Single phase high entropy alloys, as predicted in the early 2000s, have been completed by compositionally complex alloys with two or more phases. It has been found that the Al10Co25Cr8Fe15Ni36Ti6 alloy stands out for its good mechanical properties, due to its main gamma-gamma' morphology which is comparable to Ni- and Co-based superalloys. In order to enhance the alloy's properties, B, Hf, Mo or Zr are added as trace elements and their influence on the microstructure and the hardness is studied by scanning and transmission electron microscopy, and x-ray diffraction. One important factor for the enhancing is the difference in lattice parameter of the gamma and the gamma prime phase. These are measured by synchrotron radiation. This work focuses on the influence of 0.5 % B, 0.5 at.% Hf, 1 at.% Mo or 0,5 at. % Zr.