Papers by Author: Yi Shan Li

Abstract: In this experiment Al2O3 gradient ceramics coating is cladded on the high Cr cast steel by 5kW crosscurrent CO2 laser with Ni-based alloy which is used as transitive metal. The microstructure is analyzed with optics microstructure analyzer and the crystal grain characteristic is studied. The microstructure of the laser cladding layer have the plane crystal zone, the butcher crystal zone, the dendrite zone and the surface equiaxed grain zone that grow along the substrate. The microstructure of the coating compared with the substrate is extremely tiny, and the microstructure of the multi-layer cladding presents stratification. The phase composition of the clad coating is composed primarily of NiAl intermetallic compound, but also includes γ-FeNi and a little Ni3Al compound. In the coating the Al2O3 pellet that some present the unit crystal form, and some little accumulate in together, plays the dissemination strengthening role in the coating material. The massive twin crystals and the dislocation staffing are presented in the clad coating.

Abstract: In order to improve surface properties, high chromium austenitic base heat-resistant cast steel was scanned with a 5kW continuous wave CO2 laser, the specimen was aged at the temperature of 600°C~900°C. The microstructure and phase composition of the specimen were analysed with optical microscopy, electronic microscope and X-ray diffractionse. The hardness was measured. The results show that as-cast structure of high chromium cast steel is coarse and non-homogeneous, and mainly consist of austenite, ledeburite and carbides. After laser surface melting, the section is divided into the melted zone consisted of fine austenite and carbides, the heat affected zone composed of austenite and eutectic carbides, and the base meta1. The melted zone is very fine structures with dendritic crystals, only at the bottom a cellular structure is observed. A continuous carbide network is located in the austenitic grain boundaries at the heat affected zone. Carbides particles distribute dispersed out, the hardness of melted zone increases 35% than the base metal after aging. The area and the hardness of various zones are related to the laser processing parameters. The hardening depth of melted zone and heat affected zone may be up to 200μm~300μm.