Study On Microstructures And Properties Of TC4/IN625 Gradient Structural Materials By Laser Melting Deposition

TC4 and IN625 are widely used in aerospace fields because of the high specific strength of TC4 and the high temperature oxidation resistance of IN625.In order to reduce the weight of the vehicle and increase its thrust-to-weight ratio,attempts were made to combine two metals to form a bimetallic structure in order to make the most of their respective properties.However,the TC4/IN625 bimetallic structure is prone to the formation of brittle intermetallic compounds in the bonding region,which to a certain extent limits its application.In this study,TC4/IN625gradient structural material samples were prepared by laser melting deposition(LMD)technique,and their tissue evolution pattern and microhardness distribution were investigated.The TC4/IN625 bimetallic structure samples were deposited directly by LMD technology at room temperature and preheated at 400?,respectively.At room temperature,the sample fractures in the bonding zone of the TC4/IN625 bimetallic structure,and the fracture profile is characterised by cleavage fracture.At a preheat of 400°C,the sample exhibited crystalline cracks in the bonding zone of the TC4/IN625 bimetallic structure,with a large number of Ti₂Ni,Ti Ni and Ti Ni₃ brittle intermetallic compounds and the presence of deviations of Cr and Mo elements in the vicinity of the cracks.The hardness in the bonding zone is high,with a maximum hardness value of approximately 822 HV.TC4/IN625 gradient structural samples were prepared by LMD technique under preheating400°C.The transition form was 100%TC4?80%TC4+20%IN625?60%TC4+40%IN625?40%TC4+60%IN625?20%TC4+80%IN625?100%IN625.Six zones and five interfaces were formed and the organisation and property evolution patterns were investigated.The experimental results show that the gradient structure samples gradually transition from the 100%TC4 zone to the 100%IN625 zone,with the microstructure evolving in the order of?-Ti+((?-Ti)+(?-Ti))??-Ti+Ti₂Ni+(?-Ti+Ti₂Ni)?Ti₂Ni+(?-Ti+Ti₂Ni)??-Ti+Ti₂Ni+(Ti₂Ni+Ti Ni)?(Ti Ni+Ti Ni₃)+(Cr,Mo)??-Ni+laves.The gradient structure of the material increases and then decreases in hardness.The 40%TC4+60%IN625 zone achieves the highest hardness value of approximately 803 HV and the next highest Vickers value of approximately770 HV is obtained in the 20%TC4+80%IN625 zone.The 40%TC4+60%IN625 and 20%TC4+80%IN625 zones produce transverse cracks and exhibit cold cracking characteristics.The cold crack sensitivity of the deposited layer is proportional to the Vickers hardness value.A reasonable ratio of TC4 to IN625 mixed powder for LMD TC4/IN625 gradient structure material ranges from IN625?40%.By avoiding the composition zone where cracks exist.The transition form of the gradient structure sample is 100%TC4?80%TC4+20%IN625?60%TC4+40%IN625?100%IN625.It is found that the organization of each composition zone is uniform and dense,and the number of Ti₂Ni,Ti Ni and Ti Ni₃ brittle intermetallic compounds is significantly reduced.The Vickers hardness is also significantly reduced,with the highest hardness of about 569 HV in the 60%TC4+40%IN625 zone.The avoidance of cracked component areas effectively controls cracking in the gradient structure of the sample,resulting in a crack-free sample with no defects and a metallurgical bond.