Study On Microstructure And Properties Of Ti Alloy Repaired By Laser Deposited TA15 Powder Assisted With Static Magnetic Field

Laser deposition,also known as laser cladding,is one of the remanufacturing technologies.The selection of process parameters has a great influence on the forming.The improper process parameters will lead to the bad combination between the deposited layer and the matrix or even the failure of forming.It is crucial to choose the appropriate process parameters.At the same time,the application of the assisted energy field is usually beneficial to the process.To obtain better process parameters,this paper takes titanium alloy as an example to study the effects of process parameters of laser deposition of TA15powder on microstructure,friction and wear and corrosion resistance by introducing a steady static magnetic field.The main research results are as follows:（1）Parameter selection:the mixed orthogonal test method was used to study the influence of laser power,scanning speed and powder feeding rate on the quality of laser deposition.The range of parameters was as follows:laser power was 1100W-1900W,scanning speed was 2mm/s-8mm/s,and powder feeding rate was 2g/min-80g/min.Laser deposition characteristics of different parameters during the experiment were recorded to provide guidance for subsequent experiments.（2）Microstructure:Under single-track-deposition condition,when the static magnetic field was not applied,the microstructure was uneven columnar crystal,accompanied by pores and poor metallurgical bonding between the deposited layer and the matrix.Under the action of Lorentz force with assisted magnetic field,the top of the deposited layer was transformed from columnar to equiaxed,and white light layer was formed at the interface between the deposited layer and matrix.When the laser power was 1500W and 1900W,the powder feeding rate was 3g/min,and the scanning speed was 6mm/s,the microstructure was in the form of basket weaving,and the properties of the matrix were significantly improved.Under multi-track-deposition condition,under the action of static magnetic field,the microstructure was evenly distributed under the action of Lorentz force,and more fine ellipsoidal and spherical structures were produced.When the laser power was 1700W,the basket-weaving dendrites were composed of ternaryαphases and quarticαphases,and there were a lot of dislocations in the quarticαphases.When the laser power was 1900W,the crystal distorted and there were a lot of dislocations in the crystal.EBSD results showed that the top of the deposited layer was mainly composed of recrystallized grains and substructured grains,and recrystallization could improve the properties of the material.（3）Hardness and friction and wear:Under the action of static magnetic field,the hardness distribution at the top of the laser deposition layer was relatively uniform,which was about 350HV_0.2.When the number of deposition layers was three,the laser power was1900W,the scanning speed was 7mm/s,and the powder feeding rate was 12g/min,the friction coefficient in the stable stage was low,the friction resistance was good,the wear morphology was mostly shallow groove,and the wear mode was plowing wear.When the laser power was 1500W,the wear morphology was mainly deep plowing groove,and the wear mode was mainly plowing wear and abrasive wear.When the laser power was 1700W,the wear morphology was short deep plowing groove,the friction coefficient was large,the wear resistance was poor,and the wear mode was mainly plowing wear.（4）Electrochemical corrosion performance:In general,the static magnetic field assisted laser deposition of TA15 is more corrosion resistant than the matrix.When the laser power was 1900W,the scanning speed was 5mm/s,and the powder feeding rate was8g/min,the self-corrosion potential increased from-0.562m V to-0.468m V,the corrosion tendency decreased,and the corrosion current density increased from 71.7n A/cm² to93.7n A/cm².The overall corrosion current density varied within an order of magnitude.