Experimental Study Of Laser Cladding High-entropy Alloy Coatings On Titanium Alloy Surface

Titanium alloy has been widely used in many fields due to its high-quality performances,such as low specific gravity,high strength and good corrosion resistance.However,the unfavorable performances seem to have an effect on its development,especially considering high friction coefficient and poor wear resistance.For the purpose of improving hardness and wear resistance of titanium alloy,it's the key point to improve its surface performances.As a new hotspot in the field of alloy,high-entropy alloy can have excellent performances by selecting the appropriate composition and component ratio.Thus,laser cladding technology was applied to preparation of high-entropy alloy coatings with suitable cladding morphology,uniform compositon and good mechanical properties,being of beneficial reference to the preparation and research of laser cladding high-entropy alloy coatings on titanium alloy surface.In this paper,AlB_xCoCrNiTi,Al_xBCoCrNiTi and AlCoCrNiTi+WC high-entropy alloy were used as cladding powder respectively for the preparation of corresponding high-entropy alloy coatings by applying the laser cladding technology.Then,the microstructure and composition of cladding coatings were analyzed by scanning electron microscopy,X-ray diffraction and electron microprobe.What's more,the microhardness of the samples was measured with a Vickers hardness tester.At last,the wear resistance of cladding coatings and matrix was tested on a CFT-I multifunctional material surface performance tester.For laser cladding Al B_xCoCrNiTi high-entropy alloy coatings,the results show that there is a good metallurgical bond between the coatings and the substrate.And without B element in the coatings,the main generating phase is BBC and the crystal structure is similar to(Co,Ni)Ti2 phase.However,the existence of B refines the dendritic structure and TiB2 is dispersed in situ in the cladding coatings.Further studies indicate that with the increase of B content,the BBC phase and TiB2 phase increase gradually,as a result of which,the microhardness and abrasion resistance of cladding coatings are also improved.In particular,when x=1,the average microhardness value is 814 HV proved to be the largest and approximately 2.5 times that of the substrate.Moreover,the abrasion resistance value is 29 times that of matrix materials.The experimental study on laser cladding Al_xBCoCrNiTi high-entropy alloy coatings implies that the cladding coatings are mainly composed of BBC phase,(Co,Ni)Ti2 phase and TiB2 phase generated in situ.Due to the addition of Al,eutectic structure in the coatings disappears and the lattice distortion of BBC phase turns out to be larger,resulting in the shifting of the diffraction peak.Simultaneously,the number of pores in the coatings decreases.Further analysis backs up the idea that the microhardness and wear-resisting property increase with the increasement of Al content,showing that the addition of Al is conducive to improving the quality of cladding coatings.The experimental results of laser cladding AlCoCrNiTi+WC high-entropy alloy coatings show that cladding coatings are mainly composed of(Co,Ni)Ti2 phase,Cr2 Ti phase and TiC phase on account of the addition of WC.When the content of WC is low,the cladding coatings are of good quality.However,along with the further increasement of WC content,both the cracking tendency and the crack increase.In this case,when the content of WC reaches 5 wt%,the average microhardness value is 754 HV,showing to be the maximum and more than 2 times that of the TC4 titanium alloy matrix.Morever,the corresponding wear resistance value turns out to be the best,reaching about 27 times that of the matrix.Taking into consideration that the addition of excessive WC will reduce the quality of cladding coatings instead,it is vital to choose the proper quantity of WC to add.