In order to improve sliding wear characteristics at high temperature, the overlay weld metals for Co-based alloys with various amount of MoB particles were prepared using a plasma transferred arc welding process. Effects of amount of MoB particles on wear behaviors and friction coefficient of the overlay weld metals at high temperature were investigated using Ohgoshi wear tester and cylinder friction tester.
The microstructures of overlay weld metals were consisted of Co-based matrix (βCo), lamellar structure of Cr₂₃C₆ and βCo, lamellar structure of M₂B and βCo and primary crystal of CoMo₂B₂. The volume fraction of CoMo₂B₂ and hardness of overlay weld metals increased with the increase in the additional boron quantity.
When the values subtracting the hardness of overlay weld metals from the hardness of S45C carbon steel were above HV300, the sliding wear resistance at high temperature was extremely improved. The friction coefficient of the overlay weld metals decreased with the increase of the test temperature. The reason is that the boride prevented the adhesion of S45C carbon steel to the overlay weld metals.