Abstract: Crack is the most common and great destructive defect in selective laser melting (SLM) Ti6Al4V (TC4) alloy process. A TC4 alloy test specimen is fabricated by progressive alternative scan strategy in SLM process. The cracking behavior and formation mechanism is discussed in TC4 alloy SLM processing using scanning electron microscopy and X-ray energy spectrum analysis. The experimental results show that the crack is considered as cold cracking in SLM TC4 alloy part, which has typical characteristic of the transgranular fracture. By using the progressive alternative scan strategy, the basket-like martensitic structure is formed in SLM process. The high residual stress is caused by high temperature in forming process of SLM part. Under the residual stress, the crackle will occur in the martensitic structure because it has poor cracking strength. Finally, the coarse crack decomposes into smaller cracks in the process of expansion and the extension is terminated. Further research shows that by improving the process parameters, the microstructure of TC4 alloy will be changed and the residual stress will be weakened. At the same time, achieving to the purpose of weakening or eliminating cracks.

Key words: Cracking, Formation mechanism, Selective laser melting, TC4 alloy