Effect of Die Surface Composition on Friction and Adhesion in Deformation Processing

An experimental investigation was carried out to determine interface friction and adhesion characteristics of workpiece and die materials under pressures and temperatures typical of plastic deformation. Evaluations were made using a twist-compression technique, which provided conditions of enforced sliding, and a ring upsetting technique in which sticking friction was predominant. Hot-rolling tests were performed to correlate the results with conventional metalworking practices. Workpiece materials included aluminum, titanium, and molybdenum alloys, low-alloy steel, and a nickel-base superalloy. Tools were made of die steels, tungsten carbide, and diffusion-coated die materials to evaluate the effects of surface chemistry and hardness in unlubricated contact with the workpiece material. Significant variations in friction due to die surface composition were observed, the effects being more marked with forced interface sliding. The most promising die materials were boronized 4140 steel and titanium carbide-coated 4140 steel. The investigation has shown that with the proper choice of die and workpiece material combinations, friction can be reduced and more importantly, adhesion can be minimized thereby avoiding or delaying catastrophic die failure in the event of lubricant breakdown.