Wear Properties Of Ni-based WC Coating Prepared On The Surface Of Shield Disc Cutter Material

With the rapid development of rail transportation and ore mining in the world,shield machine is an important equipment for tunneling,which is widely used because of its efficient construction.As the "tooth" of the shield tunneling system,the shield cutter directly contact with the excavation face.It is one of the most easily damaged parts in the process of tunneling due to its harsh working environment,unstable load and large impact,especially shield disc cutter for tunneling in hard rock strata.At present,the manufacturing technology and performance evaluation standards of disc cutter are mainly monopolized by companies in Germany,Japan and the United States,resulting in expensive shield cutters.However,the development of Chinese disc cutter started late and lacked technical support,resulting in a long research and development cycle,low useful life and high cost.Therefore,it is especially urgent to break the technical blockade of foreign companies and obtain a disc cutter with good wear resistance,long useful life and high cost performance.At the same time,the geology of tunneling formation is complex,which causes the complex wear types of disc cutter.Therefore,it is difficult to evaluate the wear properties of disc cutter scientifically and reasonably.As the current surface treatment technology,coating technology is widely used in areas such as tool wear resistance,heat resistance,oxidation resistance,and chemical corrosion resistance.Therefore,it is especially important to prepare a coating disc cutter with high wear resistance and long useful life,and to evaluate its performance effectively and reasonably.Firstly,this paper ran an in-depth analysis of the damage patterns and mechanisms of the shield disc cutter at different wear stages based on field surveys,which laid the foundation for evaluating disc cutter wear performance and developing a new disc cutter.Secondly,Ni-based WC(Ni-WC)coating was deposited on the disc cutter surface by means of plasma transfer arc welding.Finally,the friction and wear tests of Ni-WC coating and uncoated substrate were conducted under two relative motion modes of reciprocating sliding and impact-sliding.The damage patterns and mechanism of Ni-WC coating and H13 steel were compared.The main conclusions reached are as follows:1.The mode of the relative movement between the shield disc cutter and the rock is complicated.The disc cutter is often subjected to the impact-sliding wear,aggravating the wear of disc cutter.At the beginning of wear,the contact stress on the blade of the disc cutter is relatively large,and the disc cutter is easy to tipping.With the increase of wear time,abrasive wear is main wear behavior.In the later period of wear,fatigue wear appeared on the surface of the disc cutter.2.The Ni-WC coating shows good wear stability during the reciprocating sliding wear.During the wear process,the main wear mechanisms of the Ni-WC coating is the two-body abrasive wear,and the peeling is the main damage patterns of the coating.Compared with NiWC coating,the normal load has a significant effect on the reciprocating sliding wear of H13 steel.The H13 steel surface has better wear stability under low normal load(5 N),and the wear of H13 steel surface shows greater instability under the high normal load(10 N and 20N).During the wear process,the main wear mechanisms of the H13 steel are the two-body abrasive wear and three-body abrasion,the ploughing and peeling are the main damage patterns of the coating.3.In the process of impact-sliding wear,the increase of structural stiffness changes the wear mechanism and damage characteristics of Ni-WC coating by changing the types of load.For a low structural stiffness,the impact-sliding wear is dominated by the impact loading.With the increase of the structural stiffness,the impact-sliding wear is dominated by the press loading.The main wear mechanisms of the Ni-WC coating are the fatigue wear and abrasive wear.The brittleness shedding of WC particles and peeling of Ni alloy are the main damage patterns of the coating.In addition,the structural stiffness also has a significant effect on the impact-sliding wear of H13 steel.With the increase of structural stiffness,the main damage zone shifts from the impact zone to the sliding zone,and the main damage pattern of impactsliding wear changes from ploughing to peeling.4.The wear resistance and impact resistance of Ni-WC coating are better than uncoated substrate.The main reason for the increased wear resistance and impact resistance of Ni-WC coatings is that the high hardness WC particles on the surface can prevent the abrasive particles from ploughing and impact with the Ni alloy,and the WC can prevent continuous wear of NiWC coating by abrasive particles.