Research on the cracking of Ti6Al4V-CoCrMo gradient material fabricated by laser metal direct forming

Ti6Al4V-CoCrMo gradient multi-pass wall is fabricated by laser metal direct forming, with the CoCrMo volume fraction of 10%, 20%, 30%, respectively. The part of 10% CoCrMo volume fraction is crackles, while 20%, 30% parts crack seriously. Advanced investigations are made on the cracking of 20%, 30% CoCrMo volume fraction parts from three aspects: fracture morphology, microstructure and residual stress. The results show that the cracking of gradient material is a kind of cold cracking. The fracture displays the features of quasi-cleavage and transgranular. Reasons of the cracking mainly include of Ti6Al4V and CoCrMo form limited solid solution, increasing the brittle of the material. With the content of CoCrMo increasing, the microstructure of the Ti6Al4V-CoCrMo gradient material changes. Around the Ti6Al4V-CoCrMo limited solid solution network CoCrMo precipitated, not only the possibility of stress concentration improves, leading to crack source appearing in some cases, but also the stress due to the differences of thermal physcial parameters of two materials increases.