Wear performance of metamorphic alloy coatings

Two Fe-Cr-B based gas atomized powders, proposed as metamorphic alloys (Armacor M and Armacor 16), were thermally sprayed using the HVOF (High Velocity Oxygen Fuel) process. Armacor M was also weld-surfaced by PTA (Plasma Transferred Are) process. The resultant deposits were subsequently characterized, using X-ray diffraction, scanning electron microscopy, and microhardness measurement. The wear performances of the different coatings were investigated by two-body abrasive and pin-on-disc dry sliding wear tests. The results from microstructural analysis of as-sprayed deposits reveal oxide and boride phases such as Fe3O4 and Cr1.65Fe0.35B0.96 in a matrix for HVOF-sprayed Armacor 16 coating, and only the boride phases (Cr1.65Fe0.35B0.96 and Cr2B) in alpha matrix for HVOF-sprayed Armacor M coating. PTA weld-surfaced Armacor M coating contains needle-type long precipitates of large Cr2B and Cr1.65Fe0.35B0.96 in alpha matrix. Wear test results show that HVOF-sprayed Armacor 16 coating exhibits the lowest wear resistance. While HVOF-sprayed and PTA weld-surfaced Armacor M coatings have the same hardness, the latter shows better abrasive and sliding wear resistance because of the size and orientation of its boride phases. More broadening in XRD patterns and hardness increase after wear testing suggest that the transformation from crystalline to amorphous structure has occurred on the uppermost layer during the wear testing. However, the wear resistance of the metamorphic alloy coatings depends more on the density and microstructure of the coatings rather than on the formation of amorphous surface structure. (C) 1999 Elsevier Science S.A. All rights reserved.