Study On Microstructure And Properties Of Titanium Matrix Composite Coating By Friction Surfacing

Particle reinforced metal matrix composite(PGMMC)was made by adding reinforcement particles into the metal matrix,which could improve strength,hardness and other comprehensive mechanical properties conditioned with retaining excellent properties of the metal matrix.To manufacture PGMMC by means of Friction Surfacing(FS),holes were drilled at the center of the metal rod.Then reinforcement particles with high melting point and hardness were added into the central holes.After that,the rod with reinforcement particles was utilized to manufacture PGMMC by FS.The rotational motion of the consumable rod and material flow during FS process can realized the dispersion of reinforcement particles.However,the rolling and sliding of reinforcement particles can cause adverse effect on the stability of FS process and it is more likely to cause defects between particles and the matrix.To solve this problem,aluminum instead of reinforcement particles was added into the hole in this paper,so that in-situ reaction between A1 and Ti would occur.The Ti-Al intermetallic compounds can be used as reinforcement particles.A better process performance and good bonding between particles and the matrix can be realized.The formation of FS coating and the microstructure evolution of consumable rods and FS coatings were systematically studied by means of infrared temperature measurement,X-ray diffraction,scanning electron microscopy and EDS energy spectrum analysis.Hardness measurement and electrochemical experiment were carried out to analyse the hardness distribution and corrosion resistance of FS coatings.The results are as follow:The temperature change during FS process is an important factor affecting the appearance and shape of the coating.The infrared temperature measurement shows that the heat production of FS mainly comes from the plastic deformation of the consumable rod.Adding aluminum can improve the formation of FS coatings by improving the temperature stability and eliminating defects at the retreating side.However,the macro metallograph shows that aluminum hinders the material transition of titanium,leading to the reduction of thickness and width of the coating.Excessive aluminum can cause great failure of deposition.The microstructure of consumable rod shows a Widmanstatten structure,which presents different morphology along the axial temperature gradient.The TiA13 and Ti3Al intermetallic compounds were observed in the consumable rod.Ti3Al presents rod-like morphology for consumable rods added aluminum wire and globular morphology for rods added aluminum powder.The FS coatings consist of Widmanstatten structure and banded structure.The morphology of Widmanstatten structure varies at different region.Martensitic transformation takes place partially in FS coatings.The banded structure distributes along a three-dimensional helix,which increases the structure inhomogeneity.A large number of Al Ti metal compound particles are produced near the aluminum band.The results of microhardness show that the martensitic transformation can effectively improve the hardness of the material.There are a lot of equiaxed a,Ti3Al and TiAl3 strengthening particles near the banded structure region where the hardness is the highest.However,strengthening particles can only improve the hardness locally,and have limited impact on the average hardness of FS coatings.The polarization curves and AC impedance spectrum of coatings in 3.5wt%NaCl solution show that aluminum can form contact couple with titanium matrix,which will accelerate the corrosion rate and increase the pitting sensitivity of the material.Aluminum addition has adverse effect on the stability of the passive film and reduce the corrosion resistance of FS coatings.The metal matrix composite with the reinforcement of a,Ti3Al and TiA13 particles can be successfully prepared by adding aluminum into Ti-6Al-4V consumable rod using friction surfacing.Adding aluminum can improve the formation and hardness of coatings,but it can reduce the corrosion resistance in NaCl solution.It isurgent to improve the microstructure uniformity of FS coatings,to eliminate the banded structure and to disperse the reinforcement particles in the whole matrix.