| Titanium and titanium alloys are widely used in aerospace because of their high specific strength,high temperature resistance and corrosion resistance.However,conventional titanium alloys are prone to " titanium fire" failure in harsh environment,and the burn resistant of titanium alloys has become a key problem to be solved in the aviation industry.In order to reduce the influence of " titanium fire" on aviation structure and improve the safety of aircraft operation,it is a feasible technical way to develop integral burn-resistant titanium alloy.At present,the most mature burn-resistant titanium alloy is Ti-V-Cr burn-resistant titanium alloy.However,due to the expensive cost and high specific gravity of element content in Ti-V-Cr burn-resistant titanium alloy,it not only greatly improves the preparation cost,but also reduces the overall specific strength of burn-resistant titanium alloy and makes the deformation resistance too large during forging,so as to lead the processing is difficult.Therefore,there is unurgent need to find low-cost burn-resistant titanium alloy preparation and processing technology.Based on this,laser cladding deposition technology was used to deposit Ti40 burn-resistant titanium alloy on the surface of forging TC4 in order to improve the surface anti-combustion performance of conventional titanium alloy on the premise of maintaining good comprehensive properties of forging TC4 alloy.Firstly,the influence of laser cladding deposition process parameters on the geometric size and hardness distribution of Ti40 alloy deposited on TC4 surface by single-line and single-layer deposition was studied.Secondly,the microstructure and hardness distribution of Ti40 alloy deposited on TC4 surface were studied.Finally,the tensile properties of laser cladding deposited specimens at room temperature perpendicular to and parallel to the cladding interface were characterized.Based on the fracture morphology analysis of the specimens in two tensile directions,the fracture mechanism was revealed.The main conclusions are as follows:1.The effect of deposition process parameters on the metallurgical quality of single-line and single-layer Ti40 burn-resistant titanium alloy deposited on the surface of TC4 substrate was studied by laser cladding deposition.The results show that when the laser power is in the range of 1800~2700 W,the scanning speed is in 10~20 mm/s,and the powder feeding rate is in 8~17 g/min,the single-line and single-layer deposited samples have good metallurgical quality,and no porosity,crack,unmelted powder and other metallurgical defects appear.The single-line and single-layer deposited sample can be divided into cladding layer,remelting region,heat affected region and substrate region from the top of cladding layer to substrate region.2.The influence of deposition process parameters(laser power,scanning speed and powder feeding rate)on the geometry size,composition distribution and micro-hardness of single-line and single-layer deposited layer was studied.The results show that with the increase of laser power and the decrease of scanning speed,the size of cladding layer,remelting zone and heat affected zone increase.With the increase of powder feeding rate,the size of cladding layer increases,while the size of remelting zone and heat affected zone increases first and then decreases.The micro-hardness and composition analysis results of the cladding layer,remelting zone,heat affected zone and substrate show that the micro-hardness of the heat affected zone is significantly higher than that of the substrate zone,remelting zone and cladding layer under various process conditions.When the laser power is in the range of 1800~2700 W,scanning speed is 10 mm/s,powder feeding rate is 11 g/min and laser power is 2400 W,scanning speed is 10 mm / s,powder feeding rate is in the range of 8~17 g/min,we can obtain composition,hardness distribution of remelting zone and cladding layer,which shows that under the above process conditions,the convection in the molten pool is sufficient,the substrate and cladding layer Ti40 material fully mixed and alloyed.3.Ti40 burn-resistant titanium alloy was deposited on the surface of TC4 substrate by semiconductor laser cladding deposition technique with P=1800 W,V=10 mm/s and M=11 g/min.The microstructure of the deposited samples was studied.The results show that the deposited samples can be divided into substrate,heat affected zone,transition zone and Ti40 deposition zone according to their composition and microstructure.Both TC4 substrate and heat affected zone are α+β phase.The transition region and Ti40 deposition layer are composed of β phase,the transition region is mainly composed of relatively coarse epitaxial grown columnar crystals,the middle and lower parts of Ti40 deposition region are composed of relatively fine columnar crystals and a small amount of equated crystals,and the top of Ti40 deposition region is composed of fine equated crystals;The bonding mode between the deposited layer and the substrate is good metallurgical bonding,and there is no metallurgical defect in the deposited layer.4.The tensile properties of Ti40 samples deposited on TC4 surface of forgings along the direction parallel to the fusion line and perpendicular to the fusion line at room temperature were studied,and the fracture morphology of the deposited samples was analyzed.The results show that the tensile strength at room temperature is 980.17 MPa,and the elongation is about 9 % when the fracture occurs in the transition zone and extends to the Ti40 deposition zone along the direction perpendicular to the fusion line.At room temperature,that fracture occur in the region of the cladding interface and propagate to the transition zone,the tensile strength is about 950.11 MPa,slightly lower than that perpendicular to the fusion line,and the elongation is about 9.8%.The fracture morphology analysis shows that the fracture forms perpendicular to and parallel to the fusion line are ductile fracture and mixed fracture along the grain fracture.The tensile properties at room temperature show that the tensile properties at room temperature are better in both directions. |
PDF Full Text Request