Study On Vacuum Infiltration Casting Technique And Tribological Properties Of Ni-based Surface Infiltrated Layer On Cast Steel Substrate

The oxidation and wear was the main failure form for materials under elevated temperature, high speed and over loading rigorous conditions. These parts fabricated using wear-resisting materials could meet the requirement for wear resistance under elevated temperature. But the toughness of materials would be decreased obviously, which could not meet the basal toughness requirement for structural materials. However these parts could not meet the whole service propeties and the cost of the materials are high, which resulted in their service life could not be prolonged. The surface engineering technology was good method for setting this kind of problem. These surface technologies were carried out after the parts forming. The sources of energy would be expended additionally and the deformation was concomitant during the fabrication of surface coating. The surface properties were finite owing to the mechanical bond between the surface coatings and substrate.The infiltration technique is a novel process for producing surface materials. The surface infiltrated layer was obtained during the casting process using the superheat of pouring melt and the latent heat during solidification. The infiltration casting technology has become a kind effectual technology for improving the surface properties of casting steel. It has potential advantages to achieve a near-net shape product in a simple and cost effective manner, widely select the substrate, and have good bonding between the surface layer and substrate.Guide plate is an important accessory for steel line rolling production, which mainly used for booting and carrying the steel wire passed the rolling equipment. On the actual production line, the abrasion of guide plate is very serious. Based on the special working conditions of guide plate, guide plate material has become really important for innovation and improvement. In this paper, a wear-resistant and high temperature oxidation-resistance of the infiltrated Ni based alloying infiltrated layer and Ni/ZrO2 infiltrated composite layer were fabricated on the ZG45 surface through vacuum infiltration casting technique. The washing pasty technics was put forward on the bassis of the merit of coating and pasty was combined. The surface infiltrated layer or composite layer was fabricated using washing pasty technics on the cast steel substrate. The novelty checking report results show that this technics have no correlative reports during the process of fabricating infiltrated layer on cast steel surface.The surface appearance of infiltrated layer, micro-structure of infiltrated layer, hardness of infiltrated layer, the binding strength between the surface infiltrated layer and substrate were investigated by using all kinds of analysis methods. The wear behaviour of infiltrated layer was studied by using ordinary temperature friction tester under room temperature and high temperature. The application of Ni-based infiltrated layer on the guide plate was realized, and the application effect was good. The service life of guide plate with infiltrated layer was improved by 2-3 times.The results show that the major phase of the Ni based infiltrated layer were Ni-Cr-Fe, Cr-Ni, FeNi and NiB. The macro-hardness of infiltrated layer reached HRC58.6. The distribution of micro-hardness of the Ni based infiltrated layer presents the gradient variation from surface of infiltrated layer to substrate. The micro-hardness reached the maximum value at the sub-surface of infiltrated layer. Three point bending tests suggest that the infiltrated layer could deform accommodating with the deformation of substrate while bending. The binding strength was 80.23 MPa when the infiltrated layer failed. The results show that wear rate of infiltrated layer increased with the increasing testing temperature. The wear resistance of infiltrated layer was excellent than that of the ZG45. The friction coefficient of infiltrated layer was less than that of substrate under any temperature conditions.Ni/ZrO2 composite infiltrated layer was composed of ZrO2?Cr2B?NiB?NiFe and solid solution. The macro-hardness could reach HRC60 to HRC64 that was much higher than that of the substrate. The micro-hardness presents gradient changes from the surface of infiltrated composite layer to substrate, and the maximum happened at the sub-surface of the whole infiltrated layer. The composite infiltrated layer could deform accommodating with the deformation of substrate. The yielding phenomenon appeared during the bending process, and the bending strength was 66.3MPa when the yielding phenomenon happened that was 42% higher than that of the substrate. The bending strength was 87.6 MPa when the infiltrated layer failed. The wear rate of composite infiltrated layer was 4.6% of wear rate of ZG45.The wear performance at high temperature condition was investigated using SisN4 as counterbody. The wear rate increased and the friction coefficient decreased with the increasing temperature. The wear resistance of Ni/ZrO2 composite infiltrated layer with 15% content was superior to that of Ni/ZrO2 composite infiltrated layer with 10% content under any temperature conditions.During the wearing process under elevated temperature, the oxidation would happen and the oxides changed the surface circumstance, which made a decision about the wear performance. The performance of infiltrated layer and composite infiltrated layer was better than that of ZG45 under elevated temperature. The wear performance was improved comparing with the substrate ZG45. The oxidation interacted with wear under elevated temperature condition, which decided the wear performance of infiltrated layer.The main influencing parameters include the pressure difference between the entrance and exit of capillary, the radius of capillary, the viscosity of liquid metal and the holding liquid time for substrate through analyzing the flow of metal liquid among the capillary of preform. The processes maybe include two steps. One was the infiltration of ZG45 melt liquid, and the second was the compacting process of infiltrated layer. The Ni-based infiltrated layer belongs to metallurgical infiltrated layer, and the Ni/ZrO2 infiltrated layer belong to that the Ni-based powder melted and surrounded the ZrO2 ceramic particles.The vacuum infiltration casting technology has been applied on the guide plate for obtaining excellent surfacial modification. The results investigated that the main processing parameters affecting the infiltrated layer are pouring temperature and processing technique of preformed layer. This would be the foundation for the application of this technology on other parts.