Study On The Microstructure And Mechanical Properties Of TiVCrHfNb High-entropy Alloy Fabricated By Selective Laser Melting

As a new type of structural material,high-entropy aloys have attracted great attention from researchers in the past decades.Due to the excelent comprehensive mechanica l properties of TiVCrHfNb high-entropy aloy,we selected it as the matrix material.However,it is difficult for conventional processing methods to directly fabricate TiVCrHfNb highentropy aloy parts with complex structures.Selective Laser Melting(SLM)is an emerging additive manufacturing technology,which uses highly focused lasers as a heat source beam to selectively stratify molten metal powders,has the capability of quickly and integrally building metal parts with complex structures based on 3D CAD models.SLM shows the potential of process high-entropy aloys.However,in the SLM process of TiVCrHfNb high-entropy aloy,due to the large temperature gradient and residual stress caused by rapid melting and rapid cooling,the SLM-processed TiVCrHfNb high-entropy aloy shows microcracks.Therefore,in this work,nano-boron(nano-B)was added to the TiVCrHfNb high-entropy aloy matrix can effectively reduce microcracks and refine grains,thereby improving the mechanical properties of SLM-formed TiVCrHfNb metal parts.The evolution of microstructure and mechanica l properties of SLM-processed TiVCrHfNb high-entropy aloys with different nano-B contents were studied.The specific research contents and results are as follows:(1)The SLM processing parameters of TiVCrHfNb high-entropy aloy were optimized,and the variation of micro-cracks in SLM-formed TiVCrHfNb metal parts with different nanoB contents was studied.When the nano-B content was 0 wt.%-0.8 wt.%,the micro-cracks decreases rapidly with the increase of nano-B content.When the nano-B content is 0.8 wt.%-1.6 wt.%,the microcracks increases slightly with the increase of nano-B content.Therefore,nano-B has an inhibitory effect on the microcracks of SLM-processed TiVCrHfNb highentropy aloy.The evolution of microstructure of SLM-processed TiVCrHfNb high-entrop y aloys with different nano-B contents was studied.It was found that the grain size decreases with the increase of nano-B content,and the grain orientation significantly changes.The(111)orientation gradually changes to(001)orientation.In addition,it was found that with the increase of nano-B content,the Schmidt index of SLM-processed TiVCrHfNb high-entrop y aloy gradually decreases indicating that with the increase of nano-B content,the deformatio n resistance of the SLM-processed TiVCrHfNb high-entropy aloy is gradually improved.(2)The effect of nano-B content on the phase composition and mechanical properties of SLM formed TiVCrHfNb high-entropy aloy was studied.It is found that the TiVCrHfNb high-entropy aloy only exists in the BCC matrix phase as the nano-B content is gradually increased from 0% to 0.4 wt.%,and the TiVCrHfNb high-entropy aloy is derived from the matrix BCC when the nano-B content is increased to 0.8 wt.%.Nano-B,nano-TiB2 and nanoHfB2 are composed,accompanied by the formation of equiaxed crystals.With the increase of nano-B content,the tensile strength of SLM-processed TiVCrHfNb first increases and then decreases.When the nano-B content is 0.8 wt.%,the yield strength reaches a maximum of 619±23 MPa.