C17200 / ALLOY 25 is an alloy which contains 2 % Beryllium Copper Alloy. This alloy achieves highest mechanical strength and hardness after heat treatment. 

Properties:

Fast Heating & Fast Cooling
Excellent Conductivity
High Tensile Strength
Non Oxidizing Acid Resistance
Wear & Gall Resistant
Non Sparkling
High Fatigue Resistance
Elevated Temperature Strength
Corrosion Resistance
Ductile, Weldable & Machinable
High Melting Point
Dimension Stability

C17500 / C17510
C17500 is [CuCo2Be] COPPER - COBALT - BERYLLIUM ALLOYS  containing Be 0.4 ~ 0.7 % ; Co 2.4 ~ 2.7% ; Cu is Balance. 
C17510 is [CuNi2Be] COPPER - NICKEL - BERYLLIUM ALLOYS  containing Be 0.4 ~ 0.7 % ; Ni 1.7% ~ 2.0% ; Cu is Balance.
Both these alloys are very similar. It has better Strength and Thermal Conductivity compared to C17200. Highly used for Resistance Welding Applications.
Welding: Soldering is rated as 'good', Brazing is rated as 'good', oxyacetylene welding is 'not recommended', gas shielding arc welding is rated as 'fair', coated metal arc welding is rated as 'fair', spot welding is rated as 'good', seam and butt welding is rated 'fair.