Fundamental Research On Modified Layers On The Surface Of The Mould Copper Plate Fabricated By Infiltration

In recent years, the study on the CCM copper mould surface modification which is aim to improve copper surface wearing resistance, ensure the excellent bonding strength and thermal conductivity between the modified layer and the substrate has become an important issue in the field Ironmaking & Steelmaking. Many techniques such as electroplating, electroless plating and, thermal spraying electroplating, have been widely used to prepare the modified layer of copper mould surface. These techniques can improve the wearing resistance of mould copper plate, but they have bad effect on the bonding strength and thermal conductivity between the modified layer and the substrate. W-Cu/WC-Cu composites possess the high hardness, wearing resistance and excellent thermal conductivity, which can acquire good bonding strength between the composites and the copper substrate by improving copper content of the composites. Therefore, a new method named infiltration has been applied to fabricate W-Cu/WC-Cu surface modified layer of copper mould firstly in order to promote the life span of the CCM mould, which is the basic research for practical application of W-Cu/WC-Cu modified layers on the surface of CCM mould copper plate.In this paper, the W powder size, sintering temperature of W skeleton and infiltrating way are adjusted to gaining homogeneous microstructure of W-Cu modified layer. Also, the WC particle size, sintering temperature of WC skeleton and infiltrating temperature are adjusted to gaining homogeneous microstructure of W-Cu modified layer. The result show:(1)The better fabrication process of W-Cu40 modified layers:-300 meshes W powders sintered at 1300℃and infiltrated horizontally at 1350℃, which obtained homogeneous microstructure and high density of W-Cu40 modified layers.(2)The better fabrication process of WC-Cu50 modified layers:1μm WC powders sintered at 1120℃and infiltrated at 1350℃, which obtained homogeneous microstructure and high density of W-Cu40 modified layers.Many properties of the W-Cu/WC-Cu modified layers, such as density, wearing resistance, interface bonding strength and thermal fatigue performance, have been detected in this paper. The results show:(1)The wear resistance of W-Cu40 modified layer was more than pure Ni. As W particle size increased, the wear resistance of W-Cu40 modified layer decreased. As W content increased, the wear resistance of W-Cu modified layer also increased.(2)The WC-Cu50 modified layers had excellent wear resistance. As WC particle size decreased, the wear resistance of WC-Cu50 modified layer increased. The results of shear test show:Shear fracture was located on the side of copper substrate rather than the interface, which showed the good bonding strength between W-Cu40 modified layers and copper substrate.The thermal fatigue test result show:(1) W-Cu40 modified layers had good thermal fatigue performance. As W content increased, fatigue crack of W-Cu modified layers increased. As W particle size increased, the probability of fatigue crack grown decreased, and the width of fatigue crack also decreased. As test temperature increased, the width of fatigue crack also increased. (2) There had not founded any fatigue crack at the interface between WC-Cu50 modified layers and copper substrate after 200 times psychro-thermal cycles at 600℃, which showed the high thermal fatigue performance of modified layers.