Study On Microstructure And Properties Of Particulate-reinforced Titanium Matrix Composites By Laser Cladding

Titanium matrix composites(TMCs)are widely used in aerospace,medical engineering,chemical industry due to higher specific strength than titanium alloys,excellent creep resistance and fatigue property.Compared with titanium alloys,the wear resistance and elastic modulus of TMCs are higher.In this paper,laser cladding experiments in single channel and layer were processed to choose the appropriate process parameters of laser cladding for particulate-reinforced titanium matrix composites.The in situ synthesized TiB-TiC reinforced titanium matrix composites were manufactured by laser cladding technique with the ball milled TA15+B4C powders with different compositions of B and C elements.The microstructure,mechanical properties and wear-resistant properties of the prepared TMCs were studied by XRD,SEM,EDS,hardness test,tensile test and wear resistance test.The experimental results showed that the appropriate process parameters of laser cladding forparticulate-reinforced titanium matrix composites were: laser power is 1600~2000W,scanning speed is 6~8mm/s,powder feeding rate is 7.5~9.5g/min.It was observed that the quantity and size of reinforcements in the four types of TMCs were different by analyzing microstructure.But their microstructure was composed of identical phases: ?-Ti??-Ti?TiC and TiB.The reinforcements exhibited three kinds of morphologies,i.e.prismatic shape,whisker shape and near-equiaxed shape.With the increasing of additive B4 C,the quantity and size of reinforcements raised gradually.The reinforcement with prismatic shape or whisker shape was TiB,whereas the reinforcement with near-equiaxed shape was TiC.The morphologies of reinforcements were correlated closely with their crystal structure and solidification.TiB tends to take on prismatic or whisker shape due to its B27 structure,whereas TiC with NaCl structure is apt to grow in near-equiaxed shape.Hardness test,tensile test and wear resistance test revealed that with the increase in the reinforcement content,the hardness of TMCs improved,the friction coefficient might be unchangeable,the wear mass loss and tensile strength increased first and then decreased and the strain to failure declined.The tensile strength of the TMC containing 0.83 wt% boron and 0.44 wt % carbon was highest,and its friction coefficient was smallest.showed better wear-resistant properties.The wear mass loss of the TMC containing 1.2 wt% boron and 0.84 wt % carbon was least,which reduced by 48% compared with substrate.The fracture surfaces of TMCs exhibited quasi-cleavage fracture and the wear mechanism involved abrasive wear and a small amount of oxidation wear.By comparison,when the boron content and carbon content of TMC is from 0.83 wt% to 1.2wt% and 0.44 wt% to 0.84wt%,the TMC showed favourable comprehensive properties,which not only effectively improved the wear resistance but also obviously enhanced the hardness and tensile strength.