Features of obtaining TiNi alloy samples from commercial powders with high oxygen content using the SLM technique

Abstract

Additive technologies, in particular selective laser melting (SLM), enable to manufacture the products with complex geo­metries. The SLM technique can help to effectively expand the titanium nickelide scope of application. However, SLM is a complex process – numerous factors significantly affect the characteristics of the resulting alloy. When the SLM technique is used, as the material is subject to laser processing, the content of nickel in the alloy drops due to evaporation, which can lead to changes in the tempe­ratures of martensitic transformations. This impact on the resulting alloy characteristics can be regulated by changing the para­meters of the SLM process. The objective of our research was to develop the processing methods for manufacturing samples from two commercial TiNi alloy powders using the SLM technique and to analyze the factors causing defects in the obtained samples. At the same time, processing methods with low values of volumetric energy density were used to reduce possible evaporation of nickel during printing. The initial powders were examined for the presence of impurities or other factors affecting the quality of the manufactured samples. The processing method A4 that we have developed for powder 1 enables to obtain a defect-free sample with the density of 6.45 g/cm3. It was found that none of the processing methods used enabled to obtain a defect-free sample from powder 2 due to presence of a large amount of oxygen impurities, including in particular Ti4Ni2Oх secondary phase, which leads to embrittlement and destruction of the samples. Therefore, high content of oxygen in the initial powders has a negative impact on the quality of the samples manufactured using the SLM technique.