Study On Fretting Wear Characteristics Of Welded Jiont And Deposited Metals In Gross Slip Zone

Fretting is a relative movement of small amplitude occurring at the interface of two contacting surfaces. Usually, fretting results in friction, wear of the two contacting surfaces, causing the material loss or size variation of the mechanical members. The interlocking, loosening of the components can be induced by fretting. Moreover, the nucleation and the growth of the fatigue cracks can be accelerated because of fretting, which results in the significant decrease of the component fatigue lifetime. Fretting has become one of the main reasons that lead to the failure of many key parts or components. Many fretting experiments have been conducted by many researchers to investigate the fretting damage mechanism, affecting factors and the protective precautions. But the research concerning fretting wear characteristics of the welded joint metals or the deposited metals has not been reported so far. Therefore, it is of practical importance to study on the fretting wear characteristics of the welded joint and deposited metals for the comprehensive characterization of the micro-region properties of welded joint metals or deposited metals.Fretting experiments are performed using the electro-hydraulic servo fretting test rig for the metals of the welded joint prepared by steel materials 16Mn, 1Cr18Ni9Ti and Domex700MC, respectively, and the deposited metals obtained by surfacing process for the combination of substrate material A3 steel with surfacing electrode CHR322 and the combination of substrate material 45# steel with electrode CHR207,227 and 237, respectively. The microscopic examination of the fretting wear scars has been performed through optical microscope, scanning electron microscope, profilometer, confocal laser scanning microscope and energy dispersive spectroscope to study the fretting wear characteristics of the welded joint metals and deposited metals. The main research work done and conclusions obtained are as follows. 1. The outer profile shape of fretting wear scars of the welded joint metals is an ellipse with a slightly smaller minor axis than the major axis which parallels to the fretting direction. The morphology of fretting wear scars on weld metals or heat-affected zone (HAZ) metals with different location for the same one welded joint is differentiated. There are different maximum wear depth and wear area of the fretting scars at different locations on welded joint. For 16Mn steel welded joints prepared by double-wire submerged arc welding process, the variation of the maximum wear depth on weld metal and HAZ metal is greater than that of the wear area. For 1Cr18Ni9Ti stainless steel joints made by shielded metal arc welding process, the fluctuation of wear area is larger than that of the maximum wear depth for weld metal, but this fluctuation is inverted for HAZ metal. For Domex700MC steel welded joints prepared by carbon-dioxide arc welding process, the variation of the wear volume and the maximum wear depth is greater than that of the wear area for both weld metal and HAZ metal.2. The relationship curves between the coefficient of friction and the cycle number for the weld metal at different location have the same shape as the HAZ. Initially, the coefficient of friction increases rapidly, after it goes through the maximum, it decreases, and the steady-state friction coefficient is then reached. The hysteresis loops of fretting log are quasi-rectangular-shaped for weld and HAZ metals. The curve which represents the friction coefficient of better wear resistance metal exists at the utmost right-handed side.3. The micro-cracks on the fretting wear scars for weld and HAZ metals can be observed. The growth and intersection of these micro-cracks which are perpendicular to or with different angle to the fretting direction leads to the metal detachment, and the craters with irregular outer boundary are formed. The craters formed are beneficial to the nucleation of new micro-cracks. The wear loss of the weld and HAZ metals is piece delaminated and particle detached.4. The dissipated energy of the weld and HAZ metals varies with the each fretting cycle. The dissipated energy is increased with the increase of fretting cycles, after the maximum, it becomes decreased and the constancy is then approached. The area enclosed by maximum quasi-rectangular-shaped hysteresis loop is corresponded to the maximum dissipated energy.5. The deposited metals obtained by surfacing process using electrode of different types have differential fretting wear characteristics. The surfacing current used influences the fretting wear properties of the deposited metals. The curve between the friction coefficient and cycle numbers moves toward right-handed side with the increase of surfacing current. Compared with fretting wear resistance of substrate metal, the fretting wear resistance of the deposited metals is better. The effect of the substrate metal on the deposited metal property can be characterized by penetration ratio. The amount of the substrate metal molten will affect the fretting wear characteristics of the deposited metal. On the other hand, the effect of the substrate metal on the deposited metal properties becomes decreased with the increase of deposited metal layer number.