The Research Of Modification Of Plasma Spurt Spraying On Improving Fatigue Property Of Welded Joint

Modification of Plasma Spurt Spraying (MPSS), which is a new method, wasused to improve the fatigue strength of welded joint. The basic principle of MPSS isto spray fusing a complete metallurgical bonding layer of high curvature appearanceon the surface of the whole welded joint, which can greatly reduce the stressconcentration of welded joint. As a result, fatigue strength of welded joint will besubstantially improved.Take as-supplied, cross-shaped welded joints of Q235B steel as testing object.The comparative analysis of fatigue behavior for TIG-dressing joint, welded jointstreated by ultrasonic peening treatment (UPT) and spraying fused joint. The bondinglayer between coating and weld was studied by optical microscopy, scanning electronmicroscopy (SEM). Material properties of metallurgy bonding zone were performedat room temperature using a nano-indentation device equipped with a Berkovich tip.In order to gain compressive residual stress, the low transformation temperature (LTT)alloy powder was developed. The temperature field and stress field of spraying fusedjoint were simulated by ANSYS software.Performance tests show that: the orthogonal experiment design won the optimalparameters of MPSS. The hard phase exists in the coating spray fused byNi65Cr16B3.1Si4.5alloy powder. There is the existence of a crack in the hard phase,and the fracture toughness of hard phase was determined according to the size ofcrack. The constitutive equation of metallurgy bonding zone was founded accordingto Reverse Analysis Algorithms.High cycle fatigue test results indicate that fatigue strength of MOSS-joint andMPSS-joint corresponding to2×10~6cycles is217MPa and220MPa, respectively.Compared with as-welded joints, Fatigue strength increases by60.7%and62.96%,respectively. Low cycle fatigue test results show that fatigue life of MOSS-joint islower than MPSS-joint.Through the analysis of residual stress, impact toughness and hardness of plasmaspurt spraying coating, LTT alloy powder system of5Cr-8Ni was determined.The method of simulating welding was used to simulate temperature field andresidual stress field of joint spray fused by LTT powder. Results show that, thereexists a certain range of residual compression stress at weld toe of joint spray fused by LTT powder. The existence of residual compression stress will improve fatiguestrength of welded joint further.