Research On Microstructure,Properties And Wear Mechanism Of Ductile Iron With Non-smooth Surface Processed By Laser

Wear is a primary die failure mechanism, and improving the wear resistance is an important way to improve the service life of mold surface. To improve the wear resistance of the metal mold surface, combining bionic non-smooth theory, laser process is adopted to produce strip non-smooth units and non-smooth surface on mold materials by pulsed laser. The shape of the specimens processed with various energy densities is observed and analyzed. The wear mechanism of specimens with non-smooth surface is discussed through observing the microstructure and measuring properties.The results show that when the energy density is relatively high, the shape of non-smooth units’cross-section likes a "nail". The depth of non-smooth units is greater than350μm which is much deeper than that of the specimens processed with low energy density. When the energy density is relatively low, the shape of non-smooth units’ cross-section likes a "new moon". When the energy density is relatively high, non-smooth units are easy to form thermal stress and organizational stress, thus are easy to appear cracks. When the energy density is relatively low, the thermal stress small, there are some martensites in non-smooth units. The martensite can reduce the stress concentration and inhibit crack initiation.All kinds of non-smooth specimens processed by laser their wear resistance is better than the smooth specimen without laser processing. The cross-sectional area of unit processed in water is smaller than the units processed in air. A certain amount of nanocrystalline exist in the surface of specimens processed in water which results higher hardness The average micro-hardness values and wear property of specimens processed in water is better than the specimens processed in air. In the same medium, cross-sectional area of non-smooth unit increase with the increasing of laser energy density, the ability of wear resistance improves.The improvement of wear resistance of non-smooth specimens depends on the cooperation of micro-hardness and effective cross-section area. The micro-hardness and cross-sectional area is related to the energy density. Only the laser energy density is appropriate, the non-smooth units could have the best wear properties.Larger cross-sectional area is conducive to maintaining its morphology longer of non-smooth unit, and protects the matrix from direct wear, hinders wear process. The friction coefficient of non-smooth surfaces is reduced by the high hardness of non-smooth unit. Non-smooth unit can form a smooth surface and be able to maintaining its morphology then support the structure of worn surface stably. Non-smooth unit can slow down the rise recover rate of friction coefficient, thus hinders the wear process which improve the wear resistance. During the wear process, the lubrication of graphite reduces the friction coefficient which is more conducive to improve the wear resistance of non-smooth specimens.