| Titanium alloy with the advantages of good characteristics of low specific gravity,high specific strength,excellent corrosion resistance and biocompatibility is widely used in variety of critical structures in various industrial fields of aerospace,aviation,marine,post-nuclear spent fuel processing and petrochemical valves etc.Nevertheless,their applications have been limited by high coefficient of friction,poor wear resistance and high coefficient of friction.The alloy has excellent mechanical properties,thermal processing and forming properties,corrosion resistance and weldability,it can satisfy the use requirements of key equipment in post-nuclear spent fuel processing.Ti35 alloy is designed and developed by NIN as a new type of Ti-Ta binary of pure ?-type boiling nitric acid corrosion-resistant titanium alloy,which is used specifically for critical equipment in post-nuclear spent fuel processing material.The key equipments and important process pipes of post-nuclear spent fuel processing engineering are working in corrosive medium with radioactive ions,Ti35 alloy with excellent corrosion resistance need to be adopted in preparing the valves as fluid control device.The hardness requirement of hard sealing surface is designed to be higher than 200 HV,meanwhile,it need to withstand high concentrations of boiling nitric acid corrosion with a variety of radioactive ions,hard sealing surface with good abrasion resistance and long service life under high stress load are also required in long-term use of the process.Although Ti35 alloy has excellent corrosion resistance,but poor wear resistance and low hardness are difficult to satisfy the application requirements of hard seal of the valve,it is how to get in close conjunction with the base on Ti35 alloy base,high hardness,good corrosion resistance,a thickness greater than 3.5mm high hardness layer is a basic technical problem to be solved firstly.Solving problems of hard seal of the Ti35 alloy valve is important for ensuring long-term safe and reliable operation of post-nuclear spent fuel processing system and improve the fuel efficiency of recovery.Hard sealing surface of the valve of the project not only stands in a unique work position,but also requires a certain thickness(?3.5mm),the routine use of micro-arc oxidation,hydrogen-oxygen permeation,thermal spraying Sintering,physical vapor deposition and other methods can not meet the requirements.Laser cladding has become one of the effective means to improve the surface properties of titanium alloys due to the advantages of the metallurgical bonding combination to the substrate,high bonding strength,small cladding layer organization,and controllable composition and thickness.Taking use of Ti-Ta alloy in the same system as the Ti35 alloy as the cladding material of hard sealed surface of the valve,both to ensure the tightness of binding with the substrate,but also facilitate further to adjust cladding layer's hardness and strength by adding the hard phase.In order to ensure long-term safe and reliable operation of closed nuclear fuel cycle system,the cladding layer also needs to ensure sufficient corrosion resistance and resistance to stress corrosion fatigue properties,it is necessary to research the different components of Ti-Ta alloy laser cladding.The topic mainly for the shortcomings of low hardness,poor wear resistance of Ti35 alloy,is going to improve its hardness and wear resistance in the surface of Ti35 alloy matrix reinforced with hard ceramic composite coating by laser cladding.It is expected in ensuring the premise of its corrosion resistance,improve its hardness,wear resistance and compression fatigue properties,get preparation method of no pores,cracks and of the cladding layer and the base takes the shape of a good metallurgical bonding of a certain thickness to provide technical information of titanium valve manufacturing hard sealing surface.All of the conclusions are as follows:(1)Preset Ti-10Ta+5-10 TiC powder on Ti35 alloy substrate,the composite coating can be formed and satisfy hardness and corrosion resistance requirements of hard sealed surface of Ti35 alloy valve by laser cladding method.(2)With increases of TiC content of Ti-10Ta+XTiC cladding material,microstructure of cladding layer has a coarse trend,which is gradually replaced by fibrous tissue columnar structure,binding region tissue is more dense.When the TiC content exceeds 10%,the small amount of porosity defects in cladding layer appear.(3)With increases of TiC content of Ti-10 Ta + XTiC cladding material,the cladding layer hardness increases,the microhardness increas a little firstly and then decreased from the surface to the substrate takes the shape of the trend,hardness of 5-20% TiC cladding material meet the requirements;With increases of TiC content,the corrosion rate of the cladding layer has a rising trend.(4)Thickness of oxide film on the surface Ti-Ta+XTiC alloy cladding layer after corrosion is not obvious in the scanning electron microscope;the oxide film of Ti-10 Ta is more dense than Ti-10Ta+5-20%TiC alloy's oxide film. |
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