| Ti-48Al-2Cr-2Nb is one of the TiAl alloys with the best comprehensive properties.However,due to the large columnar structure of the as cast structure,there are many problems in the investment casting and EDM,such as many processes,difficulty in balancing strength and ductility,and difficult to eliminate pores,which seriously limits its engineering application.SLM(selective laser melting)forming specimen have fine grains,uniform structure and excellent mechanical properties,but there are some problems in the forming process,such as high residual stress and online quality control difficulties,which lead to obvious differences in microstructure and properties between SLM and traditional methods.Therefore,in this paper,Ti-48Al-2Cr-2Nb alloy powder is taken as the research object.By means of orthogonal test,metallographic analysis,scanning electron microscope,XRD and other testing methods,the technological law,microstructure and mechanical properties of SLM forming Ti-48Al-2Cr-2Nb alloy are studied,and the parameters and ways of improving its properties and weaving are discussed.The test results show that:1.The effects of laser power,scanning speed,scanning distance and powder layer thickness on the densification,microstructure and Vickers hardness of Ti-48Al-2Cr-2Nb alloy formed by SLM were studied.The molten pool formed by laser scanning can be divided into three areas: coarse crystal area,transition area and fine product area.The main factors affecting the forming quality are laser power and scanning speed.When the laser power is 90 W,scanning speed is 1000mm/s,scanning distance is 90?m,and the thickness of powder layer is 40?m,the forming test block has good quality.2.Different laser remelting schemes were designed and their effects on the microstructure and Vickers hardness of Ti-48Al-2Cr-2Nb alloy formed by SLM were summarized.Based on the optimization of process parameters,four groups of parameters with the best forming quality were selected,and the remelting strategy was set as no remelting(control group),no offset,90° rotation,one layer apart,two layers apart and three layers apart.It is found that the remelting strategy can improve the density and microstructure of the formed specimen,and the cracks caused by too fast temperature change are also reduced.However,the strategy of no offset and 90° rotation can not improve the quality of the formed test block or even form due to the excessive energy input.3.In view of the warping and cracking problems existing in SLM forming Ti-48Al-2Cr-2Nb alloy,the relationship between the surface temperature change and the cracking was studied.Based on the simulation calculation of the surface temperature field of the forming part,the physical model is simplified and the laser scanning path is simulated under the condition that the substrate temperature is set at 180 ?(the highest temperature in the stable state).The simulation process is solved according to different laser scanning strategies,and the temperature change curve of the forming test block surface is obtained,which verifies the process of SLM forming alloy test block. |
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