If the material is manufactured by 3D printing (laser sintering) then what will be change in its mechanical properties than the properties by casting and machined part? What would be appropriate failure criteria for it?
This depends on the alloy type (and specific alloy) and the quality of the material after it's been produced which can change depending on the manufacturing parameters.
The strengths of additive manufactured material are often better than cast when it's done properly, but I have yet to see any that are better than forged/rolled material. I have seen material with large amounts of porosity which had properties considerable worse than cast.
The failure Criteria also depends on the application, e.g. voids in SLM material can act as initiation points for fatigue failures greatly decrease the fatigue life of a material with good strength properties. Unfortunately the only way to definitively determine the properties for a material (suitable for structural designs) is to test it.