Research On Microstructures And Properties Of Ti-6Al-4V Titanium Alloy In Laser Rapid Forming Processing

Ti-6Al-4V alloys, as α/β titanium alloys with medium strength and outstanding comprehensive mechanical properties, have a large number of applications in the aerospace industry. Traditional processing methods have disadvantages of lower material utilization, longer development cycle and higher manufacturing cost. Laser Rapid Forming (LRF) is an advanced technology which was developed on the basis of rapid prototyping (RP) technologies and laser cladding, which have the advantages of low cost, short lead times and the ability to fabricate complex, near net shape geometries without using dies or molds. To develop LRF of titanium alloys parts is in favor of solving the previous processing handicap mentioned above. But in order to ensure the reliability, stability of LRF process, how to control the sample's comprehensive mechanical properties by controlling microstructure after and during LRF should be mastered.In this paper, LRF of Ti-6Al-4V (TC4) alloys was experimentally investigated systematically, the influence of the processing parameters, laser power, scanning velocity, powder feeder, overlaps and single-layer distance of Z axis, on microstructures were analyzed. the influence of heat treatment on the microstructure and properties was also investigated. The way to improve the LRF microstructure and comprehensive mechanical properties of TC4 alloys was explored. The main results are as follows:1. The macrostructure of LRF Ti-6Al-4V alloy shows huge .columnar grains that grow epitaxially along the deposited direction (Z). It can be seen that there exhibits a continuously epitaxial columnar β cellular growth across several deposit layers, whose growth direction is along the deposited direction and inclines towards the scanning direction in some sort. The as-deposited microstructures were composed of acicular α and Widmanst(a|¨)tten a in prior β grain.2. With the increase of laser power and the decrease of scanning velocity, columnar grains shorten and coarsen, final change to irregular coarsen equiaxed-like grains.3. There exists a critical overlap ratio. When overlap is 30%, the microstructure present fine quality just with a little ill-bonding between the traces near substrate. If overlap less than 30%, irregular ill-bonding will occur in the region of adjacent cladding layer. Otherwise, there is no defect in the cladding layers. In addition, that single-layer distance of Z axis is larger than the height of single cladding...