Studies On Microstructure And Properties Of WC/Ti-6Al-4V Composite Coatings By Laser-induction Hybrid Melt Injection

Laser-induction hybrid melt injection（LIHMI）was introduced to prepare spherical WC particle reinforced metal matrix composite coatings on Ti-6Al-4V substrate,which solved the problems that the thickness of coatings,processing efficiency and coatings quality of the traditional laser melt injection（LMI）.At the same time,the relationships among the processing parameters-the macroscopic dimension and the microstructure-the mechanical properties of the WC/Ti-6Al-4V matrix composite coatings were established.Furthermore,cracking behavior,and wear resistance of the composite coatings prepared by LMI and LIHMI were studied systematically.The main results are as follows:The WC/Ti-6Al-4V matrix composite coatings prepared by LIHMI with induction preheating（pre-LIHMI）and LIHMI with induction preheating and postheating（pre/post-LIHMI）,the interface of coatings/substrate and the interface of different tracks coatings have good formability,without macro defects,such as pores and cracks.When the laser power is 4000 W,the thickness of composite coatings prepared by LIHMI can reach 1.26mm-1.28mm,about 2-2.2 times as much as that by LMI,and the maximum WC injection efficiency can reach 68.4%-73.4%,which is 1.4-1.5 times of that of the LMI.In the process of LIHMI,due to the decrease of cooling rate,the nucleation of primary Ti C dendrites in the laser molten pool between adjacent WC are restrained,so that the total amount of Ti C in the laser-induction hybrid melt injected coatings was far less than that in the laser melt injected coatings.Under the same process parameters,the（5.9-6.3）%Ti C,β-Ti,andβ-Ti/α-Ti formed in the laser-induction hybrid melt injected coatings,while 19.8%Ti C,（Ti,W）C_1-X andβ-Ti formed in the laser melt injected coatings.With the decrease of the total amount of brittle carbide Ti C,the tensile strength of the composite coatings prepared by pre-LIHMI and pre/post-LIHMI is 34%and 12%higher than that of the composite coatings prepared by LMI,respectively.In addition,pre/post-LIHMI led to a drastic WC/Ti interfacial reaction due to the longest dwell time and the highest temperature of the laser molten pool,which greatly reduced the mechanical properties of the composite coatings.But in the process of pre-LIHMI,the cooling rate and the temperature of the molten pool are moderate,and the WC/Ti interface reaction decreases,which make the ultimate tensile strength of the samples prepared by pre-LIHMI is 1.2 times of that of the pre/post-LIHMI.Due to the“shielding effect”of high-hardness WC particles on the matrix,the wear rate of WC/Ti-6Al-4V matrix composite coatings prepared by LMI,pre-LIHMI and pre/post-LIHMI is about 0.032-0.034 mm³/N m,which is lower than that of Ti-6Al-4V（7.100 mm³/N）by 99.46%-99.55%,showing good wear resistance.The main wear behavior of WC/Ti-6Al-4V matrix composite coatings is fatigue cracking of WC,and the flaking WC and Ti C become abrasive particles on the wear surface and form abrasive wear.Therefore,the wear mechanism of the composite coatings is fatigue wear and abrasive wear.