Tribological Behavior Of Laser In-situ Synthesized Self-healing Composite Coatings On TC4 Alloy

With excellent properties such as high specific strength,good corrosion resistance,good biocompatibility,and non-magnetic properties,titanium and titanium alloys have become one of the most promising materials in the aerospace,marine,chemical,and medical fields.However,the poor wear resistance of titanium alloys limits their service under demanding conditions such as high speeds and heavy loads.The traditional wear-reducing composite coatings cannot guarantee the reliability of the service parts,let alone extend the service life of the parts.If the coating is given a self-healing function,to achieve the material surface and internal damage in situ self-healing function,to enhance the service life of equipment,and reliability,has essential significance.This paper aims to improve the surface wear resistance of TC4 titanium alloy,using laser melting technology and in-situ synthesis technology to introduce aluminum powder and boron carbide powder into titanium powder,to prepare a composite coating on the surface of titanium alloy,and to introduce micro and nano serpentine into the metal coating material system to give the friction surface damage self-healing function.Details of the research are as follows:Firstly,the powder system for the self-healing composite coating was determined.Aluminum powder,boron carbide powder,and micro-nano-serpentine were introduced into the metal coating system to improve the wear resistance of the TC4 titanium alloy surface,and the Gibbs free energy was used to determine whether the selected powders could react spontaneously with each other.Six titanium-based composites agglomerated powders with different compositions and good flowability was then prepared and analyzed using scanning electron microscopy to determine whether the agglomerated powders met the requirements of the laser cladding tests.Secondly,a study on the coating process for laser melting of in-situ titanium-based selfhealing coatings.Based on the single-pass coating,the influence of laser power,scanning speed,powder feeding speed,and defocusing amount on the quality of the composite coating was investigated by orthogonal tests and extreme difference analysis.The titanium-based composite coatings of six powders were prepared using the optimum process parameters.The microscopic morphology,phase composition,microhardness,and nano-mechanical properties of the composite coatings were investigated with laser confocal microscopy,scanning electron microscopy,microhardness tester,and nanoindentation tester.Then,the frictional wear properties of the composite coating under oil lubrication conditions were then investigated using an SRV-4 reciprocating sliding wear tester.The friction coefficient,wear volume,wear surface morphology,and elemental composition of the wear surface were analyzed to investigate the effect of different loads on the tribological properties of the composite coating and to explore the friction and wear reduction and selfhealing mechanism of the composite coating.Finally,the reaction mechanism in laser melting of in-situ reinforced titanium-based composite coatings is investigated.The composition of the physical phases and the distribution of elements in the coating were analyzed by scanning electron microscopy and energy spectrometry.The reaction mechanism between the powders during the in-situ reaction was determined based on the analysis results.