Design And Research Of Ni-based Composite Powder Used In Laser Cladding With Low Sensitivity Of Cracks And High Reliability

As a key technology in remanufacturing engineering,laser cladding technology has been studied widely.The property of cladding material directly determines the quality of cladding layer.At present,Ni-based powder is the most cost-effective cladding material in the three alloy powder systems,and has been widely used to strengthen and repaire surface parts under the conditions of wear-resistant,corrosion resistance,impact resistance.However,the application of Ni-based powders is hindered by cracks in the clad layer.For this problem,the process optimization strategy was adopted,but there are some limitations in this method.In view of the current situation of the research on special powder for laser cladding,based on the material theory,the Ni-based composite powder with low sensitivity of cracks and high reliability is studied by a large amount of experimental research in this paper,and a useful exploration was performed in the reliable laser cladding layer materials.First of all,the mechanism of generation and control of crack in cladding layer was research and analysis.Cracks in the clad layer were examined using a nondestructive flaw detection reagent.Further the dilution rate and wettability of the clad layer were measured using a digital stereomicroscope,and the microstructure was observed and recorded by digital metallographic microscope,and the hardness of cladding layer was measured by Vickers microhardness tester.At last,the abrasion resistance of cladding layer was studied by universal friction and wear tester,and the test results were compared and analyzed.Then,the Ni-based and Co-based alloy powders were used for laser cladding experiments,and the surface quality,dilution rate,crack sensitivity,microstructure,microhardness and abrasion resistance of the two cladding layers were studied,and the shortcomings of the existing cladding powder were found out.The results show that the Ni-based powder has higher cladding hardness and wear resistance than the Co-based powder,and the cladding layer with no crack is obtained at the parameters of P = 3500 W and v = 360 mm/min.Co-based cladding cracks only appeared in the crater,cladding layer of the main body without cracks.But both powders can not meet the performance requirements of the substrate.Considering the lower cost of Ni-based powder,it is suitable as a cladding material for remanufacturing of mechanical equipment by strengthening and component improvement.Further,the effects of different content of CeO₂,Y₂O₃ and Cr on the properties of Ni60 A cladding were studied at P = 900 W,v = 360 m/min of the process parameters.The experimental results show that CeO₂ content of 5% can reduces the crack susceptibility and increases the hardness of the cladding layer.The addition of Y₂O₃ can reduce the crack sensitivity,but the coating hardness and surface quality of the adverse effects,Y₂O₃ is not suitable for improving the performance of the cladding layer.15% of the additive amount of Cr can significantly reduce the cracking tendency of cladding layer,while not adversely affecting the performance of the substrate.A Ni-based composite powder was designed based on the mechanism of grain boundary strengthening,grain refining strengthening and solid solution strengthening,which belongs to Ni-Co-Fe-Cr-Si system and is strengthened by WC ceramic phase.The best speed of powder preparation was 175 r/min and the best mixing time was 50 min.WC-free alloy powders were subjected to cladding tests at various powers,and no cracks were observed in the clad layers.The experiments were carried out respectively with WC contents of 0%,10%,30%,50% and 75% at P = 1200 W,v = 360 mm /min of the process parameters.The results show that the optimum content of WC is 30%,and this is the highest performance of the cladding without cracks,and the hardness of cladding is 562 HV_0.2.This powder cladding layer has good wettability to 20 CrMnTi substrate,the cladding performance is close to that of Ni60 A,and the cladding crack does not appear.The Ni-based composite powder is a kind of high reliable cladding material with low crack sensitivity.This paper provides not only a reference for the design of special powder for laser cladding,but also technical support and theoretical guidance for the laser cladding remanufacturing and repair of the damaged parts.At the same time,a certain contribution to the industrial application of laser cladding technology was made.