Abstract
Carbide tools applied for plastic deformation often reach a tool life due to bending fatigue under repeated stress at their use. Therefore, as it is very important to acquire knowledge on bending fatigue of carbide tool, the effects of HIP treatment and surface conditions on the bending fatigue characteristics of WC-12mass%Co alloys were mainly investigated. The results obtained were as follows: (1) The bending fatigue characteristics of HIP-treated alloys was improved at lower repeated cycle, compared with that of normal sintered alloy. The fracture origin observed after fatigue fracture was pore in normal sintered alloy, while it was coarse carbide or Cc pool with a step-shaped form in HIP-treated alloy. (2) The specimens with different surface roughness had almost same bending strength, but the fatigue strength decreased with decreasing surface roughness. The cause of this decrease was considered to be due to the decrease of the surface compressive residual stress. (3) The fatigue strength of PVD-coated alloy with TiN layer decreased at lower. repeated cycle and that of CVD-coated alloy remarkably decreased, compared with that of non-coated alloy. The cause of these decrease in the coated alloys were mainly discussed in relation to the residual stress of the substrate alloy and the coated layer and the adhesion between them.
