Crit[gf_]:=gf/(1-Sqrt[gf*(2-gf)])
TMax[gf_]:=(gf*(gf*(gf*(2*Sqrt[gf*(2-gf)]+3)-3*Sqrt[gf*(2-gf)]-4) + 4*Sqrt[gf*(2-gf)]+4))/((1-gf)^2*(4+gf*(gf-2)))
ThrMax[gf_]:=(2*(1-gf)*gf*(gf*(gf-2) + 2*Sqrt[gf*(2-gf)]))/((gf*(gf*(gf*(Sqrt[gf*(2-gf)]-4)-4*Sqrt[gf*(2-gf)]+14) + Sqrt[gf*(2-gf)]-12))+4*Sqrt[gf*(2-gf)])
Plot[{Crit[gf],TMax[gf],ThrMax[gf]},{gf,0,1},PlotRange->{{0.0,1.0},{0,20.0}},PlotStyle->{Black,Blue,Red}]