because of grain refining. The surface residual stress of UIET specimen is-1786 MPa.The wear and corrosion performance of UIET surface are improved due to the coating and the metallurgic combination between coating and base material. The fatigue performance is also improved at low and middle stress level. The mechanism improving fatigue performance is that the possible stack-shaped defects are remelted by electrospark heating, and the coating can reduce the mechanical relaxation ofresidual stress in order to delay the initiation and extension of fatigue cracks.
Keywords/Search Tags:Ultrasonic impact treatment, electrospark deposition, coating, residual stress, wear, fatigue, corrosion
PDF Full Text Request
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