Study On Microstructure And Properties Of Ti-V-15Cr Alloy By Laser Solid Forming

Laser solid forming(LSF)is an advanced technology that balance the need of precise forming and mechanical properties of metal parts,and it has been widely used in the design of new titanium alloys and engineering applications.At present,Ti-V-Cr burn-resistant titanium alloys are mature materials for aero-engine because of good combination of mechanical properties and burn resistant performance.In this research,a mixture of pure Ti,V and Cr elemental powders were used as raw material,and the Ti-xV-15Cr(20?x?35)alloys were deposited by high absorptivity laser and continuous fast axial CO2 laser.The microstructure evolution and some typical properties of LSFed Ti-xV-15Cr(20?x?35)alloy samples were investigated.The main conclusions are as follows:1.The measured compositions of as-deposited Ti-xV-15Cr(20?x?35)samples from blended elemental powders are consistent with target compositions.Phase identification using XRD analysis showed that the Ti-xV-15Cr(20?x?35)alloys are all composed by body centered cubic single-beta phase,and there is no second phase precipitation.The microstructure evolution of LSFed Ti-xV-15Cr(20?x?35)alloys deposited by semiconductor laser were investigated firstly,and it was found that there is little effect of V elements content on the morphology of prior ? grains of LSFed Ti-xV-15Cr(20?x?35).Laser solid forming of Ti-xV-15Cr(20?x?35)alloys are all composed by small bamboo-like columnar grains or near-equiaxed grains,and the top of deposited is composed of fine equiaxed grain layer.The average width of prior ? grains and the thickness of top equiaxed grains layer decrease gradually with the increase of V elements content.2.The formation mechanism of prior ? grains of laser solid forming Ti-xV-15 Cr were revealed based on columnar to equiaxed transition(CET)model and the analysis of the solidification in molten pool,It showed that when the solidification conditions keep stable,the increasing of V content has minimal impact on the critical condition of CET and no affect on the solidification organization,and thus the high absorptivity laser solid forming Ti-xV-15(20?x?35)alloy,V elements content increased from 20 wt% to 35 wt%,the morphology of alloy solidification organization did not significantly change,which is consistent with the theoretical analysis.In addition,this result shows that molten pool solidification conditions are the key factors for the organization form of solidification.Based on the above analysis,this research selects the typical composition of alloy Ti-35V-15 Cr adopting CO2 laser deposition to change the molten pool solidification conditions significantly.The results show that a full ?-columnar grains composed of Ti-35V-15 Cr alloy specimens is obtained under the reasonable design condition of deposited process.Besides the solidification of laser solid forming Ti-V-15 Cr alloy has high controllability.3.Based on the research of the evolution of the solidification,various tests have been carried out in laser solid forming Ti-xV-15Cr(20?x?35)alloy in different areas,including nano-indentation test,micro-hardness test and burn-resistant properties test.The results demonstrated that under the same condition of the process,the average hardness of Ti-xV-15Cr(20?x?35)alloy at maximum load increase gradually with the increase of V element content.At addition,series component load-displacement curve found that at the bottom to the top,the hardness and modulus of the deposited increase gradually,while the displacement marginally decreases,at the same time,the micro-hardness of series alloy increase slowly.In the burn-resistant properties,when V elements content more than 20wt%,the burning rate of alloy reduced gradually,while the burn-resistant properties of alloy increase gradually.