Research On Laser Cladding And Forging Technology With Ultrasonic Vibration Assistance

TC4 titanium alloy,which combines many excellent properties,is a common and important material in aerospace field,for example,engine blade.3D printing is a new type of blade manufacturing technology.It is suitable for complex and difficult to process materials.It has the advantages of short period and high precision,but its forming parts are not strong enough,the surface is not fine,and the internal stress is complex.In this paper,aiming at the problems existing in 3D printing and the shortcomings of titanium alloy itself,such as easy wear and oxidation,etc.Laser cladding technology,which is similar to 3D printing,is used to prepare the TC4 and Ni60WC25 alloy powder cladding layer on the surface of TC4 titanium alloy.The influence of process parameters on the quality of cladding layer and the causes of cracks and pores in cladding layer are analyzed.In order to improve the surface roughness of the cladding layer,the ultrasonic vibration auxiliary forging device was designed and built.Under this device,the experimental research on the common forging and ultrasonic vibration aided forging TC4 cladding layer is carried out,and the influence rules of these two kinds of forging methods on the microstructures of the TC4 cladding layer are analyzed.The effect of acoustic amplitude and forging force on the microstructure change of TC4 titanium alloy during plastic deformation in two-phase region is studied,which provides a new idea for optimizing the performance of TC4 surface.In the experiment,it is tested respectively by metallographic microscope,SEM,EDS,Rockwell hardness,surface morphology and microstructure of the cladding layers and components distribution and surface hardness.The main work and conclusions are as follows:(1)An ultrasonic vibration assisted forging device is designed and built.Incomplete gear mechanism is used to achieve the purpose of combining ultrasonic vibration forging and ordinary low frequency forging.(2)By laser cladding,the fine microstructure,no pores and no cracks are prepared on the surface of TC4 titanium alloy with the cladding layer well combined with the matrix metallurgy.The optimum technological parameters of TC4 powder and Ni60WC25 powder cladded on the surface of TC4 is found.(3)TC4 titanium alloy is transformed from the original Weisman structure to the basket or double structure or equiaxed structure after the normal forging in the(alpha + beta)two-phase region.If we want to transform into equiaxed structure,we need to achieve a certain degree of deformation.Compared with conventional forging,ultrasonic vibration assisted forging can reduce the forming force of TC4 plastic deformation,making TC4 grains smaller and tending to equiaxed.(4)When plastic forming is assisted by the ultrasonic vibration,the stress superposition effect and the softening effect reduce the stress in the plastic forming of the TC4.The increase of the ultrasonic amplitude and the forging force will be beneficial to the refinement of the grain of the TC4 tissue,coming to the network basket or the double state structure,which is better than that of the Wechsler.The increase of ultrasonic amplitude makes the force of TC4 plastic forming decrease,and the decrease is directly proportional to the ultrasonic amplitude.The increase of the forging force can cause the enhancement of the dynamic recovery and recrystallization,resulting in the production of new small grains at the coarse grain boundary,which aggravates the movement of dislocation,and is helpful to the coarse grain refinement.