= Co, Ir*

The heavy-fermion compoundURu₂Si₂ was substituted with M = Co and Ir to form polycrystalline samples of the pseudo-ternary system URu_2-xM_xSi₂. Phase diagrams are presented based on electrical resistivity, magnetization, specific heat, and x-ray diffraction measurements. Substitution with M = Co and Ir suppresses the hidden order features by x = 0.1, after which, no ordering is observed for 0.1 < x < 0.3. For M = Ir, an antiferromagnetic phase (AFM-1) gradually emerges with a Néel temperature (T_N1) that increases from T_N1 = 28 to 40 K over the region 0.3 < x < 0.5. At x = 0.5, the AFM-1 phase separates into three distinct peaks, each of which persists with little temperature change until x = 1.0. For higher x, there is again a region with no ordered phase, which persists until a structural phase transition occurs at x = 1.35. For M = Co, an AFM-2 phase emerges at x = 1.0 with T_N2 = 80 (5) K; the phase boundary varies with x reaching a maximum of T_N2 = 106 (5) K. The results of this study are compared with previous studies for M = Rh, Fe, Os, Re, and P in the context of electron doping, the chemical pressure, and structural disorder.