Research On Metal Based Ceramic Composite Coatings And The Wear Resistance Prepared By Laser Cladding On H13 Die Steel

Wear is a common failure form of die steel. The layer prepared by laser cladding and other surface modification technology ameliorates the structure and properties of the surface of materials, which can effectively improve the service life of the die. TiC particles reinforced Ni based alloy composite coatings were prepared on the surface of H13 die steel by YAG laser cladding, and the composition of the coatings was optimized by adding different contents of high temperature lubricant CaF₂ and rare earth element oxide Y₂O₃. The microstructure, chemical elements distribution and phase composition of different coatings were analyzed by means of optical microscope, the scanning electron microscope with energy dispersive spectrum, and X-ray diffraction. And micro-hardness of different coatings were tested, and wear resistance of different coatings were characterized under the conditions of loading of 300 N, speed of 180r/min, and distance of 1000 r. The effects of the contents of TiC, CaF₂, and Y₂O₃ were discussed.The results indicated that, TiC/Ni60 laser cladding composite coating was mainly composed of FCC γ-（Fe, Ni） as the matrix, and Fe3 C, Cr23C6, Ni2 Si and TiC evenly distribute as strengthening phases in γ-（Fe, Ni） supersaturation. γ-（Fe, Ni） was distributed inside the dendrites and the eutectic compounds were mainly composed of Cr23C6 and Ni2 Si. By adding TiC, the microstructure of coatings was refined obviously, and the structure became even more refined because of the increasing liquidity after adding Ca F2. The composite coatings still crystallized in a sub eutectic way, in which network eutectic structure was formed by Ca F2 and the supersaturated Ni and Cr. And with the increase of the content of CaF₂, eutectic compounds were interrupted and became thin. After adding Y₂O₃, the structure of composite coatings turned more uniform and compact, and the sizes of grains were refined further into a sub-micro scale.The results of micro-hardness test showed that, the micro-hardness of cladding coatings was enhanced obviously than that of the substrate, the value of micro-hardness of the samples of laser remelting was higher than H13, and lower than the composite coatings. The average micro-hardness of composite coatings improved with the increase of TiC content, the maximum micro-hardness was obtained when TiC content was 30%（mass fraction）,which was 873 HV0.2. The mcro-hardness of 20%TiC（mass fraction） coating decreased after adding CaF₂, and continuously declined with the raise of CaF₂ content. By adding Y₂O₃ into the composite coatings, the micro-hardness went up and the maximum and minimum of micro-hardness was obtained respectively when the TiC content reaching to 1% and 1.5%（mass fraction）.The results of wear test indicated that, the average friction coefficient of 100%Ni60（mass fraction） laser cladding coatings was 0.34, which is the maximum value among laser cladding coatings, while it was obtained 0.41 of H13 steel. The friction coefficient could be diminished by adding TiC, but the content of TiC affected the friction coefficient barely. The wear resistance of cladding coatings improved remarkable and that of laser remelting sample also enhanced comparing with H13 steel. The wear mechanism of H13 steel and laser remelting sample was mainly micro-cutting, while it turned into brittle spalling when composite coatings during test. The average friction coefficient of coatings declined by adding CaF₂. The minimum mass loss was obtained when CaF₂ content was 5%（mass fraction）,which was 1.8mg. The mass loss became more when CaF₂ content was beyond 10%（mass fraction） than that before adding, and the maximum mass loss was acquired when CaF₂ content was 15%（mass fraction）. The wear mechanism of CaF₂/TiC/Ni60 composite coatings was also mainly brittle spalling and micro-cutting, but the spalling pit marks became shallow. The content of Y₂O₃ barely affected the friction coefficient. The mass loss of Y₂O₃/CaF₂/TiC/Ni60 composite coatings decreased when Y₂O₃ content was 0.5%（mass fraction）, which was 1.6mg, however the mass loss became rising with the raise Y₂O₃ content when the content passed 0.5%（1%, 1.5%, mass fraction） comparing with Ca F2/TiC/Ni60 composite coatings, and the maximum mass loss was obtained when Y₂O₃ content came to 1.5%（mass fraction）. The wear mechanism of Y₂O₃/CaF₂/TiC/Ni60 composite coatings was also brittle fracture and spalling with a very small amount of micro-cutting marks.